Template literal types for contextually typed template literal expressions

src/compiler/checker.ts

@@ -31799,7 +31799,12 @@ namespace ts {
                 texts.push(span.literal.text);
                 types.push(isTypeAssignableTo(type, templateConstraintType) ? type : stringType);
             }
-            return isConstContext(node) ? getTemplateLiteralType(texts, types) : stringType;
+            return isConstContext(node) || someType(getContextualType(node) || unknownType, isTemplateLiteralContextualType) ? getTemplateLiteralType(texts, types) : stringType;
+        }
+
+        function isTemplateLiteralContextualType(type: Type): boolean {
+            return !!(type.flags & (TypeFlags.StringLiteral | TypeFlags.TemplateLiteral) ||
+                type.flags & TypeFlags.InstantiableNonPrimitive && maybeTypeOfKind(getBaseConstraintOfType(type) || unknownType, TypeFlags.StringLike));
         }
 
         function getContextNode(node: Expression): Node {

tests/baselines/reference/stringLiteralTypesWithTemplateStrings02.errors.txt

@@ -1,12 +1,9 @@
 tests/cases/conformance/types/stringLiteral/stringLiteralTypesWithTemplateStrings02.ts(1,5): error TS2322: Type '"AB\nC"' is not assignable to type '"AB\r\nC"'.
-tests/cases/conformance/types/stringLiteral/stringLiteralTypesWithTemplateStrings02.ts(3,5): error TS2322: Type 'string' is not assignable to type '"DE\nF"'.
 
