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In switch case, narrow base constraint of type #21483

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61551d6
In switch, narrow base constraint of type
sandersn Jan 30, 2018
926f2e5
Test:narrowing in switch w/constrained type variable
sandersn Jan 30, 2018
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1 change: 1 addition & 0 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -12666,6 +12666,7 @@ namespace ts {
if (!switchTypes.length) {
return type;
}
type = getBaseConstraintOfType(type) || type;
const clauseTypes = switchTypes.slice(clauseStart, clauseEnd);
const hasDefaultClause = clauseStart === clauseEnd || contains(clauseTypes, neverType);
const discriminantType = getUnionType(clauseTypes);
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41 changes: 41 additions & 0 deletions tests/baselines/reference/switchWithConstrainedTypeVariable.errors.txt
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@@ -0,0 +1,41 @@
tests/cases/conformance/controlFlow/switchWithConstrainedTypeVariable.ts(22,19): error TS2322: Type '"a"' is not assignable to type 'never'.
tests/cases/conformance/controlFlow/switchWithConstrainedTypeVariable.ts(23,19): error TS2322: Type '"b"' is not assignable to type 'never'.
tests/cases/conformance/controlFlow/switchWithConstrainedTypeVariable.ts(24,19): error TS2322: Type '"c"' is not assignable to type 'never'.


==== tests/cases/conformance/controlFlow/switchWithConstrainedTypeVariable.ts (3 errors) ====
// Repro from #20840

function function1<T extends 'a' | 'b'>(key: T) {
switch (key) {
case 'a':
key.toLowerCase();
break;
default:
key.toLowerCase();
break;
}
}

// #20375

declare var n: never;
declare function never(never: never): never;
function f<T extends 'a' | 'b' | 'c'>(t: T): void {
switch (t) {
// in a/b/c branches, assignment should fail as t narrows to a/b/c
// in default branch, assignment should be fine
case 'a': n = t; break;
~
!!! error TS2322: Type '"a"' is not assignable to type 'never'.
case 'b': n = t; break;
~
!!! error TS2322: Type '"b"' is not assignable to type 'never'.
case 'c': n = t; break;
~
!!! error TS2322: Type '"c"' is not assignable to type 'never'.
default: n = t; break;
}
}


34 changes: 34 additions & 0 deletions tests/baselines/reference/switchWithConstrainedTypeVariable.js
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Expand Up @@ -11,6 +11,22 @@ function function1<T extends 'a' | 'b'>(key: T) {
break;
}
}

// #20375

declare var n: never;
declare function never(never: never): never;
function f<T extends 'a' | 'b' | 'c'>(t: T): void {
switch (t) {
// in a/b/c branches, assignment should fail as t narrows to a/b/c
// in default branch, assignment should be fine
case 'a': n = t; break;
case 'b': n = t; break;
case 'c': n = t; break;
default: n = t; break;
}
}



//// [switchWithConstrainedTypeVariable.js]
Expand All @@ -26,3 +42,21 @@ function function1(key) {
break;
}
}
function f(t) {
switch (t) {
// in a/b/c branches, assignment should fail as t narrows to a/b/c
// in default branch, assignment should be fine
case 'a':
n = t;
break;
case 'b':
n = t;
break;
case 'c':
n = t;
break;
default:
n = t;
break;
}
}
39 changes: 39 additions & 0 deletions tests/baselines/reference/switchWithConstrainedTypeVariable.symbols
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Expand Up @@ -27,3 +27,42 @@ function function1<T extends 'a' | 'b'>(key: T) {
}
}

// #20375

declare var n: never;
>n : Symbol(n, Decl(switchWithConstrainedTypeVariable.ts, 15, 11))

declare function never(never: never): never;
>never : Symbol(never, Decl(switchWithConstrainedTypeVariable.ts, 15, 21))
>never : Symbol(never, Decl(switchWithConstrainedTypeVariable.ts, 16, 23))

function f<T extends 'a' | 'b' | 'c'>(t: T): void {
>f : Symbol(f, Decl(switchWithConstrainedTypeVariable.ts, 16, 44))
>T : Symbol(T, Decl(switchWithConstrainedTypeVariable.ts, 17, 11))
>t : Symbol(t, Decl(switchWithConstrainedTypeVariable.ts, 17, 38))
>T : Symbol(T, Decl(switchWithConstrainedTypeVariable.ts, 17, 11))

switch (t) {
>t : Symbol(t, Decl(switchWithConstrainedTypeVariable.ts, 17, 38))

