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JS-1789 - S4782 resolve type alias #7135

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b824107
Resolve Type Alias with type checker
guillemsarda May 29, 2026
a383a32
Update ruling expected issues
guillemsarda May 29, 2026
c60ea4d
Update service type
guillemsarda May 29, 2026
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78 changes: 78 additions & 0 deletions its/ruling/src/test/expected/ant-design/typescript-S4782.json
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Original file line number Diff line number Diff line change
@@ -1,5 +1,83 @@
{
"ant-design:components/button/button-group.tsx": [
8
],
"ant-design:components/button/button.tsx": [
105
],
"ant-design:components/cascader/index.tsx": [
104
],
"ant-design:components/collapse/Collapse.tsx": [
32
],
"ant-design:components/config-provider/DisabledContext.tsx": [
8
],
"ant-design:components/config-provider/SizeContext.tsx": [
8
],
"ant-design:components/config-provider/context.tsx": [
41
],
"ant-design:components/config-provider/index.tsx": [
83,
85
],
"ant-design:components/date-picker/generatePicker/index.tsx": [
82
],
"ant-design:components/drawer/index.tsx": [
66
],
"ant-design:components/form/Form.tsx": [
31
],
"ant-design:components/input-number/index.tsx": [
25
],
"ant-design:components/input/ClearableLabeledInput.tsx": [
31,
40
],
"ant-design:components/input/Input.tsx": [
117
],
"ant-design:components/input/TextArea.tsx": [
51
],
"ant-design:components/menu/MenuContext.tsx": [
10
],
"ant-design:components/modal/Modal.tsx": [
124
],
"ant-design:components/progress/Line.tsx": [
9
],
"ant-design:components/radio/interface.tsx": [
14,
15
],
"ant-design:components/segmented/index.tsx": [
41
],
"ant-design:components/select/index.tsx": [
40
],
"ant-design:components/table/Table.tsx": [
88
],
"ant-design:components/tabs/index.tsx": [
22
],
"ant-design:components/transfer/operation.tsx": [
17
],
"ant-design:components/tree-select/index.tsx": [
50
],
"ant-design:components/typography/Editable.tsx": [
19
]
}
3 changes: 3 additions & 0 deletions its/ruling/src/test/expected/eigen/typescript-S4782.json
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Original file line number Diff line number Diff line change
@@ -1,4 +1,7 @@
{
"eigen:src/app/Scenes/Artwork/Components/ImageCarousel/ImageCarousel.tsx": [
34
],
"eigen:src/app/Scenes/Fair/Components/FairArtworks.tsx": [
25
],
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6 changes: 6 additions & 0 deletions its/ruling/src/test/expected/vitest/typescript-S4782.json
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,9 @@
78,
384
],
"vitest:packages/pretty-format/src/types.ts": [
108
],
"vitest:packages/runner/src/fixture.ts": [
633
],
Expand All @@ -22,6 +25,9 @@
238,
1266
],
"vitest:packages/utils/src/diff/types.ts": [
31
],
"vitest:packages/vitest/src/node/cli/filter.ts": [
31
],
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10 changes: 10 additions & 0 deletions its/ruling/src/test/expected/vuetify/typescript-S4782.json
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Original file line number Diff line number Diff line change
@@ -1,10 +1,20 @@
{
"vuetify:packages/vuetify/src/composables/color.ts": [
21,
21
],
"vuetify:packages/vuetify/src/composables/group.ts": [
21,
22
],
"vuetify:packages/vuetify/src/composables/rounded.ts": [
11
],
"vuetify:packages/vuetify/src/composables/router.tsx": [
42,
43
],
"vuetify:packages/vuetify/src/framework.ts": [
27
]
}
38 changes: 33 additions & 5 deletions packages/analysis/src/jsts/rules/S4782/rule.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -20,9 +20,10 @@ import type { AST, Rule } from 'eslint';
import type estree from 'estree';
import type { TSESTree } from '@typescript-eslint/utils';
import { generateMeta } from '../helpers/generate-meta.js';
import { isRequiredParserServices } from '../helpers/parser-services.js';
import { isRequiredParserServices, RequiredParserServices } from '../helpers/parser-services.js';
import { report, toSecondaryLocation } from '../helpers/location.js';
import * as meta from './generated-meta.js';
import ts from 'typescript';

export const rule: Rule.RuleModule = {
meta: generateMeta(meta, { hasSuggestions: true }),
Expand All @@ -45,8 +46,10 @@ export const rule: Rule.RuleModule = {
if (!tsNode.optional || !optionalToken) {
return;
}

const typeNode = getUndefinedTypeAnnotation(tsNode.typeAnnotation);
const typeNode = getUndefinedTypeAnnotation(
tsNode.typeAnnotation,
context.sourceCode.parserServices,
);
if (typeNode) {
const suggest = getQuickFixSuggestions(context, optionalToken, typeNode);