 
-==== tests/cases/conformance/types/stringLiteral/stringLiteralTypesWithTemplateStrings02.ts (2 errors) ====
+==== tests/cases/conformance/types/stringLiteral/stringLiteralTypesWithTemplateStrings02.ts (1 errors) ====
     let abc: "AB\r\nC" = `AB
         ~~~
 !!! error TS2322: Type '"AB\nC"' is not assignable to type '"AB\r\nC"'.
     C`;
-    let de_NEWLINE_f: "DE\nF" = `DE${"\n"}F`;
-        ~~~~~~~~~~~~
-!!! error TS2322: Type 'string' is not assignable to type '"DE\nF"'.
+    let de_NEWLINE_f: "DE\nF" = `DE${"\n"}F`;

tests/baselines/reference/stringLiteralTypesWithTemplateStrings02.types

@@ -6,6 +6,6 @@ let abc: "AB\r\nC" = `AB
 C`;
 let de_NEWLINE_f: "DE\nF" = `DE${"\n"}F`;
 >de_NEWLINE_f : "DE\nF"
->`DE${"\n"}F` : string
+>`DE${"\n"}F` : "DE\nF"
 >"\n" : "\n"
 

tests/baselines/reference/templateLiteralTypes1.types

@@ -8,7 +8,7 @@ const createScopedActionType = <S extends string>(scope: S) => <T extends string
 ><T extends string>(type: T) => `${scope}/${type}` as `${S}/${T}` : <T extends string>(type: T) => `${S}/${T}`
 >type : T
 >`${scope}/${type}` as `${S}/${T}` : `${S}/${T}`
->`${scope}/${type}` : string
+>`${scope}/${type}` : `${S}/${T}`
 >scope : S
 >type : T
 

tests/baselines/reference/templateLiteralTypes2.errors.txt

@@ -1,37 +1,22 @@
-tests/cases/conformance/types/literal/templateLiteralTypes2.ts(6,11): error TS2322: Type 'string' is not assignable to type '`abc${string}`'.
-tests/cases/conformance/types/literal/templateLiteralTypes2.ts(7,11): error TS2322: Type 'string' is not assignable to type '`abc${number}`'.
-tests/cases/conformance/types/literal/templateLiteralTypes2.ts(8,11): error TS2322: Type 'string' is not assignable to type '"abcfoo" | "abcbar" | "abcbaz"'.
-tests/cases/conformance/types/literal/templateLiteralTypes2.ts(9,11): error TS2322: Type 'string' is not assignable to type '`abc${T}`'.
-tests/cases/conformance/types/literal/templateLiteralTypes2.ts(21,11): error TS2322: Type 'string' is not assignable to type '`abc${string}`'.
 tests/cases/conformance/types/literal/templateLiteralTypes2.ts(23,11): error TS2322: Type 'string' is not assignable to type '`abc${string}`'.
 tests/cases/conformance/types/literal/templateLiteralTypes2.ts(29,11): error TS2322: Type 'string' is not assignable to type '`foo${string}` | `bar${string}`'.
 tests/cases/conformance/types/literal/templateLiteralTypes2.ts(32,11): error TS2322: Type 'string' is not assignable to type '`foo${string}` | `bar${string}` | `baz${string}`'.
-tests/cases/conformance/types/literal/templateLiteralTypes2.ts(43,11): error TS2322: Type 'string' is not assignable to type '`foo${string}`'.
 tests/cases/conformance/types/literal/templateLiteralTypes2.ts(67,9): error TS2322: Type '`foo${number}`' is not assignable to type 'String'.
 tests/cases/conformance/types/literal/templateLiteralTypes2.ts(68,9): error TS2322: Type '`foo${number}`' is not assignable to type 'Object'.
 tests/cases/conformance/types/literal/templateLiteralTypes2.ts(69,9): error TS2322: Type '`foo${number}`' is not assignable to type '{}'.
 tests/cases/conformance/types/literal/templateLiteralTypes2.ts(70,9): error TS2322: Type '`foo${number}`' is not assignable to type '{ length: number; }'.
-tests/cases/conformance/types/literal/templateLiteralTypes2.ts(98,7): error TS2322: Type 'string' is not assignable to type '`${number}px`'.
 
 
-==== tests/cases/conformance/types/literal/templateLiteralTypes2.ts (14 errors) ====
+==== tests/cases/conformance/types/literal/templateLiteralTypes2.ts (7 errors) ====
     function ft1<T extends string>(s: string, n: number, u: 'foo' | 'bar' | 'baz', t: T) {
         const c1 = `abc${s}`;  // `abc${string}`
         const c2 = `abc${n}`;  // `abc${number}`
         const c3 = `abc${u}`;  // "abcfoo" | "abcbar" | "abcbaz"
         const c4 = `abc${t}`;  // `abc${T}
         const d1: `abc${string}` = `abc${s}`;
-              ~~
-!!! error TS2322: Type 'string' is not assignable to type '`abc${string}`'.
         const d2: `abc${number}` = `abc${n}`;
-              ~~
-!!! error TS2322: Type 'string' is not assignable to type '`abc${number}`'.
         const d3: `abc${'foo' | 'bar' | 'baz'}` = `abc${u}`;
-              ~~
-!!! error TS2322: Type 'string' is not assignable to type '"abcfoo" | "abcbar" | "abcbaz"'.
         const d4: `abc${T}` = `abc${t}`;
-              ~~
-!!! error TS2322: Type 'string' is not assignable to type '`abc${T}`'.
     }
 
     function ft2(s: string) {
@@ -44,8 +29,6 @@ tests/cases/conformance/types/literal/templateLiteralTypes2.ts(98,7): error TS23
         const c2 = c1;  // Widening type `abc${string}`
         let v2 = c2;  // Type string
         const c3: `abc${string}` = `abc${s}`;
-              ~~
-!!! error TS2322: Type 'string' is not assignable to type '`abc${string}`'.
         let v3 = c3;  // Type `abc${string}`
         const c4: `abc${string}` = c1;  // Type `abc${string}`
               ~~
@@ -74,8 +57,6 @@ tests/cases/conformance/types/literal/templateLiteralTypes2.ts(98,7): error TS23
         const c1 = `foo${s}`;
         let v1 = c1;
         const c2: `foo${string}` = `foo${s}`;
-              ~~
-!!! error TS2322: Type 'string' is not assignable to type '`foo${string}`'.
         let v2 = c2;
         const c3 = `foo${s}` as `foo${string}`;
         let v3 = c3;
@@ -139,6 +120,10 @@ tests/cases/conformance/types/literal/templateLiteralTypes2.ts(98,7): error TS23
     const pixelString: PixelValueType = `22px`;
 
     const pixelStringWithTemplate: PixelValueType = `${pixelValue}px`;
-          ~~~~~~~~~~~~~~~~~~~~~~~
-!!! error TS2322: Type 'string' is not assignable to type '`${number}px`'.
+
+    // Repro from #43143
+
+    function getCardTitle(title: string): `test-${string}` {
+        return `test-${title}`;
+    }
 

tests/baselines/reference/templateLiteralTypes2.js

@@ -97,6 +97,12 @@ type PixelValueType = `${number}px`;
 const pixelString: PixelValueType = `22px`;
 
 const pixelStringWithTemplate: PixelValueType = `${pixelValue}px`;
+
+// Repro from #43143
+
+function getCardTitle(title: string): `test-${string}` {
+    return `test-${title}`;
+}
 
