diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 3d3f908d82c79..397a424ee7b27 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -38682,7 +38682,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             // A missing not-equal flag indicates that the type wasn't handled by some case.
             return !someType(operandConstraint, t => getTypeFacts(t, notEqualFacts) === notEqualFacts);
         }
-        const type = checkExpressionCached(node.expression);
+        const type = getBaseConstraintOrType(checkExpressionCached(node.expression));
         if (!isLiteralType(type)) {
             return false;
         }
diff --git a/tests/baselines/reference/dependentReturnType9.errors.txt b/tests/baselines/reference/dependentReturnType9.errors.txt
new file mode 100644
index 0000000000000..da12eeaab2eb4
--- /dev/null
+++ b/tests/baselines/reference/dependentReturnType9.errors.txt
@@ -0,0 +1,71 @@
+dependentReturnType9.ts(57,4): error TS2366: Function lacks ending return statement and return type does not include 'undefined'.
+
+
+==== dependentReturnType9.ts (1 errors) ====
+    type Payload =
+      | { _tag: "auth"; username: string; password: string }
+      | { _tag: "cart"; items: Array<{ id: string; quantity: number }> }
+      | { _tag: "person"; name: string; age: number };
+    
+    type PayloadContent = {
+      [P in Payload as P["_tag"]]: Omit<P, "_tag">;
+    };
+    
+    // ok, exhaustive cases and default case with throw
+    function mockPayload<P_TAG extends Payload["_tag"]>(
+      str: P_TAG,
+    ): PayloadContent[P_TAG] {
+      switch (str) {
+        case "auth":
+          return { username: "test", password: "admin" };
+        case "cart":
+          return { items: [{ id: "123", quantity: 123 }] };
+        case "person":
+          return { name: "andrea", age: 27 };
+        default:
+          throw new Error("unknown tag");
+      }
+    }
+    
+    // ok, non-exhaustive cases but default case with throw
+    function mockPayload2<P_TAG extends Payload["_tag"]>(
+      str: P_TAG,
+    ): PayloadContent[P_TAG] {
+      switch (str) {
+        case "auth":
+          return { username: "test", password: "admin" };
+        case "cart":
+          return { items: [{ id: "123", quantity: 123 }] };
+        default:
+          throw new Error("unhandled tag");
+      }
+    }
+    
+    // ok, exhaustive cases
+    function mockPayload3<P_TAG extends Payload["_tag"]>(
+      str: P_TAG,
+    ): PayloadContent[P_TAG] {
+      switch (str) {
+        case "auth":
+          return { username: "test", password: "admin" };
+        case "cart":
+          return { items: [{ id: "123", quantity: 123 }] };
+        case "person":
+          return { name: "andrea", age: 27 };
+      }
+    }
+    
+    // error, non-exhaustive cases
+    function mockPayload4<P_TAG extends Payload["_tag"]>(
+      str: P_TAG,
+    ): PayloadContent[P_TAG] {
+       ~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2366: Function lacks ending return statement and return type does not include 'undefined'.
