diff --git a/CHANGELOG.md b/CHANGELOG.md
index 91ac0114b37..4b0fabd4676 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -21,7 +21,9 @@
 - **Breaking Change**: Non-`mixin` classes in the platform libraries
   can no longer be mixed in, unless they are explicitly marked as `mixin class`.
   The following existing classes have been made mixin classes:
-  * `IterableMixin`
+  * `Iterable`
+  * `IterableMixin` (now alias for `Iterable`)
+  * `IterableBase` (now alias for `Iterable`)
   * `ListMixin`
   * `SetMixin`
   * `MapMixin`
diff --git a/pkg/front_end/testcases/general/constants/const_collections.dart.strong.expect b/pkg/front_end/testcases/general/constants/const_collections.dart.strong.expect
index b8db0312f1d..0a1f2fb7260 100644
--- a/pkg/front_end/testcases/general/constants/const_collections.dart.strong.expect
+++ b/pkg/front_end/testcases/general/constants/const_collections.dart.strong.expect
@@ -180,14 +180,14 @@ library /*isNonNullableByDefault*/;
 //                     ^
 //
 import self as self;
-import "dart:collection" as col;
 import "dart:core" as core;
+import "dart:collection" as col;
 
 import "dart:collection";
 
-class ConstIterable extends col::IterableBase<core::int> /*hasConstConstructor*/  {
+class ConstIterable extends core::Iterable<core::int> /*hasConstConstructor*/  {
   const constructor •() → self::ConstIterable
-    : super col::IterableBase::•()
+    : super core::Iterable::•()
     ;
   get iterator() → core::Iterator<core::int>
     return <core::int>[].{core::Iterable::iterator}{core::Iterator<core::int>};
@@ -201,9 +201,9 @@ class WithEquals extends core::Object /*hasConstConstructor*/  {
     return o is{ForNonNullableByDefault} self::WithEquals && (o{self::WithEquals} as{ForNonNullableByDefault} self::WithEquals).{self::WithEquals::i}{core::int} =={core::num::==}{(core::Object) → core::bool} this.{self::WithEquals::i}{core::int};
   }
 }
-class CustomIterable extends col::IterableBase<core::String> /*hasConstConstructor*/  {
+class CustomIterable extends core::Iterable<core::String> /*hasConstConstructor*/  {
   const constructor •() → self::CustomIterable
-    : super col::IterableBase::•()
+    : super core::Iterable::•()
     ;
   get iterator() → core::Iterator<core::String>
     return <core::String>[].{core::Iterable::iterator}{core::Iterator<core::String>};
@@ -383,7 +383,6 @@ constants  {
 Constructor coverage from constants:
 org-dartlang-testcase:///const_collections.dart:
 - CustomIterable. (from org-dartlang-testcase:///const_collections.dart:79:9)
-- IterableBase. (from org-dartlang-sdk:///sdk/lib/collection/iterable.dart)
 - Iterable. (from org-dartlang-sdk:///sdk/lib/core/iterable.dart)
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 - WithEquals. (from org-dartlang-testcase:///const_collections.dart:72:9)
diff --git a/pkg/front_end/testcases/general/constants/const_collections.dart.strong.transformed.expect b/pkg/front_end/testcases/general/constants/const_collections.dart.strong.transformed.expect
index cc9846de7b2..dfe7623c243 100644
--- a/pkg/front_end/testcases/general/constants/const_collections.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/general/constants/const_collections.dart.strong.transformed.expect
@@ -180,14 +180,14 @@ library /*isNonNullableByDefault*/;
 //                     ^
 //
 import self as self;
-import "dart:collection" as col;
 import "dart:core" as core;
+import "dart:collection" as col;
 
 import "dart:collection";
 
-class ConstIterable extends col::IterableBase<core::int> /*hasConstConstructor*/  {
+class ConstIterable extends core::Iterable<core::int> /*hasConstConstructor*/  {
   const constructor •() → self::ConstIterable
-    : super col::IterableBase::•()
+    : super core::Iterable::•()
     ;
   get iterator() → core::Iterator<core::int>
     return core::_GrowableList::•<core::int>(0).{core::Iterable::iterator}{core::Iterator<core::int>};
@@ -201,9 +201,9 @@ class WithEquals extends core::Object /*hasConstConstructor*/  {
     return o is{ForNonNullableByDefault} self::WithEquals && o{self::WithEquals}.{self::WithEquals::i}{core::int} =={core::num::==}{(core::Object) → core::bool} this.{self::WithEquals::i}{core::int};
   }
 }
-class CustomIterable extends col::IterableBase<core::String> /*hasConstConstructor*/  {
+class CustomIterable extends core::Iterable<core::String> /*hasConstConstructor*/  {
   const constructor •() → self::CustomIterable
-    : super col::IterableBase::•()
+    : super core::Iterable::•()
     ;
   get iterator() → core::Iterator<core::String>
     return core::_GrowableList::•<core::String>(0).{core::Iterable::iterator}{core::Iterator<core::String>};
@@ -383,7 +383,6 @@ constants  {
 Constructor coverage from constants:
 org-dartlang-testcase:///const_collections.dart:
 - CustomIterable. (from org-dartlang-testcase:///const_collections.dart:79:9)
-- IterableBase. (from org-dartlang-sdk:///sdk/lib/collection/iterable.dart)
 - Iterable. (from org-dartlang-sdk:///sdk/lib/core/iterable.dart)
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 - WithEquals. (from org-dartlang-testcase:///const_collections.dart:72:9)
diff --git a/pkg/front_end/testcases/general/constants/const_collections.dart.weak.expect b/pkg/front_end/testcases/general/constants/const_collections.dart.weak.expect
index fbd2858f4a1..6e718b8677e 100644
--- a/pkg/front_end/testcases/general/constants/const_collections.dart.weak.expect
+++ b/pkg/front_end/testcases/general/constants/const_collections.dart.weak.expect
@@ -180,14 +180,14 @@ library /*isNonNullableByDefault*/;
 //                     ^
 //
 import self as self;
-import "dart:collection" as col;
 import "dart:core" as core;
+import "dart:collection" as col;
 
 import "dart:collection";
 
-class ConstIterable extends col::IterableBase<core::int> /*hasConstConstructor*/  {
+class ConstIterable extends core::Iterable<core::int> /*hasConstConstructor*/  {
   const constructor •() → self::ConstIterable
-    : super col::IterableBase::•()
+    : super core::Iterable::•()
     ;
   get iterator() → core::Iterator<core::int>
     return <core::int>[].{core::Iterable::iterator}{core::Iterator<core::int>};
@@ -201,9 +201,9 @@ class WithEquals extends core::Object /*hasConstConstructor*/  {
     return o is{ForNonNullableByDefault} self::WithEquals && (o{self::WithEquals} as{ForNonNullableByDefault} self::WithEquals).{self::WithEquals::i}{core::int} =={core::num::==}{(core::Object) → core::bool} this.{self::WithEquals::i}{core::int};
   }
 }
-class CustomIterable extends col::IterableBase<core::String> /*hasConstConstructor*/  {
+class CustomIterable extends core::Iterable<core::String> /*hasConstConstructor*/  {
   const constructor •() → self::CustomIterable
-    : super col::IterableBase::•()
+    : super core::Iterable::•()
     ;
   get iterator() → core::Iterator<core::String>
     return <core::String>[].{core::Iterable::iterator}{core::Iterator<core::String>};
@@ -383,7 +383,6 @@ constants  {
 Constructor coverage from constants:
 org-dartlang-testcase:///const_collections.dart:
 - CustomIterable. (from org-dartlang-testcase:///const_collections.dart:79:9)
-- IterableBase. (from org-dartlang-sdk:///sdk/lib/collection/iterable.dart)
 - Iterable. (from org-dartlang-sdk:///sdk/lib/core/iterable.dart)
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 - WithEquals. (from org-dartlang-testcase:///const_collections.dart:72:9)
diff --git a/pkg/front_end/testcases/general/constants/const_collections.dart.weak.modular.expect b/pkg/front_end/testcases/general/constants/const_collections.dart.weak.modular.expect
index fbd2858f4a1..6e718b8677e 100644
--- a/pkg/front_end/testcases/general/constants/const_collections.dart.weak.modular.expect
+++ b/pkg/front_end/testcases/general/constants/const_collections.dart.weak.modular.expect
@@ -180,14 +180,14 @@ library /*isNonNullableByDefault*/;
 //                     ^
 //
 import self as self;
-import "dart:collection" as col;
 import "dart:core" as core;
+import "dart:collection" as col;
 
 import "dart:collection";
 
-class ConstIterable extends col::IterableBase<core::int> /*hasConstConstructor*/  {
+class ConstIterable extends core::Iterable<core::int> /*hasConstConstructor*/  {
   const constructor •() → self::ConstIterable
-    : super col::IterableBase::•()
+    : super core::Iterable::•()
     ;
   get iterator() → core::Iterator<core::int>
     return <core::int>[].{core::Iterable::iterator}{core::Iterator<core::int>};
@@ -201,9 +201,9 @@ class WithEquals extends core::Object /*hasConstConstructor*/  {
     return o is{ForNonNullableByDefault} self::WithEquals && (o{self::WithEquals} as{ForNonNullableByDefault} self::WithEquals).{self::WithEquals::i}{core::int} =={core::num::==}{(core::Object) → core::bool} this.{self::WithEquals::i}{core::int};
   }
 }
-class CustomIterable extends col::IterableBase<core::String> /*hasConstConstructor*/  {
+class CustomIterable extends core::Iterable<core::String> /*hasConstConstructor*/  {
   const constructor •() → self::CustomIterable
-    : super col::IterableBase::•()
+    : super core::Iterable::•()
     ;
   get iterator() → core::Iterator<core::String>
     return <core::String>[].{core::Iterable::iterator}{core::Iterator<core::String>};
@@ -383,7 +383,6 @@ constants  {
 Constructor coverage from constants:
 org-dartlang-testcase:///const_collections.dart:
 - CustomIterable. (from org-dartlang-testcase:///const_collections.dart:79:9)
-- IterableBase. (from org-dartlang-sdk:///sdk/lib/collection/iterable.dart)
 - Iterable. (from org-dartlang-sdk:///sdk/lib/core/iterable.dart)
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 - WithEquals. (from org-dartlang-testcase:///const_collections.dart:72:9)
diff --git a/pkg/front_end/testcases/general/constants/const_collections.dart.weak.outline.expect b/pkg/front_end/testcases/general/constants/const_collections.dart.weak.outline.expect
index c83eee41f4e..0bb7aa2d881 100644
--- a/pkg/front_end/testcases/general/constants/const_collections.dart.weak.outline.expect
+++ b/pkg/front_end/testcases/general/constants/const_collections.dart.weak.outline.expect
@@ -37,14 +37,13 @@ library /*isNonNullableByDefault*/;
 //                                              ^
 //
 import self as self;
-import "dart:collection" as col;
 import "dart:core" as core;
 
 import "dart:collection";
 
