diff --git a/.dart_tool/package_config.json b/.dart_tool/package_config.json
index 9a6403f3d3a..35fc3b9ac1d 100644
--- a/.dart_tool/package_config.json
+++ b/.dart_tool/package_config.json
@@ -11,7 +11,7 @@
     "constraint, update this by running tools/generate_package_config.dart."
   ],
   "configVersion": 2,
-  "generated": "2020-03-11T09:16:09.767708",
+  "generated": "2020-04-21T17:36:03.446742",
   "generator": "tools/generate_package_config.dart",
   "packages": [
     {
@@ -66,19 +66,18 @@
       "name": "args",
       "rootUri": "../third_party/pkg/args",
       "packageUri": "lib/",
-      "languageVersion": "2.0"
+      "languageVersion": "2.3"
     },
     {
       "name": "async",
       "rootUri": "../third_party/pkg/async",
       "packageUri": "lib/",
-      "languageVersion": "2.0"
+      "languageVersion": "2.2"
     },
     {
       "name": "async_helper",
       "rootUri": "../pkg/async_helper",
-      "packageUri": "lib/",
-      "languageVersion": "2.7"
+      "packageUri": "lib/"
     },
     {
       "name": "bazel_worker",
@@ -116,12 +115,6 @@
       "packageUri": "lib/",
       "languageVersion": "2.0"
     },
-    {
-      "name": "code_transformers",
-      "rootUri": "../third_party/pkg/code_transformers",
-      "packageUri": "lib/",
-      "languageVersion": "1.0"
-    },
     {
       "name": "collection",
       "rootUri": "../third_party/pkg/collection",
@@ -180,7 +173,7 @@
       "name": "dart_style",
       "rootUri": "../third_party/pkg_tested/dart_style",
       "packageUri": "lib/",
-      "languageVersion": "2.3"
+      "languageVersion": "2.7"
     },
     {
       "name": "dartdev",
@@ -192,7 +185,7 @@
       "name": "dartdoc",
       "rootUri": "../third_party/pkg/dartdoc",
       "packageUri": "lib/",
-      "languageVersion": "2.6"
+      "languageVersion": "2.7"
     },
     {
       "name": "dartfix",
@@ -204,7 +197,7 @@
       "name": "dds",
       "rootUri": "../pkg/dds",
       "packageUri": "lib/",
-      "languageVersion": "2.3"
+      "languageVersion": "2.6"
     },
     {
       "name": "dev_compiler",
@@ -221,8 +214,7 @@
     {
       "name": "expect",
       "rootUri": "../pkg/expect",
-      "packageUri": "lib/",
-      "languageVersion": "2.0"
+      "packageUri": "lib/"
     },
     {
       "name": "ffi",
@@ -273,12 +265,6 @@
       "packageUri": "lib/",
       "languageVersion": "2.7"
     },
-    {
-      "name": "func",
-      "rootUri": "../third_party/pkg/func",
-      "packageUri": "lib/",
-      "languageVersion": "1.9"
-    },
     {
       "name": "gardening",
       "rootUri": "../tools/gardening",
@@ -333,17 +319,11 @@
       "packageUri": "lib/",
       "languageVersion": "2.0"
     },
-    {
-      "name": "initialize",
-      "rootUri": "../third_party/pkg/initialize",
-      "packageUri": "lib/",
-      "languageVersion": "1.9"
-    },
     {
       "name": "intl",
       "rootUri": "../third_party/pkg/intl",
       "packageUri": "lib/",
-      "languageVersion": "2.0"
+      "languageVersion": "2.5"
     },
     {
       "name": "js",
@@ -379,7 +359,7 @@
       "name": "linter",