+      switch (str) {
+        case "auth":
+          return { username: "test", password: "admin" };
+        case "cart":
+          return { items: [{ id: "123", quantity: 123 }] };
+      }
+    }
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/dependentReturnType9.symbols b/tests/baselines/reference/dependentReturnType9.symbols
new file mode 100644
index 0000000000000..d66bb2d76f040
--- /dev/null
+++ b/tests/baselines/reference/dependentReturnType9.symbols
@@ -0,0 +1,173 @@
+//// [tests/cases/compiler/dependentReturnType9.ts] ////
+
+=== dependentReturnType9.ts ===
+type Payload =
+>Payload : Symbol(Payload, Decl(dependentReturnType9.ts, 0, 0))
+
+  | { _tag: "auth"; username: string; password: string }
+>_tag : Symbol(_tag, Decl(dependentReturnType9.ts, 1, 5))
+>username : Symbol(username, Decl(dependentReturnType9.ts, 1, 19))
+>password : Symbol(password, Decl(dependentReturnType9.ts, 1, 37))
+
+  | { _tag: "cart"; items: Array<{ id: string; quantity: number }> }
+>_tag : Symbol(_tag, Decl(dependentReturnType9.ts, 2, 5))
+>items : Symbol(items, Decl(dependentReturnType9.ts, 2, 19))
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>id : Symbol(id, Decl(dependentReturnType9.ts, 2, 34))
+>quantity : Symbol(quantity, Decl(dependentReturnType9.ts, 2, 46))
+
+  | { _tag: "person"; name: string; age: number };
+>_tag : Symbol(_tag, Decl(dependentReturnType9.ts, 3, 5))
+>name : Symbol(name, Decl(dependentReturnType9.ts, 3, 21))
+>age : Symbol(age, Decl(dependentReturnType9.ts, 3, 35))
+
+type PayloadContent = {
+>PayloadContent : Symbol(PayloadContent, Decl(dependentReturnType9.ts, 3, 50))
+
+  [P in Payload as P["_tag"]]: Omit<P, "_tag">;
+>P : Symbol(P, Decl(dependentReturnType9.ts, 6, 3))
+>Payload : Symbol(Payload, Decl(dependentReturnType9.ts, 0, 0))
+>P : Symbol(P, Decl(dependentReturnType9.ts, 6, 3))
+>Omit : Symbol(Omit, Decl(lib.es5.d.ts, --, --))
+>P : Symbol(P, Decl(dependentReturnType9.ts, 6, 3))
+
+};
+
+// ok, exhaustive cases and default case with throw
+function mockPayload<P_TAG extends Payload["_tag"]>(
+>mockPayload : Symbol(mockPayload, Decl(dependentReturnType9.ts, 7, 2))
+>P_TAG : Symbol(P_TAG, Decl(dependentReturnType9.ts, 10, 21))
+>Payload : Symbol(Payload, Decl(dependentReturnType9.ts, 0, 0))
+
+  str: P_TAG,
+>str : Symbol(str, Decl(dependentReturnType9.ts, 10, 52))
+>P_TAG : Symbol(P_TAG, Decl(dependentReturnType9.ts, 10, 21))
+
+): PayloadContent[P_TAG] {
+>PayloadContent : Symbol(PayloadContent, Decl(dependentReturnType9.ts, 3, 50))
+>P_TAG : Symbol(P_TAG, Decl(dependentReturnType9.ts, 10, 21))
+
+  switch (str) {
+>str : Symbol(str, Decl(dependentReturnType9.ts, 10, 52))
+
+    case "auth":
+      return { username: "test", password: "admin" };
+>username : Symbol(username, Decl(dependentReturnType9.ts, 15, 14))
+>password : Symbol(password, Decl(dependentReturnType9.ts, 15, 32))
+
+    case "cart":
+      return { items: [{ id: "123", quantity: 123 }] };
+>items : Symbol(items, Decl(dependentReturnType9.ts, 17, 14))
+>id : Symbol(id, Decl(dependentReturnType9.ts, 17, 24))
+>quantity : Symbol(quantity, Decl(dependentReturnType9.ts, 17, 35))
+
+    case "person":
+      return { name: "andrea", age: 27 };
+>name : Symbol(name, Decl(dependentReturnType9.ts, 19, 14))
+>age : Symbol(age, Decl(dependentReturnType9.ts, 19, 30))
+
+    default:
+      throw new Error("unknown tag");
+>Error : Symbol(Error, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+  }
+}
+
+// ok, non-exhaustive cases but default case with throw
+function mockPayload2<P_TAG extends Payload["_tag"]>(
+>mockPayload2 : Symbol(mockPayload2, Decl(dependentReturnType9.ts, 23, 1))
+>P_TAG : Symbol(P_TAG, Decl(dependentReturnType9.ts, 26, 22))