-class ConstIterable extends col::IterableBase<core::int> /*hasConstConstructor*/  {
+class ConstIterable extends core::Iterable<core::int> /*hasConstConstructor*/  {
   const constructor •() → self::ConstIterable
-    : super col::IterableBase::•()
+    : super core::Iterable::•()
     ;
   get iterator() → core::Iterator<core::int>
     ;
@@ -57,9 +56,9 @@ class WithEquals extends core::Object /*hasConstConstructor*/  {
   operator ==(core::Object o) → core::bool
     ;
 }
-class CustomIterable extends col::IterableBase<core::String> /*hasConstConstructor*/  {
+class CustomIterable extends core::Iterable<core::String> /*hasConstConstructor*/  {
   const constructor •() → self::CustomIterable
-    : super col::IterableBase::•()
+    : super core::Iterable::•()
     ;
   get iterator() → core::Iterator<core::String>
     ;
diff --git a/pkg/front_end/testcases/general/constants/const_collections.dart.weak.transformed.expect b/pkg/front_end/testcases/general/constants/const_collections.dart.weak.transformed.expect
index 454355d1f3a..9b315897e80 100644
--- a/pkg/front_end/testcases/general/constants/const_collections.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/general/constants/const_collections.dart.weak.transformed.expect
@@ -180,14 +180,14 @@ library /*isNonNullableByDefault*/;
 //                     ^
 //
 import self as self;
-import "dart:collection" as col;
 import "dart:core" as core;
+import "dart:collection" as col;
 
 import "dart:collection";
 
-class ConstIterable extends col::IterableBase<core::int> /*hasConstConstructor*/  {
+class ConstIterable extends core::Iterable<core::int> /*hasConstConstructor*/  {
   const constructor •() → self::ConstIterable
-    : super col::IterableBase::•()
+    : super core::Iterable::•()
     ;
   get iterator() → core::Iterator<core::int>
     return core::_GrowableList::•<core::int>(0).{core::Iterable::iterator}{core::Iterator<core::int>};
@@ -201,9 +201,9 @@ class WithEquals extends core::Object /*hasConstConstructor*/  {
     return o is{ForNonNullableByDefault} self::WithEquals && o{self::WithEquals}.{self::WithEquals::i}{core::int} =={core::num::==}{(core::Object) → core::bool} this.{self::WithEquals::i}{core::int};
   }
 }
-class CustomIterable extends col::IterableBase<core::String> /*hasConstConstructor*/  {
+class CustomIterable extends core::Iterable<core::String> /*hasConstConstructor*/  {
   const constructor •() → self::CustomIterable
-    : super col::IterableBase::•()
+    : super core::Iterable::•()
     ;
   get iterator() → core::Iterator<core::String>
     return core::_GrowableList::•<core::String>(0).{core::Iterable::iterator}{core::Iterator<core::String>};
@@ -383,7 +383,6 @@ constants  {
 Constructor coverage from constants:
 org-dartlang-testcase:///const_collections.dart:
 - CustomIterable. (from org-dartlang-testcase:///const_collections.dart:79:9)
-- IterableBase. (from org-dartlang-sdk:///sdk/lib/collection/iterable.dart)
 - Iterable. (from org-dartlang-sdk:///sdk/lib/core/iterable.dart)
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 - WithEquals. (from org-dartlang-testcase:///const_collections.dart:72:9)
diff --git a/pkg/front_end/testcases/general/sdk_diagnostic.dart.strong.expect b/pkg/front_end/testcases/general/sdk_diagnostic.dart.strong.expect
index 20c715f6dc8..78eea88887e 100644
--- a/pkg/front_end/testcases/general/sdk_diagnostic.dart.strong.expect
+++ b/pkg/front_end/testcases/general/sdk_diagnostic.dart.strong.expect
@@ -12,7 +12,7 @@ library /*isNonNullableByDefault*/;
 //
 // class C extends Iterable<Object> {
 //       ^
-// sdk/lib/core/iterable.dart:148:19: Context: 'Iterable.iterator' is defined here.
+// sdk/lib/core/iterable.dart:169:19: Context: 'Iterable.iterator' is defined here.
 //   Iterator<E> get iterator;
 //                   ^^^^^^^^
 //
diff --git a/pkg/front_end/testcases/general/sdk_diagnostic.dart.strong.transformed.expect b/pkg/front_end/testcases/general/sdk_diagnostic.dart.strong.transformed.expect
index 20c715f6dc8..78eea88887e 100644
--- a/pkg/front_end/testcases/general/sdk_diagnostic.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/general/sdk_diagnostic.dart.strong.transformed.expect
@@ -12,7 +12,7 @@ library /*isNonNullableByDefault*/;
 //
 // class C extends Iterable<Object> {
 //       ^
-// sdk/lib/core/iterable.dart:148:19: Context: 'Iterable.iterator' is defined here.
+// sdk/lib/core/iterable.dart:169:19: Context: 'Iterable.iterator' is defined here.
 //   Iterator<E> get iterator;
 //                   ^^^^^^^^
 //
diff --git a/pkg/front_end/testcases/general/sdk_diagnostic.dart.weak.expect b/pkg/front_end/testcases/general/sdk_diagnostic.dart.weak.expect
index 20c715f6dc8..78eea88887e 100644
--- a/pkg/front_end/testcases/general/sdk_diagnostic.dart.weak.expect
+++ b/pkg/front_end/testcases/general/sdk_diagnostic.dart.weak.expect
@@ -12,7 +12,7 @@ library /*isNonNullableByDefault*/;
 //
 // class C extends Iterable<Object> {
 //       ^
-// sdk/lib/core/iterable.dart:148:19: Context: 'Iterable.iterator' is defined here.
+// sdk/lib/core/iterable.dart:169:19: Context: 'Iterable.iterator' is defined here.
 //   Iterator<E> get iterator;
 //                   ^^^^^^^^
 //
diff --git a/pkg/front_end/testcases/general/sdk_diagnostic.dart.weak.modular.expect b/pkg/front_end/testcases/general/sdk_diagnostic.dart.weak.modular.expect
index 20c715f6dc8..78eea88887e 100644
--- a/pkg/front_end/testcases/general/sdk_diagnostic.dart.weak.modular.expect
+++ b/pkg/front_end/testcases/general/sdk_diagnostic.dart.weak.modular.expect
@@ -12,7 +12,7 @@ library /*isNonNullableByDefault*/;
 //
 // class C extends Iterable<Object> {
 //       ^
-// sdk/lib/core/iterable.dart:148:19: Context: 'Iterable.iterator' is defined here.
+// sdk/lib/core/iterable.dart:169:19: Context: 'Iterable.iterator' is defined here.
 //   Iterator<E> get iterator;
 //                   ^^^^^^^^
 //
diff --git a/pkg/front_end/testcases/general/sdk_diagnostic.dart.weak.outline.expect b/pkg/front_end/testcases/general/sdk_diagnostic.dart.weak.outline.expect
index b08de4bc13c..e081d7b3323 100644
--- a/pkg/front_end/testcases/general/sdk_diagnostic.dart.weak.outline.expect
+++ b/pkg/front_end/testcases/general/sdk_diagnostic.dart.weak.outline.expect
@@ -12,7 +12,7 @@ library /*isNonNullableByDefault*/;
 //
 // class C extends Iterable<Object> {
 //       ^
-// sdk/lib/core/iterable.dart:148:19: Context: 'Iterable.iterator' is defined here.
+// sdk/lib/core/iterable.dart:169:19: Context: 'Iterable.iterator' is defined here.
 //   Iterator<E> get iterator;
 //                   ^^^^^^^^
 //
diff --git a/pkg/front_end/testcases/general/sdk_diagnostic.dart.weak.transformed.expect b/pkg/front_end/testcases/general/sdk_diagnostic.dart.weak.transformed.expect
index 20c715f6dc8..78eea88887e 100644
--- a/pkg/front_end/testcases/general/sdk_diagnostic.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/general/sdk_diagnostic.dart.weak.transformed.expect
@@ -12,7 +12,7 @@ library /*isNonNullableByDefault*/;
 //
 // class C extends Iterable<Object> {
 //       ^
-// sdk/lib/core/iterable.dart:148:19: Context: 'Iterable.iterator' is defined here.
+// sdk/lib/core/iterable.dart:169:19: Context: 'Iterable.iterator' is defined here.
 //   Iterator<E> get iterator;
 //                   ^^^^^^^^
 //
diff --git a/pkg/front_end/testcases/incremental/no_outline_change_22.yaml.world.1.expect b/pkg/front_end/testcases/incremental/no_outline_change_22.yaml.world.1.expect
index 47243c0fa0d..3ee33183297 100644
--- a/pkg/front_end/testcases/incremental/no_outline_change_22.yaml.world.1.expect
+++ b/pkg/front_end/testcases/incremental/no_outline_change_22.yaml.world.1.expect
@@ -514,7 +514,7 @@ library from "org-dartlang-test:///main.dart" as main {
       return dart.core::Comparable::compare(a as{ForNonNullableByDefault} dart.core::Comparable<dynamic>, b as{ForNonNullableByDefault} dart.core::Comparable<dynamic>);
     }
     static method /* from org-dartlang-sdk:///sdk/lib/collection/list.dart */ listToString(dart.core::List<dart.core::Object?> list) → dart.core::String
-      return dart.collection::IterableBase::iterableToFullString(list, "[", "]");
+      return dart.core::Iterable::iterableToFullString(list, "[", "]");
   }
   class WithListMixin extends main::_WithListMixin&Object&ListMixin {
     field dart.core::int length = 2;
diff --git a/pkg/front_end/testcases/incremental/no_outline_change_22.yaml.world.2.expect b/pkg/front_end/testcases/incremental/no_outline_change_22.yaml.world.2.expect
index 47243c0fa0d..3ee33183297 100644
--- a/pkg/front_end/testcases/incremental/no_outline_change_22.yaml.world.2.expect
+++ b/pkg/front_end/testcases/incremental/no_outline_change_22.yaml.world.2.expect
@@ -514,7 +514,7 @@ library from "org-dartlang-test:///main.dart" as main {
       return dart.core::Comparable::compare(a as{ForNonNullableByDefault} dart.core::Comparable<dynamic>, b as{ForNonNullableByDefault} dart.core::Comparable<dynamic>);
     }
     static method /* from org-dartlang-sdk:///sdk/lib/collection/list.dart */ listToString(dart.core::List<dart.core::Object?> list) → dart.core::String
-      return dart.collection::IterableBase::iterableToFullString(list, "[", "]");
+      return dart.core::Iterable::iterableToFullString(list, "[", "]");
   }
   class WithListMixin extends main::_WithListMixin&Object&ListMixin {
     field dart.core::int length = 2;
diff --git a/pkg/front_end/testcases/patterns/cache_lookups.dart.strong.transformed.expect b/pkg/front_end/testcases/patterns/cache_lookups.dart.strong.transformed.expect
index d4fb3999cc6..90964c775e9 100644
--- a/pkg/front_end/testcases/patterns/cache_lookups.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/patterns/cache_lookups.dart.strong.transformed.expect
@@ -589,7 +589,7 @@ abstract class _CustomList&Object&ListMixin<E extends core::Object? = dynamic> e
     return core::Comparable::compare(a as{ForNonNullableByDefault} core::Comparable<dynamic>, b as{ForNonNullableByDefault} core::Comparable<dynamic>);
   }
   static method /* from org-dartlang-sdk:///sdk/lib/collection/list.dart */ listToString(core::List<core::Object?> list) → core::String
-    return col::IterableBase::iterableToFullString(list, "[", "]");
+    return core::Iterable::iterableToFullString(list, "[", "]");
 }
 class CustomList<E extends core::Object? = dynamic> extends cac::_CustomList&Object&ListMixin<cac::CustomList::E%> {
   final field core::List<cac::CustomList::E%> list;
diff --git a/pkg/front_end/testcases/patterns/cache_lookups.dart.weak.transformed.expect b/pkg/front_end/testcases/patterns/cache_lookups.dart.weak.transformed.expect
index f7b2c9ab3ab..0ce369f137d 100644
--- a/pkg/front_end/testcases/patterns/cache_lookups.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/patterns/cache_lookups.dart.weak.transformed.expect
@@ -589,7 +589,7 @@ abstract class _CustomList&Object&ListMixin<E extends core::Object? = dynamic> e
     return core::Comparable::compare(a as{ForNonNullableByDefault} core::Comparable<dynamic>, b as{ForNonNullableByDefault} core::Comparable<dynamic>);
   }
   static method /* from org-dartlang-sdk:///sdk/lib/collection/list.dart */ listToString(core::List<core::Object?> list) → core::String
-    return col::IterableBase::iterableToFullString(list, "[", "]");
+    return core::Iterable::iterableToFullString(list, "[", "]");
 }
 class CustomList<E extends core::Object? = dynamic> extends cac::_CustomList&Object&ListMixin<cac::CustomList::E%> {
   final field core::List<cac::CustomList::E%> list;
diff --git a/pkg/front_end/testcases/patterns/caching_constants.dart.strong.transformed.expect b/pkg/front_end/testcases/patterns/caching_constants.dart.strong.transformed.expect
index 392d1ca5b24..f19c8b42bde 100644
--- a/pkg/front_end/testcases/patterns/caching_constants.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/patterns/caching_constants.dart.strong.transformed.expect
@@ -2,6 +2,7 @@ library /*isNonNullableByDefault*/;
 import self as self;
 import "dart:core" as core;
 import "dart:collection" as col;
+import "dart:_internal" as _in;
 
