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fix(eslint-plugin): [prefer-return-this-type] don't report an error when returning a union type that includes a classType #11432

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Merged
JoshuaKGoldberg merged 4 commits into from
Sep 8, 2025
+58 −0
Merged

fix(eslint-plugin): [prefer-return-this-type] don't report an error when returning a union type that includes a classType #11432

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b3d8075
fix: Add logic when returning a union type.
mdm317 Jul 29, 2025
602a349
test: add test
mdm317 Jul 29, 2025
306fda0
Merge branch 'main' into fix-11225
JoshuaKGoldberg Sep 3, 2025
9a559d3
Math.random()
JoshuaKGoldberg Sep 8, 2025
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9 changes: 9 additions & 0 deletions packages/eslint-plugin/src/rules/prefer-return-this-type.ts
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
import type { TSESTree } from '@typescript-eslint/utils';

import { AST_NODE_TYPES } from '@typescript-eslint/utils';
import { isUnionType } from 'ts-api-utils';
import * as ts from 'typescript';

import { createRule, forEachReturnStatement, getParserServices } from '../util';
Expand Down Expand Up @@ -116,6 +117,14 @@ export default createRule({
return;
}

if (
isUnionType(type) &&
type.types.some(typePart => typePart === classType)
) {
hasReturnClassType = true;
return true;
}

return;
});

Expand Down
49 changes: 49 additions & 0 deletions packages/eslint-plugin/tests/rules/prefer-return-this-type.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -98,6 +98,19 @@ class Foo {
`
class Foo {
f?: string;
}
`,
`
declare const valueUnion: BaseUnion | string;

class BaseUnion {
f(): BaseUnion | string {
if (Math.random()) {
return this;
}

return valueUnion;
}
}
`,
],
Expand Down Expand Up @@ -395,6 +408,42 @@ class Animal<T> {
console.log("I'm moving!");
return this;
}
}
`,
},
{
code: `
declare const valueUnion: number | string;

class BaseUnion {
f(): BaseUnion | string {
if (Math.random()) {
return this;
}

return valueUnion;
}
}
`,
errors: [
{
column: 8,
endColumn: 17,
line: 5,
messageId: 'useThisType',
},
],
output: `
declare const valueUnion: number | string;

class BaseUnion {
f(): this | string {
if (Math.random()) {
return this;
}

return valueUnion;
}
}
`,
},
Expand Down
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