+>Payload : Symbol(Payload, Decl(dependentReturnType9.ts, 0, 0))
+
+  str: P_TAG,
+>str : Symbol(str, Decl(dependentReturnType9.ts, 26, 53))
+>P_TAG : Symbol(P_TAG, Decl(dependentReturnType9.ts, 26, 22))
+
+): PayloadContent[P_TAG] {
+>PayloadContent : Symbol(PayloadContent, Decl(dependentReturnType9.ts, 3, 50))
+>P_TAG : Symbol(P_TAG, Decl(dependentReturnType9.ts, 26, 22))
+
+  switch (str) {
+>str : Symbol(str, Decl(dependentReturnType9.ts, 26, 53))
+
+    case "auth":
+      return { username: "test", password: "admin" };
+>username : Symbol(username, Decl(dependentReturnType9.ts, 31, 14))
+>password : Symbol(password, Decl(dependentReturnType9.ts, 31, 32))
+
+    case "cart":
+      return { items: [{ id: "123", quantity: 123 }] };
+>items : Symbol(items, Decl(dependentReturnType9.ts, 33, 14))
+>id : Symbol(id, Decl(dependentReturnType9.ts, 33, 24))
+>quantity : Symbol(quantity, Decl(dependentReturnType9.ts, 33, 35))
+
+    default:
+      throw new Error("unhandled tag");
+>Error : Symbol(Error, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+  }
+}
+
+// ok, exhaustive cases
+function mockPayload3<P_TAG extends Payload["_tag"]>(
+>mockPayload3 : Symbol(mockPayload3, Decl(dependentReturnType9.ts, 37, 1))
+>P_TAG : Symbol(P_TAG, Decl(dependentReturnType9.ts, 40, 22))
+>Payload : Symbol(Payload, Decl(dependentReturnType9.ts, 0, 0))
+
+  str: P_TAG,
+>str : Symbol(str, Decl(dependentReturnType9.ts, 40, 53))
+>P_TAG : Symbol(P_TAG, Decl(dependentReturnType9.ts, 40, 22))
+
+): PayloadContent[P_TAG] {
+>PayloadContent : Symbol(PayloadContent, Decl(dependentReturnType9.ts, 3, 50))
+>P_TAG : Symbol(P_TAG, Decl(dependentReturnType9.ts, 40, 22))
+
+  switch (str) {
+>str : Symbol(str, Decl(dependentReturnType9.ts, 40, 53))
+
+    case "auth":
+      return { username: "test", password: "admin" };
+>username : Symbol(username, Decl(dependentReturnType9.ts, 45, 14))
+>password : Symbol(password, Decl(dependentReturnType9.ts, 45, 32))
+
+    case "cart":
+      return { items: [{ id: "123", quantity: 123 }] };
+>items : Symbol(items, Decl(dependentReturnType9.ts, 47, 14))
+>id : Symbol(id, Decl(dependentReturnType9.ts, 47, 24))
+>quantity : Symbol(quantity, Decl(dependentReturnType9.ts, 47, 35))
+
+    case "person":
+      return { name: "andrea", age: 27 };
+>name : Symbol(name, Decl(dependentReturnType9.ts, 49, 14))
+>age : Symbol(age, Decl(dependentReturnType9.ts, 49, 30))
+  }
+}
+
+// error, non-exhaustive cases
+function mockPayload4<P_TAG extends Payload["_tag"]>(
+>mockPayload4 : Symbol(mockPayload4, Decl(dependentReturnType9.ts, 51, 1))
+>P_TAG : Symbol(P_TAG, Decl(dependentReturnType9.ts, 54, 22))
+>Payload : Symbol(Payload, Decl(dependentReturnType9.ts, 0, 0))
+
+  str: P_TAG,
+>str : Symbol(str, Decl(dependentReturnType9.ts, 54, 53))
+>P_TAG : Symbol(P_TAG, Decl(dependentReturnType9.ts, 54, 22))
+
+): PayloadContent[P_TAG] {
+>PayloadContent : Symbol(PayloadContent, Decl(dependentReturnType9.ts, 3, 50))
+>P_TAG : Symbol(P_TAG, Decl(dependentReturnType9.ts, 54, 22))
+
+  switch (str) {
+>str : Symbol(str, Decl(dependentReturnType9.ts, 54, 53))
+
+    case "auth":
+      return { username: "test", password: "admin" };
+>username : Symbol(username, Decl(dependentReturnType9.ts, 59, 14))
+>password : Symbol(password, Decl(dependentReturnType9.ts, 59, 32))
+
+    case "cart":
+      return { items: [{ id: "123", quantity: 123 }] };
+>items : Symbol(items, Decl(dependentReturnType9.ts, 61, 14))
+>id : Symbol(id, Decl(dependentReturnType9.ts, 61, 24))
+>quantity : Symbol(quantity, Decl(dependentReturnType9.ts, 61, 35))
+  }
+}
+
diff --git a/tests/baselines/reference/dependentReturnType9.types b/tests/baselines/reference/dependentReturnType9.types