 import "dart:collection";
 
@@ -134,12 +135,12 @@ abstract class _MyMap&Object&MapMixin<K extends core::Object? = dynamic, V exten
   method /* from org-dartlang-sdk:///sdk/lib/collection/maps.dart */ toString() → core::String
     return col::MapBase::mapToString(this);
   static method /* from org-dartlang-sdk:///sdk/lib/collection/maps.dart */ mapToString(core::Map<core::Object?, core::Object?> m) → core::String {
-    if(col::_isToStringVisiting(m)) {
+    if(_in::isToStringVisiting(m)) {
       return "{...}";
     }
     core::StringBuffer result = new core::StringBuffer::•();
     try {
-      col::_toStringVisiting.{core::List::add}(m){(core::Object) → void};
+      _in::toStringVisiting.{core::List::add}(m){(core::Object) → void};
       result.{core::StringBuffer::write}("{"){(core::Object?) → void};
       core::bool first = true;
       m.{core::Map::forEach}((core::Object? k, core::Object? v) → void {
@@ -154,8 +155,8 @@ abstract class _MyMap&Object&MapMixin<K extends core::Object? = dynamic, V exten
       result.{core::StringBuffer::write}("}"){(core::Object?) → void};
     }
     finally {
-      assert(core::identical(col::_toStringVisiting.{core::Iterable::last}{core::Object}, m));
-      col::_toStringVisiting.{core::List::removeLast}(){() → core::Object};
+      assert(core::identical(_in::toStringVisiting.{core::Iterable::last}{core::Object}, m));
+      _in::toStringVisiting.{core::List::removeLast}(){() → core::Object};
     }
     return result.{core::StringBuffer::toString}(){() → core::String};
   }
diff --git a/pkg/front_end/testcases/patterns/caching_constants.dart.weak.transformed.expect b/pkg/front_end/testcases/patterns/caching_constants.dart.weak.transformed.expect
index ea21d58eccf..50f97e002e8 100644
--- a/pkg/front_end/testcases/patterns/caching_constants.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/patterns/caching_constants.dart.weak.transformed.expect
@@ -2,6 +2,7 @@ library /*isNonNullableByDefault*/;
 import self as self;
 import "dart:core" as core;
 import "dart:collection" as col;
+import "dart:_internal" as _in;
 
 import "dart:collection";
 
@@ -134,12 +135,12 @@ abstract class _MyMap&Object&MapMixin<K extends core::Object? = dynamic, V exten
   method /* from org-dartlang-sdk:///sdk/lib/collection/maps.dart */ toString() → core::String
     return col::MapBase::mapToString(this);
   static method /* from org-dartlang-sdk:///sdk/lib/collection/maps.dart */ mapToString(core::Map<core::Object?, core::Object?> m) → core::String {
-    if(col::_isToStringVisiting(m)) {
+    if(_in::isToStringVisiting(m)) {
       return "{...}";
     }
     core::StringBuffer result = new core::StringBuffer::•();
     try {
-      col::_toStringVisiting.{core::List::add}(m){(core::Object) → void};
+      _in::toStringVisiting.{core::List::add}(m){(core::Object) → void};
       result.{core::StringBuffer::write}("{"){(core::Object?) → void};
       core::bool first = true;
       m.{core::Map::forEach}((core::Object? k, core::Object? v) → void {
@@ -154,8 +155,8 @@ abstract class _MyMap&Object&MapMixin<K extends core::Object? = dynamic, V exten
       result.{core::StringBuffer::write}("}"){(core::Object?) → void};
     }
     finally {
-      assert(core::identical(col::_toStringVisiting.{core::Iterable::last}{core::Object}, m));
-      col::_toStringVisiting.{core::List::removeLast}(){() → core::Object};
+      assert(core::identical(_in::toStringVisiting.{core::Iterable::last}{core::Object}, m));
+      _in::toStringVisiting.{core::List::removeLast}(){() → core::Object};
     }
     return result.{core::StringBuffer::toString}(){() → core::String};
   }
diff --git a/pkg/front_end/testcases/patterns/matching_and_capturing_accesses_list_element_once.dart.strong.transformed.expect b/pkg/front_end/testcases/patterns/matching_and_capturing_accesses_list_element_once.dart.strong.transformed.expect
index 2ffaec0db16..a29b8a2e9af 100644
--- a/pkg/front_end/testcases/patterns/matching_and_capturing_accesses_list_element_once.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/patterns/matching_and_capturing_accesses_list_element_once.dart.strong.transformed.expect
@@ -518,7 +518,7 @@ abstract class _A&Object&ListMixin extends core::Object implements col::ListBase
     return core::Comparable::compare(a as{ForNonNullableByDefault} core::Comparable<dynamic>, b as{ForNonNullableByDefault} core::Comparable<dynamic>);
   }
   static method /* from org-dartlang-sdk:///sdk/lib/collection/list.dart */ listToString(core::List<core::Object?> list) → core::String
-    return col::IterableBase::iterableToFullString(list, "[", "]");
+    return core::Iterable::iterableToFullString(list, "[", "]");
 }
 class A extends self::_A&Object&ListMixin {
   field core::int count = 0;
diff --git a/pkg/front_end/testcases/patterns/matching_and_capturing_accesses_list_element_once.dart.weak.transformed.expect b/pkg/front_end/testcases/patterns/matching_and_capturing_accesses_list_element_once.dart.weak.transformed.expect
index 30337eaa12e..04e05873c55 100644
--- a/pkg/front_end/testcases/patterns/matching_and_capturing_accesses_list_element_once.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/patterns/matching_and_capturing_accesses_list_element_once.dart.weak.transformed.expect
@@ -518,7 +518,7 @@ abstract class _A&Object&ListMixin extends core::Object implements col::ListBase
     return core::Comparable::compare(a as{ForNonNullableByDefault} core::Comparable<dynamic>, b as{ForNonNullableByDefault} core::Comparable<dynamic>);
   }
   static method /* from org-dartlang-sdk:///sdk/lib/collection/list.dart */ listToString(core::List<core::Object?> list) → core::String
-    return col::IterableBase::iterableToFullString(list, "[", "]");
+    return core::Iterable::iterableToFullString(list, "[", "]");
 }
 class A extends self::_A&Object&ListMixin {
   field core::int count = 0;
diff --git a/pkg/front_end/testcases/patterns/negative_length.dart.strong.transformed.expect b/pkg/front_end/testcases/patterns/negative_length.dart.strong.transformed.expect
index 4b6d539a5cf..c7aaf2be0ce 100644
--- a/pkg/front_end/testcases/patterns/negative_length.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/patterns/negative_length.dart.strong.transformed.expect
@@ -518,7 +518,7 @@ abstract class _NegativeLengthList&Object&ListMixin<E extends core::Object? = dy
     return core::Comparable::compare(a as{ForNonNullableByDefault} core::Comparable<dynamic>, b as{ForNonNullableByDefault} core::Comparable<dynamic>);
   }
   static method /* from org-dartlang-sdk:///sdk/lib/collection/list.dart */ listToString(core::List<core::Object?> list) → core::String
-    return col::IterableBase::iterableToFullString(list, "[", "]");
+    return core::Iterable::iterableToFullString(list, "[", "]");
 }
 class NegativeLengthList<E extends core::Object? = dynamic> extends self::_NegativeLengthList&Object&ListMixin<self::NegativeLengthList::E%> {
   final field core::List<self::NegativeLengthList::E%> _list;
diff --git a/pkg/front_end/testcases/patterns/negative_length.dart.weak.transformed.expect b/pkg/front_end/testcases/patterns/negative_length.dart.weak.transformed.expect
index e297255e10f..d3c97a86829 100644
--- a/pkg/front_end/testcases/patterns/negative_length.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/patterns/negative_length.dart.weak.transformed.expect
@@ -518,7 +518,7 @@ abstract class _NegativeLengthList&Object&ListMixin<E extends core::Object? = dy
     return core::Comparable::compare(a as{ForNonNullableByDefault} core::Comparable<dynamic>, b as{ForNonNullableByDefault} core::Comparable<dynamic>);
   }
   static method /* from org-dartlang-sdk:///sdk/lib/collection/list.dart */ listToString(core::List<core::Object?> list) → core::String
-    return col::IterableBase::iterableToFullString(list, "[", "]");
+    return core::Iterable::iterableToFullString(list, "[", "]");
 }
 class NegativeLengthList<E extends core::Object? = dynamic> extends self::_NegativeLengthList&Object&ListMixin<self::NegativeLengthList::E%> {
   final field core::List<self::NegativeLengthList::E%> _list;
diff --git a/runtime/observatory/tests/service/sdk_break_with_mixin_test.dart b/runtime/observatory/tests/service/sdk_break_with_mixin_test.dart
index eaaa0568700..785e0ddf16a 100644
--- a/runtime/observatory/tests/service/sdk_break_with_mixin_test.dart
+++ b/runtime/observatory/tests/service/sdk_break_with_mixin_test.dart
@@ -36,7 +36,7 @@ List<String> stops = [];
 // THIS TEST DEPENDS ON SPECIFIC LINE NUMBERS IN UNRELATED PLATFORM LIBRARIES
 // STAYING FIXED. VERY FRAGILE. SHOULD BE FIXED OR REMOVED.
 List<String> expected = [
-  "set.dart:142:23 (sdk_break_with_mixin_test.dart:20:5)",
+  "set.dart:142:21 (sdk_break_with_mixin_test.dart:20:5)",
 ];
 
