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fix(eslint-plugin): [no-unnecessary-condition] don't flag values of an unconstrained or valid type parameter #10473

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Merged
merged 4 commits into from
Dec 21, 2024
Merged

fix(eslint-plugin): [no-unnecessary-condition] don't flag values of an unconstrained or valid type parameter #10473

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40a0961
[no-unnecessary-condition] don't flag values of an unconstrained or v…
ronami Dec 7, 2024
991ff23
use a much simpelr for loop instead of several confusing .some() checks
ronami Dec 14, 2024
d33a7d4
bail early if both a possibly-truthy and a possibly-falsy have been d…
ronami Dec 16, 2024
ff59a13
put back code that checks non-callables
ronami Dec 16, 2024
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47 changes: 39 additions & 8 deletions packages/eslint-plugin/src/rules/no-unnecessary-condition.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -646,22 +646,53 @@ export default createRule<Options, MessageId>({
.getCallSignaturesOfType(
getConstrainedTypeAtLocation(services, callback),
)
.map(sig => sig.getReturnType());
/* istanbul ignore if */ if (returnTypes.length === 0) {
// Not a callable function
.map(sig => sig.getReturnType())
.map(t => {
// TODO: use `getConstraintTypeInfoAtLocation` once it's merged
// https://github.com/typescript-eslint/typescript-eslint/pull/10496
if (tsutils.isTypeParameter(t)) {
return checker.getBaseConstraintOfType(t);
}

return t;
});

if (returnTypes.length === 0) {
// Not a callable function, e.g. `any`
return;
}
// Predicate is always necessary if it involves `any` or `unknown`
if (returnTypes.some(t => isTypeAnyType(t) || isTypeUnknownType(t))) {
return;

let hasFalsyReturnTypes = false;
let hasTruthyReturnTypes = false;

for (const type of returnTypes) {
// Predicate is always necessary if it involves `any` or `unknown`
if (!type || isTypeAnyType(type) || isTypeUnknownType(type)) {
return;
}

if (isPossiblyFalsy(type)) {
hasFalsyReturnTypes = true;
}

if (isPossiblyTruthy(type)) {
hasTruthyReturnTypes = true;
}

// bail early if both a possibly-truthy and a possibly-falsy have been detected
if (hasFalsyReturnTypes && hasTruthyReturnTypes) {
return;
}
}
if (!returnTypes.some(isPossiblyFalsy)) {

if (!hasFalsyReturnTypes) {
return context.report({
node: callback,
messageId: 'alwaysTruthyFunc',
});
}
if (!returnTypes.some(isPossiblyTruthy)) {

if (!hasTruthyReturnTypes) {
return context.report({
node: callback,
messageId: 'alwaysFalsyFunc',
Expand Down
24 changes: 24 additions & 0 deletions packages/eslint-plugin/tests/rules/no-unnecessary-condition.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -286,6 +286,22 @@ function count(
) {
return list.filter(predicate).length;
}
`,
`
declare const test: <T>() => T;

[1, null].filter(test);
`,
`
declare const test: <T extends boolean>() => T;

[1, null].filter(test);
`,
`
[1, null].filter(1 as any);
`,
`
[1, null].filter(1 as never);
`,
// Ignores non-array methods of the same name
`
Expand Down Expand Up @@ -1598,6 +1614,14 @@ function nothing3(x: [string, string]) {
{ column: 25, line: 17, messageId: 'alwaysFalsy' },
],
},
{
code: `
declare const test: <T extends true>() => T;

[1, null].filter(test);
`,
errors: [{ column: 18, line: 4, messageId: 'alwaysTruthyFunc' }],
},
// Indexing cases
{
// This is an error because 'dict' doesn't represent
Expand Down
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