new file mode 100644
index 0000000000000..834e5f578388b
--- /dev/null
+++ b/tests/baselines/reference/dependentReturnType9.types
@@ -0,0 +1,306 @@
+//// [tests/cases/compiler/dependentReturnType9.ts] ////
+
+=== dependentReturnType9.ts ===
+type Payload =
+>Payload : Payload
+>        : ^^^^^^^
+
+  | { _tag: "auth"; username: string; password: string }
+>_tag : "auth"
+>     : ^^^^^^
+>username : string
+>         : ^^^^^^
+>password : string
+>         : ^^^^^^
+
+  | { _tag: "cart"; items: Array<{ id: string; quantity: number }> }
+>_tag : "cart"
+>     : ^^^^^^
+>items : { id: string; quantity: number; }[]
+>      : ^^^^^^      ^^^^^^^^^^^^      ^^^^^
+>id : string
+>   : ^^^^^^
+>quantity : number
+>         : ^^^^^^
+
+  | { _tag: "person"; name: string; age: number };
+>_tag : "person"
+>     : ^^^^^^^^
+>name : string
+>     : ^^^^^^
+>age : number
+>    : ^^^^^^
+
+type PayloadContent = {
+>PayloadContent : PayloadContent
+>               : ^^^^^^^^^^^^^^
+
+  [P in Payload as P["_tag"]]: Omit<P, "_tag">;
+};
+
+// ok, exhaustive cases and default case with throw
+function mockPayload<P_TAG extends Payload["_tag"]>(
+>mockPayload : <P_TAG extends Payload["_tag"]>(str: P_TAG) => PayloadContent[P_TAG]
+>            : ^     ^^^^^^^^^               ^^   ^^     ^^^^^                     
+
+  str: P_TAG,
+>str : P_TAG
+>    : ^^^^^
+
+): PayloadContent[P_TAG] {
+  switch (str) {
+>str : P_TAG
+>    : ^^^^^
+
+    case "auth":
+>"auth" : "auth"
+>       : ^^^^^^
+
+      return { username: "test", password: "admin" };
+>{ username: "test", password: "admin" } : { username: string; password: string; }
+>                                        : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>username : string
+>         : ^^^^^^
+>"test" : "test"
+>       : ^^^^^^
+>password : string
+>         : ^^^^^^
+>"admin" : "admin"
+>        : ^^^^^^^
+
+    case "cart":
+>"cart" : "cart"
+>       : ^^^^^^
+
+      return { items: [{ id: "123", quantity: 123 }] };
+>{ items: [{ id: "123", quantity: 123 }] } : { items: { id: string; quantity: number; }[]; }
+>                                          : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>items : { id: string; quantity: number; }[]
+>      : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>[{ id: "123", quantity: 123 }] : { id: string; quantity: number; }[]
+>                               : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>{ id: "123", quantity: 123 } : { id: string; quantity: number; }
+>                             : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>id : string
+>   : ^^^^^^
+>"123" : "123"
+>      : ^^^^^
+>quantity : number
+>         : ^^^^^^
+>123 : 123
+>    : ^^^
+
+    case "person":
+>"person" : "person"
+>         : ^^^^^^^^
+
+      return { name: "andrea", age: 27 };
+>{ name: "andrea", age: 27 } : { name: string; age: number; }
+>                            : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>name : string
+>     : ^^^^^^
+>"andrea" : "andrea"
+>         : ^^^^^^^^
+>age : number
+>    : ^^^^^^
+>27 : 27
+>   : ^^
+
+    default:
+      throw new Error("unknown tag");
+>new Error("unknown tag") : Error
+>                         : ^^^^^
+>Error : ErrorConstructor
+>      : ^^^^^^^^^^^^^^^^
+>"unknown tag" : "unknown tag"
+>              : ^^^^^^^^^^^^^
+  }
+}
+
+// ok, non-exhaustive cases but default case with throw
+function mockPayload2<P_TAG extends Payload["_tag"]>(
+>mockPayload2 : <P_TAG extends Payload["_tag"]>(str: P_TAG) => PayloadContent[P_TAG]
+>             : ^     ^^^^^^^^^               ^^   ^^     ^^^^^                     
+
+  str: P_TAG,
+>str : P_TAG
+>    : ^^^^^
+