       "rootUri": "../third_party/pkg/linter",
       "packageUri": "lib/",
-      "languageVersion": "2.2"
+      "languageVersion": "2.6"
     },
     {
       "name": "logging",
@@ -405,12 +385,6 @@
       "packageUri": "lib/",
       "languageVersion": "1.12"
     },
-    {
-      "name": "metatest",
-      "rootUri": "../third_party/pkg/metatest",
-      "packageUri": "lib/",
-      "languageVersion": "1.8"
-    },
     {
       "name": "mime",
       "rootUri": "../third_party/pkg/mime",
@@ -453,12 +427,6 @@
       "packageUri": "lib/",
       "languageVersion": "2.0"
     },
-    {
-      "name": "observable",
-      "rootUri": "../third_party/pkg/observable",
-      "packageUri": "lib/",
-      "languageVersion": "1.19"
-    },
     {
       "name": "observatory",
       "rootUri": "../runtime/observatory",
@@ -470,12 +438,6 @@
       "rootUri": "../runtime/observatory/tests/service/observatory_test_package",
       "languageVersion": "2.7"
     },
-    {
-      "name": "observe",
-      "rootUri": "../third_party/pkg/observe",
-      "packageUri": "lib/",
-      "languageVersion": "1.9"
-    },
     {
       "name": "package_config",
       "rootUri": "../third_party/pkg_tested/package_config",
@@ -494,30 +456,12 @@
       "packageUri": "lib/",
       "languageVersion": "2.1"
     },
-    {
-      "name": "platform",
-      "rootUri": "../third_party/pkg/platform",
-      "packageUri": "lib/",
-      "languageVersion": "1.24"
-    },
-    {
-      "name": "plugin",
-      "rootUri": "../third_party/pkg/plugin",
-      "packageUri": "lib/",
-      "languageVersion": "1.0"
-    },
     {
       "name": "pool",
       "rootUri": "../third_party/pkg/pool",
       "packageUri": "lib/",
       "languageVersion": "2.0"
     },
-    {
-      "name": "process",
-      "rootUri": "../third_party/pkg/process",
-      "packageUri": "lib/",
-      "languageVersion": "2.0"
-    },
     {
       "name": "protobuf",
       "rootUri": "../third_party/pkg/protobuf/protobuf",
@@ -534,7 +478,7 @@
       "name": "pub_semver",
       "rootUri": "../third_party/pkg/pub_semver",
       "packageUri": "lib/",
-      "languageVersion": "1.0"
+      "languageVersion": "2.0"
     },
     {
       "name": "quiver",
@@ -548,12 +492,6 @@
       "packageUri": "lib/",
       "languageVersion": "2.0"
     },
-    {
-      "name": "scheduled_test",
-      "rootUri": "../third_party/pkg/scheduled_test",
-      "packageUri": "lib/",
-      "languageVersion": "1.22"
-    },
     {
       "name": "sdk_library_metadata",
       "rootUri": "../sdk/lib/_internal/sdk_library_metadata",
@@ -570,13 +508,13 @@
       "name": "shelf_packages_handler",
       "rootUri": "../third_party/pkg/shelf_packages_handler",
       "packageUri": "lib/",
-      "languageVersion": "1.22"
+      "languageVersion": "2.0"
     },
     {
       "name": "shelf_proxy",
       "rootUri": "../third_party/pkg/shelf_proxy",
       "packageUri": "lib/",
-      "languageVersion": "2.3"
+      "languageVersion": "2.0"
     },
     {
       "name": "shelf_static",
@@ -596,17 +534,11 @@
       "packageUri": "lib/",
