v0.12.1

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Patch Changes

• Updated dependencies [35544c5]
  • @​arethetypeswrong/core@​0.12.1

v0.12.0

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Patch Changes

• Updated dependencies [a578211]
  • @​arethetypeswrong/core@​0.12.0

v8.51.0

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Features

• 0a9c433 feat: Add --no-warn-ignored CLI option for flat config (#​17569) (Domantas Petrauskas)
• 977e67e feat: logical-assignment-operators to report expressions with 3 operands (#​17600) (Yosuke Ota)

Bug Fixes

• f976b2f fix: make rule severity case-sensitive in flat config (#​17619) (Milos Djermanovic)
• 0edfe36 fix: Ensure crash error messages are not duplicated (#​17584) (Nicholas C. Zakas)
• dd79abc fix: eslint-disable to be able to parse quoted rule names (#​17612) (Yosuke Ota)
• d2f6801 fix: Ensure correct code path for && followed by ?? (#​17618) (Nicholas C. Zakas)

Documentation

• ee5be81 docs: default to sourceType: "module" in rule examples (#​17615) (Francesco Trotta)
• 1aa26df docs: Add more examples for multiline-ternary (#​17610) (George Ashiotis)
• 47d0b44 docs: Update README (GitHub Actions Bot)
• dbf831e docs: use generated og image (#​17601) (Percy Ma)
• 1866da5 docs: Update README (GitHub Actions Bot)

Chores

• 1ef39ea chore: upgrade @​eslint/js@​8.51.0 (#​17624) (Milos Djermanovic)
• f8c7403 chore: package.json update for @​eslint/js release (ESLint Jenkins)
• 2665552 test: fix flat config linter tests to use Linter in flat config mode (#​17616) (Milos Djermanovic)
• 7b77bcc chore: Refactor CodePathState (#​17510) (Nicholas C. Zakas)
• bc77c9a chore: Document and refactor ForkContext (#​17566) (Nicholas C. Zakas)
• 24e1f14 chore: Refactor and document CodePath (#​17558) (Nicholas C. Zakas)

v0.17.3

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• docs: why-is-my-assertion-failing 907b8aa
• I think the previous build was out of date somehow too, so see https://github.com/mmkal/expect-type/releases/v0.17.2

v0.17.2

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• Improve tuple errors (#​40) 4b38117

Diff(truncated - scroll right!):

test('toEqualTypeOf with tuples', () => {
  const assertion = `expectTypeOf<[[number], [1], []]>().toEqualTypeOf<[[number], [2], []]>()`
  expect(tsErrors(assertion)).toMatchInlineSnapshot(`
-    "test/test.ts:999:999 - error TS2344: Type '[[number], [2], []]' does not satisfy the constraint '{ [x: number]: { [x: number]: number; [iterator]: (() => IterableIterator<1>) | (() => IterableIterator<number>) | (() => IterableIterator<never>); [unscopables]: (() => { copyWithin: boolean; entries: boolean; fill: boolean; find: boolean; findIndex: boolean; keys: boolean; values: boolean; }) | (() => { copyWithin: boolean; entries: boolean; fill: boolean; find: boolean; findIndex: boolean; keys: boolean; values: boolean; }) | (() => { copyWithin: boolean; entries: boolean; fill: boolean; find: boolean; findIndex: boolean; keys: boolean; values: boolean; }); length: 0 | 1; toString:  ... truncated!!!!'.
-      Types of property 'sort' are incompatible.
-        Type '(compareFn?: ((a: [] | [number] | [2], b: [] | [number] | [2]) => number) | undefined) => [[number], [2], []]' is not assignable to type '\\"Expected: function, Actual: function\\"'.
+    "test/test.ts:999:999 - error TS2344: Type '[[number], [2], []]' does not satisfy the constraint '{ 0: { 0: number; }; 1: { 0: \\"Expected: literal number: 2, Actual: literal number: 1\\"; }; 2: {}; }'.
+      The types of '1[0]' are incompatible between these types.
+        Type '2' is not assignable to type '\\"Expected: literal number: 2, Actual: literal number: 1\\"'.
    999 expectTypeOf<[[number], [1], []]>().toEqualTypeOf<[[number], [2], []]>()
                                                          ~~~~~~~~~~~~~~~~~~~"
  `)
})

v0.17.1

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• disallow .not and .branded together cf38918

(this was actually documented in the v0.17.0 release but really it was only pushed here)

v0.17.0

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#​16 went in to - hopefully - significantly improve the error messages produce on failing assertions. Here's an example of how vitest's failing tests were improved:

Before:

After:

Docs copied from the readme about how to interpret these error messages

Error messages

When types don't match, .toEqualTypeOf and .toMatchTypeOf use a special helper type to produce error messages that are as actionable as possible. But there's a bit of an nuance to understanding them. Since the assertions are written "fluently", the failure should be on the "expected" type, not the "actual" type (expect<Actual>().toEqualTypeOf<Expected>()). This means that type errors can be a little confusing - so this library produces a MismatchInfo type to try to make explicit what the expectation is. For example:

expectTypeOf({a: 1}).toEqualTypeOf<{a: string}>()

Is an assertion that will fail, since {a: 1} has type {a: number} and not {a: string}. The error message in this case will read something like this:

test/test.ts:999:999 - error TS2344: Type '{ a: string; }' does not satisfy the constraint '{ a: \\"Expected: string, Actual: number\\"; }'.
  Types of property 'a' are incompatible.
    Type 'string' is not assignable to type '\\"Expected: string, Actual: number\\"'.

999 expectTypeOf({a: 1}).toEqualTypeOf<{a: string}>()

Note that the type constraint reported is a human-readable messaging specifying both the "expected" and "actual" types. Rather than taking the sentence Types of property 'a' are incompatible // Type 'string' is not assignable to type "Expected: string, Actual: number" literally - just look at the property name ('a') and the message: Expected: string, Actual: number. This will tell you what's wrong, in most cases. Extremely complex types will of course be more effort to debug, and may require some experimentation. Please raise an issue if the error messages are actually misleading.

The toBe... methods (like toBeString, toBeNumber, toBeVoid etc.) fail by resolving to a non-callable type when the Actual type under test doesn't match up. For example, the failure for an assertion like expectTypeOf(1).toBeString() will look something like this:

test/test.ts:999:999 - error TS2349: This expression is not callable.
  Type 'ExpectString<number>' has no call signatures.

999 expectTypeOf(1).toBeString()
                    ~~~~~~~~~~

The This expression is not callable part isn't all that helpful - the meaningful error is the next line, Type 'ExpectString<number> has no call signatures. This essentially means you passed a number but asserted it should be a string.

If TypeScript added support for "throw" types these error messagess could be improved. Until then they will take a certain amount of squinting.

Concrete "expected" objects vs typeargs

Error messages for an assertion like this:

expectTypeOf({a: 1}).toEqualTypeOf({a: ''})

Will be less helpful than for an assertion like this:

expectTypeOf({a: 1}).toEqualTypeOf<{a: string}>()

This is because the TypeScript compiler needs to infer the typearg for the .toEqualTypeOf({a: ''}) style, and this library can only mark it as a failure by comparing it against a generic Mismatch type. So, where possible, use a typearg rather than a concrete type for .toEqualTypeOf and toMatchTypeOf. If it's much more convenient to compare two concrete types, you can use typeof:

const one = valueFromFunctionOne({some: {complex: inputs}})
const two = valueFromFunctionTwo({some: {other: inputs}})

expectTypeOf(one).toEqualTypeof<typeof two>()

Kinda-breaking changes: essentially none, but technically, .branded no longer returns a "full" ExpectTypeOf instance at compile-time. Previously you could do this:

expectTypeOf<{a: {b: 1} & {c: 1}}>().branded.not.toEqualTypeOf<{a: {b: 1; c: ''}}>()
expectTypeOf<{a: {b: 1} & {c: 1}}>().not.branded.toEqualTypeOf<{a: {b: 1; c: ''}}>()

Now that won't work (and it was always slightly nonsensical), so you'd have to use // @​ts-expect-error instead of not if you have a negated case where you need branded:

// @​ts-expect-error
expectTypeOf<{a: {b: 1} & {c: 1}}>().branded.not.toEqualTypeOf<{a: {b: 1; c: ''}}>()

What's Changed

• Improve CLI error messages by @​mmkal in https://github.com/mmkal/expect-type/pull/16
• expect-type is usually a dev dependency by @​SerkanSipahi in https://github.com/mmkal/expect-type/pull/39

New Contributors

• @​SerkanSipahi made their first contribution in https://github.com/mmkal/expect-type/pull/39

Full Changelog: mmkal/expect-type@v0.16.0...v0.17.0

v5.21.0

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• Do not inline functions that would be retained in the toplevel (as this would cause code duplication).
• Fix precedence of arrow function and ternary operator when formatting output.