+): PayloadContent[P_TAG] {
+  switch (str) {
+>str : P_TAG
+>    : ^^^^^
+
+    case "auth":
+>"auth" : "auth"
+>       : ^^^^^^
+
+      return { username: "test", password: "admin" };
+>{ username: "test", password: "admin" } : { username: string; password: string; }
+>                                        : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>username : string
+>         : ^^^^^^
+>"test" : "test"
+>       : ^^^^^^
+>password : string
+>         : ^^^^^^
+>"admin" : "admin"
+>        : ^^^^^^^
+
+    case "cart":
+>"cart" : "cart"
+>       : ^^^^^^
+
+      return { items: [{ id: "123", quantity: 123 }] };
+>{ items: [{ id: "123", quantity: 123 }] } : { items: { id: string; quantity: number; }[]; }
+>                                          : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>items : { id: string; quantity: number; }[]
+>      : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>[{ id: "123", quantity: 123 }] : { id: string; quantity: number; }[]
+>                               : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>{ id: "123", quantity: 123 } : { id: string; quantity: number; }
+>                             : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>id : string
+>   : ^^^^^^
+>"123" : "123"
+>      : ^^^^^
+>quantity : number
+>         : ^^^^^^
+>123 : 123
+>    : ^^^
+
+    default:
+      throw new Error("unhandled tag");
+>new Error("unhandled tag") : Error
+>                           : ^^^^^
+>Error : ErrorConstructor
+>      : ^^^^^^^^^^^^^^^^
+>"unhandled tag" : "unhandled tag"
+>                : ^^^^^^^^^^^^^^^
+  }
+}
+
+// ok, exhaustive cases
+function mockPayload3<P_TAG extends Payload["_tag"]>(
+>mockPayload3 : <P_TAG extends Payload["_tag"]>(str: P_TAG) => PayloadContent[P_TAG]
+>             : ^     ^^^^^^^^^               ^^   ^^     ^^^^^                     
+
+  str: P_TAG,
+>str : P_TAG
+>    : ^^^^^
+
+): PayloadContent[P_TAG] {
+  switch (str) {
+>str : P_TAG
+>    : ^^^^^
+
+    case "auth":
+>"auth" : "auth"
+>       : ^^^^^^
+
+      return { username: "test", password: "admin" };
+>{ username: "test", password: "admin" } : { username: string; password: string; }
+>                                        : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>username : string
+>         : ^^^^^^
+>"test" : "test"
+>       : ^^^^^^
+>password : string
+>         : ^^^^^^
+>"admin" : "admin"
+>        : ^^^^^^^
+
+    case "cart":
+>"cart" : "cart"
+>       : ^^^^^^
+
+      return { items: [{ id: "123", quantity: 123 }] };
+>{ items: [{ id: "123", quantity: 123 }] } : { items: { id: string; quantity: number; }[]; }
+>                                          : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>items : { id: string; quantity: number; }[]
+>      : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>[{ id: "123", quantity: 123 }] : { id: string; quantity: number; }[]
+>                               : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>{ id: "123", quantity: 123 } : { id: string; quantity: number; }
+>                             : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>id : string
+>   : ^^^^^^
+>"123" : "123"
+>      : ^^^^^
+>quantity : number
+>         : ^^^^^^
+>123 : 123
+>    : ^^^
+
+    case "person":
+>"person" : "person"
+>         : ^^^^^^^^
+
+      return { name: "andrea", age: 27 };
+>{ name: "andrea", age: 27 } : { name: string; age: number; }
+>                            : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>name : string
+>     : ^^^^^^
+>"andrea" : "andrea"
+>         : ^^^^^^^^
+>age : number
+>    : ^^^^^^
+>27 : 27
+>   : ^^
+  }
+}
+
+// error, non-exhaustive cases