       "languageVersion": "2.3"
     },
-    {
-      "name": "smoke",
-      "rootUri": "../third_party/pkg/smoke",
-      "packageUri": "lib/",
-      "languageVersion": "1.12"
-    },
     {
       "name": "source_map_stack_trace",
       "rootUri": "../third_party/pkg/source_map_stack_trace",
       "packageUri": "lib/",
-      "languageVersion": "1.8"
+      "languageVersion": "2.7"
     },
     {
       "name": "source_maps",
@@ -672,19 +604,19 @@
       "name": "test",
       "rootUri": "../third_party/pkg/test/pkgs/test",
       "packageUri": "lib/",
-      "languageVersion": "2.2"
+      "languageVersion": "2.7"
     },
     {
       "name": "test_api",
       "rootUri": "../third_party/pkg/test/pkgs/test_api",
       "packageUri": "lib/",
-      "languageVersion": "2.1"
+      "languageVersion": "2.7"
     },
     {
       "name": "test_core",
       "rootUri": "../third_party/pkg/test/pkgs/test_core",
       "packageUri": "lib/",
-      "languageVersion": "2.1"
+      "languageVersion": "2.7"
     },
     {
       "name": "test_descriptor",
@@ -722,12 +654,6 @@
       "packageUri": "lib/",
       "languageVersion": "2.6"
     },
-    {
-      "name": "tuple",
-      "rootUri": "../third_party/pkg/tuple",
-      "packageUri": "lib/",
-      "languageVersion": "1.6"
-    },
     {
       "name": "typed_data",
       "rootUri": "../third_party/pkg/typed_data",
@@ -740,12 +666,6 @@
       "packageUri": "lib/",
       "languageVersion": "2.0"
     },
-    {
-      "name": "utf",
-      "rootUri": "../third_party/pkg/utf",
-      "packageUri": "lib/",
-      "languageVersion": "2.0"
-    },
     {
       "name": "vm",
       "rootUri": "../pkg/vm",
@@ -762,7 +682,7 @@
       "name": "watcher",
       "rootUri": "../third_party/pkg/watcher",
       "packageUri": "lib/",
-      "languageVersion": "2.0"
+      "languageVersion": "2.2"
     },
     {
       "name": "web_components",
@@ -783,4 +703,4 @@
       "languageVersion": "2.0"
     }
   ]
-}
+}
\ No newline at end of file
diff --git a/pkg/analyzer_cli/pubspec.yaml b/pkg/analyzer_cli/pubspec.yaml
index cf57798799f..295f5cf3e19 100644
--- a/pkg/analyzer_cli/pubspec.yaml
+++ b/pkg/analyzer_cli/pubspec.yaml
@@ -1,6 +1,8 @@
 name: analyzer_cli
 description: Command line interface for the Dart Analyzer.
 publish_to: none
+environment:
+  sdk: "^2.7.0"
 dependencies:
   analyzer: ^0.37.0
   args: '>=0.13.0 <2.0.0'
diff --git a/pkg/async_helper/lib/async_helper.dart b/pkg/async_helper/lib/async_helper.dart
index d5bcc08076a..1f3acb1b329 100644
--- a/pkg/async_helper/lib/async_helper.dart
+++ b/pkg/async_helper/lib/async_helper.dart
@@ -107,7 +107,10 @@ void asyncExpectThrows<T>(Future<void> f(),
     [bool check(T error) = _pass, String reason = ""]) {
   var type = "";
   if (T != dynamic && T != Object) type = "<$T>";
-  var header = "asyncExpectThrows$type(${reason ?? ''}):";
+  // Handle null being passed in from legacy code while also avoiding producing
+  // an unnecessary null check warning here.
+  if ((reason as dynamic) == null) reason = "";
+  var header = "asyncExpectThrows$type(${reason}):";
 
