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feat(eslint-plugin): [no-base-to-string] add checkUnknown Option #11128

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feat(eslint-plugin): [no-base-to-string] add checkUnknown Option #11128

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efb5f30
feat: add type and option
developer-bandi May 4, 2025
d601fd3
feat: apply checkUnknown option and test case
developer-bandi May 6, 2025
3bdc647
fix: ci error
developer-bandi May 18, 2025
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11 changes: 11 additions & 0 deletions packages/eslint-plugin/docs/rules/no-base-to-string.mdx
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Original file line number Diff line number Diff line change
Expand Up @@ -99,6 +99,17 @@ let text = `${value}`;
String(/regex/);
```

### `checkUnknown`

{/* insert option description */}

The following patterns are considered incorrect with the options `{ checkUnknown: true }`:

```ts option='{ "checkUnknown": true }' showPlaygroundButton
declare const x: unknown;
x.toString();
```

## When Not To Use It

If you don't mind a risk of `"[object Object]"` or incorrect type coercions in your values, then you will not need this rule.
Expand Down
18 changes: 16 additions & 2 deletions packages/eslint-plugin/src/rules/no-base-to-string.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@ enum Usefulness {
export type Options = [
{
ignoredTypeNames?: string[];
checkUnknown?: boolean;
},
];
export type MessageIds = 'baseArrayJoin' | 'baseToString';
Expand All @@ -46,6 +47,12 @@ export default createRule<Options, MessageIds>({
type: 'object',
additionalProperties: false,
properties: {
checkUnknown: {
type: 'boolean',
default: false,
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[Cleanup] This actually doesn't do anything in our stack (long story...)

Suggested change
default: false,

description:
'Checks the case where toString is applied to unknown type',
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[Docs] A little bit of phrasing alignment:

Suggested change
'Checks the case where toString is applied to unknown type',
'Whether to also check values of type `unknown`',

},
ignoredTypeNames: {
type: 'array',
description:
Expand All @@ -60,6 +67,7 @@ export default createRule<Options, MessageIds>({
},
defaultOptions: [
{
checkUnknown: false,
ignoredTypeNames: ['Error', 'RegExp', 'URL', 'URLSearchParams'],
},
],
Expand All @@ -76,6 +84,7 @@ export default createRule<Options, MessageIds>({
type ?? services.getTypeAtLocation(node),
new Set(),
);

if (certainty === Usefulness.Always) {
return;
}
Expand Down Expand Up @@ -213,7 +222,7 @@ export default createRule<Options, MessageIds>({
return collectToStringCertainty(constraint, visited);
}
// unconstrained generic means `unknown`
return Usefulness.Always;
return option.checkUnknown ? Usefulness.Sometimes : Usefulness.Always;
}

// the Boolean type definition missing toString()
Expand Down Expand Up @@ -251,8 +260,13 @@ export default createRule<Options, MessageIds>({
const toString =
checker.getPropertyOfType(type, 'toString') ??
checker.getPropertyOfType(type, 'toLocaleString');

if (!toString) {
// e.g. any/unknown
// unknown
if (option.checkUnknown && type.flags === ts.TypeFlags.Unknown) {
return Usefulness.Sometimes;
}
// e.g. any
return Usefulness.Always;
}

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6 changes: 6 additions & 0 deletions packages/eslint-plugin/tests/docs-eslint-output-snapshots/no-base-to-string.shot
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179 changes: 170 additions & 9 deletions packages/eslint-plugin/tests/rules/no-base-to-string.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -475,15 +475,6 @@ declare const bb: ExtendedGuildChannel;
bb.toString();
`,
`
function foo<T>(x: T) {
String(x);
}
`,
`
declare const u: unknown;
String(u);
`,
`
type Value = string | Value[];
declare const v: Value;

Expand Down Expand Up @@ -511,8 +502,178 @@ String(v);
declare const v: ('foo' | 'bar')[][];
String(v);
`,
`
declare const x: unknown;
\`\${x})\`;
`,
`
declare const x: unknown;
x.toString();
`,
`
declare const x: unknown;
x.toLocaleString();
`,
`
declare const x: unknown;
'' + x;
`,
`
declare const x: unknown;
String(x);
`,
`
declare const x: unknown;
'' += x;
`,
`
function foo<T>(x: T) {
String(x);
}
`,
],
invalid: [
{
code: `
declare const x: unknown;
\`\${x})\`;
`,
errors: [
{
data: {
certainty: 'may',
name: 'x',
},
messageId: 'baseToString',
},
],
options: [
{
checkUnknown: true,
},
],
},
{
code: `
declare const x: unknown;
x.toString();
`,
errors: [
{
data: {
certainty: 'may',
name: 'x',
},
messageId: 'baseToString',
},
],
options: [
{
checkUnknown: true,
},
],
},
{
code: `
declare const x: unknown;
x.toLocaleString();
`,
errors: [
{
data: {
certainty: 'may',
name: 'x',
},
messageId: 'baseToString',
},
],
options: [
{
checkUnknown: true,
},
],
},
{
code: `
declare const x: unknown;
'' + x;
`,
errors: [
{
data: {
certainty: 'may',
name: 'x',
},
messageId: 'baseToString',
},
],
options: [
{
checkUnknown: true,
},
],
},
{
code: `
declare const x: unknown;
String(x);
`,
errors: [
{
data: {
certainty: 'may',
name: 'x',
},
messageId: 'baseToString',
},
],
options: [
{
checkUnknown: true,
},
],
},
{
code: `
declare const x: unknown;
'' += x;
`,
errors: [
{
data: {
certainty: 'may',
name: 'x',
},
messageId: 'baseToString',
},
],
options: [
{
checkUnknown: true,
},
],
},
{
code: `
function foo<T>(x: T) {
String(x);
}
`,
errors: [
{
data: {
certainty: 'may',
name: 'x',
},
messageId: 'baseToString',
},
],
options: [
{
checkUnknown: true,
},
],
},
{
code: '`${{}})`;',
errors: [
Expand Down
7 changes: 7 additions & 0 deletions packages/eslint-plugin/tests/schema-snapshots/no-base-to-string.shot
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