Detect doubled unnecessary_parenthesis, but allow ternary and equality (dart-archive/linter#3887)

* Detect doubled unnecessary_parenthesis, but allow ternary and equality

This implements new rules for `unnecessary_parenthesis` lint:
* `${(  )}` and `((  ))` are never OK, drop the inner ones
else,
* `(a ? b : c)` is always OK
* `(a == b)` and `(a != b)` are OK in assignment-like and return-like statements.

* More cases of doubled parentheses and exemptions for equality

Author: oprypin

lib/src/rules/unnecessary_parenthesis.dart

@@ -131,11 +131,25 @@ class _Visitor extends SimpleAstVisitor<void> {
       }
     }
 
-    if (parent is ParenthesizedExpression) {
+    // Directly wrapped into parentheses already - always report.
+    if (parent is ParenthesizedExpression ||
+        parent is InterpolationExpression ||
+        (parent is ArgumentList && parent.arguments.length == 1) ||
+        (parent is IfStatement && node == parent.condition) ||
+        (parent is IfElement && node == parent.condition) ||
+        (parent is WhileStatement && node == parent.condition) ||
+        (parent is DoStatement && node == parent.condition) ||
+        (parent is SwitchStatement && node == parent.expression) ||
+        (parent is SwitchExpression && node == parent.expression)) {
       rule.reportLint(node);
       return;
     }
 
+    // `(foo ? bar : baz)` is OK.
+    if (expression is ConditionalExpression) {
+      return;
+    }
+
     // `a..b = (c..d)` is OK.
     if (expression is CascadeExpression ||
         node.thisOrAncestorMatching(
@@ -152,6 +166,19 @@ class _Visitor extends SimpleAstVisitor<void> {
       return;
     }
 
+    // `foo = (a == b)` is OK, `return (count != 0)` is OK.
+    if (expression is BinaryExpression &&
+        (expression.operator.type == TokenType.EQ_EQ ||
+            expression.operator.type == TokenType.BANG_EQ)) {
+      if (parent is AssignmentExpression ||
+          parent is VariableDeclaration ||
+          parent is ReturnStatement ||
+          parent is YieldStatement ||
+          parent is ConstructorFieldInitializer) {
+        return;
+      }
+    }
+
     if (parent is Expression) {
       if (parent is BinaryExpression) return;
       if (parent is ConditionalExpression) return;

test_data/rules/unnecessary_parenthesis.dart

@@ -125,8 +125,54 @@ main() async {
   (a?.abs())!;
   (a?..abs())!;
   (a?[0])!;
+
+  print(!({"a": "b"}["a"]!.isEmpty)); // LINT
+
+  print((1 + 2)); // LINT
+
+  print((1 == 1 ? 2 : 3)); // LINT
+  print('a'.substring((1 == 1 ? 2 : 3), 4)); // OK
+  var a1 = (1 == 1 ? 2 : 3); // OK
+  print('${(1 == 1 ? 2 : 3)}'); // LINT
+  print([(1 == 1 ? 2 : 3)]); // OK
+
+  var a2 = (1 == 1); // OK
+  a2 = (1 == 1); // OK
+  a2 = (1 == 1) || "".isEmpty; // OK
+  var a3 = (1 + 1); // LINT
 }
 
+bool testTernaryAndEquality() {
+  if ((1 == 1 ? true : false)) // LINT
+  {
+    return (1 != 1); // OK
+  } else if ((1 == 1 ? true : false)) // LINT
+  {
+    return (1 > 1); // LINT
+  }
+  while ((1 == 1)) // LINT
+  {
+    print('');
+  }
+  switch ((5 == 6)) // LINT
+  {
+    case true:
+      return false;
+    default:
+      return true;
+  }
+}
+
+class TestConstructorFieldInitializer {
+  bool _x, _y;
+  TestConstructorFieldInitializer()
+      : _x = (1 == 2), // OK
+        _y = (true && false); // LINT
+}
+
+int test2() => (1 == 1 ? 2 : 3); // OK
+bool test3() => (1 == 1); // LINT
+
 Invocation? invocation() => null;
 
 m({p}) => null;