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Experiment: Remove lower priority from contextual signature instantiation return type inference #58321
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Experiment: Remove lower priority from contextual signature instantiation return type inference #58321
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45 changes: 45 additions & 0 deletions
45
tests/baselines/reference/callbackAssignabilityErrorMessage.errors.txt
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,45 @@ | ||
| callbackAssignabilityErrorMessage.ts(31,1): error TS2322: Type 'Source1' is not assignable to type 'Target'. | ||
| Types of property 'map' are incompatible. | ||
| Types of parameters 'callbackfn' and 'callbackfn' are incompatible. | ||
| Type 'T | undefined' is not assignable to type 'T'. | ||
| 'T' could be instantiated with an arbitrary type which could be unrelated to 'T | undefined'. | ||
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| ==== callbackAssignabilityErrorMessage.ts (1 errors) ==== | ||
| export interface Source1 { | ||
| map: <S>(callbackfn: (value: string) => S) => S[]; | ||
| } | ||
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| export interface Target { | ||
| map: <T>(callbackfn: (value: string) => T | undefined) => T[]; | ||
| } | ||
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| declare let s1: Source1; | ||
| declare let t: Target; | ||
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| // During the following assignment, `Source1["map"]` gets | ||
| // instantiated with the contextual type `Target["map"]` before checking | ||
| // assignability. To do that, an inference is made to `S`. For `Source1`, | ||
| // the only candidate is `T | undefined` from the return type of `callbackfn`. | ||
| // Inference also runs on `map` return types `S[]` and `T[]`, but the result | ||
| // is discarded because it’s run with a lower inference priority. As a result, | ||
| // we end up seeing if the contextually instantiated source signature: | ||
| // | ||
| // (callbackfn: (value: string) => T | undefined) => (T | undefined)[] | ||
| // | ||
| // is assignable to the target signature: | ||
| // | ||
| // (callbackfn: (value: string) => T | undefined) => T[] | ||
| // | ||
| // and the return types cause the failed assignability. But as a human reader | ||
| // interpreting why `s1` is not assignable to `t`, I instead equate `S` and `T` | ||
| // and identify the “real” problem as the return type of `callbackfn` in `Target` | ||
| // (`T | undefined`) being a supertype of the one in `Source1` (`S` → `T`). | ||
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| t = s1; // Bad: instantiates `S` with `T | undefined`, fails `map` return type assignability | ||
| ~ | ||
| !!! error TS2322: Type 'Source1' is not assignable to type 'Target'. | ||
| !!! error TS2322: Types of property 'map' are incompatible. | ||
| !!! error TS2322: Types of parameters 'callbackfn' and 'callbackfn' are incompatible. | ||
| !!! error TS2322: Type 'T | undefined' is not assignable to type 'T'. | ||
| !!! error TS2322: 'T' could be instantiated with an arbitrary type which could be unrelated to 'T | undefined'. |
56 changes: 56 additions & 0 deletions
56
tests/baselines/reference/callbackAssignabilityErrorMessage.js
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,56 @@ | ||
| //// [tests/cases/compiler/callbackAssignabilityErrorMessage.ts] //// | ||
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| //// [callbackAssignabilityErrorMessage.ts] | ||
| export interface Source1 { | ||
| map: <S>(callbackfn: (value: string) => S) => S[]; | ||
| } | ||
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| export interface Target { | ||
| map: <T>(callbackfn: (value: string) => T | undefined) => T[]; | ||
| } | ||
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| declare let s1: Source1; | ||
| declare let t: Target; | ||
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| // During the following assignment, `Source1["map"]` gets | ||
| // instantiated with the contextual type `Target["map"]` before checking | ||
| // assignability. To do that, an inference is made to `S`. For `Source1`, | ||
| // the only candidate is `T | undefined` from the return type of `callbackfn`. | ||
| // Inference also runs on `map` return types `S[]` and `T[]`, but the result | ||
| // is discarded because it’s run with a lower inference priority. As a result, | ||
| // we end up seeing if the contextually instantiated source signature: | ||
| // | ||
| // (callbackfn: (value: string) => T | undefined) => (T | undefined)[] | ||
