Add test and implementation for replacing final with var in for loops.

Change-Id: If32b0f77cae3f1e3d3b8880b70d161fc22a973b7
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/436541
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Brian Wilkerson <[email protected]>
Reviewed-by: Konstantin Shcheglov <[email protected]>

Author: fshcheglov

pkg/analysis_server/lib/src/services/correction/dart/replace_final_with_var.dart

@@ -46,6 +46,11 @@ class ReplaceFinalWithVar extends ResolvedCorrectionProducer {
       keyword: var keywordToken,
     )) {
       finalKeyword = keywordToken;
+    } else if (context.node case DeclaredIdentifier(
+      keyword: var keywordToken?,
+    )) {
+      assert(keywordToken.keyword == Keyword.FINAL);
+      finalKeyword = keywordToken;
     }
 
     return ReplaceFinalWithVar._(

pkg/analysis_server/test/src/services/correction/fix/replace_final_with_var_test.dart

@@ -50,6 +50,21 @@ class ReplaceFinalWithVarTest extends FixProcessorLintTest {
   @override
   String get lintCode => LintNames.unnecessary_final;
 
+  Future<void> test_function_forLoop() async {
+    await resolveTestCode('''
+void f(List<int> values) {
+  // ignore:unused_local_variable
+  for (final v in values) {}
+}
+''');
+    await assertHasFix('''
+void f(List<int> values) {
+  // ignore:unused_local_variable
+  for (var v in values) {}
+}
+''');
+  }
+
   Future<void> test_function_variableTyped() async {
     await resolveTestCode('''
 void f() {