feat(36048): Apply uncalled function checks to ternaries

src/compiler/checker.ts

@@ -27929,7 +27929,8 @@ namespace ts {
  }
 
  function checkConditionalExpression(node: ConditionalExpression, checkMode?: CheckMode): Type {
- checkTruthinessExpression(node.condition);
+ const type = checkTruthinessExpression(node.condition);
+ checkTestingKnownTruthyCallableType(node.condition, node.whenTrue, type);
  const type1 = checkExpression(node.whenTrue, checkMode);
  const type2 = checkExpression(node.whenFalse, checkMode);
  return getUnionType([type1, type2], UnionReduction.Subtype);
@@ -31051,9 +31052,8 @@ namespace ts {
  function checkIfStatement(node: IfStatement) {
  // Grammar checking
  checkGrammarStatementInAmbientContext(node);
-
  const type = checkTruthinessExpression(node.expression);
- checkTestingKnownTruthyCallableType(node, type);
+ checkTestingKnownTruthyCallableType(node.expression, node.thenStatement, type);
  checkSourceElement(node.thenStatement);
 
  if (node.thenStatement.kind === SyntaxKind.EmptyStatement) {
@@ -31063,15 +31063,15 @@ namespace ts {
  checkSourceElement(node.elseStatement);
  }
 
- function checkTestingKnownTruthyCallableType(ifStatement: IfStatement, type: Type) {
+ function checkTestingKnownTruthyCallableType(condExpr: Expression, body: Statement | Expression, type: Type) {
  if (!strictNullChecks) {
  return;
  }
 
- const testedNode = isIdentifier(ifStatement.expression)
- ? ifStatement.expression
- : isPropertyAccessExpression(ifStatement.expression)
- ? ifStatement.expression.name
+ const testedNode = isIdentifier(condExpr)
+ ? condExpr
+ : isPropertyAccessExpression(condExpr)
+ ? condExpr.name
  : undefined;
 
  if (!testedNode) {
@@ -31098,7 +31098,7 @@ namespace ts {
  return;
  }
 
- const functionIsUsedInBody = forEachChild(ifStatement.thenStatement, function check(childNode): boolean | undefined {
+ const functionIsUsedInBody = forEachChild(body, function check(childNode): boolean | undefined {
  if (isIdentifier(childNode)) {
  const childSymbol = getSymbolAtLocation(childNode);
  if (childSymbol && childSymbol.id === testedFunctionSymbol.id) {
@@ -31110,7 +31110,7 @@ namespace ts {
  });
 
  if (!functionIsUsedInBody) {
- error(ifStatement.expression, Diagnostics.This_condition_will_always_return_true_since_the_function_is_always_defined_Did_you_mean_to_call_it_instead);
+ error(condExpr, Diagnostics.This_condition_will_always_return_true_since_the_function_is_always_defined_Did_you_mean_to_call_it_instead);
  }
  }
 

