microsoft · Andarist · Dec 2, 2025 · Dec 4, 2025
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -18932,7 +18932,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             type.flags & TypeFlags.Union ? getIntersectionType(map((type as UnionType).types, t => getIndexType(t, indexFlags))) :
             type.flags & TypeFlags.Intersection ? getUnionType(map((type as IntersectionType).types, t => getIndexType(t, indexFlags))) :
             getObjectFlags(type) & ObjectFlags.Mapped ? getIndexTypeForMappedType(type as MappedType, indexFlags) :
-            type === wildcardType ? wildcardType :
+            type === wildcardType || type === silentNeverType ? type :
             type.flags & TypeFlags.Unknown ? neverType :
             type.flags & (TypeFlags.Any | TypeFlags.Never) ? stringNumberSymbolType :
             getLiteralTypeFromProperties(type, (indexFlags & IndexFlags.NoIndexSignatures ? TypeFlags.StringLiteral : TypeFlags.StringLike) | (indexFlags & IndexFlags.StringsOnly ? 0 : TypeFlags.NumberLike | TypeFlags.ESSymbolLike), indexFlags === IndexFlags.None);

diff --git a/tests/baselines/reference/noSilentNeverTypeLeak1.symbols b/tests/baselines/reference/noSilentNeverTypeLeak1.symbols
@@ -0,0 +1,36 @@
+//// [tests/cases/compiler/noSilentNeverTypeLeak1.ts] ////
+
+=== noSilentNeverTypeLeak1.ts ===
+type Fn<T> = (arg: T) => void;
+>Fn : Symbol(Fn, Decl(noSilentNeverTypeLeak1.ts, 0, 0))
+>T : Symbol(T, Decl(noSilentNeverTypeLeak1.ts, 0, 8))
+>arg : Symbol(arg, Decl(noSilentNeverTypeLeak1.ts, 0, 14))
+>T : Symbol(T, Decl(noSilentNeverTypeLeak1.ts, 0, 8))
+
+declare function fn1<T>(): Fn<T>;
+>fn1 : Symbol(fn1, Decl(noSilentNeverTypeLeak1.ts, 0, 30))
+>T : Symbol(T, Decl(noSilentNeverTypeLeak1.ts, 2, 21))
+>Fn : Symbol(Fn, Decl(noSilentNeverTypeLeak1.ts, 0, 0))
+>T : Symbol(T, Decl(noSilentNeverTypeLeak1.ts, 2, 21))
+
+declare function fn2<T>(
+>fn2 : Symbol(fn2, Decl(noSilentNeverTypeLeak1.ts, 2, 33))
+>T : Symbol(T, Decl(noSilentNeverTypeLeak1.ts, 4, 21))
+
+  cb: Fn<{
+>cb : Symbol(cb, Decl(noSilentNeverTypeLeak1.ts, 4, 24))
+>Fn : Symbol(Fn, Decl(noSilentNeverTypeLeak1.ts, 0, 0))
+
+    [K in keyof T & string]: T[K];
+>K : Symbol(K, Decl(noSilentNeverTypeLeak1.ts, 6, 5))
+>T : Symbol(T, Decl(noSilentNeverTypeLeak1.ts, 4, 21))
+>T : Symbol(T, Decl(noSilentNeverTypeLeak1.ts, 4, 21))
+>K : Symbol(K, Decl(noSilentNeverTypeLeak1.ts, 6, 5))
+
+  }>,
+): void;
+
+fn2(fn1());
+>fn2 : Symbol(fn2, Decl(noSilentNeverTypeLeak1.ts, 2, 33))
+>fn1 : Symbol(fn1, Decl(noSilentNeverTypeLeak1.ts, 0, 30))
+
diff --git a/tests/baselines/reference/noSilentNeverTypeLeak1.types b/tests/baselines/reference/noSilentNeverTypeLeak1.types
@@ -0,0 +1,35 @@
+//// [tests/cases/compiler/noSilentNeverTypeLeak1.ts] ////
+
+=== noSilentNeverTypeLeak1.ts ===
+type Fn<T> = (arg: T) => void;
+>Fn : Fn<T>
+>   : ^^^^^
+>arg : T
+>    : ^
+
+declare function fn1<T>(): Fn<T>;
+>fn1 : <T>() => Fn<T>
+>    : ^ ^^^^^^^     
+
+declare function fn2<T>(
+>fn2 : <T>(cb: Fn<{ [K in keyof T & string]: T[K]; }>) => void
+>    : ^ ^^  ^^                                      ^^^^^    
+
+  cb: Fn<{
+>cb : Fn<{ [K in keyof T & string]: T[K]; }>
+>   : ^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+    [K in keyof T & string]: T[K];
+  }>,
+): void;
+
+fn2(fn1());
+>fn2(fn1()) : void
+>           : ^^^^
+>fn2 : <T>(cb: Fn<{ [K in keyof T & string]: T[K]; }>) => void
+>    : ^ ^^  ^^                                      ^^^^^    
+>fn1() : Fn<{}>
+>      : ^^^^^^
+>fn1 : <T>() => Fn<T>
+>    : ^ ^^^^^^^     
+
diff --git a/tests/baselines/reference/noSilentNeverTypeLeak2.errors.txt b/tests/baselines/reference/noSilentNeverTypeLeak2.errors.txt
@@ -0,0 +1,60 @@
+noSilentNeverTypeLeak2.ts(36,3): error TS2322: Type 'ActionFunction<number, ToParameterizedObject<{ doStuff: unknown; doOtherStuff: string; }>>' is not assignable to type 'ActionFunction<number, ToParameterizedObject<{ doStuff: number; doOtherStuff: string; }>>'.
