From 275581bca14724093b8cdd36b033dd5978a6bf7c Mon Sep 17 00:00:00 2001
From: FMorschel <git@fmorschel.dev>
Date: Tue, 16 Dec 2025 09:07:37 -0800
Subject: [PATCH] [DAS] Fixes completion for switch expression pattern after
 `when`

Fixes: https://github.com/dart-lang/sdk/issues/62210
Change-Id: I42a3d6f3f93a8ecc8f4b866d89119a6cc49bd3e8
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/467160
Commit-Queue: Keerti Parthasarathy <keertip@google.com>
Reviewed-by: Samuel Rawlins <srawlins@google.com>
Auto-Submit: Felipe Morschel <git@fmorschel.dev>
Reviewed-by: Keerti Parthasarathy <keertip@google.com>
---
 .../completion/dart/declaration_helper.dart   |  2 +
 .../dart/in_scope_completion_pass.dart        | 15 +++-
 .../dart/location/switch_expression_test.dart | 89 ++++++++++++++++++-
 3 files changed, 100 insertions(+), 6 deletions(-)

diff --git a/pkg/analysis_server/lib/src/services/completion/dart/declaration_helper.dart b/pkg/analysis_server/lib/src/services/completion/dart/declaration_helper.dart
index b4d75a21d58..ee410236644 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/declaration_helper.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/declaration_helper.dart
@@ -1301,6 +1301,8 @@ class DeclarationHelper {
         case FunctionExpression():
           _visitParameterList(currentNode.parameters);
           _visitTypeParameterList(currentNode.typeParameters);
+        case GuardedPattern():
+          _visitPattern(currentNode.pattern);
         case IfElement():
           _visitIfElement(currentNode);
         case IfStatement():
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/in_scope_completion_pass.dart b/pkg/analysis_server/lib/src/services/completion/dart/in_scope_completion_pass.dart
index 07e264556f0..bbbe9d26321 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/in_scope_completion_pass.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/in_scope_completion_pass.dart
@@ -3010,7 +3010,7 @@ class InScopeCompletionPass extends SimpleAstVisitor<void> {
 
   @override
   void visitSwitchExpressionCase(SwitchExpressionCase node) {
-    if (node.arrow.isSynthetic) {
+    if (node.arrow.isSynthetic || node.arrow.offset >= offset) {
       // The user is completing in the pattern.
       collector.completionLocation = 'SwitchExpression_body';
       _forPattern(node);
@@ -3021,7 +3021,18 @@ class InScopeCompletionPass extends SimpleAstVisitor<void> {
     if (endToken == expression.beginToken || endToken.isSynthetic) {
       // The user is completing in the expression.
       collector.completionLocation = 'SwitchExpressionCase_expression';
-      _forExpression(node.expression);
+      var type =
+          _computeContextType(node.expression) ?? DynamicTypeImpl.instance;
+      _forExpression(
+        node.expression,
+        canBeBool: _canBeBool(type),
+        canBeNull: _canBeNull(type),
+        // TODO(FMorschel): Determine if the parameter type has a constant
+        //  constructor.
+        // Function tear-offs and closures cannot have the `const` keyword
+        // before it
+        canSuggestConst: !type.isDartCoreFunction && type is! FunctionType,
+      );
     }
   }
 
diff --git a/pkg/analysis_server/test/services/completion/dart/location/switch_expression_test.dart b/pkg/analysis_server/test/services/completion/dart/location/switch_expression_test.dart
index d41c806a415..097908a9d44 100644
--- a/pkg/analysis_server/test/services/completion/dart/location/switch_expression_test.dart
+++ b/pkg/analysis_server/test/services/completion/dart/location/switch_expression_test.dart
@@ -17,6 +17,45 @@ class SwitchExpressionTest extends AbstractCompletionDriverTest
     with SwitchExpressionTestCases {}
 
 mixin SwitchExpressionTestCases on AbstractCompletionDriverTest {
+  Future<void> test_beforeArrow() async {
+    await computeSuggestions('''
+int f(Object p01) {
+  return switch (p01) {
+    ^ => 0,
+  };
+}
+
+class A1 {
+  A1.named();
+}
+
+const c01 = 0;
+
+final v01 = 0;
+
+int f01() => 0;
+''');
+    assertResponse(r'''
+suggestions
+  A1
+    kind: class
+  c01
+    kind: topLevelVariable
+  const
+    kind: keyword
+  false
+    kind: keyword
+  final
+    kind: keyword
+  null
+    kind: keyword
+  true
+    kind: keyword
+  var
+    kind: keyword
+''');
+  }
+
   Future<void> test_body_afterArrow() async {
     await computeSuggestions('''
 int f(Object p01) {
@@ -29,12 +68,27 @@ int f(Object p01) {
 suggestions
   p01
     kind: parameter
-  false
+  const
     kind: keyword
-  null
-    kind: keyword
-  true
+  switch
     kind: keyword
+''');
+  }
+
+  Future<void> test_body_afterArrow_newVar() async {
+    await computeSuggestions('''
+int f(Object p01) {
+  return switch (p01) {
+    var v01 => ^
+  };
+}
+''');
+    assertResponse(r'''
+suggestions
+  v01
+    kind: localVariable
+  p01
+    kind: parameter
   const
     kind: keyword
   switch
@@ -72,6 +126,33 @@ suggestions
 ''');
   }
 
+  Future<void> test_body_afterWhen_newVar() async {
+    await computeSuggestions('''
+int f(Object p01) {
+  return switch (p01) {
+    var v01 when ^
+  };
+}
+''');
+    assertResponse(r'''
+suggestions
+  v01
+    kind: localVariable
+  false
+    kind: keyword
+  true
+    kind: keyword
+  p01
+    kind: parameter
+  null
+    kind: keyword
+  const
+    kind: keyword
+  switch
+    kind: keyword
+''');
+  }
+
   Future<void> test_body_empty() async {
     await computeSuggestions('''
 int f(Object p01) {