 
 //// [templateLiteralTypes2.js]
@@ -172,6 +178,10 @@ var t5 = takesLiteral("foo.bar." + someUnion); // "abc" | "def" | "ghi"
 var pixelValue = 22;
 var pixelString = "22px";
 var pixelStringWithTemplate = pixelValue + "px";
+// Repro from #43143
+function getCardTitle(title) {
+    return "test-" + title;
+}
 
 
 //// [templateLiteralTypes2.d.ts]
@@ -190,12 +200,13 @@ declare const t1: "baz";
 declare const id2 = "foo.bar.baz";
 declare const t2: "baz";
 declare const someString: string;
-declare const t3: unknown;
+declare const t3: string;
 declare const id4: string;
 declare const t4: unknown;
 declare const someUnion: 'abc' | 'def' | 'ghi';
-declare const t5: unknown;
+declare const t5: "abc" | "def" | "ghi";
 declare const pixelValue: number;
 declare type PixelValueType = `${number}px`;
 declare const pixelString: PixelValueType;
 declare const pixelStringWithTemplate: PixelValueType;
+declare function getCardTitle(title: string): `test-${string}`;

tests/baselines/reference/templateLiteralTypes2.symbols

@@ -322,3 +322,13 @@ const pixelStringWithTemplate: PixelValueType = `${pixelValue}px`;
 >PixelValueType : Symbol(PixelValueType, Decl(templateLiteralTypes2.ts, 91, 30))
 >pixelValue : Symbol(pixelValue, Decl(templateLiteralTypes2.ts, 91, 5))
 
+// Repro from #43143
+
+function getCardTitle(title: string): `test-${string}` {
+>getCardTitle : Symbol(getCardTitle, Decl(templateLiteralTypes2.ts, 97, 66))
+>title : Symbol(title, Decl(templateLiteralTypes2.ts, 101, 22))
+
+    return `test-${title}`;
+>title : Symbol(title, Decl(templateLiteralTypes2.ts, 101, 22))
+}
+

tests/baselines/reference/templateLiteralTypes2.types

@@ -28,22 +28,22 @@ function ft1<T extends string>(s: string, n: number, u: 'foo' | 'bar' | 'baz', t
 
     const d1: `abc${string}` = `abc${s}`;
 >d1 : `abc${string}`
->`abc${s}` : string
+>`abc${s}` : `abc${string}`
 >s : string
 
     const d2: `abc${number}` = `abc${n}`;
 >d2 : `abc${number}`
->`abc${n}` : string
+>`abc${n}` : `abc${number}`
 >n : number
 
     const d3: `abc${'foo' | 'bar' | 'baz'}` = `abc${u}`;
 >d3 : "abcfoo" | "abcbar" | "abcbaz"
->`abc${u}` : string
+>`abc${u}` : "abcfoo" | "abcbar" | "abcbaz"
 >u : "foo" | "bar" | "baz"
 
     const d4: `abc${T}` = `abc${t}`;
 >d4 : `abc${T}`
->`abc${t}` : string
+>`abc${t}` : `abc${T}`
 >t : T
 }
 
@@ -79,7 +79,7 @@ function ft10(s: string) {
 
     const c3: `abc${string}` = `abc${s}`;
 >c3 : `abc${string}`
->`abc${s}` : string
+>`abc${s}` : `abc${string}`
 >s : string
 
     let v3 = c3;  // Type `abc${string}`
@@ -168,7 +168,7 @@ function ft12(s: string) {
 
     const c2: `foo${string}` = `foo${s}`;
 >c2 : `foo${string}`
->`foo${s}` : string
+>`foo${s}` : `foo${string}`
 >s : string
 
