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fix(eslint-plugin): [prefer-reduce-type-parameter] don't report cases in which the fix results in a type error #10494

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Merged
merged 4 commits into from
Dec 21, 2024
Merged

fix(eslint-plugin): [prefer-reduce-type-parameter] don't report cases in which the fix results in a type error #10494

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e526696
initial implementation
ronami Dec 13, 2024
525a109
cover a missing test
ronami Dec 13, 2024
505f513
Merge branch 'main' into prefer-reduce-type-parameter-unfixable-repor…
ronami Dec 13, 2024
906407e
change comment wording
ronami Dec 13, 2024
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24 changes: 23 additions & 1 deletion packages/eslint-plugin/src/rules/prefer-reduce-type-parameter.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -57,7 +57,29 @@ export default createRule({

const [, secondArg] = callee.parent.arguments;

if (callee.parent.arguments.length < 2 || !isTypeAssertion(secondArg)) {
if (callee.parent.arguments.length < 2) {
return;
}

if (isTypeAssertion(secondArg)) {
const initializerType = services.getTypeAtLocation(
secondArg.expression,
);

const assertedType = services.getTypeAtLocation(
secondArg.typeAnnotation,
);

const isAssertionNecessary = !checker.isTypeAssignableTo(
initializerType,
assertedType,
);

// don't report this if the resulting fix will be a type error
if (isAssertionNecessary) {
return;
}
} else {
return;
}

Expand Down
111 changes: 108 additions & 3 deletions packages/eslint-plugin/tests/rules/prefer-reduce-type-parameter.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -57,23 +57,70 @@ ruleTester.run('prefer-reduce-type-parameter', rule, {
return a.concat(1);
}, [] as number[]);
`,
`
['a', 'b'].reduce(
(accum, name) => ({
...accum,
[name]: true,
}),
{} as Record<'a' | 'b', boolean>,
);
`,
// Object literal may only specify known properties, and 'c' does not exist in
// type 'Record<"a" | "b", boolean>'.
`
['a', 'b'].reduce(
(accum, name) => ({
...accum,
[name]: true,
}),
{ a: true, b: false, c: true } as Record<'a' | 'b', boolean>,
);
Comment on lines +72 to +78
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@ronami ronami Dec 13, 2024 •
edited
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I'm not sure if it's necessary to cover this, but it's somewhat of an edge case with TypeScript's assignability.

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Heh, yeah, I say let's cover it.

`,
// '{}' is assignable to the constraint of type 'T', but 'T' could be
// instantiated with a different subtype of constraint 'Record<string, boolean>'.
`
function f<T extends Record<string, boolean>>() {
['a', 'b'].reduce(
(accum, name) => ({
...accum,
[name]: true,
}),
{} as T,
);
}
Comment on lines +83 to +91
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This was a missing edge case in #10453.

`,
`
function f<T>() {
['a', 'b'].reduce(
(accum, name) => ({
...accum,
[name]: true,
}),
{} as T,
);
}
`,
`
['a', 'b'].reduce((accum, name) => \`\${accum} | hello \${name}!\`);
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@ronami ronami Dec 13, 2024 •
edited
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This isn't directly related to the change, but it was previously missing coverage, and because it is on its own line now, it fails codecov.

`,
],
invalid: [
{
code: `
declare const arr: string[];
arr.reduce<string>(acc => acc, arr.shift() as string);
arr.reduce<string | undefined>(acc => acc, arr.shift() as string | undefined);
`,
errors: [
{
column: 32,
column: 44,
line: 3,
messageId: 'preferTypeParameter',
},
],
output: `
declare const arr: string[];
arr.reduce<string>(acc => acc, arr.shift());
arr.reduce<string | undefined>(acc => acc, arr.shift());
`,
},
{
Expand Down Expand Up @@ -275,5 +322,63 @@ declare const tuple: [number, number, number] & number[];
tuple.reduce<number[]>((a, s) => a.concat(s * 2), []);
`,
},
{
code: `
['a', 'b'].reduce(
(accum, name) => ({
...accum,
[name]: true,
}),
{} as Record<string, boolean>,
);
`,
errors: [
{
column: 3,
line: 7,
messageId: 'preferTypeParameter',
},
],
output: `
['a', 'b'].reduce<Record<string, boolean>>(
(accum, name) => ({
...accum,
[name]: true,
}),
{},
);
`,
},
{
code: `
function f<T extends Record<string, boolean>>(t: T) {
['a', 'b'].reduce(
(accum, name) => ({
...accum,
[name]: true,
}),
t as Record<string, boolean | number>,
);
}
`,
errors: [
{
column: 5,
line: 8,
messageId: 'preferTypeParameter',
},
],
output: `
function f<T extends Record<string, boolean>>(t: T) {
['a', 'b'].reduce<Record<string, boolean | number>>(
(accum, name) => ({
...accum,
[name]: true,
}),
t,
);
}
`,
},
],
});
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