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[WIP] Support condition always true in prefix unary expression #60068

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7942777
Support checking that condition will always return `true` when used w…
tjenkinson Sep 13, 2024
41eb788
Update baselines
tjenkinson Sep 13, 2024
72c3c8b
Update to only check for missing `await` for `!` case
tjenkinson Sep 25, 2024
5eb8478
Go back to checking everything for `!` case
tjenkinson Sep 26, 2024
1274b62
Merge remote-tracking branch 'upstream/main' into support-condition-a…
tjenkinson Sep 26, 2024
9630147
Run formatter
tjenkinson Sep 26, 2024
16ae8dc
Switch to checking for assignment when inverted
tjenkinson Dec 29, 2024
8f8b45c
Only check single inversion
tjenkinson Dec 30, 2024
70b70fb
Make it work for the `if (!fnOrPromise)` case
tjenkinson Dec 30, 2024
fcb0c21
Just check if it's referenced later, and if so ignore
tjenkinson Jan 26, 2025
7a14b9d
Add test that currently fails
tjenkinson Jan 26, 2025
4e47c53
Find the nearest block
tjenkinson Jan 26, 2025
5099e88
Fix looping through all children
tjenkinson Jan 26, 2025
75f941d
Use `findAncestor`
tjenkinson Jan 26, 2025
de99724
Resimplify check
tjenkinson Jan 26, 2025
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48 changes: 32 additions & 16 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -44536,31 +44536,36 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
checkSourceElement(node.elseStatement);
}

function checkTestingKnownTruthyCallableOrAwaitableOrEnumMemberType(condExpr: Expression, condType: Type, body?: Statement | Expression) {
function checkTestingKnownTruthyCallableOrAwaitableOrEnumMemberType(inputCondExpr: Expression, condType: Type, body?: Statement | Expression) {
if (!strictNullChecks) return;
bothHelper(condExpr, body);

function bothHelper(condExpr: Expression, body: Expression | Statement | undefined) {
condExpr = skipParentheses(condExpr);

helper(condExpr, body);
bothHelper(inputCondExpr);

function bothHelper(condExpr: Expression) {
condExpr = skipParentheses(condExpr);
helper(condExpr);
while (isBinaryExpression(condExpr) && (condExpr.operatorToken.kind === SyntaxKind.BarBarToken || condExpr.operatorToken.kind === SyntaxKind.QuestionQuestionToken)) {
condExpr = skipParentheses(condExpr.left);
helper(condExpr, body);
helper(condExpr);
}
}

function helper(condExpr: Expression, body: Expression | Statement | undefined) {
const location = isLogicalOrCoalescingBinaryExpression(condExpr) ? skipParentheses(condExpr.right) : condExpr;
function helper(condExpr: Expression) {
let inverted = false;
let location = condExpr;
if (isPrefixUnaryExpression(condExpr) && condExpr.operator === SyntaxKind.ExclamationToken) {
location = skipParentheses(condExpr.operand);
inverted = true;
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Another thing to consider (and probably add a test) is that we can have an expression that flips between the negative and positive case, if we have nested negation expressions, e.g.: if (a && !(b || !c)) ...

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ah 🙈

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I don't think there's really any special handling needed here?

}
location = isLogicalOrCoalescingBinaryExpression(location) ? skipParentheses(location.right) : location;
if (isModuleExportsAccessExpression(location)) {
return;
}
if (isLogicalOrCoalescingBinaryExpression(location)) {
bothHelper(location, body);
bothHelper(location);
return;
}
const type = location === condExpr ? condType : checkExpression(location);
const type = location === inputCondExpr ? condType : checkExpression(location);
if (type.flags & TypeFlags.EnumLiteral && isPropertyAccessExpression(location) && (getNodeLinks(location.expression).resolvedSymbol ?? unknownSymbol).flags & SymbolFlags.Enum) {
// EnumLiteral type at condition with known value is always truthy or always falsy, likely an error
error(location, Diagnostics.This_condition_will_always_return_0, !!(type as LiteralType).value ? "true" : "false");
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I think this was a bug before? It's an optimisation to not need to call checkExpression to get the type and use the provided condType, if the location still matched the provided condExpr?

Expand All @@ -44575,8 +44580,9 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
// are too many false positives for values sourced from type
// definitions without strictNullChecks otherwise.
const callSignatures = getSignaturesOfType(type, SignatureKind.Call);
const isFnCall = callSignatures.length > 0;
const isPromise = !!getAwaitedTypeOfPromise(type);
if (callSignatures.length === 0 && !isPromise) {
if (!isFnCall && !isPromise) {
return;
}

Expand All @@ -44588,8 +44594,17 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
return;
}

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Why do we call isSymbolUsedInConditionBody with location instead of condExpr, in the first case?

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For some reason without this it wouldn't detect if (!something), but still detect if (!something.else). Didn't dig much into why yet

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@tjenkinson tjenkinson Jan 26, 2025 •
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I think it probably should be location and before was a potential bug?

For the inverted case and if (!someVar) we need to pass in the resolved someVar not !someVar so that it passes isIdentifier(expr) and does the

// If the test was a simple identifier, the above check is sufficient

check.