 var tests = <IsolateTest>[
diff --git a/runtime/observatory_2/tests/service_2/sdk_break_with_mixin_test.dart b/runtime/observatory_2/tests/service_2/sdk_break_with_mixin_test.dart
index d7b87cae42f..a5ab4496efd 100644
--- a/runtime/observatory_2/tests/service_2/sdk_break_with_mixin_test.dart
+++ b/runtime/observatory_2/tests/service_2/sdk_break_with_mixin_test.dart
@@ -35,7 +35,7 @@ class MySet extends Object with SetMixin {
 
 List<String> stops = [];
 List<String> expected = [
-  "set.dart:142:23 (sdk_break_with_mixin_test.dart:21:5)",
+  "set.dart:142:21 (sdk_break_with_mixin_test.dart:21:5)",
 ];
 
 var tests = <IsolateTest>[
diff --git a/sdk/lib/_internal/js_dev_runtime/private/js_helper.dart b/sdk/lib/_internal/js_dev_runtime/private/js_helper.dart
index 344b247a4b0..e303cd9febb 100644
--- a/sdk/lib/_internal/js_dev_runtime/private/js_helper.dart
+++ b/sdk/lib/_internal/js_dev_runtime/private/js_helper.dart
@@ -53,7 +53,7 @@ class DartIterator<E> implements Iterator<E> {
 }
 
 /// Used to compile `sync*`.
-class SyncIterable<E> extends IterableBase<E> {
+class SyncIterable<E> extends Iterable<E> {
   final Function() _initGenerator;
   SyncIterable(this._initGenerator);
 
diff --git a/sdk/lib/_internal/js_dev_runtime/private/regexp_helper.dart b/sdk/lib/_internal/js_dev_runtime/private/regexp_helper.dart
index 64af42d3763..15f05b56e06 100644
--- a/sdk/lib/_internal/js_dev_runtime/private/regexp_helper.dart
+++ b/sdk/lib/_internal/js_dev_runtime/private/regexp_helper.dart
@@ -230,7 +230,7 @@ class _MatchImplementation implements RegExpMatch {
   }
 }
 
-class _AllMatchesIterable extends IterableBase<RegExpMatch> {
+class _AllMatchesIterable extends Iterable<RegExpMatch> {
   final JSSyntaxRegExp _re;
   final String _string;
   final int _start;
diff --git a/sdk/lib/_internal/js_runtime/lib/async_patch.dart b/sdk/lib/_internal/js_runtime/lib/async_patch.dart
index b2fcf453979..e731cb4897f 100644
--- a/sdk/lib/_internal/js_runtime/lib/async_patch.dart
+++ b/sdk/lib/_internal/js_runtime/lib/async_patch.dart
@@ -18,8 +18,6 @@ import 'dart:_foreign_helper' show JS, JS_GET_FLAG;
 
 import 'dart:_async_await_error_codes' as async_error_codes;
 
-import "dart:collection" show IterableBase;
-
 @patch
 class _AsyncRun {
   @patch
@@ -686,7 +684,7 @@ _SyncStarIterable<T> _makeSyncStarIterable<T>(body) {
 /// An Iterable corresponding to a sync* method.
 ///
 /// Each invocation of a sync* method will return a new instance of this class.
-class _SyncStarIterable<T> extends IterableBase<T> {
+class _SyncStarIterable<T> extends Iterable<T> {
   // This is a function that will return a helper function that does the
   // iteration of the sync*.
   //
diff --git a/sdk/lib/_internal/js_runtime/lib/regexp_helper.dart b/sdk/lib/_internal/js_runtime/lib/regexp_helper.dart
index 4ba4ae51859..ef52926cc69 100644
--- a/sdk/lib/_internal/js_runtime/lib/regexp_helper.dart
+++ b/sdk/lib/_internal/js_runtime/lib/regexp_helper.dart
@@ -230,7 +230,7 @@ class _MatchImplementation implements RegExpMatch {
   }
 }
 
-class _AllMatchesIterable extends IterableBase<RegExpMatch> {
+class _AllMatchesIterable extends Iterable<RegExpMatch> {
   final JSSyntaxRegExp _re;
   final String _string;
   final int _start;
diff --git a/sdk/lib/_internal/vm/lib/core_patch.dart b/sdk/lib/_internal/vm/lib/core_patch.dart
index 7833080335d..0bc6e082354 100644
--- a/sdk/lib/_internal/vm/lib/core_patch.dart
+++ b/sdk/lib/_internal/vm/lib/core_patch.dart
@@ -42,7 +42,6 @@ import "dart:async" show Completer, DeferredLoadException, Future, Timer, Zone;
 import "dart:collection"
     show
         HashMap,
-        IterableBase,
         LinkedHashMap,
         LinkedList,
         LinkedListEntry,
diff --git a/sdk/lib/_internal/vm/lib/regexp_patch.dart b/sdk/lib/_internal/vm/lib/regexp_patch.dart
index d906954d7c8..cc25bcf9aea 100644
--- a/sdk/lib/_internal/vm/lib/regexp_patch.dart
+++ b/sdk/lib/_internal/vm/lib/regexp_patch.dart
@@ -323,7 +323,7 @@ class _RegExp implements RegExp {
       Int32List(_initialBacktrackingStackSize);
 }
 
-class _AllMatchesIterable extends IterableBase<RegExpMatch> {
+class _AllMatchesIterable extends Iterable<RegExpMatch> {
   final _RegExp _re;
   final String _str;
   final int _start;
diff --git a/sdk/lib/_internal/wasm/lib/core_patch.dart b/sdk/lib/_internal/wasm/lib/core_patch.dart
index 19784e4598a..4f95ee3a80b 100644
--- a/sdk/lib/_internal/wasm/lib/core_patch.dart
+++ b/sdk/lib/_internal/wasm/lib/core_patch.dart
@@ -35,7 +35,6 @@ import 'dart:_js_helper' show JS, JSSyntaxRegExp, quoteStringForRegExp;
 import "dart:collection"
     show
         HashMap,
-        IterableBase,
         LinkedHashMap,
         LinkedList,
         LinkedListEntry,
diff --git a/sdk/lib/_internal/wasm/lib/regexp_helper.dart b/sdk/lib/_internal/wasm/lib/regexp_helper.dart
index 89e4922ba27..11a7b57f29a 100644
--- a/sdk/lib/_internal/wasm/lib/regexp_helper.dart
+++ b/sdk/lib/_internal/wasm/lib/regexp_helper.dart
@@ -219,7 +219,7 @@ class _MatchImplementation implements RegExpMatch {
   }
 }
 