// in a/b/c branches, assignment should fail as t narrows to a/b/c
// in default branch, assignment should be fine
case 'a': n = t; break;
>n : Symbol(n, Decl(switchWithConstrainedTypeVariable.ts, 15, 11))
>t : Symbol(t, Decl(switchWithConstrainedTypeVariable.ts, 17, 38))

case 'b': n = t; break;
>n : Symbol(n, Decl(switchWithConstrainedTypeVariable.ts, 15, 11))
>t : Symbol(t, Decl(switchWithConstrainedTypeVariable.ts, 17, 38))

case 'c': n = t; break;
>n : Symbol(n, Decl(switchWithConstrainedTypeVariable.ts, 15, 11))
>t : Symbol(t, Decl(switchWithConstrainedTypeVariable.ts, 17, 38))

default: n = t; break;
>n : Symbol(n, Decl(switchWithConstrainedTypeVariable.ts, 15, 11))
>t : Symbol(t, Decl(switchWithConstrainedTypeVariable.ts, 17, 38))
}
}


50 changes: 48 additions & 2 deletions tests/baselines/reference/switchWithConstrainedTypeVariable.types
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Original file line number Diff line number Diff line change
Expand Up @@ -16,18 +16,64 @@ function function1<T extends 'a' | 'b'>(key: T) {
key.toLowerCase();
>key.toLowerCase() : string
>key.toLowerCase : () => string
>key : T
>key : "a"
>toLowerCase : () => string

break;
default:
key.toLowerCase();
>key.toLowerCase() : string
>key.toLowerCase : () => string
>key : T
>key : "b"
>toLowerCase : () => string

break;
}
}

// #20375

declare var n: never;
>n : never

declare function never(never: never): never;
>never : (never: never) => never
>never : never

function f<T extends 'a' | 'b' | 'c'>(t: T): void {
>f : <T extends "a" | "b" | "c">(t: T) => void
>T : T
>t : T
>T : T

switch (t) {
>t : T

// in a/b/c branches, assignment should fail as t narrows to a/b/c
// in default branch, assignment should be fine
case 'a': n = t; break;
>'a' : "a"
>n = t : "a"
>n : never
>t : "a"

case 'b': n = t; break;
>'b' : "b"
>n = t : "b"
>n : never
>t : "b"

case 'c': n = t; break;
>'c' : "c"
>n = t : "c"
>n : never
>t : "c"

default: n = t; break;
>n = t : never
>n : never
>t : never
}
}


16 changes: 16 additions & 0 deletions tests/cases/conformance/controlFlow/switchWithConstrainedTypeVariable.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -12,3 +12,19 @@ function function1<T extends 'a' | 'b'>(key: T) {
break;
}
}

// #20375

declare var n: never;
declare function never(never: never): never;
function f<T extends 'a' | 'b' | 'c'>(t: T): void {
switch (t) {
// in a/b/c branches, assignment should fail as t narrows to a/b/c
// in default branch, assignment should be fine
case 'a': n = t; break;
case 'b': n = t; break;
case 'c': n = t; break;
default: n = t; break;
}
}

2 changes: 1 addition & 1 deletion tests/cases/user/TypeScript-Node-Starter/TypeScript-Node-Starter
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Submodule TypeScript-Node-Starter updated 11 files
+23 −1 .env.example
+1 −2 README.md
+4,050 −5,174 package-lock.json
+37 −39 package.json
+0 −122 src/app.ts
+138 −3 src/server.ts
+6 −3 test/api.test.ts
+4 −3 test/app.test.ts
+4 −3 test/contact.test.ts
+4 −3 test/home.test.ts
+9 −8 test/user.test.ts