Otherwise it's treating it as a nested object, which will fail

const isUsed = testedSymbol && isBinaryExpression(condExpr.parent) && isSymbolUsedInBinaryExpressionChain(condExpr.parent, testedSymbol)
|| testedSymbol && body && isSymbolUsedInConditionBody(condExpr, body, testedNode, testedSymbol);
let isUsed: boolean;
if (inverted) {
const closestBlock = findAncestor(condExpr.parent, isBlock);
const isUsedLater = !!(testedSymbol && closestBlock && isSymbolUsedInBody(location, closestBlock, testedNode, testedSymbol, condExpr.end + 1));
isUsed = isUsedLater;
}
else {
const isUsedInBody = !!(testedSymbol && body && isSymbolUsedInBody(location, body, testedNode, testedSymbol, 0));
isUsed = isUsedInBody || !!(testedSymbol && isBinaryExpression(condExpr.parent) && isSymbolUsedInBinaryExpressionChain(condExpr.parent, testedSymbol));
}

if (!isUsed) {
if (isPromise) {
errorAndMaybeSuggestAwait(
Expand All @@ -44606,15 +44621,16 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
}
}

function isSymbolUsedInConditionBody(expr: Expression, body: Statement | Expression, testedNode: Node, testedSymbol: Symbol): boolean {
function isSymbolUsedInBody(expr: Expression, body: Statement | Expression | Node, testedNode: Node, testedSymbol: Symbol, startPos: number): boolean {
return !!forEachChild(body, function check(childNode): boolean | undefined {
if (isIdentifier(childNode)) {
if (childNode.pos >= startPos && isIdentifier(childNode)) {
const childSymbol = getSymbolAtLocation(childNode);
if (childSymbol && childSymbol === testedSymbol) {
// If the test was a simple identifier, the above check is sufficient
if (isIdentifier(expr) || isIdentifier(testedNode) && isBinaryExpression(testedNode.parent)) {
return true;
}

// Otherwise we need to ensure the symbol is called on the same target
let testedExpression = testedNode.parent;
let childExpression = childNode.parent;
Expand Down
140 changes: 140 additions & 0 deletions tests/baselines/reference/falsinessCallExpressionCoercion.errors.txt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,140 @@
falsinessCallExpressionCoercion.ts(4,10): error TS2774: This condition will always return true since this function is always defined. Did you mean to call it instead?
falsinessCallExpressionCoercion.ts(25,10): error TS2774: This condition will always return true since this function is always defined. Did you mean to call it instead?
falsinessCallExpressionCoercion.ts(41,10): error TS2774: This condition will always return true since this function is always defined. Did you mean to call it instead?
falsinessCallExpressionCoercion.ts(66,14): error TS2774: This condition will always return true since this function is always defined. Did you mean to call it instead?
falsinessCallExpressionCoercion.ts(91,10): error TS2774: This condition will always return true since this function is always defined. Did you mean to call it instead?
falsinessCallExpressionCoercion.ts(107,10): error TS2774: This condition will always return true since this function is always defined. Did you mean to call it instead?


==== falsinessCallExpressionCoercion.ts (6 errors) ====
function test1() {
function canAccess() { return false; }

if (!canAccess) { // error
~~~~~~~~~
!!! error TS2774: This condition will always return true since this function is always defined. Did you mean to call it instead?
}
}

function test2() {
function canAccess() { return false; }

if (!canAccess) { // ok
}

canAccess();
}

function test3() {
function canAccess() { return false; }

if (!!!canAccess) { // ok
}
}

function test4(canAccess: () => boolean) {
if (!canAccess) { // error
~~~~~~~~~
!!! error TS2774: This condition will always return true since this function is always defined. Did you mean to call it instead?
}
}

function test5(canAccess?: () => boolean) {
if (!canAccess) { // ok
}
}

function test6() {
const x = {
foo: {
bar() { return true; }
}
};

if (!x.foo.bar) { // error
~~~~~~~~~
!!! error TS2774: This condition will always return true since this function is always defined. Did you mean to call it instead?
}
}

function test7() {
const x = {
foo: {
bar() { return true; }
}
};

if (!x.foo.bar) { // ok
}

x.foo.bar();
}

class Test8 {
maybeIsUser?: () => boolean;

isUser() {
return true;
}

test() {
if (!this.isUser) { // error
~~~~~~~~~~~
!!! error TS2774: This condition will always return true since this function is always defined. Did you mean to call it instead?
}

if (!this.maybeIsUser) { // ok
}
}
}

class Test9 {
isUser() {
return true;
}

test() {
if (!this.isUser) { // ok
}

this.isUser();
}
}

function test10() {
function canAccess() { return false; }

const res = canAccess
if (!res) { // error
~~~
!!! error TS2774: This condition will always return true since this function is always defined. Did you mean to call it instead?
}
}

function test11() {
function canAccess() { return false; }

if (!canAccess) { // ok
} else {
canAccess()
}
}

function test12() {
function canAccess() { return false; }

if (!canAccess || Math.random()) { // error
~~~~~~~~~
!!! error TS2774: This condition will always return true since this function is always defined. Did you mean to call it instead?
}
}

function test13() {
function canAccess() { return false; }

if (!canAccess || Math.random()) { // ok
}

canAccess()
}

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