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feat(eslint-plugin): [restrict-plus-operands] add intersection type determination logic #2628

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merged 6 commits into from Oct 18, 2020
Merged

feat(eslint-plugin): [restrict-plus-operands] add intersection type determination logic #2628

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bd842e0
fix: test case , check intersection type
Sep 28, 2020
ca5a50e
chore: test case of intersection type
sunghyunjo Oct 2, 2020
5520ffd
chore: add original test
sunghyunjo Oct 2, 2020
7b5f7ee
Merge branch 'master' into issue/#2506
sunghyunjo Oct 2, 2020
ee2014a
chore: add tc that doesn't contain a string
sunghyunjo Oct 3, 2020
6bc4c39
Merge branch 'issue/#2506' of https://github.com/sunghyunjo/typescrip…
sunghyunjo Oct 3, 2020
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5 changes: 5 additions & 0 deletions packages/eslint-plugin/src/rules/restrict-plus-operands.ts
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Expand Up @@ -70,6 +70,11 @@ export default util.createRule<Options, MessageIds>({
return types.every(value => value === types[0]) ? types[0] : 'invalid';
}

if (type.isIntersection()) {
const types = type.types.map(getBaseTypeOfLiteralType);
return types.some(value => value === 'string') ? 'string' : 'invalid';
}
Comment on lines +73 to +76
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it took me a second to figure out why this works for valid cases.
For the weird cases we care about (like {} & string), typescript tells us the type is an intersection type.

For other cases like unknown & string, typescript tells us the type is just string!
And for bad cases like number & string, typescript again tells us the type is just never!

This is pretty awesome! 😄


const stringType = typeChecker.typeToString(type);

if (
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104 changes: 104 additions & 0 deletions packages/eslint-plugin/tests/rules/restrict-plus-operands.test.ts
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Expand Up @@ -90,6 +90,26 @@ function foo<T extends number>(a: T) {
function foo<T extends 1>(a: T) {
return a + 1;
}
`,
`
declare const a: {} & string;
declare const b: string;
const x = a + b;
`,
`
declare const a: unknown & string;
declare const b: string;
const x = a + b;
`,
`
declare const a: string & string;
declare const b: string;
const x = a + b;
`,
`
declare const a: 'string literal' & string;
declare const b: string;
const x = a + b;
`,
{
code: `
Expand Down Expand Up @@ -411,6 +431,90 @@ function foo<T extends 1>(a: T) {
},
],
},
{
code: `
declare const a: boolean & string;
declare const b: string;
const x = a + b;
`,
errors: [
{
messageId: 'notStrings',
line: 4,
column: 19,
},
],
},
{
code: `
declare const a: number & string;
declare const b: string;
const x = a + b;
`,
errors: [
{
messageId: 'notStrings',
line: 4,
column: 19,
},
],
},
{
code: `
declare const a: symbol & string;
declare const b: string;
const x = a + b;
`,
errors: [
{
messageId: 'notStrings',
line: 4,
column: 19,
},
],
},
{
code: `
declare const a: object & string;
declare const b: string;
const x = a + b;
`,
errors: [
{
messageId: 'notStrings',
line: 4,
column: 19,
},
],
},
{
code: `
declare const a: never & string;
declare const b: string;
const x = a + b;
`,
errors: [
{
messageId: 'notStrings',
line: 4,
column: 19,
},
],
},
{
code: `
declare const a: any & string;
declare const b: string;
const x = a + b;
`,
errors: [
{
messageId: 'notStrings',
line: 4,
column: 19,
},
],
},
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{
code: `
let foo: string | undefined;
Expand Down