+  Type 'ToParameterizedObject<{ doStuff: unknown; doOtherStuff: string; }>' is not assignable to type 'ToParameterizedObject<{ doStuff: number; doOtherStuff: string; }>'.
+    Type '{ type: "doStuff"; params: unknown; }' is not assignable to type 'ToParameterizedObject<{ doStuff: number; doOtherStuff: string; }>'.
+      Type '{ type: "doStuff"; params: unknown; }' is not assignable to type '{ type: "doStuff"; params: number; }'.
+        Types of property 'params' are incompatible.
+          Type 'unknown' is not assignable to type 'number'.
+
+
+==== noSilentNeverTypeLeak2.ts (1 errors) ====
+    type Values<T> = T[keyof T];
+
+    interface ParameterizedObject {
+      type: string;
+      params?: unknown;
+    }
+
+    type ActionFunction<TParams, TAction extends ParameterizedObject> = {
+      (params: TParams): void;
+      _out_TAction?: TAction;
+    };
+
+    type ToParameterizedObject<TParameterizedMap> = Values<{
+      [K in keyof TParameterizedMap & string]: {
+        type: K;
+        params: TParameterizedMap[K];
+      };
+    }>;
+
+    declare function enqueueActions<TParams, TAction extends ParameterizedObject>(
+      collect: (params: TParams) => void,
+    ): ActionFunction<TParams, TAction>;
+
+    declare function setup<TActions>(actions: {
+      [K in keyof TActions]: ActionFunction<
+        TActions[K],
+        ToParameterizedObject<TActions>
+      >;
+    }): void;
+
+    setup({
+      doStuff: enqueueActions((params: number) => {}),
+    });
+
+    setup({
+      doStuff: enqueueActions((params: number) => {}),
+      ~~~~~~~
+!!! error TS2322: Type 'ActionFunction<number, ToParameterizedObject<{ doStuff: unknown; doOtherStuff: string; }>>' is not assignable to type 'ActionFunction<number, ToParameterizedObject<{ doStuff: number; doOtherStuff: string; }>>'.
+!!! error TS2322:   Type 'ToParameterizedObject<{ doStuff: unknown; doOtherStuff: string; }>' is not assignable to type 'ToParameterizedObject<{ doStuff: number; doOtherStuff: string; }>'.
+!!! error TS2322:     Type '{ type: "doStuff"; params: unknown; }' is not assignable to type 'ToParameterizedObject<{ doStuff: number; doOtherStuff: string; }>'.
+!!! error TS2322:       Type '{ type: "doStuff"; params: unknown; }' is not assignable to type '{ type: "doStuff"; params: number; }'.
+!!! error TS2322:         Types of property 'params' are incompatible.
+!!! error TS2322:           Type 'unknown' is not assignable to type 'number'.
