Questions on null_check_on_nullable_type_parameter

[srawlins]

I was looking at test cases in order to implement a quick fix for null_check_on_nullable_type_parameter but came across some test cases that surprised me.

Future<T> / await p!:

Future<T> m40<T extends Object?>(T? p) async => await p!; // LINT

This case does not generate a lint report, but I expected it would.

List<T> / [p!]:

void ff<T>(T? p) {
  <T>[p!]; // LINT
}

This case also does not generate a lint report, but I expected it would.

Stream<T> / yield p!:

Stream<T> m41<T extends Object?>(T? p) async* { yield p!; }

This case also does not generate a lint report, but I expected it would.

[srawlins]

CC @leafpetersen who filed the initial lint rule request

CC @a14n who implemented the lint rule

CC @goderbauer in case this affects the decision to add this to lints/recommended.yaml as per dart-lang/lints#64

[a14n]

This case also does not generate a lint report, but I expected it would.

I expected the same. Those cases were just forgotten during the implementation. I guess the following method should be extended to cover those cases.

linter/lib/src/rules/unnecessary_null_checks.dart

Lines 39 to 83 in 8c01f68

	DartType? getExpectedType(PostfixExpression node) {
	var realNode =
	node.thisOrAncestorMatching((e) => e.parent is! ParenthesizedExpression);
	var parent = realNode?.parent;
	// in return value
	if (parent is ReturnStatement || parent is ExpressionFunctionBody) {
	var parentExpression = parent?.thisOrAncestorOfType<FunctionExpression>();
	if (parentExpression == null) {
	return null;
	}
	var staticType = parentExpression.staticType;
	return staticType is FunctionType ? staticType.returnType : null;
	}
	// assignment
	if (parent is AssignmentExpression &&
	parent.operator.type == TokenType.EQ &&
	(parent.leftHandSide is! Identifier ||
	node.operand is! Identifier ||
	(parent.leftHandSide as Identifier).name !=
	(node.operand as Identifier).name)) {
	return parent.writeType;
	}
	// in variable declaration
	if (parent is VariableDeclaration) {
	return parent.declaredElement?.type;
	}
	// as right member of binary operator
	if (parent is BinaryExpression && parent.rightOperand == realNode) {
	var parentElement = parent.staticElement;
	if (parentElement == null) {
	return null;
	}
	return parentElement.parameters.first.type;
	}
	// as parameter of function
	if (parent is NamedExpression) {
	realNode = parent;
	parent = parent.parent;
	}
	if (parent is ArgumentList && realNode is Expression) {
	return realNode.staticParameterElement?.type;
	}
	return null;
	}

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