Consistently check assignability to template literal placeholders (#56598)

Author: ahejlsberg

src/compiler/checker.ts

@@ -25017,12 +25017,12 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
     }
 
     function isValidTypeForTemplateLiteralPlaceholder(source: Type, target: Type): boolean {
-        if (source === target || target.flags & (TypeFlags.Any | TypeFlags.String)) {
-            return true;
-        }
         if (target.flags & TypeFlags.Intersection) {
             return every((target as IntersectionType).types, t => t === emptyTypeLiteralType || isValidTypeForTemplateLiteralPlaceholder(source, t));
         }
+        if (target.flags & TypeFlags.String || isTypeAssignableTo(source, target)) {
+            return true;
+        }
         if (source.flags & TypeFlags.StringLiteral) {
             const value = (source as StringLiteralType).value;
             return !!(target.flags & TypeFlags.Number && isValidNumberString(value, /*roundTripOnly*/ false) ||
@@ -25035,7 +25035,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             const texts = (source as TemplateLiteralType).texts;
             return texts.length === 2 && texts[0] === "" && texts[1] === "" && isTypeAssignableTo((source as TemplateLiteralType).types[0], target);
         }
-        return isTypeAssignableTo(source, target);
+        return false;
     }
 
     function inferTypesFromTemplateLiteralType(source: Type, target: TemplateLiteralType): Type[] | undefined {

tests/baselines/reference/templateLiteralTypes3.errors.txt

@@ -221,4 +221,12 @@ templateLiteralTypes3.ts(141,9): error TS2367: This comparison appears to be uni
     // Repro from #52685
 
     type Boom = 'abc' | 'def' | `a${string}` | Lowercase<string>;
+    
+    // Repro from #56582
+    
+    function a<T extends {id: string}>() {
+        let x: keyof T & string | `-${keyof T & string}`;
+        x = "id";
+        x = "-id";
+    }
 

tests/baselines/reference/templateLiteralTypes3.js

@@ -195,6 +195,14 @@ function ft1<T extends string>(t: T, u: Uppercase<T>, u1: Uppercase<`1.${T}.3`>,
 // Repro from #52685
 
 type Boom = 'abc' | 'def' | `a${string}` | Lowercase<string>;
+
+// Repro from #56582
+
+function a<T extends {id: string}>() {
+    let x: keyof T & string | `-${keyof T & string}`;
+    x = "id";
+    x = "-id";
+}
 
 
 //// [templateLiteralTypes3.js]
@@ -291,6 +299,12 @@ function ft1(t, u, u1, u2) {
     spread("1.".concat(u, ".3"), "1.".concat(u, ".4"));
     spread(u1, u2);
 }
+// Repro from #56582
+function a() {
+    var x;
+    x = "id";
+    x = "-id";
+}
 
 
 //// [templateLiteralTypes3.d.ts]
@@ -363,3 +377,6 @@ declare function noSpread<P extends DotString>(args: P[]): P;
 declare function spread<P extends DotString>(...args: P[]): P;
 declare function ft1<T extends string>(t: T, u: Uppercase<T>, u1: Uppercase<`1.${T}.3`>, u2: Uppercase<`1.${T}.4`>): void;
 type Boom = 'abc' | 'def' | `a${string}` | Lowercase<string>;
+declare function a<T extends {
+    id: string;
+}>(): void;

tests/baselines/reference/templateLiteralTypes3.symbols

@@ -588,3 +588,22 @@ type Boom = 'abc' | 'def' | `a${string}` | Lowercase<string>;
 >Boom : Symbol(Boom, Decl(templateLiteralTypes3.ts, 189, 1))
 >Lowercase : Symbol(Lowercase, Decl(lib.es5.d.ts, --, --))
 
+// Repro from #56582
+
+function a<T extends {id: string}>() {
+>a : Symbol(a, Decl(templateLiteralTypes3.ts, 193, 61))
+>T : Symbol(T, Decl(templateLiteralTypes3.ts, 197, 11))
+>id : Symbol(id, Decl(templateLiteralTypes3.ts, 197, 22))
+
+    let x: keyof T & string | `-${keyof T & string}`;
+>x : Symbol(x, Decl(templateLiteralTypes3.ts, 198, 7))
+>T : Symbol(T, Decl(templateLiteralTypes3.ts, 197, 11))
+>T : Symbol(T, Decl(templateLiteralTypes3.ts, 197, 11))
+
+    x = "id";
+>x : Symbol(x, Decl(templateLiteralTypes3.ts, 198, 7))
+
+    x = "-id";
+>x : Symbol(x, Decl(templateLiteralTypes3.ts, 198, 7))
+}
+

tests/baselines/reference/templateLiteralTypes3.types

@@ -601,3 +601,23 @@ function ft1<T extends string>(t: T, u: Uppercase<T>, u1: Uppercase<`1.${T}.3`>,
 type Boom = 'abc' | 'def' | `a${string}` | Lowercase<string>;
 >Boom : `a${string}` | Lowercase<string> | "def"
 
+// Repro from #56582
+
+function a<T extends {id: string}>() {
+>a : <T extends { id: string; }>() => void
+>id : string
+
+    let x: keyof T & string | `-${keyof T & string}`;
+>x : (keyof T & string) | `-${keyof T & string}`
+
+    x = "id";
+>x = "id" : "id"
+>x : (keyof T & string) | `-${keyof T & string}`
+>"id" : "id"
+
+    x = "-id";
+>x = "-id" : "-id"
+>x : (keyof T & string) | `-${keyof T & string}`
+>"-id" : "-id"
+}
+

tests/cases/conformance/types/literal/templateLiteralTypes3.ts

@@ -195,3 +195,11 @@ function ft1<T extends string>(t: T, u: Uppercase<T>, u1: Uppercase<`1.${T}.3`>,
 // Repro from #52685
 
 type Boom = 'abc' | 'def' | `a${string}` | Lowercase<string>;
+
+// Repro from #56582
+
+function a<T extends {id: string}>() {
+    let x: keyof T & string | `-${keyof T & string}`;
+    x = "id";
+    x = "-id";
+}