-class _AllMatchesIterable extends IterableBase<RegExpMatch> {
+class _AllMatchesIterable extends Iterable<RegExpMatch> {
   final JSSyntaxRegExp _re;
   final String _string;
   final int _start;
diff --git a/sdk/lib/collection/iterable.dart b/sdk/lib/collection/iterable.dart
index 340c093bebf..d062dd60ca4 100644
--- a/sdk/lib/collection/iterable.dart
+++ b/sdk/lib/collection/iterable.dart
@@ -7,396 +7,12 @@ part of dart.collection;
 /// This [Iterable] mixin implements all [Iterable] members except `iterator`.
 ///
 /// All other methods are implemented in terms of `iterator`.
-abstract mixin class IterableMixin<E> implements Iterable<E> {
-  // This class has methods copied verbatim into:
-  // - IterableBase
-  // - SetMixin
-  // If changing a method here, also change the other copies.
-
-  Iterable<R> cast<R>() => Iterable.castFrom<E, R>(this);
-  Iterable<T> map<T>(T toElement(E element)) =>
-      MappedIterable<E, T>(this, toElement);
-
-  Iterable<E> where(bool test(E element)) => WhereIterable<E>(this, test);
-
-  Iterable<T> whereType<T>() => WhereTypeIterable<T>(this);
-
-  Iterable<T> expand<T>(Iterable<T> toElements(E element)) =>
-      ExpandIterable<E, T>(this, toElements);
-
-  Iterable<E> followedBy(Iterable<E> other) {
-    // Type workaround because IterableMixin<E> doesn't promote
-    // to EfficientLengthIterable<E>.
-    Iterable<E> self = this;
-    if (self is EfficientLengthIterable<E>) {
-      return FollowedByIterable<E>.firstEfficient(self, other);
-    }
-    return FollowedByIterable<E>(this, other);
-  }
-
-  bool contains(Object? element) {
-    for (E e in this) {
-      if (e == element) return true;
-    }
-    return false;
-  }
-
-  void forEach(void action(E element)) {
-    for (E element in this) action(element);
-  }
-
-  E reduce(E combine(E value, E element)) {
-    Iterator<E> iterator = this.iterator;
-    if (!iterator.moveNext()) {
-      throw IterableElementError.noElement();
-    }
-    E value = iterator.current;
-    while (iterator.moveNext()) {
-      value = combine(value, iterator.current);
-    }
-    return value;
-  }
-
-  T fold<T>(T initialValue, T combine(T previousValue, E element)) {
-    var value = initialValue;
-    for (E element in this) value = combine(value, element);
-    return value;
-  }
-
-  bool every(bool test(E element)) {
-    for (E element in this) {
-      if (!test(element)) return false;
-    }
-    return true;
-  }
-
-  String join([String separator = ""]) {
-    Iterator<E> iterator = this.iterator;
-    if (!iterator.moveNext()) return "";
-    StringBuffer buffer = StringBuffer();
-    if (separator == null || separator == "") {
-      do {
-        buffer.write("${iterator.current}");
-      } while (iterator.moveNext());
-    } else {
-      buffer.write("${iterator.current}");
-      while (iterator.moveNext()) {
-        buffer.write(separator);
-        buffer.write("${iterator.current}");
-      }
-    }
-    return buffer.toString();
-  }
-
-  bool any(bool test(E element)) {
-    for (E element in this) {
-      if (test(element)) return true;
-    }
-    return false;
-  }
-
-  List<E> toList({bool growable = true}) =>
-      List<E>.from(this, growable: growable);
-
-  Set<E> toSet() => Set<E>.from(this);
-
-  int get length {
-    assert(this is! EfficientLengthIterable);
-    int count = 0;
-    Iterator it = iterator;
-    while (it.moveNext()) {
-      count++;
-    }
-    return count;
-  }
-
-  bool get isEmpty => !iterator.moveNext();
-
-  bool get isNotEmpty => !isEmpty;
-
-  Iterable<E> take(int count) {
-    return TakeIterable<E>(this, count);
-  }
-
-  Iterable<E> takeWhile(bool test(E value)) {
-    return TakeWhileIterable<E>(this, test);
-  }
-
-  Iterable<E> skip(int count) {
-    return SkipIterable<E>(this, count);
-  }
-
-  Iterable<E> skipWhile(bool test(E value)) {
-    return SkipWhileIterable<E>(this, test);
-  }
-
-  E get first {
-    Iterator<E> it = iterator;
-    if (!it.moveNext()) {
-      throw IterableElementError.noElement();
-    }
-    return it.current;
-  }
-
-  E get last {
-    Iterator<E> it = iterator;
-    if (!it.moveNext()) {
-      throw IterableElementError.noElement();
-    }
-    E result;
-    do {
-      result = it.current;
-    } while (it.moveNext());
-    return result;
-  }
-
-  E get single {
-    Iterator<E> it = iterator;
-    if (!it.moveNext()) throw IterableElementError.noElement();
-    E result = it.current;
-    if (it.moveNext()) throw IterableElementError.tooMany();
-    return result;
-  }
-
-  E firstWhere(bool test(E value), {E Function()? orElse}) {
-    for (E element in this) {
-      if (test(element)) return element;
-    }
-    if (orElse != null) return orElse();
-    throw IterableElementError.noElement();
-  }
-
-  E lastWhere(bool test(E value), {E Function()? orElse}) {
-    late E result;
-    bool foundMatching = false;
-    for (E element in this) {
-      if (test(element)) {
-        result = element;
-        foundMatching = true;
-      }
-    }
-    if (foundMatching) return result;
-    if (orElse != null) return orElse();
-    throw IterableElementError.noElement();
-  }
-
-  E singleWhere(bool test(E element), {E Function()? orElse}) {
-    late E result;
-    bool foundMatching = false;
-    for (E element in this) {
-      if (test(element)) {
-        if (foundMatching) {
-          throw IterableElementError.tooMany();
-        }
-        result = element;
-        foundMatching = true;
-      }
-    }
-    if (foundMatching) return result;
-    if (orElse != null) return orElse();
-    throw IterableElementError.noElement();
-  }
-
-  E elementAt(int index) {
-    checkNotNullable(index, "index");
-    RangeError.checkNotNegative(index, "index");
-    int elementIndex = 0;
-    for (E element in this) {
-      if (index == elementIndex) return element;
-      elementIndex++;
-    }
-    throw IndexError.withLength(index, elementIndex,
-        indexable: this, name: "index");
-  }
-
-  String toString() => IterableBase.iterableToShortString(this, '(', ')');
-}
+// @Deprecated("Use Iterable instead")
+typedef IterableMixin<E> = Iterable<E>;
 
 /// Base class for implementing [Iterable].
 ///
 /// This class implements all methods of [Iterable], except [Iterable.iterator],
 /// in terms of `iterator`.
-abstract class IterableBase<E> extends Iterable<E> {
-  const IterableBase();
-
-  /// Convert an `Iterable` to a string like [IterableBase.toString].
-  ///
-  /// Allows using other delimiters than '(' and ')'.
-  ///
-  /// Handles circular references where converting one of the elements
-  /// to a string ends up converting [iterable] to a string again.
-  static String iterableToShortString(Iterable iterable,
-      [String leftDelimiter = '(', String rightDelimiter = ')']) {
-    if (_isToStringVisiting(iterable)) {
-      if (leftDelimiter == "(" && rightDelimiter == ")") {
-        // Avoid creating a new string in the "common" case.
-        return "(...)";
-      }
-      return "$leftDelimiter...$rightDelimiter";
-    }
-    List<String> parts = <String>[];
-    _toStringVisiting.add(iterable);
-    try {
-      _iterablePartsToStrings(iterable, parts);
-    } finally {
-      assert(identical(_toStringVisiting.last, iterable));
-      _toStringVisiting.removeLast();
-    }
-    return (StringBuffer(leftDelimiter)
-          ..writeAll(parts, ", ")
-          ..write(rightDelimiter))
-        .toString();
-  }
-
-  /// Converts an `Iterable` to a string.
-  ///
-  /// Converts each elements to a string, and separates the results by ", ".
-  /// Then wraps the result in [leftDelimiter] and [rightDelimiter].
-  ///
-  /// Unlike [iterableToShortString], this conversion doesn't omit any
-  /// elements or puts any limit on the size of the result.
-  ///
-  /// Handles circular references where converting one of the elements
-  /// to a string ends up converting [iterable] to a string again.
-  static String iterableToFullString(Iterable iterable,
-      [String leftDelimiter = '(', String rightDelimiter = ')']) {
-    if (_isToStringVisiting(iterable)) {
-      return "$leftDelimiter...$rightDelimiter";
-    }
-    StringBuffer buffer = StringBuffer(leftDelimiter);
-    _toStringVisiting.add(iterable);
-    try {
-      buffer.writeAll(iterable, ", ");
-    } finally {
-      assert(identical(_toStringVisiting.last, iterable));
-      _toStringVisiting.removeLast();
-    }
-    buffer.write(rightDelimiter);
-    return buffer.toString();
-  }
-}
-
-/// A collection used to identify cyclic lists during toString() calls.
-final List<Object> _toStringVisiting = [];
-
-/// Check if we are currently visiting `o` in a toString call.
-bool _isToStringVisiting(Object o) {
-  for (int i = 0; i < _toStringVisiting.length; i++) {
-    if (identical(o, _toStringVisiting[i])) return true;
-  }
-  return false;
-}
-
-/// Convert elements of [iterable] to strings and store them in [parts].
-void _iterablePartsToStrings(Iterable<Object?> iterable, List<String> parts) {
-  /*
-   * This is the complicated part of [iterableToShortString].
-   * It is extracted as a separate function to avoid having too much code
-   * inside the try/finally.
-   */
-  /// Try to stay below this many characters.
-  const int lengthLimit = 80;
-
-  /// Always at least this many elements at the start.
-  const int headCount = 3;
-
-  /// Always at least this many elements at the end.
-  const int tailCount = 2;
-
-  /// Stop iterating after this many elements. Iterables can be infinite.
-  const int maxCount = 100;
-  // Per entry length overhead. It's for ", " for all after the first entry,
-  // and for "(" and ")" for the initial entry. By pure luck, that's the same
-  // number.
-  const int overhead = 2;
-  const int ellipsisSize = 3; // "...".length.
-
-  int length = 0;
-  int count = 0;
-  Iterator<Object?> it = iterable.iterator;
-  // Initial run of elements, at least headCount, and then continue until
-  // passing at most lengthLimit characters.
-  while (length < lengthLimit || count < headCount) {
-    if (!it.moveNext()) return;
-    String next = "${it.current}";
-    parts.add(next);
-    length += next.length + overhead;
-    count++;
-  }
-
-  String penultimateString;
-  String ultimateString;
-
-  // Find last two elements. One or more of them may already be in the
-  // parts array. Include their length in `length`.
-  if (!it.moveNext()) {
-    if (count <= headCount + tailCount) return;
-    ultimateString = parts.removeLast();
-    penultimateString = parts.removeLast();
-  } else {
-    Object? penultimate = it.current;
-    count++;
-    if (!it.moveNext()) {
-      if (count <= headCount + 1) {
-        parts.add("$penultimate");
-        return;
-      }
-      ultimateString = "$penultimate";
-      penultimateString = parts.removeLast();
-      length += ultimateString.length + overhead;
-    } else {
-      Object? ultimate = it.current;
-      count++;
-      // Then keep looping, keeping the last two elements in variables.
-      assert(count < maxCount);
-      while (it.moveNext()) {
-        penultimate = ultimate;
-        ultimate = it.current;
-        count++;
-        if (count > maxCount) {
-          // If we haven't found the end before maxCount, give up.
-          // This cannot happen in the code above because each entry
-          // increases length by at least two, so there is no way to
-          // visit more than ~40 elements before this loop.
-
-          // Remove any surplus elements until length, including ", ...)",
-          // is at most lengthLimit.
-          while (length > lengthLimit - ellipsisSize - overhead &&
-              count > headCount) {
-            length -= parts.removeLast().length + overhead;
-            count--;
-          }
-          parts.add("...");
-          return;
-        }
-      }
-      penultimateString = "$penultimate";
-      ultimateString = "$ultimate";
-      length += ultimateString.length + penultimateString.length + 2 * overhead;
-    }
-  }
-
-  // If there is a gap between the initial run and the last two,
-  // prepare to add an ellipsis.
-  String? elision;
-  if (count > parts.length + tailCount) {
-    elision = "...";
-    length += ellipsisSize + overhead;
-  }
-
-  // If the last two elements were very long, and we have more than
-  // headCount elements in the initial run, drop some to make room for
-  // the last two.
-  while (length > lengthLimit && parts.length > headCount) {
-    length -= parts.removeLast().length + overhead;
-    if (elision == null) {
-      elision = "...";
-      length += ellipsisSize + overhead;
-    }
-  }
-  if (elision != null) {
-    parts.add(elision);
-  }
-  parts.add(penultimateString);
-  parts.add(ultimateString);
-}
+// @Deprecated("Use Iterable instead")
+typedef IterableBase<E> = Iterable<E>;
diff --git a/sdk/lib/collection/maps.dart b/sdk/lib/collection/maps.dart
index 793e11e5ea4..b217e2d07e2 100644
--- a/sdk/lib/collection/maps.dart
+++ b/sdk/lib/collection/maps.dart
@@ -109,14 +109,14 @@ abstract mixin class MapBase<K, V> implements Map<K, V> {
   String toString() => mapToString(this);
 