+!!! related TS6500 noSilentNeverTypeLeak2.ts:36:3: The expected type comes from property 'doStuff' which is declared here on type '{ doStuff: ActionFunction<number, ToParameterizedObject<{ doStuff: number; doOtherStuff: string; }>>; doOtherStuff: ActionFunction<string, ToParameterizedObject<{ doStuff: number; doOtherStuff: string; }>>; }'
+      doOtherStuff: (params: string) => {},
+    });
+
+    setup({
+      doStuff: enqueueActions((params: number) => {}),
+      doOtherStuff: (params) => {},
+    });
diff --git a/tests/baselines/reference/noSilentNeverTypeLeak2.symbols b/tests/baselines/reference/noSilentNeverTypeLeak2.symbols
@@ -0,0 +1,130 @@
+//// [tests/cases/compiler/noSilentNeverTypeLeak2.ts] ////
+
+=== noSilentNeverTypeLeak2.ts ===
+type Values<T> = T[keyof T];
+>Values : Symbol(Values, Decl(noSilentNeverTypeLeak2.ts, 0, 0))
+>T : Symbol(T, Decl(noSilentNeverTypeLeak2.ts, 0, 12))
+>T : Symbol(T, Decl(noSilentNeverTypeLeak2.ts, 0, 12))
+>T : Symbol(T, Decl(noSilentNeverTypeLeak2.ts, 0, 12))
+
+interface ParameterizedObject {
+>ParameterizedObject : Symbol(ParameterizedObject, Decl(noSilentNeverTypeLeak2.ts, 0, 28))
+
+  type: string;
+>type : Symbol(ParameterizedObject.type, Decl(noSilentNeverTypeLeak2.ts, 2, 31))
+
+  params?: unknown;
+>params : Symbol(ParameterizedObject.params, Decl(noSilentNeverTypeLeak2.ts, 3, 15))
+}
+
+type ActionFunction<TParams, TAction extends ParameterizedObject> = {
+>ActionFunction : Symbol(ActionFunction, Decl(noSilentNeverTypeLeak2.ts, 5, 1))
+>TParams : Symbol(TParams, Decl(noSilentNeverTypeLeak2.ts, 7, 20))
+>TAction : Symbol(TAction, Decl(noSilentNeverTypeLeak2.ts, 7, 28))
+>ParameterizedObject : Symbol(ParameterizedObject, Decl(noSilentNeverTypeLeak2.ts, 0, 28))
+
+  (params: TParams): void;
+>params : Symbol(params, Decl(noSilentNeverTypeLeak2.ts, 8, 3))
+>TParams : Symbol(TParams, Decl(noSilentNeverTypeLeak2.ts, 7, 20))
+
+  _out_TAction?: TAction;
+>_out_TAction : Symbol(_out_TAction, Decl(noSilentNeverTypeLeak2.ts, 8, 26))
+>TAction : Symbol(TAction, Decl(noSilentNeverTypeLeak2.ts, 7, 28))
+
+};
+
+type ToParameterizedObject<TParameterizedMap> = Values<{
+>ToParameterizedObject : Symbol(ToParameterizedObject, Decl(noSilentNeverTypeLeak2.ts, 10, 2))
+>TParameterizedMap : Symbol(TParameterizedMap, Decl(noSilentNeverTypeLeak2.ts, 12, 27))
+>Values : Symbol(Values, Decl(noSilentNeverTypeLeak2.ts, 0, 0))
+
+  [K in keyof TParameterizedMap & string]: {
+>K : Symbol(K, Decl(noSilentNeverTypeLeak2.ts, 13, 3))
+>TParameterizedMap : Symbol(TParameterizedMap, Decl(noSilentNeverTypeLeak2.ts, 12, 27))
+
+    type: K;
+>type : Symbol(type, Decl(noSilentNeverTypeLeak2.ts, 13, 44))
+>K : Symbol(K, Decl(noSilentNeverTypeLeak2.ts, 13, 3))
+
+    params: TParameterizedMap[K];
+>params : Symbol(params, Decl(noSilentNeverTypeLeak2.ts, 14, 12))
+>TParameterizedMap : Symbol(TParameterizedMap, Decl(noSilentNeverTypeLeak2.ts, 12, 27))
+>K : Symbol(K, Decl(noSilentNeverTypeLeak2.ts, 13, 3))
+
+  };
+}>;
+
+declare function enqueueActions<TParams, TAction extends ParameterizedObject>(