     let v2 = c2;
@@ -178,7 +178,7 @@ function ft12(s: string) {
     const c3 = `foo${s}` as `foo${string}`;
 >c3 : `foo${string}`
 >`foo${s}` as `foo${string}` : `foo${string}`
->`foo${s}` : string
+>`foo${s}` : `foo${string}`
 >s : string
 
     let v3 = c3;
@@ -188,7 +188,7 @@ function ft12(s: string) {
     const c4 = <`foo${string}`>`foo${s}`;
 >c4 : `foo${string}`
 ><`foo${string}`>`foo${s}` : `foo${string}`
->`foo${s}` : string
+>`foo${s}` : `foo${string}`
 >s : string
 
     let v4 = c4;
@@ -237,20 +237,20 @@ function ft13(s: string, cond: boolean) {
 >s : string
 
     let y1 = nonWidening(`foo${s}`);
->y1 : string
->nonWidening(`foo${s}`) : string
+>y1 : `foo${string}`
+>nonWidening(`foo${s}`) : `foo${string}`
 >nonWidening : <T extends string | number | symbol>(x: T) => T
->`foo${s}` : string
+>`foo${s}` : `foo${string}`
 >s : string
 
     let y2 = nonWidening(cond ? 'a' : `foo${s}`);
->y2 : string
->nonWidening(cond ? 'a' : `foo${s}`) : string
+>y2 : `foo${string}` | "a"
+>nonWidening(cond ? 'a' : `foo${s}`) : `foo${string}` | "a"
 >nonWidening : <T extends string | number | symbol>(x: T) => T
->cond ? 'a' : `foo${s}` : string
+>cond ? 'a' : `foo${s}` : `foo${string}` | "a"
 >cond : boolean
 >'a' : "a"
->`foo${s}` : string
+>`foo${s}` : `foo${string}`
 >s : string
 }
 
@@ -309,10 +309,10 @@ declare const someString: string;
 >someString : string
 
 const t3 = takesLiteral(`foo.bar.${someString}`);  // string
->t3 : unknown
->takesLiteral(`foo.bar.${someString}`) : unknown
+>t3 : string
+>takesLiteral(`foo.bar.${someString}`) : string
 >takesLiteral : <T extends string>(literal: T) => T extends `foo.bar.${infer R}` ? R : unknown
->`foo.bar.${someString}` : string
+>`foo.bar.${someString}` : `foo.bar.${string}`
 >someString : string
 
 const id4 = `foo.bar.${someString}`;
@@ -330,10 +330,10 @@ declare const someUnion: 'abc' | 'def' | 'ghi';
 >someUnion : "abc" | "def" | "ghi"
 
 const t5 = takesLiteral(`foo.bar.${someUnion}`);  // "abc" | "def" | "ghi"
->t5 : unknown
->takesLiteral(`foo.bar.${someUnion}`) : unknown
+>t5 : "abc" | "def" | "ghi"
+>takesLiteral(`foo.bar.${someUnion}`) : "abc" | "def" | "ghi"
 >takesLiteral : <T extends string>(literal: T) => T extends `foo.bar.${infer R}` ? R : unknown
->`foo.bar.${someUnion}` : string
+>`foo.bar.${someUnion}` : "foo.bar.abc" | "foo.bar.def" | "foo.bar.ghi"
 >someUnion : "abc" | "def" | "ghi"
 
 // Repro from #41732
@@ -351,6 +351,17 @@ const pixelString: PixelValueType = `22px`;
 
 const pixelStringWithTemplate: PixelValueType = `${pixelValue}px`;
 >pixelStringWithTemplate : `${number}px`
->`${pixelValue}px` : string
+>`${pixelValue}px` : `${number}px`
 >pixelValue : number
 
+// Repro from #43143
+
+function getCardTitle(title: string): `test-${string}` {
+>getCardTitle : (title: string) => `test-${string}`
+>title : string
+
+    return `test-${title}`;
+>`test-${title}` : `test-${string}`
+>title : string
+}
+

tests/cases/conformance/types/literal/templateLiteralTypes2.ts

@@ -99,3 +99,9 @@ type PixelValueType = `${number}px`;
 const pixelString: PixelValueType = `22px`;
 
 const pixelStringWithTemplate: PixelValueType = `${pixelValue}px`;
+
+// Repro from #43143
+
+function getCardTitle(title: string): `test-${string}` {
+    return `test-${title}`;
+}