   static String mapToString(Map<Object?, Object?> m) {
-    // Reuses the list in IterableBase for detecting toString cycles.
-    if (_isToStringVisiting(m)) {
+    // Reuses the list used by Iterable for detecting toString cycles.
+    if (isToStringVisiting(m)) {
       return '{...}';
     }
 
     var result = StringBuffer();
     try {
-      _toStringVisiting.add(m);
+      toStringVisiting.add(m);
       result.write('{');
       bool first = true;
       m.forEach((Object? k, Object? v) {
@@ -130,8 +130,8 @@ abstract mixin class MapBase<K, V> implements Map<K, V> {
       });
       result.write('}');
     } finally {
-      assert(identical(_toStringVisiting.last, m));
-      _toStringVisiting.removeLast();
+      assert(identical(toStringVisiting.last, m));
+      toStringVisiting.removeLast();
     }
 
     return result.toString();
diff --git a/sdk/lib/collection/queue.dart b/sdk/lib/collection/queue.dart
index a55b8ff4ff4..8a0e3b4aee3 100644
--- a/sdk/lib/collection/queue.dart
+++ b/sdk/lib/collection/queue.dart
@@ -483,7 +483,7 @@ final class DoubleLinkedQueue<E> extends Iterable<E> implements Queue<E> {
     return _DoubleLinkedQueueIterator<E>(this);
   }
 
-  String toString() => IterableBase.iterableToFullString(this, '{', '}');
+  String toString() => Iterable.iterableToFullString(this, '{', '}');
 }
 
 class _DoubleLinkedQueueIterator<E> implements Iterator<E> {
@@ -803,7 +803,7 @@ final class ListQueue<E> extends ListIterable<E> implements Queue<E> {
     }
   }
 
-  String toString() => IterableBase.iterableToFullString(this, "{", "}");
+  String toString() => Iterable.iterableToFullString(this, "{", "}");
 
   // Queue interface.
 
diff --git a/sdk/lib/collection/set.dart b/sdk/lib/collection/set.dart
index 4baf1aaf754..5742cdcded5 100644
--- a/sdk/lib/collection/set.dart
+++ b/sdk/lib/collection/set.dart
@@ -133,6 +133,7 @@ abstract mixin class SetBase<E> implements Set<E> {
 
   // Copied from Iterable.
   // Should be inherited if we had multi-level mixins.
+
   Iterable<E> where(bool f(E element)) => WhereIterable<E>(this, f);
 
   Iterable<T> expand<T>(Iterable<T> f(E element)) =>
@@ -170,17 +171,20 @@ abstract mixin class SetBase<E> implements Set<E> {
   String join([String separator = ""]) {
     Iterator<E> iterator = this.iterator;
     if (!iterator.moveNext()) return "";
-    StringBuffer buffer = StringBuffer();
-    if (separator == null || separator == "") {
+    var first = iterator.current.toString();
+    if (!iterator.moveNext()) return first;
+    var buffer = StringBuffer(first);
+    // TODO(51681): Drop null check when de-supporting pre-2.12 code.
+    if (separator == null || separator.isEmpty) {
       do {
         buffer.write(iterator.current);
       } while (iterator.moveNext());
     } else {
-      buffer.write(iterator.current);
-      while (iterator.moveNext()) {
-        buffer.write(separator);
-        buffer.write(iterator.current);
-      }
+      do {
+        buffer
+          ..write(separator)
+          ..write(iterator.current);
+      } while (iterator.moveNext());
     }
     return buffer.toString();
   }
@@ -237,45 +241,47 @@ abstract mixin class SetBase<E> implements Set<E> {
   }
 
   E lastWhere(bool test(E value), {E Function()? orElse}) {
-    late E result;
-    bool foundMatching = false;
-    for (E element in this) {
-      if (test(element)) {
-        result = element;
-        foundMatching = true;
+    var iterator = this.iterator;
+    E result;
+    do {
+      if (!iterator.moveNext()) {
+        if (orElse != null) return orElse();
+        throw IterableElementError.noElement();
       }
+      result = iterator.current;
+    } while (!test(result));
+    while (iterator.moveNext()) {
+      var current = iterator.current;
+      if (test(current)) result = current;
     }
-    if (foundMatching) return result;
-    if (orElse != null) return orElse();
-    throw IterableElementError.noElement();
+    return result;
   }
 
   E singleWhere(bool test(E value), {E Function()? orElse}) {
-    late E result;
-    bool foundMatching = false;
-    for (E element in this) {
-      if (test(element)) {
-        if (foundMatching) {
-          throw IterableElementError.tooMany();
-        }
-        result = element;
-        foundMatching = true;
+    var iterator = this.iterator;
+    E result;
+    do {
+      if (!iterator.moveNext()) {
+        if (orElse != null) return orElse();
+        throw IterableElementError.noElement();
       }
+      result = iterator.current;
+    } while (!test(result));
+    while (iterator.moveNext()) {
+      if (test(iterator.current)) throw IterableElementError.tooMany();
     }
-    if (foundMatching) return result;
-    if (orElse != null) return orElse();
-    throw IterableElementError.noElement();
+    return result;
   }
 
   E elementAt(int index) {
-    checkNotNullable(index, "index");
     RangeError.checkNotNegative(index, "index");
-    int elementIndex = 0;
-    for (E element in this) {
-      if (index == elementIndex) return element;
-      elementIndex++;
+    var iterator = this.iterator;
+    var skipCount = index;
+    while (iterator.moveNext()) {
+      if (skipCount == 0) return iterator.current;
+      skipCount--;
     }
-    throw IndexError.withLength(index, elementIndex,
+    throw IndexError.withLength(index, index - skipCount,
         indexable: this, name: "index");
   }
 
diff --git a/sdk/lib/collection/splay_tree.dart b/sdk/lib/collection/splay_tree.dart
index 54627b72148..8c6df2dad9b 100644
--- a/sdk/lib/collection/splay_tree.dart
+++ b/sdk/lib/collection/splay_tree.dart
@@ -947,7 +947,7 @@ class _SplayTreeMapEntryIterator<K, V>
 /// * [HashSet] the order of the objects in the iterations is not guaranteed.
 /// * [LinkedHashSet] objects stored based on insertion order.
 final class SplayTreeSet<E> extends _SplayTree<E, _SplayTreeSetNode<E>>
-    with IterableMixin<E>, SetMixin<E> {
+    with Iterable<E>, SetMixin<E> {
   _SplayTreeSetNode<E>? _root;
 
   Comparator<E> _compare;
@@ -1188,5 +1188,5 @@ final class SplayTreeSet<E> extends _SplayTree<E, _SplayTreeSetNode<E>>
 
   Set<E> toSet() => _clone();
 
-  String toString() => IterableBase.iterableToFullString(this, '{', '}');
+  String toString() => Iterable.iterableToFullString(this, '{', '}');
 }
diff --git a/sdk/lib/core/iterable.dart b/sdk/lib/core/iterable.dart
index be894489a1d..474e1fb1da3 100644
--- a/sdk/lib/core/iterable.dart
+++ b/sdk/lib/core/iterable.dart
@@ -81,9 +81,19 @@ part of dart.core;
 /// For methods like [map] and [where], the returned iterable will execute the
 /// argument function on every iteration, so those functions should also not
 /// have side effects.
-abstract class Iterable<E> {
-  // TODO(lrn): When we allow forwarding const constructors through
-  // mixin applications, make this class implement [IterableMixin].
+///
+/// The `Iterable` declaration provides a default implementation,
+/// which can be extended or mixed in to implement the `Iterable` interface.
+/// It implements every member other than the [iterator] getter,
+/// using the [Iterator] provided by [iterator].
+/// An implementation of the `Iterable` interface should
+/// provide a more efficient implementation of the members of `Iterable`
+/// when it can do so.
+abstract mixin class Iterable<E> {
+  // This class has methods copied verbatim into:
+  // - SetMixin
+  // If changing a method here, also change other copies.
+
   const Iterable();
 
   /// Creates an `Iterable` which generates its elements dynamically.
@@ -100,7 +110,19 @@ abstract class Iterable<E> {
   /// As an `Iterable`, `Iterable.generate(n, generator))` is equivalent to
   /// `const [0, ..., n - 1].map(generator)`.
   factory Iterable.generate(int count, [E generator(int index)?]) {
+    // Always OK to omit generator when count is zero.
     if (count <= 0) return EmptyIterable<E>();
+    if (generator == null) {
+      // If generator is omitted, we generate integers.
+      // If `E` does not allow integers, it's an error.
+      Function id = _GeneratorIterable._id;
+      if (id is! E Function(int)) {
+        throw ArgumentError(
+            "Generator must be supplied or element type must allow integers",
+            "generator");
+      }
+      generator = id;
+    }
     return _GeneratorIterable<E>(count, generator);
   }
 
