Propagate constness of type parameters in variadic tuples (#52129)

Author: ahejlsberg

src/compiler/checker.ts

@@ -13256,6 +13256,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
 
     function isConstTypeVariable(type: Type): boolean {
         return !!(type.flags & TypeFlags.TypeParameter && some((type as TypeParameter).symbol?.declarations, d => hasSyntacticModifier(d, ModifierFlags.Const)) ||
+            isGenericTupleType(type) && findIndex(getTypeArguments(type), (t, i) => !!(type.target.elementFlags[i] & ElementFlags.Variadic) && isConstTypeVariable(t)) >= 0 ||
             type.flags & TypeFlags.IndexedAccess && isConstTypeVariable((type as IndexedAccessType).objectType));
     }
 

tests/baselines/reference/typeParameterConstModifiers.errors.txt

@@ -79,4 +79,14 @@ tests/cases/conformance/types/typeParameters/typeParameterLists/typeParameterCon
     declare let value: "123";
 
     set(obj, ['a', 'b', 'c'], value);
+    
+    // Repro from #52007
+    
+    declare function inners<const T extends readonly any[]>(...args: readonly [unknown, ...T, unknown]): T;
+    
+    const test = inners(1,2,3,4,5);
+    
+    declare function inners2<const T extends readonly any[]>(args: readonly [unknown, ...T, unknown]): T;
+    
+    const test2 = inners2([1,2,3,4,5]);
 

tests/baselines/reference/typeParameterConstModifiers.js

@@ -71,6 +71,16 @@ declare let obj: Obj;
 declare let value: "123";
 
 set(obj, ['a', 'b', 'c'], value);
+
+// Repro from #52007
+
+declare function inners<const T extends readonly any[]>(...args: readonly [unknown, ...T, unknown]): T;
+
+const test = inners(1,2,3,4,5);
+
+declare function inners2<const T extends readonly any[]>(args: readonly [unknown, ...T, unknown]): T;
+
+const test2 = inners2([1,2,3,4,5]);
 
 
 //// [typeParameterConstModifiers.js]
@@ -105,3 +115,5 @@ var fx1 = function (x) { return x; };
 var fx2 = function (x) { return x; };
 function set(obj, path, value) { }
 set(obj, ['a', 'b', 'c'], value);
+var test = inners(1, 2, 3, 4, 5);
+var test2 = inners2([1, 2, 3, 4, 5]);

tests/baselines/reference/typeParameterConstModifiers.symbols

@@ -272,3 +272,27 @@ set(obj, ['a', 'b', 'c'], value);
 >obj : Symbol(obj, Decl(typeParameterConstModifiers.ts, 68, 11))
 >value : Symbol(value, Decl(typeParameterConstModifiers.ts, 69, 11))
 
+// Repro from #52007
+
+declare function inners<const T extends readonly any[]>(...args: readonly [unknown, ...T, unknown]): T;
+>inners : Symbol(inners, Decl(typeParameterConstModifiers.ts, 71, 33))
+>T : Symbol(T, Decl(typeParameterConstModifiers.ts, 75, 24))
+>args : Symbol(args, Decl(typeParameterConstModifiers.ts, 75, 56))
+>T : Symbol(T, Decl(typeParameterConstModifiers.ts, 75, 24))
+>T : Symbol(T, Decl(typeParameterConstModifiers.ts, 75, 24))
+
+const test = inners(1,2,3,4,5);
+>test : Symbol(test, Decl(typeParameterConstModifiers.ts, 77, 5))
+>inners : Symbol(inners, Decl(typeParameterConstModifiers.ts, 71, 33))
+
+declare function inners2<const T extends readonly any[]>(args: readonly [unknown, ...T, unknown]): T;
+>inners2 : Symbol(inners2, Decl(typeParameterConstModifiers.ts, 77, 31))
+>T : Symbol(T, Decl(typeParameterConstModifiers.ts, 79, 25))
+>args : Symbol(args, Decl(typeParameterConstModifiers.ts, 79, 57))
+>T : Symbol(T, Decl(typeParameterConstModifiers.ts, 79, 25))
+>T : Symbol(T, Decl(typeParameterConstModifiers.ts, 79, 25))
+
+const test2 = inners2([1,2,3,4,5]);
+>test2 : Symbol(test2, Decl(typeParameterConstModifiers.ts, 81, 5))
+>inners2 : Symbol(inners2, Decl(typeParameterConstModifiers.ts, 77, 31))
+

tests/baselines/reference/typeParameterConstModifiers.types

@@ -300,3 +300,34 @@ set(obj, ['a', 'b', 'c'], value);
 >'c' : "c"
 >value : "123"
 
+// Repro from #52007
+
+declare function inners<const T extends readonly any[]>(...args: readonly [unknown, ...T, unknown]): T;
+>inners : <const T extends readonly any[]>(...args: readonly [unknown, ...T, unknown]) => T
+>args : readonly [unknown, ...T, unknown]
+
+const test = inners(1,2,3,4,5);
+>test : [2, 3, 4]
+>inners(1,2,3,4,5) : [2, 3, 4]
+>inners : <const T extends readonly any[]>(...args: readonly [unknown, ...T, unknown]) => T
+>1 : 1
+>2 : 2
+>3 : 3
+>4 : 4
+>5 : 5
+
+declare function inners2<const T extends readonly any[]>(args: readonly [unknown, ...T, unknown]): T;
+>inners2 : <const T extends readonly any[]>(args: readonly [unknown, ...T, unknown]) => T
+>args : readonly [unknown, ...T, unknown]
+
+const test2 = inners2([1,2,3,4,5]);
+>test2 : [2, 3, 4]
+>inners2([1,2,3,4,5]) : [2, 3, 4]
+>inners2 : <const T extends readonly any[]>(args: readonly [unknown, ...T, unknown]) => T
+>[1,2,3,4,5] : [number, 2, 3, 4, number]
+>1 : 1
+>2 : 2
+>3 : 3
+>4 : 4
+>5 : 5
+

tests/cases/conformance/types/typeParameters/typeParameterLists/typeParameterConstModifiers.ts

@@ -72,3 +72,13 @@ declare let obj: Obj;
 declare let value: "123";
 
 set(obj, ['a', 'b', 'c'], value);
+
+// Repro from #52007
+
+declare function inners<const T extends readonly any[]>(...args: readonly [unknown, ...T, unknown]): T;
+
+const test = inners(1,2,3,4,5);
+
+declare function inners2<const T extends readonly any[]>(args: readonly [unknown, ...T, unknown]): T;
+
+const test2 = inners2([1,2,3,4,5]);