   // TODO(rnystrom): It might useful to validate that T is not bound to
   // ExpectException since that won't work.
@@ -124,7 +127,7 @@ void asyncExpectThrows<T>(Future<void> f(),
   }
 
   asyncStart();
-  result.then((_) {
+  result.then<Null>((_) {
     throw ExpectException("$header Did not throw.");
   }).catchError((error, stack) {
     // A test failure doesn't count as throwing.
diff --git a/pkg/async_helper/lib/async_minitest.dart b/pkg/async_helper/lib/async_minitest.dart
index 57a05eb1a49..fa5d319cf02 100644
--- a/pkg/async_helper/lib/async_minitest.dart
+++ b/pkg/async_helper/lib/async_minitest.dart
@@ -310,9 +310,7 @@ final _testToken = Object();
 bool _initializedTestNameCallback = false;
 
 /// The current combined name of the nesting [group] or [test].
-// TODO(rnystrom): Type this "String?" when this library does not need to be
-// NNBD agnostic.
-dynamic _currentName = null;
+String _currentName = "";
 
 String _pushName(String newName) {
   // Look up the current test name from the zone created for the test.
@@ -322,7 +320,7 @@ String _pushName(String newName) {
   }
 
   var oldName = _currentName;
-  if (oldName == null) {
+  if (oldName == "") {
     _currentName = newName;
   } else {
     _currentName = "$oldName $newName";
diff --git a/pkg/async_helper/pubspec.yaml b/pkg/async_helper/pubspec.yaml
index df92b533c57..9497752af42 100644
--- a/pkg/async_helper/pubspec.yaml
+++ b/pkg/async_helper/pubspec.yaml
@@ -7,6 +7,5 @@ description: >-
  language tests.
  Third parties are discouraged from using this, and should use
  the facilities provided in package:test.
-
 dependencies:
   expect: any
diff --git a/pkg/dart2native/pubspec.yaml b/pkg/dart2native/pubspec.yaml
index feca449c328..c89834f8b8a 100644
--- a/pkg/dart2native/pubspec.yaml
+++ b/pkg/dart2native/pubspec.yaml
@@ -1,6 +1,9 @@
 name: dart2native
 publish_to: none
 
+environment:
+  sdk: "^2.7.0"
+
 # Add the bin/dart2native.dart script to the scripts pub installs.
 executables:
   dart2native:
diff --git a/pkg/expect/lib/expect.dart b/pkg/expect/lib/expect.dart
index 0e993bcd877..4a177ab93a8 100644
--- a/pkg/expect/lib/expect.dart
+++ b/pkg/expect/lib/expect.dart
@@ -490,7 +490,7 @@ class Expect {
    *
    * If the objects are iterables or maps, recurses into them.
    */
-  static void deepEquals(Object expected, Object actual) {
+  static void deepEquals(dynamic expected, dynamic actual) {
     // Early exit check for equality.
     if (expected == actual) return;
 
@@ -560,8 +560,10 @@ class Expect {
     // TODO(vsm): Make check and reason nullable or change call sites.
     // Existing tests pass null to set a reason and/or pass them through
     // via helpers.
-    check ??= _defaultCheck;
-    reason ??= "";
+    // TODO(rnystrom): Using the strange form below instead of "??=" to avoid
+    // warnings of unnecessary null checks when analyzed as NNBD code.
+    if ((check as dynamic) == null) check = _defaultCheck;
+    if ((reason as dynamic) == null) reason = "";
     String msg = reason.isEmpty ? "" : "($reason)";
     if (f is! Function()) {
       // Only throws from executing the function body should count as throwing.
@@ -570,7 +572,7 @@ class Expect {
     }
     try {
       f();
-    } on Object catch (e, s) {
+    } catch (e, s) {
       // A test failure doesn't count as throwing.
       if (e is ExpectException) rethrow;
       if (e is T && check(e as dynamic)) return;
diff --git a/pkg/expect/lib/minitest.dart b/pkg/expect/lib/minitest.dart
index 350b6aa6b9e..0021ada6b96 100644
--- a/pkg/expect/lib/minitest.dart
+++ b/pkg/expect/lib/minitest.dart
@@ -26,7 +26,7 @@ import 'dart:async';
 import 'package:expect/expect.dart';
 
 typedef dynamic _Action();
-typedef void _ExpectationFunction(Object actual);
+typedef void _ExpectationFunction(dynamic actual);
 
 final List<_Group> _groups = [new _Group()];
 
@@ -124,7 +124,7 @@ void tearDown(body()) {
   _groups.last.tearDownFunction = body;
 }
 
