fix omit_local_variable_types where local type is required for infe…

…rence (#3024)

* fix `omit_local_variable_types` where type required for inference

* fmt

* + test

lib/src/rules/omit_local_variable_types.dart

@@ -4,6 +4,7 @@
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
+import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 
 import '../analyzer.dart';
@@ -99,6 +100,20 @@ class _Visitor extends SimpleAstVisitor<void> {
     _visitVariableDeclarationList(node.variables);
   }
 
+  bool _dependsOnDeclaredTypeForInference(Expression? initializer) {
+    if (initializer is MethodInvocation) {
+      if (initializer.typeArguments == null) {
+        var element = initializer.methodName.staticElement;
+        if (element is FunctionElement) {
+          if (element.returnType is TypeParameterType) {
+            return true;
+          }
+        }
+      }
+    }
+    return false;
+  }
+
   void _visitVariableDeclarationList(VariableDeclarationList node) {
     var staticType = node.type?.type;
     if (staticType == null ||
@@ -107,7 +122,11 @@ class _Visitor extends SimpleAstVisitor<void> {
       return;
     }
     for (var child in node.variables) {
-      if (child.initializer?.staticType != staticType) {
+      var initializer = child.initializer;
+      if (initializer?.staticType != staticType) {
+        return;
+      }
+      if (_dependsOnDeclaredTypeForInference(initializer)) {
         return;
       }
     }

test/rules/all.dart

@@ -14,6 +14,7 @@ import 'missing_whitespace_between_adjacent_strings.dart'
     as missing_whitespace_between_adjacent_strings;
 import 'non_constant_identifier_names.dart' as non_constant_identifier_names;
 import 'null_closures.dart' as null_closures;
+import 'omit_local_variable_types.dart' as omit_local_variable_types;
 import 'overridden_fields.dart' as overridden_fields;
 import 'prefer_asserts_in_initializer_lists.dart'
     as prefer_asserts_in_initializer_lists;
@@ -43,6 +44,7 @@ void main() {
   missing_whitespace_between_adjacent_strings.main();
   non_constant_identifier_names.main();
   null_closures.main();
+  omit_local_variable_types.main();
   overridden_fields.main();
   prefer_asserts_in_initializer_lists.main();
   prefer_collection_literals.main();

test/rules/omit_local_variable_types.dart

@@ -0,0 +1,60 @@
+// Copyright (c) 2021, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:test_reflective_loader/test_reflective_loader.dart';
+
+import '../rule_test_support.dart';
+
+main() {
+  defineReflectiveSuite(() {
+    defineReflectiveTests(OmitLocalVariableTypesTest);
+  });
+}
+
+@reflectiveTest
+class OmitLocalVariableTypesTest extends LintRuleTest {
+  @override
+  String get lintRule => 'omit_local_variable_types';
+
+  /// https://github.com/dart-lang/linter/issues/3016
+  @failingTest
+  test_paramIsType() async {
+    await assertDiagnostics(r'''
+T bar<T>(T d) => d;
+
+String f() {
+  String h = bar('');
+  return h;
+}
+''', [
+      lint('omit_local_variable_types', 42, 26),
+    ]);
+  }
+
+  /// https://github.com/dart-lang/linter/issues/3016
+  test_typeNeededForInference() async {
+    await assertNoDiagnostics(r'''
+T bar<T>(dynamic d) => d;
+
+String f() {
+  String h = bar('');
+  return h;
+}
+''');
+  }
+
+  /// https://github.com/dart-lang/linter/issues/3016
+  test_typeParamProvided() async {
+    await assertDiagnostics(r'''
+T bar<T>(dynamic d) => d;
+
+String f() {
+  String h = bar<String>('');
+  return h;
+}
+''', [
+      lint('omit_local_variable_types', 42, 26),
+    ]);
+  }
+}