+>enqueueActions : Symbol(enqueueActions, Decl(noSilentNeverTypeLeak2.ts, 17, 3))
+>TParams : Symbol(TParams, Decl(noSilentNeverTypeLeak2.ts, 19, 32))
+>TAction : Symbol(TAction, Decl(noSilentNeverTypeLeak2.ts, 19, 40))
+>ParameterizedObject : Symbol(ParameterizedObject, Decl(noSilentNeverTypeLeak2.ts, 0, 28))
+
+  collect: (params: TParams) => void,
+>collect : Symbol(collect, Decl(noSilentNeverTypeLeak2.ts, 19, 78))
+>params : Symbol(params, Decl(noSilentNeverTypeLeak2.ts, 20, 12))
+>TParams : Symbol(TParams, Decl(noSilentNeverTypeLeak2.ts, 19, 32))
+
+): ActionFunction<TParams, TAction>;
+>ActionFunction : Symbol(ActionFunction, Decl(noSilentNeverTypeLeak2.ts, 5, 1))
+>TParams : Symbol(TParams, Decl(noSilentNeverTypeLeak2.ts, 19, 32))
+>TAction : Symbol(TAction, Decl(noSilentNeverTypeLeak2.ts, 19, 40))
+
+declare function setup<TActions>(actions: {
+>setup : Symbol(setup, Decl(noSilentNeverTypeLeak2.ts, 21, 36))
+>TActions : Symbol(TActions, Decl(noSilentNeverTypeLeak2.ts, 23, 23))
+>actions : Symbol(actions, Decl(noSilentNeverTypeLeak2.ts, 23, 33))
+
+  [K in keyof TActions]: ActionFunction<
+>K : Symbol(K, Decl(noSilentNeverTypeLeak2.ts, 24, 3))
+>TActions : Symbol(TActions, Decl(noSilentNeverTypeLeak2.ts, 23, 23))
+>ActionFunction : Symbol(ActionFunction, Decl(noSilentNeverTypeLeak2.ts, 5, 1))
+
+    TActions[K],
+>TActions : Symbol(TActions, Decl(noSilentNeverTypeLeak2.ts, 23, 23))
+>K : Symbol(K, Decl(noSilentNeverTypeLeak2.ts, 24, 3))
+
+    ToParameterizedObject<TActions>
+>ToParameterizedObject : Symbol(ToParameterizedObject, Decl(noSilentNeverTypeLeak2.ts, 10, 2))
+>TActions : Symbol(TActions, Decl(noSilentNeverTypeLeak2.ts, 23, 23))
+
+  >;
+}): void;
+
+setup({
+>setup : Symbol(setup, Decl(noSilentNeverTypeLeak2.ts, 21, 36))
+
+  doStuff: enqueueActions((params: number) => {}),
+>doStuff : Symbol(doStuff, Decl(noSilentNeverTypeLeak2.ts, 30, 7))
+>enqueueActions : Symbol(enqueueActions, Decl(noSilentNeverTypeLeak2.ts, 17, 3))
+>params : Symbol(params, Decl(noSilentNeverTypeLeak2.ts, 31, 27))
+
+});
+
+setup({
+>setup : Symbol(setup, Decl(noSilentNeverTypeLeak2.ts, 21, 36))
+
+  doStuff: enqueueActions((params: number) => {}),
+>doStuff : Symbol(doStuff, Decl(noSilentNeverTypeLeak2.ts, 34, 7))
+>enqueueActions : Symbol(enqueueActions, Decl(noSilentNeverTypeLeak2.ts, 17, 3))
+>params : Symbol(params, Decl(noSilentNeverTypeLeak2.ts, 35, 27))
+
+  doOtherStuff: (params: string) => {},
+>doOtherStuff : Symbol(doOtherStuff, Decl(noSilentNeverTypeLeak2.ts, 35, 50))
+>params : Symbol(params, Decl(noSilentNeverTypeLeak2.ts, 36, 17))
+
+});
+
+setup({
+>setup : Symbol(setup, Decl(noSilentNeverTypeLeak2.ts, 21, 36))
+
+  doStuff: enqueueActions((params: number) => {}),
+>doStuff : Symbol(doStuff, Decl(noSilentNeverTypeLeak2.ts, 39, 7))
+>enqueueActions : Symbol(enqueueActions, Decl(noSilentNeverTypeLeak2.ts, 17, 3))
+>params : Symbol(params, Decl(noSilentNeverTypeLeak2.ts, 40, 27))
+
+  doOtherStuff: (params) => {},
+>doOtherStuff : Symbol(doOtherStuff, Decl(noSilentNeverTypeLeak2.ts, 40, 50))
+>params : Symbol(params, Decl(noSilentNeverTypeLeak2.ts, 41, 17))
+
+});