-void expect(Object actual, Object expected, {String reason = ""}) {
+void expect(dynamic actual, dynamic expected, {String reason = ""}) {
   // TODO(rnystrom): Do something useful with reason.
   if (expected is! _Expectation) {
     expected = equals(expected);
@@ -138,19 +138,19 @@ void fail(String message) {
   Expect.fail(message);
 }
 
-Object equals(Object value) => new _Expectation((actual) {
+Object equals(dynamic value) => new _Expectation((actual) {
       Expect.deepEquals(value, actual);
     });
 
-Object notEquals(Object value) => new _Expectation((actual) {
+Object notEquals(dynamic value) => new _Expectation((actual) {
       Expect.notEquals(value, actual);
     });
 
-Object unorderedEquals(Object value) => new _Expectation((actual) {
+Object unorderedEquals(dynamic value) => new _Expectation((actual) {
       Expect.setEquals(value as Iterable, actual as Iterable);
     });
 
-Object predicate(bool fn(Object value), [String description = ""]) =>
+Object predicate(bool fn(dynamic value), [String description = ""]) =>
     new _Expectation((actual) {
       Expect.isTrue(fn(actual), description);
     });
@@ -169,7 +169,7 @@ Object greaterThan(num value) => new _Expectation((actual) {
       }
     });
 
-Object same(Object value) => new _Expectation((actual) {
+Object same(dynamic value) => new _Expectation((actual) {
       Expect.identical(value, actual);
     });
 
diff --git a/pkg/expect/pubspec.yaml b/pkg/expect/pubspec.yaml
index 5e6beb67310..595d26caf6e 100644
--- a/pkg/expect/pubspec.yaml
+++ b/pkg/expect/pubspec.yaml
@@ -6,8 +6,5 @@ description: >
  Third parties are discouraged from using this, and should use
  the expect() function in the unit test library instead for
  test assertions.
-environment:
-  sdk: ">=2.0.0 <3.0.0"
-
 dependencies:
   meta: any
diff --git a/pkg/frontend_server/pubspec.yaml b/pkg/frontend_server/pubspec.yaml
index c14c3b82220..2effb3bfb73 100644
--- a/pkg/frontend_server/pubspec.yaml
+++ b/pkg/frontend_server/pubspec.yaml
@@ -3,6 +3,9 @@ name: frontend_server
 # version: do-not-upload
 description: A resident kernel compiler
 
+environment:
+  sdk: "^2.7.0"
+
 dependencies:
   build_integration:
     path: ../build_integration
diff --git a/pkg/vm/pubspec.yaml b/pkg/vm/pubspec.yaml
index ef74ee068d2..27d6379d38c 100644
--- a/pkg/vm/pubspec.yaml
+++ b/pkg/vm/pubspec.yaml
@@ -3,6 +3,9 @@ name: vm
 # version: do-not-upload
 description: VM specific Dart code and helper scripts
 
+environment:
+  sdk: "^2.7.0"
+
 dependencies:
   build_integration:
     path: ../build_integration
diff --git a/runtime/observatory/tests/service/observatory_test_package/pubspec.yaml b/runtime/observatory/tests/service/observatory_test_package/pubspec.yaml
new file mode 100644
index 00000000000..db61a01f499
--- /dev/null
+++ b/runtime/observatory/tests/service/observatory_test_package/pubspec.yaml
@@ -0,0 +1,4 @@
+name: observatory_test_package
+publish_to: none
+environment:
+  sdk: '^2.7.0'
diff --git a/tests/corelib/regexp/regexp_test.dart b/tests/corelib/regexp/regexp_test.dart
index 1cb8ac7f8c5..9f42f430b91 100644
--- a/tests/corelib/regexp/regexp_test.dart
+++ b/tests/corelib/regexp/regexp_test.dart
@@ -32,10 +32,12 @@ void testEscape(str, regexp) {
   assertEquals("foo:bar:baz", str.split(regexp).join(":"));
 }
 