tests/baselines/reference/truthinessCallExpressionCoercion1.errors.txt

@@ -0,0 +1,85 @@
+tests/cases/compiler/truthinessCallExpressionCoercion1.ts(3,5): error TS2774: This condition will always return true since the function is always defined. Did you mean to call it instead?
+tests/cases/compiler/truthinessCallExpressionCoercion1.ts(19,5): error TS2774: This condition will always return true since the function is always defined. Did you mean to call it instead?
+tests/cases/compiler/truthinessCallExpressionCoercion1.ts(33,5): error TS2774: This condition will always return true since the function is always defined. Did you mean to call it instead?
+tests/cases/compiler/truthinessCallExpressionCoercion1.ts(46,5): error TS2774: This condition will always return true since the function is always defined. Did you mean to call it instead?
+tests/cases/compiler/truthinessCallExpressionCoercion1.ts(61,9): error TS2774: This condition will always return true since the function is always defined. Did you mean to call it instead?
+
+
+==== tests/cases/compiler/truthinessCallExpressionCoercion1.ts (5 errors) ====
+ function onlyErrorsWhenTestingNonNullableFunctionType(required: () => boolean, optional?: () => boolean) {
+ // error
+ required ? console.log('required') : undefined;
+ ~~~~~~~~
+!!! error TS2774: This condition will always return true since the function is always defined. Did you mean to call it instead?
+
+ // ok
+ optional ? console.log('optional') : undefined;
+
+ // ok
+ !!required ? console.log('not required') : undefined;
+
+ // ok
+ required() ? console.log('required call') : undefined;
+ }
+
+ function onlyErrorsWhenUnusedInBody() {
+ function test() { return Math.random() > 0.5; }
+
+ // error
+ test ? console.log('test') : undefined;
+ ~~~~
+!!! error TS2774: This condition will always return true since the function is always defined. Did you mean to call it instead?
+
+ // ok
+ test ? console.log(test) : undefined;
+
+ // ok
+ test ? test() : undefined;
+
+ // ok
+ test
+ ? [() => null].forEach(() => { test(); })
+ : undefined;
+
+ // error
+ test
+ ~~~~
+!!! error TS2774: This condition will always return true since the function is always defined. Did you mean to call it instead?
+ ? [() => null].forEach(test => { test() })
+ : undefined;
+ }
+
+ function checksPropertyAccess() {
+ const x = {
+ foo: {
+ bar() { return true; }
+ }
+ }
+
+ // error
+ x.foo.bar ? console.log('x.foo.bar') : undefined;
+ ~~~~~~~~~
+!!! error TS2774: This condition will always return true since the function is always defined. Did you mean to call it instead?
+
+ // ok
+ x.foo.bar ? x.foo.bar : undefined;
+ }
+
+ class Foo {
+ maybeIsUser?: () => boolean;
+
+ isUser() {
+ return true;
+ }
+
+ test() {
+ // error
+ this.isUser ? console.log('this.isUser') : undefined;
+ ~~~~~~~~~~~
+!!! error TS2774: This condition will always return true since the function is always defined. Did you mean to call it instead?
+
+ // ok
+ this.maybeIsUser ? console.log('this.maybeIsUser') : undefined;
+ }
+ }
+

tests/baselines/reference/truthinessCallExpressionCoercion1.js

@@ -0,0 +1,122 @@
+//// [truthinessCallExpressionCoercion1.ts]
+function onlyErrorsWhenTestingNonNullableFunctionType(required: () => boolean, optional?: () => boolean) {
+ // error
+ required ? console.log('required') : undefined;
+
+ // ok
+ optional ? console.log('optional') : undefined;
+
+ // ok
+ !!required ? console.log('not required') : undefined;
+
+ // ok
+ required() ? console.log('required call') : undefined;
+}
+
+function onlyErrorsWhenUnusedInBody() {
+ function test() { return Math.random() > 0.5; }
+
+ // error
+ test ? console.log('test') : undefined;
+
+ // ok
+ test ? console.log(test) : undefined;
+
+ // ok
+ test ? test() : undefined;
+
+ // ok
+ test
+ ? [() => null].forEach(() => { test(); })
+ : undefined;
+
+ // error
+ test
+ ? [() => null].forEach(test => { test() })
+ : undefined;
+}
+
+function checksPropertyAccess() {
+ const x = {
+ foo: {
+ bar() { return true; }
+ }
+ }
+
+ // error
+ x.foo.bar ? console.log('x.foo.bar') : undefined;
+
+ // ok
+ x.foo.bar ? x.foo.bar : undefined;
+}
+
+class Foo {
+ maybeIsUser?: () => boolean;
+
+ isUser() {
+ return true;
+ }
+
+ test() {
+ // error
+ this.isUser ? console.log('this.isUser') : undefined;
+
+ // ok
+ this.maybeIsUser ? console.log('this.maybeIsUser') : undefined;
+ }
+}
+
+
+//// [truthinessCallExpressionCoercion1.js]
+function onlyErrorsWhenTestingNonNullableFunctionType(required, optional) {
+ // error
+ required ? console.log('required') : undefined;
+ // ok
+ optional ? console.log('optional') : undefined;
+ // ok
+ !!required ? console.log('not required') : undefined;
+ // ok
+ required() ? console.log('required call') : undefined;
+}
+function onlyErrorsWhenUnusedInBody() {
+ function test() { return Math.random() > 0.5; }
+ // error
+ test ? console.log('test') : undefined;
+ // ok
+ test ? console.log(test) : undefined;
+ // ok
+ test ? test() : undefined;
+ // ok
+ test
+ ? [function () { return null; }].forEach(function () { test(); })
+ : undefined;
+ // error
+ test
+ ? [function () { return null; }].forEach(function (test) { test(); })
+ : undefined;
+}
+function checksPropertyAccess() {
+ var x = {
+ foo: {
+ bar: function () { return true; }
+ }
+ };
+ // error
+ x.foo.bar ? console.log('x.foo.bar') : undefined;
+ // ok
+ x.foo.bar ? x.foo.bar : undefined;
+}
+var Foo = /** @class */ (function () {
+ function Foo() {
+ }
+ Foo.prototype.isUser = function () {
+ return true;
+ };
+ Foo.prototype.test = function () {
+ // error
+ this.isUser ? console.log('this.isUser') : undefined;
+ // ok
+ this.maybeIsUser ? console.log('this.maybeIsUser') : undefined;
+ };
+ return Foo;
+}());