linter: Handle more deferred cases in unnecessary_lambdas

Fixes dart-lang/linter#2182

Change-Id: I975b4d1ae84245ff66d881a42ad7ca745569fab9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/366060
Reviewed-by: Phil Quitslund <pquitslund@google.com>
Commit-Queue: Samuel Rawlins <srawlins@google.com>

pkg/linter/lib/src/rules/unnecessary_lambdas.dart

@@ -199,20 +199,16 @@ class _Visitor extends SimpleAstVisitor<void> {
 
     var parameters = nodeToLintParams.map((e) => e.declaredElement).toSet();
     if (node is FunctionExpressionInvocation) {
+      if (node.function.mightBeDeferred) return;
+
       // TODO(pq): consider checking for assignability
       // see: https://github.com/dart-lang/linter/issues/1561
       var checker = _FinalExpressionChecker(parameters);
       if (checker.isFinalNode(node.function)) {
         rule.reportLint(nodeToLint);
       }
     } else if (node is MethodInvocation) {
-      var target = node.target;
-      if (target is SimpleIdentifier) {
-        var element = target.staticElement;
-        if (element is PrefixElement) {
-          if (element.imports.any((e) => e.isDeferred)) return;
-        }
-      }
+      if (node.target.mightBeDeferred) return;
 
       var tearoffType = node.staticInvokeType;
       if (tearoffType == null) return;
@@ -239,8 +235,17 @@ class _Visitor extends SimpleAstVisitor<void> {
   }
 }
 
-extension on LibraryImportElement {
-  bool get isDeferred => prefix is DeferredImportElementPrefix;
+extension on Expression? {
+  bool get mightBeDeferred {
+    var self = this;
+    var element = switch (self) {
+      PrefixedIdentifier() => self.prefix.staticElement,
+      SimpleIdentifier() => self.staticElement,
+      _ => null,
+    };
+    return element is PrefixElement &&
+        element.imports.any((e) => e.prefix is DeferredImportElementPrefix);
+  }
 }
 
 extension on Element? {

pkg/linter/test/rules/unnecessary_lambdas_test.dart

@@ -191,6 +191,37 @@ import 'b.dart' deferred as b;
 void f() {
   [].where((o) => b.isB(o));
 }
+''');
+  }
+
+  test_importedStatic_deferred() async {
+    newFile('$testPackageLibPath/b.dart', r'''
+class C {
+static bool isB(Object o) => true;
+}
+''');
+    await assertNoDiagnostics(r'''
+import 'b.dart' deferred as b;
+
+void f() {
+  [].where((o) => b.C.isB(o));
+}
+
+''');
+  }
+
+  test_importedTearoff_deferred() async {
+    newFile('$testPackageLibPath/b.dart', r'''
+bool isB(Object o) => true;
+final isB2 = isB;
+''');
+    await assertNoDiagnostics(r'''
+import 'b.dart' deferred as b;
+
+void f() {
+  [].where((o) => b.isB2(o));
+}
+
 ''');
   }