@@ -119,8 +141,7 @@ abstract class Iterable<E> {
   static Iterable<T> castFrom<S, T>(Iterable<S> source) =>
       CastIterable<S, T>(source);
 
-  /// Returns a new `Iterator` that allows iterating the elements of this
-  /// `Iterable`.
+  /// A new `Iterator` that allows iterating the elements of this `Iterable`.
   ///
   /// Iterable classes may specify the iteration order of their elements
   /// (for example [List] always iterate in index order),
@@ -147,7 +168,7 @@ abstract class Iterable<E> {
   /// break iteration.
   Iterator<E> get iterator;
 
-  /// Provides a view of this iterable as an iterable of [R] instances.
+  /// A view of this iterable as an iterable of [R] instances.
   ///
   /// If this iterable only contains instances of [R], all operations
   /// will work correctly. If any operation tries to access an element
@@ -155,9 +176,9 @@ abstract class Iterable<E> {
   ///
   /// When the returned iterable creates a new object that depends on
   /// the type [R], e.g., from [toList], it will have exactly the type [R].
-  Iterable<R> cast<R>() => Iterable.castFrom<E, R>(this);
+  Iterable<R> cast<R>() => CastIterable<E, R>(this);
 
-  /// Returns the lazy concatenation of this iterable and [other].
+  /// Creates the lazy concatenation of this iterable and [other].
   ///
   /// The returned iterable will provide the same elements as this iterable,
   /// and, after that, the elements of [other], in the same order as in the
@@ -216,7 +237,7 @@ abstract class Iterable<E> {
   /// ```
   Iterable<T> map<T>(T toElement(E e)) => MappedIterable<E, T>(this, toElement);
 
-  /// Returns a new lazy [Iterable] with all elements that satisfy the
+  /// Creates a new lazy [Iterable] with all elements that satisfy the
   /// predicate [test].
   ///
   /// The matching elements have the same order in the returned iterable
@@ -238,7 +259,7 @@ abstract class Iterable<E> {
   /// ```
   Iterable<E> where(bool test(E element)) => WhereIterable<E>(this, test);
 
-  /// Returns a new lazy [Iterable] with all elements that have type [T].
+  /// Creates a new lazy [Iterable] with all elements that have type [T].
   ///
   /// The matching elements have the same order in the returned iterable
   /// as they have in [iterator].
@@ -421,17 +442,20 @@ abstract class Iterable<E> {
   String join([String separator = ""]) {
     Iterator<E> iterator = this.iterator;
     if (!iterator.moveNext()) return "";
-    StringBuffer buffer = StringBuffer();
-    if (separator == null || separator == "") {
+    var first = iterator.current.toString();
+    if (!iterator.moveNext()) return first;
+    var buffer = StringBuffer(first);
+    // TODO(51681): Drop null check when de-supporting pre-2.12 code.
+    if (separator == null || separator.isEmpty) {
       do {
         buffer.write(iterator.current.toString());
       } while (iterator.moveNext());
     } else {
-      buffer.write(iterator.current.toString());
-      while (iterator.moveNext()) {
-        buffer.write(separator);
-        buffer.write(iterator.current.toString());
-      }
+      do {
+        buffer
+          ..write(separator)
+          ..write(iterator.current.toString());
+      } while (iterator.moveNext());
     }
     return buffer.toString();
   }
@@ -466,9 +490,8 @@ abstract class Iterable<E> {
   /// final valuesList =
   ///     planets.values.toList(growable: false); // [Mercury, Venus, Mars]
   /// ```
-  List<E> toList({bool growable = true}) {
-    return List<E>.of(this, growable: growable);
-  }
+  List<E> toList({bool growable = true}) =>
+      List<E>.of(this, growable: growable);
 
   /// Creates a [Set] containing the same elements as this iterable.
   ///
@@ -485,15 +508,16 @@ abstract class Iterable<E> {
   /// ```
   Set<E> toSet() => Set<E>.of(this);
 
-  /// Returns the number of elements in [this].
+  /// The number of elements in [this].
   ///
   /// Counting all elements may involve iterating through all elements and can
   /// therefore be slow.
   /// Some iterables have a more efficient way to find the number of elements.
+  /// These *must* override the default implementation of `length`.
   int get length {
     assert(this is! EfficientLengthIterable);
     int count = 0;
-    Iterator it = iterator;
+    Iterator<Object?> it = iterator;
     while (it.moveNext()) {
       count++;
     }
@@ -524,7 +548,7 @@ abstract class Iterable<E> {
   /// ```
   bool get isNotEmpty => !isEmpty;
 
-  /// Returns a lazy iterable of the [count] first elements of this iterable.
+  /// Creates a lazy iterable of the [count] first elements of this iterable.
   ///
   /// The returned `Iterable` may contain fewer than `count` elements, if `this`
   /// contains fewer than `count` elements.
@@ -540,11 +564,9 @@ abstract class Iterable<E> {
   /// final result = numbers.take(4); // (1, 2, 3, 5)
   /// final takeAll = numbers.take(100); // (1, 2, 3, 5, 6, 7)
   /// ```
-  Iterable<E> take(int count) {
-    return TakeIterable<E>(this, count);
-  }
+  Iterable<E> take(int count) => TakeIterable<E>(this, count);
 
-  /// Returns a lazy iterable of the leading elements satisfying [test].
+  /// Creates a lazy iterable of the leading elements satisfying [test].
   ///
   /// The filtering happens lazily. Every new iterator of the returned
   /// iterable starts iterating over the elements of `this`.
@@ -561,11 +583,9 @@ abstract class Iterable<E> {
   /// result = numbers.takeWhile((x) => x != 4); // (1, 2, 3, 5, 6, 7)
   /// result = numbers.takeWhile((x) => x.isOdd); // (1)
   /// ```
-  Iterable<E> takeWhile(bool test(E value)) {
-    return TakeWhileIterable<E>(this, test);
-  }
+  Iterable<E> takeWhile(bool test(E value)) => TakeWhileIterable<E>(this, test);
 
-  /// Returns an [Iterable] that provides all but the first [count] elements.
+  /// Creates an [Iterable] that provides all but the first [count] elements.
   ///
   /// When the returned iterable is iterated, it starts iterating over `this`,
   /// first skipping past the initial [count] elements.
@@ -586,11 +606,9 @@ abstract class Iterable<E> {
   /// ```
   ///
   /// The [count] must not be negative.
-  Iterable<E> skip(int count) {
-    return SkipIterable<E>(this, count);
-  }
+  Iterable<E> skip(int count) => SkipIterable<E>(this, count);
 
-  /// Returns an `Iterable` that skips leading elements while [test] is satisfied.
+  /// Creates an `Iterable` that skips leading elements while [test] is satisfied.
   ///
   /// The filtering happens lazily. Every new [Iterator] of the returned
   /// iterable iterates over all elements of `this`.
@@ -609,11 +627,9 @@ abstract class Iterable<E> {
   /// result = numbers.skipWhile((x) => x != 4); // ()
   /// result = numbers.skipWhile((x) => x.isOdd); // (2, 3, 5, 6, 7)
   /// ```
-  Iterable<E> skipWhile(bool test(E value)) {
-    return SkipWhileIterable<E>(this, test);
-  }
+  Iterable<E> skipWhile(bool test(E value)) => SkipWhileIterable<E>(this, test);
 
-  /// Returns the first element.
+  /// The first element.
   ///
   /// Throws a [StateError] if `this` is empty.
   /// Otherwise returns the first element in the iteration order,
@@ -626,7 +642,7 @@ abstract class Iterable<E> {
     return it.current;
   }
 
-  /// Returns the last element.
+  /// The last element.
   ///
   /// Throws a [StateError] if `this` is empty.
   /// Otherwise may iterate through the elements and returns the last one
@@ -657,7 +673,7 @@ abstract class Iterable<E> {
     return result;
   }
 
-  /// Returns the first element that satisfies the given predicate [test].
+  /// The first element that satisfies the given predicate [test].
   ///
   /// Iterates through elements and returns the first to satisfy [test].
   ///
@@ -681,7 +697,7 @@ abstract class Iterable<E> {
     throw IterableElementError.noElement();
   }
 
-  /// Returns the last element that satisfies the given predicate [test].
+  /// The last element that satisfies the given predicate [test].
   ///
   /// An iterable that can access its elements directly may check its
   /// elements in any order (for example a list starts by checking the
@@ -703,20 +719,25 @@ abstract class Iterable<E> {
   /// function is returned.
   /// If [orElse] is omitted, it defaults to throwing a [StateError].
   E lastWhere(bool test(E element), {E orElse()?}) {
-    late E result;
-    bool foundMatching = false;
-    for (E element in this) {
-      if (test(element)) {
-        result = element;
-        foundMatching = true;
+    var iterator = this.iterator;
+    // Potential result during first loop.
+    E result;
+    do {
+      if (!iterator.moveNext()) {
+        if (orElse != null) return orElse();
+        throw IterableElementError.noElement();
       }
+      result = iterator.current;
+    } while (!test(result));
+    // Now `result` is actual result, unless a later one is found.
+    while (iterator.moveNext()) {
+      var current = iterator.current;
+      if (test(current)) result = current;
     }
-    if (foundMatching) return result;
-    if (orElse != null) return orElse();
-    throw IterableElementError.noElement();
+    return result;
   }
 
-  /// Returns the single element that satisfies [test].
+  /// The single element that satisfies [test].
   ///
   /// Checks elements to see if `test(element)` returns true.
   /// If exactly one element satisfies [test], that element is returned.
@@ -740,20 +761,19 @@ abstract class Iterable<E> {
   /// result = numbers.singleWhere((element) => element == 2); // Throws Error.
   /// ```
   E singleWhere(bool test(E element), {E orElse()?}) {
-    late E result;
-    bool foundMatching = false;
-    for (E element in this) {
-      if (test(element)) {
-        if (foundMatching) {
-          throw IterableElementError.tooMany();
-        }
-        result = element;
-        foundMatching = true;
+    var iterator = this.iterator;
+    E result;
+    do {
+      if (!iterator.moveNext()) {
+        if (orElse != null) return orElse();
+        throw IterableElementError.noElement();
       }
+      result = iterator.current;
+    } while (!test(result));
+    while (iterator.moveNext()) {
+      if (test(iterator.current)) throw IterableElementError.tooMany();
     }
-    if (foundMatching) return result;
-    if (orElse != null) return orElse();
-    throw IterableElementError.noElement();
+    return result;
   }
 