-void assertEquals(actual, expected, [message]) =>
+void assertEquals(actual, expected, [String message = ""]) =>
     Expect.equals(actual, expected, message);
-void assertTrue(actual, [message]) => Expect.isTrue(actual, message);
-void assertFalse(actual, [message]) => Expect.isFalse(actual, message);
+void assertTrue(actual, [String message = ""]) =>
+    Expect.isTrue(actual, message);
+void assertFalse(actual, [String message = ""]) =>
+    Expect.isFalse(actual, message);
 void assertThrows(fn) => Expect.throws(fn);
 
 void main() {
diff --git a/tests/corelib/uri_test.dart b/tests/corelib/uri_test.dart
index bb45fe057be..550fc57dea9 100644
--- a/tests/corelib/uri_test.dart
+++ b/tests/corelib/uri_test.dart
@@ -470,8 +470,8 @@ void testReplace() {
   });
   var params = uri.queryParametersAll;
   Expect.equals(2, params.length);
-  Expect.listEquals(["42", "37"], params["x"]);
-  Expect.listEquals(["43", "38"], params["y"]);
+  Expect.listEquals(["42", "37"], params["x"]!);
+  Expect.listEquals(["43", "38"], params["y"]!);
 }
 
 main() {
diff --git a/tests/lib/isolate/function_send_test.dart b/tests/lib/isolate/function_send_test.dart
index 4b22fa1a637..38b4698bafc 100644
--- a/tests/lib/isolate/function_send_test.dart
+++ b/tests/lib/isolate/function_send_test.dart
@@ -191,10 +191,10 @@ void testUnsendable(name, func) {
   });
   Expect.throws(() {
     noReply.sendPort.send(func);
-  }, null, "send direct");
+  }, (_) => true, "send direct");
   Expect.throws(() {
     noReply.sendPort.send([func]);
-  }, null, "send wrapped");
+  }, (_) => true, "send wrapped");
   scheduleMicrotask(() {
     noReply.close();
     asyncEnd();
diff --git a/tools/gardening/pubspec.yaml b/tools/gardening/pubspec.yaml
index ca787899c8d..dc6fcca3465 100644
--- a/tools/gardening/pubspec.yaml
+++ b/tools/gardening/pubspec.yaml
@@ -2,6 +2,8 @@
 # gardening by making it a package.
 name: gardening
 #version: do-not-upload
+environment:
+  sdk: "^2.7.0"
 dependencies:
   args:
   http:
diff --git a/tools/generate_package_config.dart b/tools/generate_package_config.dart
index 19e9c94b035..e0ddfb8c71e 100755
--- a/tools/generate_package_config.dart
+++ b/tools/generate_package_config.dart
@@ -8,9 +8,6 @@ import 'package:path/path.dart' as p;
 import 'package:pub_semver/pub_semver.dart';
 import 'package:yaml/yaml.dart';
 
-/// Version to use if a package doesn't constrain the language version.
-final defaultVersion = Version(2, 7, 0);
-
 final repoRoot = p.dirname(p.dirname(p.fromUri(Platform.script)));
 final configFilePath = p.join(repoRoot, '.dart_tool/package_config.json');
 
@@ -75,18 +72,14 @@ Iterable<Map<String, String>> makePackageConfigs(
     List<String> packageDirs) sync* {
   for (var packageDir in packageDirs) {
     var version = pubspecLanguageVersion(packageDir);
-    if (version == null) {
-      print('Warning: Unknown language version for ${p.basename(packageDir)}.');
-      version = defaultVersion;
-    }
-
     var hasLibDirectory = Directory(p.join(packageDir, 'lib')).existsSync();
 
     yield {
       'name': p.basename(packageDir),
       'rootUri': p.relative(packageDir, from: p.dirname(configFilePath)),
       if (hasLibDirectory) 'packageUri': 'lib/',
-      'languageVersion': '${version.major}.${version.minor}'
+      if (version != null)
+        'languageVersion': '${version.major}.${version.minor}'
     };
   }
 }