| // | ||
| // is assignable to the target signature: | ||
| // | ||
| // (callbackfn: (value: string) => T | undefined) => T[] | ||
| // | ||
| // and the return types cause the failed assignability. But as a human reader | ||
| // interpreting why `s1` is not assignable to `t`, I instead equate `S` and `T` | ||
| // and identify the “real” problem as the return type of `callbackfn` in `Target` | ||
| // (`T | undefined`) being a supertype of the one in `Source1` (`S` → `T`). | ||
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| t = s1; // Bad: instantiates `S` with `T | undefined`, fails `map` return type assignability | ||
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| //// [callbackAssignabilityErrorMessage.js] | ||
| // During the following assignment, `Source1["map"]` gets | ||
| // instantiated with the contextual type `Target["map"]` before checking | ||
| // assignability. To do that, an inference is made to `S`. For `Source1`, | ||
| // the only candidate is `T | undefined` from the return type of `callbackfn`. | ||
| // Inference also runs on `map` return types `S[]` and `T[]`, but the result | ||
| // is discarded because it’s run with a lower inference priority. As a result, | ||
| // we end up seeing if the contextually instantiated source signature: | ||
| // | ||
| // (callbackfn: (value: string) => T | undefined) => (T | undefined)[] | ||
| // | ||
| // is assignable to the target signature: | ||
| // | ||
| // (callbackfn: (value: string) => T | undefined) => T[] | ||
| // | ||
| // and the return types cause the failed assignability. But as a human reader | ||
| // interpreting why `s1` is not assignable to `t`, I instead equate `S` and `T` | ||
| // and identify the “real” problem as the return type of `callbackfn` in `Target` | ||
| // (`T | undefined`) being a supertype of the one in `Source1` (`S` → `T`). | ||
| t = s1; // Bad: instantiates `S` with `T | undefined`, fails `map` return type assignability | ||
| export {}; |
58 changes: 58 additions & 0 deletions
58
tests/baselines/reference/callbackAssignabilityErrorMessage.symbols
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,58 @@ | ||
| //// [tests/cases/compiler/callbackAssignabilityErrorMessage.ts] //// | ||
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| === callbackAssignabilityErrorMessage.ts === | ||
| export interface Source1 { | ||
| >Source1 : Symbol(Source1, Decl(callbackAssignabilityErrorMessage.ts, 0, 0)) | ||
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| map: <S>(callbackfn: (value: string) => S) => S[]; | ||
| >map : Symbol(Source1.map, Decl(callbackAssignabilityErrorMessage.ts, 0, 26)) | ||
| >S : Symbol(S, Decl(callbackAssignabilityErrorMessage.ts, 1, 8)) | ||
| >callbackfn : Symbol(callbackfn, Decl(callbackAssignabilityErrorMessage.ts, 1, 11)) | ||
| >value : Symbol(value, Decl(callbackAssignabilityErrorMessage.ts, 1, 24)) | ||
| >S : Symbol(S, Decl(callbackAssignabilityErrorMessage.ts, 1, 8)) | ||
| >S : Symbol(S, Decl(callbackAssignabilityErrorMessage.ts, 1, 8)) | ||
| } | ||
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| export interface Target { | ||
| >Target : Symbol(Target, Decl(callbackAssignabilityErrorMessage.ts, 2, 1)) | ||
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| map: <T>(callbackfn: (value: string) => T | undefined) => T[]; | ||
| >map : Symbol(Target.map, Decl(callbackAssignabilityErrorMessage.ts, 4, 25)) | ||
| >T : Symbol(T, Decl(callbackAssignabilityErrorMessage.ts, 5, 8)) | ||
| >callbackfn : Symbol(callbackfn, Decl(callbackAssignabilityErrorMessage.ts, 5, 11)) | ||
| >value : Symbol(value, Decl(callbackAssignabilityErrorMessage.ts, 5, 24)) | ||
| >T : Symbol(T, Decl(callbackAssignabilityErrorMessage.ts, 5, 8)) | ||
| >T : Symbol(T, Decl(callbackAssignabilityErrorMessage.ts, 5, 8)) | ||
| } | ||
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| declare let s1: Source1; | ||
| >s1 : Symbol(s1, Decl(callbackAssignabilityErrorMessage.ts, 8, 11)) | ||
| >Source1 : Symbol(Source1, Decl(callbackAssignabilityErrorMessage.ts, 0, 0)) | ||
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| declare let t: Target; | ||
| >t : Symbol(t, Decl(callbackAssignabilityErrorMessage.ts, 9, 11)) | ||
| >Target : Symbol(Target, Decl(callbackAssignabilityErrorMessage.ts, 2, 1)) | ||
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| // During the following assignment, `Source1["map"]` gets | ||
| // instantiated with the contextual type `Target["map"]` before checking | ||
| // assignability. To do that, an inference is made to `S`. For `Source1`, | ||