   /// Returns the [index]th element.
@@ -773,12 +793,13 @@ abstract class Iterable<E> {
   /// ```
   E elementAt(int index) {
     RangeError.checkNotNegative(index, "index");
-    int elementIndex = 0;
-    for (E element in this) {
-      if (index == elementIndex) return element;
-      elementIndex++;
+    var iterator = this.iterator;
+    var skipCount = index;
+    while (iterator.moveNext()) {
+      if (skipCount == 0) return iterator.current;
+      skipCount--;
     }
-    throw IndexError.withLength(index, elementIndex,
+    throw IndexError.withLength(index, index - skipCount,
         indexable: this, name: "index");
   }
 
@@ -796,10 +817,69 @@ abstract class Iterable<E> {
   /// The conversion may omit calling `toString` on some elements if they
   /// are known to not occur in the output, and it may stop iterating after
   /// a hundred elements.
-  String toString() => IterableBase.iterableToShortString(this, '(', ')');
+  String toString() => iterableToShortString(this, '(', ')');
+
+  /// Convert an `Iterable` to a string like [Iterable.toString].
+  ///
+  /// Allows using other delimiters than '(' and ')'.
+  ///
+  /// Handles circular references where converting one of the elements
+  /// to a string ends up converting [iterable] to a string again.
+  static String iterableToShortString(Iterable iterable,
+      [String leftDelimiter = '(', String rightDelimiter = ')']) {
+    if (isToStringVisiting(iterable)) {
+      if (leftDelimiter == "(" && rightDelimiter == ")") {
+        // Avoid creating a new string in the "common" case.
+        return "(...)";
+      }
+      return "$leftDelimiter...$rightDelimiter";
+    }
+    List<String> parts = <String>[];
+    toStringVisiting.add(iterable);
+    try {
+      _iterablePartsToStrings(iterable, parts);
+    } finally {
+      assert(identical(toStringVisiting.last, iterable));
+      toStringVisiting.removeLast();
+    }
+    return (StringBuffer(leftDelimiter)
+          ..writeAll(parts, ", ")
+          ..write(rightDelimiter))
+        .toString();
+  }
+
+  /// Converts an `Iterable` to a string.
+  ///
+  /// Converts each elements to a string, and separates the results by ", ".
+  /// Then wraps the result in [leftDelimiter] and [rightDelimiter].
+  ///
+  /// Unlike [iterableToShortString], this conversion doesn't omit any
+  /// elements or puts any limit on the size of the result.
+  ///
+  /// Handles circular references where converting one of the elements
+  /// to a string ends up converting [iterable] to a string again.
+  static String iterableToFullString(Iterable iterable,
+      [String leftDelimiter = '(', String rightDelimiter = ')']) {
+    if (isToStringVisiting(iterable)) {
+      return "$leftDelimiter...$rightDelimiter";
+    }
+    StringBuffer buffer = StringBuffer(leftDelimiter);
+    toStringVisiting.add(iterable);
+    try {
+      buffer.writeAll(iterable, ", ");
+    } finally {
+      assert(identical(toStringVisiting.last, iterable));
+      toStringVisiting.removeLast();
+    }
+    buffer.write(rightDelimiter);
+    return buffer.toString();
+  }
 }
 
 class _GeneratorIterable<E> extends ListIterable<E> {
+  // Methods have efficient implementations from `ListIterable`,
+  // based on `length` and `elementAt`.
+
   /// The length of the generated iterable.
   final int length;
 
@@ -807,12 +887,7 @@ class _GeneratorIterable<E> extends ListIterable<E> {
   final E Function(int) _generator;
 
   /// Creates the generated iterable.
-  ///
-  /// If [generator] is `null`, it is checked that `int` is assignable to [E].
-  _GeneratorIterable(this.length, E generator(int index)?)
-      : // The `as` below is used as check to make sure that `int` is assignable
-        // to [E].
-        _generator = generator ?? (_id as E Function(int));
+  _GeneratorIterable(this.length, this._generator);
 
   E elementAt(int index) {
     IndexError.check(index, length, indexable: this);
@@ -822,3 +897,116 @@ class _GeneratorIterable<E> extends ListIterable<E> {
   /// Helper function used as default _generator function.
   static int _id(int n) => n;
 }
+
+/// Convert elements of [iterable] to strings and store them in [parts].
+void _iterablePartsToStrings(Iterable<Object?> iterable, List<String> parts) {
+  // This is the complicated part of [iterableToShortString].
+  // It is extracted as a separate function to avoid having too much code
+  // inside the try/finally.
+
+  // Try to stay below this many characters.
+  const int lengthLimit = 80;
+
+  // Always at least this many elements at the start.
+  const int headCount = 3;
+
+  // Always at least this many elements at the end.
+  const int tailCount = 2;
+
+  // Stop iterating after this many elements. Iterables can be infinite.
+  const int maxCount = 100;
+  // Per entry length overhead. It's for ", " for all after the first entry,
+  // and for "(" and ")" for the initial entry. By pure luck, that's the same
+  // number.
+  const int overhead = 2;
+  const int ellipsisSize = 3; // "...".length.
+
+  int length = 0;
+  int count = 0;
+  Iterator<Object?> it = iterable.iterator;
+  // Initial run of elements, at least headCount, and then continue until
+  // passing at most lengthLimit characters.
+  while (length < lengthLimit || count < headCount) {
+    if (!it.moveNext()) return;
+    String next = "${it.current}";
+    parts.add(next);
+    length += next.length + overhead;
+    count++;
+  }
+
+  String penultimateString;
+  String ultimateString;
+
+  // Find last two elements. One or more of them may already be in the
+  // parts array. Include their length in `length`.
+  if (!it.moveNext()) {
+    if (count <= headCount + tailCount) return;
+    ultimateString = parts.removeLast();
+    penultimateString = parts.removeLast();
+  } else {
+    Object? penultimate = it.current;
+    count++;
+    if (!it.moveNext()) {
+      if (count <= headCount + 1) {
+        parts.add("$penultimate");
+        return;
+      }
+      ultimateString = "$penultimate";
+      penultimateString = parts.removeLast();
+      length += ultimateString.length + overhead;
+    } else {
+      Object? ultimate = it.current;
+      count++;
+      // Then keep looping, keeping the last two elements in variables.
+      assert(count < maxCount);
+      while (it.moveNext()) {
+        penultimate = ultimate;
+        ultimate = it.current;
+        count++;
+        if (count > maxCount) {
+          // If we haven't found the end before maxCount, give up.
+          // This cannot happen in the code above because each entry
+          // increases length by at least two, so there is no way to
+          // visit more than ~40 elements before this loop.
+
+          // Remove any surplus elements until length, including ", ...)",
+          // is at most lengthLimit.
+          while (length > lengthLimit - ellipsisSize - overhead &&
+              count > headCount) {
+            length -= parts.removeLast().length + overhead;
+            count--;
+          }
+          parts.add("...");
+          return;
+        }
+      }
+      penultimateString = "$penultimate";
+      ultimateString = "$ultimate";
+      length += ultimateString.length + penultimateString.length + 2 * overhead;
+    }
+  }
+
+  // If there is a gap between the initial run and the last two,
+  // prepare to add an ellipsis.
+  String? elision;
+  if (count > parts.length + tailCount) {
+    elision = "...";
+    length += ellipsisSize + overhead;
+  }
+
+  // If the last two elements were very long, and we have more than
+  // headCount elements in the initial run, drop some to make room for
+  // the last two.
+  while (length > lengthLimit && parts.length > headCount) {
+    length -= parts.removeLast().length + overhead;
+    if (elision == null) {
+      elision = "...";
+      length += ellipsisSize + overhead;
+    }
+  }
+  if (elision != null) {
+    parts.add(elision);
+  }
+  parts.add(penultimateString);
+  parts.add(ultimateString);
+}
diff --git a/sdk/lib/internal/internal.dart b/sdk/lib/internal/internal.dart
index 0ad7fb33d9b..f7f4c08c625 100644
--- a/sdk/lib/internal/internal.dart
+++ b/sdk/lib/internal/internal.dart
@@ -1040,3 +1040,16 @@ class DoubleLinkedQueueEntry<E> {
 /// through scheduled events or timers, which would put the object into
 /// an inconsistent state if simply being copied.
 const vmIsolateUnsendable = pragma("vm:isolate-unsendable");
+
+// Helpers used to detect cycles in collection `toString`s.
+
+/// A collection used to identify cyclic lists during `toString` calls.
+final List<Object> toStringVisiting = [];
+
+/// Check if we are currently visiting [object] in a `toString` call.
+bool isToStringVisiting(Object object) {
+  for (int i = 0; i < toStringVisiting.length; i++) {
+    if (identical(object, toStringVisiting[i])) return true;
+  }
+  return false;
+}
diff --git a/sdk/lib/internal/linked_list.dart b/sdk/lib/internal/linked_list.dart
index ddb0331fec3..598f583a17d 100644
--- a/sdk/lib/internal/linked_list.dart
+++ b/sdk/lib/internal/linked_list.dart
@@ -5,7 +5,7 @@
 part of dart._internal;
 
 /// A rudimentary linked list.
-class LinkedList<T extends LinkedListEntry<T>> extends IterableBase<T> {
+class LinkedList<T extends LinkedListEntry<T>> extends Iterable<T> {
   T get first => _first as T;
   T? _first;
 
diff --git a/sdk/lib/vmservice/named_lookup.dart b/sdk/lib/vmservice/named_lookup.dart
index 8431ccff9df..43c18f80988 100644
--- a/sdk/lib/vmservice/named_lookup.dart
+++ b/sdk/lib/vmservice/named_lookup.dart
@@ -5,7 +5,7 @@
 part of dart._vmservice;
 
 /// Set like contains which automatically generated String ids for its items
-class NamedLookup<E extends Object> extends Object with IterableMixin<E> {
+class NamedLookup<E extends Object> extends Iterable<E> {
   final IdGenerator _generator;
   final _elements = <String, E>{};
   final _ids = <E, String>{};