Expand All @@ -69,13 +72,38 @@ export const rule: Rule.RuleModule = {
},
};

function getUndefinedTypeAnnotation(tsTypeAnnotation?: TSESTree.TSTypeAnnotation) {
if (tsTypeAnnotation?.typeAnnotation.type === 'TSUnionType') {
function getUndefinedTypeAnnotation(
tsTypeAnnotation: TSESTree.TSTypeAnnotation | undefined,
services: RequiredParserServices,
) {
if (!tsTypeAnnotation) {
return undefined;
}

if (tsTypeAnnotation.typeAnnotation.type === 'TSTypeReference') {
return getUndefinedFromTypeAlias(tsTypeAnnotation, services);
}
if (tsTypeAnnotation.typeAnnotation.type === 'TSUnionType') {
return getUndefinedTypeNode(tsTypeAnnotation.typeAnnotation);
}
return undefined;
}

function getUndefinedFromTypeAlias(
tsTypeAnnotation: TSESTree.TSTypeAnnotation,
services: RequiredParserServices,
): TSESTree.TypeNode | undefined {
const tsTypeNode = services.esTreeNodeToTSNodeMap.get(tsTypeAnnotation.typeAnnotation);
const checker: ts.TypeChecker = services.program.getTypeChecker();
const type = checker.getTypeAtLocation(tsTypeNode);
if (!type.isUnion()) {
return undefined;
}
const hasUndefined = type.types.some(t => (t.flags & ts.TypeFlags.Undefined) !== 0);
const hasNonUndefined = type.types.some(t => (t.flags & ts.TypeFlags.Undefined) === 0);
return hasUndefined && hasNonUndefined ? tsTypeAnnotation.typeAnnotation : undefined;
}

function getUndefinedTypeNode(typeNode: TSESTree.TypeNode): TSESTree.TypeNode | undefined {
if (typeNode.type === 'TSUndefinedKeyword') {
return typeNode;
Expand Down
165 changes: 165 additions & 0 deletions packages/analysis/src/jsts/rules/S4782/unit.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -53,6 +53,56 @@ describe('S4782', () => {
specificAttribute?: undefined;
};`,
},
{
code: `
type StringOrNumber = string | number;
interface Example {
attribute?: StringOrNumber;
};
type UndefinedAlias = undefined;
interface Example2 {
attribute?: UndefinedAlias;
};
`,
},
{
code: `
type A = string;
type B = A;
type C = B;
interface Example {
attribute?: C;
};
type D = undefined;
type E = D;
type F = E;
interface Example2 {
attribute?: F;
};
`,
},
{
code: `
type Recursive = string | Recursive;
interface Example {
attribute?: Recursive;
};
type RecursiveUndefined = undefined | Recursive;
interface Example2 {
attribute?: RecursiveUndefined;
};`,
},
{
code: `
type Box<T> = T;
interface Example {
attribute?: Box<string>;
};
type BoxU<T> = T;
interface Example2 {
attribute?: BoxU<undefined>;
};`,
},
],
invalid: [
{
Expand Down Expand Up @@ -286,6 +336,121 @@ describe('S4782', () => {
},
],
},
{
code: `type StringOrUndefined = string | undefined;
interface Example {
attribute?: StringOrUndefined;
};`,
errors: [
{
message:
"Consider removing 'undefined' type or '?' specifier, one of them is redundant.",
suggestions: [
{
desc: 'Remove "?" operator',
output: `type StringOrUndefined = string | undefined;
interface Example {
attribute: StringOrUndefined;
};`,
},
],
},
],
},
{
code: `
type NumberOrUndefined = number | undefined;
type Attribute = string | NumberOrUndefined;
interface Example {
attribute?: Attribute;
};`,
errors: [
{
message:
"Consider removing 'undefined' type or '?' specifier, one of them is redundant.",
suggestions: [
{
desc: 'Remove "?" operator',
output: `
type NumberOrUndefined = number | undefined;
type Attribute = string | NumberOrUndefined;
interface Example {
attribute: Attribute;
};`,
},
],
},
],
},
{
code: `
type Maybe<T> = T | undefined;
interface Example {
attribute?: Maybe<string>;
};`,
errors: [
{
message:
"Consider removing 'undefined' type or '?' specifier, one of them is redundant.",
suggestions: [
{
desc: 'Remove "?" operator',
output: `
type Maybe<T> = T | undefined;
interface Example {
attribute: Maybe<string>;
};`,
},
],
},
],
},
{
code: `
type Box<T> = T;
interface Example {
attribute?: Box<string | undefined>;
};`,
errors: [
{
message:
"Consider removing 'undefined' type or '?' specifier, one of them is redundant.",
suggestions: [
{
desc: 'Remove "?" operator',
output: `
type Box<T> = T;
interface Example {
attribute: Box<string | undefined>;
};`,
},
],
},
],
},
{
code: `
type Wrapped = (string | undefined);
interface Example {
attribute?: Wrapped;
};`,
errors: [
{
message:
"Consider removing 'undefined' type or '?' specifier, one of them is redundant.",
suggestions: [
{
desc: 'Remove "?" operator',
output: `
type Wrapped = (string | undefined);
interface Example {
attribute: Wrapped;
};`,
},
],
},
],
},
],
},
);
Expand Down
2 changes: 1 addition & 1 deletion packages/analysis/tests/jsts/tools/testers/fixtures/tsconfig.json
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,7 @@
"allowJs": true,
"noImplicitAny": true,
"strict": false,
"strictNullChecks": false,
"strictNullChecks": true,
"lib": ["ESNext", "DOM"],
},
"include": [
Expand Down
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