| // the only candidate is `T | undefined` from the return type of `callbackfn`. | ||
| // Inference also runs on `map` return types `S[]` and `T[]`, but the result | ||
| // is discarded because it’s run with a lower inference priority. As a result, | ||
| // we end up seeing if the contextually instantiated source signature: | ||
| // | ||
| // (callbackfn: (value: string) => T | undefined) => (T | undefined)[] | ||
| // | ||
| // is assignable to the target signature: | ||
| // | ||
| // (callbackfn: (value: string) => T | undefined) => T[] | ||
| // | ||
| // and the return types cause the failed assignability. But as a human reader | ||
| // interpreting why `s1` is not assignable to `t`, I instead equate `S` and `T` | ||
| // and identify the “real” problem as the return type of `callbackfn` in `Target` | ||
| // (`T | undefined`) being a supertype of the one in `Source1` (`S` → `T`). | ||
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| t = s1; // Bad: instantiates `S` with `T | undefined`, fails `map` return type assignability | ||
| >t : Symbol(t, Decl(callbackAssignabilityErrorMessage.ts, 9, 11)) | ||
| >s1 : Symbol(s1, Decl(callbackAssignabilityErrorMessage.ts, 8, 11)) | ||
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58 changes: 58 additions & 0 deletions
58
tests/baselines/reference/callbackAssignabilityErrorMessage.types
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,58 @@ | ||
| //// [tests/cases/compiler/callbackAssignabilityErrorMessage.ts] //// | ||
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| === callbackAssignabilityErrorMessage.ts === | ||
| export interface Source1 { | ||
| map: <S>(callbackfn: (value: string) => S) => S[]; | ||
| >map : <S>(callbackfn: (value: string) => S) => S[] | ||
| > : ^ ^^ ^^ ^^^^^ | ||
| >callbackfn : (value: string) => S | ||
| > : ^ ^^ ^^^^^ | ||
| >value : string | ||
| > : ^^^^^^ | ||
| } | ||
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| export interface Target { | ||
| map: <T>(callbackfn: (value: string) => T | undefined) => T[]; | ||
| >map : <T>(callbackfn: (value: string) => T | undefined) => T[] | ||
| > : ^ ^^ ^^ ^^^^^ | ||
| >callbackfn : (value: string) => T | undefined | ||
| > : ^ ^^ ^^^^^ | ||
| >value : string | ||
| > : ^^^^^^ | ||
| } | ||
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| declare let s1: Source1; | ||
| >s1 : Source1 | ||
| > : ^^^^^^^ | ||
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| declare let t: Target; | ||
| >t : Target | ||
| > : ^^^^^^ | ||
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| // During the following assignment, `Source1["map"]` gets | ||
| // instantiated with the contextual type `Target["map"]` before checking | ||
| // assignability. To do that, an inference is made to `S`. For `Source1`, | ||
| // the only candidate is `T | undefined` from the return type of `callbackfn`. | ||
| // Inference also runs on `map` return types `S[]` and `T[]`, but the result | ||
| // is discarded because it’s run with a lower inference priority. As a result, | ||
| // we end up seeing if the contextually instantiated source signature: | ||
| // | ||
| // (callbackfn: (value: string) => T | undefined) => (T | undefined)[] | ||
| // | ||
| // is assignable to the target signature: | ||
| // | ||
| // (callbackfn: (value: string) => T | undefined) => T[] | ||
| // | ||
| // and the return types cause the failed assignability. But as a human reader | ||
| // interpreting why `s1` is not assignable to `t`, I instead equate `S` and `T` | ||
| // and identify the “real” problem as the return type of `callbackfn` in `Target` | ||
| // (`T | undefined`) being a supertype of the one in `Source1` (`S` → `T`). | ||
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| t = s1; // Bad: instantiates `S` with `T | undefined`, fails `map` return type assignability | ||
| >t = s1 : Source1 | ||
| > : ^^^^^^^ | ||
| >t : Target | ||
| > : ^^^^^^ | ||
| >s1 : Source1 | ||
| > : ^^^^^^^ | ||
|
|
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I wrote this test to exercise a very specific inference code path in the PR that introduced it, so it's not grounded in a real world scenario, but I don't think the new error is worse? Maybe the connection between the error and the actual code is more surprising now just because we end up inferring
T = { [x: string]: number }instead ofT = U.Maybe that's a separate problem with signature comparison: it's not immediately clear to users that we've done inference in order to compare two signatures, and it's not immediately clear what the result of that inference was.