fix no_leading_underscores_for_local_identifiers pattern field over-reporting (#4296)

* fix `no_leading_underscores_for_local_identifiers` pattern field over-reporting

* ++

Author: pq

lib/src/rules/no_leading_underscores_for_local_identifiers.dart

@@ -105,6 +105,7 @@ class _Visitor extends SimpleAstVisitor<void> {
 
   @override
   void visitDeclaredVariablePattern(DeclaredVariablePattern node) {
+    if (node.parent.isFieldNameShortcut) return;
     checkIdentifier(node.name);
   }
 
@@ -145,3 +146,12 @@ class _Visitor extends SimpleAstVisitor<void> {
     }
   }
 }
+
+extension on AstNode? {
+  bool get isFieldNameShortcut {
+    var node = this;
+    if (node is NullCheckPattern) node = node.parent;
+    if (node is NullAssertPattern) node = node.parent;
+    return node is PatternField && node.name != null && node.name?.name == null;
+  }
+}

test/rules/no_leading_underscores_for_local_identifiers_test.dart

@@ -97,6 +97,18 @@ f() {
     ]);
   }
 
+  test_objectPattern_destructured_field() async {
+    await assertNoDiagnostics(r'''
+class A {
+  int _a;
+  A(this._a);
+}
+f() {
+  var A(:_a) = A(1);
+}
+''');
+  }
+
   test_objectPattern_ifCase() async {
     await assertDiagnostics(r'''
 class C {
@@ -129,6 +141,24 @@ f() {
     ]);
   }
 
+  test_objectPattern_switch_field() async {
+    await assertNoDiagnostics(r'''
+class A {
+  var _a;
+}
+
+f(A a) {
+  switch (a) {
+    case A(:var _a):
+  }
+  switch (a) {
+    case A(:var _a?):
+    case A(:var _a!):
+  }
+}
+''');
+  }
+
   test_recordPattern_destructured() async {
     await assertDiagnostics(r'''
 f() {
@@ -139,6 +169,16 @@ f() {
     ]);
   }
 
+  test_recordPattern_destructured_field() async {
+    await assertDiagnostics(r'''
+f() {
+  var (a: _a, :b) = (a: 1, b: 1);
+}
+''', [
+      lint(16, 2),
+    ]);
+  }
+
   test_recordPattern_ifCase() async {
     await assertDiagnostics(r'''
 f(Object o) {
@@ -149,6 +189,16 @@ f(Object o) {
     ]);
   }
 
+  test_recordPattern_ifCase_field() async {
+    await assertDiagnostics(r'''
+f(Object o) {
+  if (o case (x: int _x, :int y)) {}
+}
+''', [
+      lint(35, 2),
+    ]);
+  }
+
   test_recordPattern_switch() async {
     await assertDiagnostics(r'''
 f() {