+function mockPayload4<P_TAG extends Payload["_tag"]>(
+>mockPayload4 : <P_TAG extends Payload["_tag"]>(str: P_TAG) => PayloadContent[P_TAG]
+>             : ^     ^^^^^^^^^               ^^   ^^     ^^^^^                     
+
+  str: P_TAG,
+>str : P_TAG
+>    : ^^^^^
+
+): PayloadContent[P_TAG] {
+  switch (str) {
+>str : P_TAG
+>    : ^^^^^
+
+    case "auth":
+>"auth" : "auth"
+>       : ^^^^^^
+
+      return { username: "test", password: "admin" };
+>{ username: "test", password: "admin" } : { username: string; password: string; }
+>                                        : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>username : string
+>         : ^^^^^^
+>"test" : "test"
+>       : ^^^^^^
+>password : string
+>         : ^^^^^^
+>"admin" : "admin"
+>        : ^^^^^^^
+
+    case "cart":
+>"cart" : "cart"
+>       : ^^^^^^
+
+      return { items: [{ id: "123", quantity: 123 }] };
+>{ items: [{ id: "123", quantity: 123 }] } : { items: { id: string; quantity: number; }[]; }
+>                                          : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>items : { id: string; quantity: number; }[]
+>      : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>[{ id: "123", quantity: 123 }] : { id: string; quantity: number; }[]
+>                               : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>{ id: "123", quantity: 123 } : { id: string; quantity: number; }
+>                             : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>id : string
+>   : ^^^^^^
+>"123" : "123"
+>      : ^^^^^
+>quantity : number
+>         : ^^^^^^
+>123 : 123
+>    : ^^^
+  }
+}
+
diff --git a/tests/cases/compiler/dependentReturnType9.ts b/tests/cases/compiler/dependentReturnType9.ts
new file mode 100644
index 0000000000000..65437a8aea1c8
--- /dev/null
+++ b/tests/cases/compiler/dependentReturnType9.ts
@@ -0,0 +1,67 @@
+// @strict: true
+// @noEmit: true
+
+type Payload =
+  | { _tag: "auth"; username: string; password: string }
+  | { _tag: "cart"; items: Array<{ id: string; quantity: number }> }
+  | { _tag: "person"; name: string; age: number };
+
+type PayloadContent = {
+  [P in Payload as P["_tag"]]: Omit<P, "_tag">;
+};
+
+// ok, exhaustive cases and default case with throw
+function mockPayload<P_TAG extends Payload["_tag"]>(
+  str: P_TAG,
+): PayloadContent[P_TAG] {
+  switch (str) {
+    case "auth":
+      return { username: "test", password: "admin" };
+    case "cart":
+      return { items: [{ id: "123", quantity: 123 }] };
+    case "person":
+      return { name: "andrea", age: 27 };
+    default:
+      throw new Error("unknown tag");
+  }
+}
+
+// ok, non-exhaustive cases but default case with throw
+function mockPayload2<P_TAG extends Payload["_tag"]>(
+  str: P_TAG,
+): PayloadContent[P_TAG] {
+  switch (str) {
+    case "auth":
+      return { username: "test", password: "admin" };
+    case "cart":
+      return { items: [{ id: "123", quantity: 123 }] };
+    default:
+      throw new Error("unhandled tag");
+  }
+}
+
+// ok, exhaustive cases
+function mockPayload3<P_TAG extends Payload["_tag"]>(
+  str: P_TAG,
+): PayloadContent[P_TAG] {
+  switch (str) {
+    case "auth":
+      return { username: "test", password: "admin" };
+    case "cart":
+      return { items: [{ id: "123", quantity: 123 }] };
+    case "person":
+      return { name: "andrea", age: 27 };
+  }
+}
+
+// error, non-exhaustive cases
+function mockPayload4<P_TAG extends Payload["_tag"]>(
+  str: P_TAG,
+): PayloadContent[P_TAG] {
+  switch (str) {
+    case "auth":
+      return { username: "test", password: "admin" };
+    case "cart":
+      return { items: [{ id: "123", quantity: 123 }] };
+  }
+}