[ADT] Add DefaultUnreachable("msg") to TypeSwitch

llvm/include/llvm/ADT/TypeSwitch.h

@@ -17,6 +17,7 @@
 
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/Casting.h"
+#include "llvm/Support/ErrorHandling.h"
 #include <optional>
 
 namespace llvm {
@@ -117,11 +118,16 @@ class TypeSwitch : public detail::TypeSwitchBase<TypeSwitch<T, ResultT>, T> {
     return defaultResult;
   }
 
-  [[nodiscard]] operator ResultT() {
-    assert(result && "Fell off the end of a type-switch");
-    return std::move(*result);
+  /// Declare default as unreachable, making sure that all cases were handled.
+  [[nodiscard]] ResultT DefaultUnreachable(
+      const char *message = "Fell off the end of a type-switch") {
+    if (result)
+      return std::move(*result);
+    llvm_unreachable(message);
   }
 
+  [[nodiscard]] operator ResultT() { return DefaultUnreachable(); }
+
 private:
   /// The pointer to the result of this switch statement, once known,
   /// null before that.
@@ -158,6 +164,13 @@ class TypeSwitch<T, void>
       defaultFn(this->value);
   }
 
+  /// Declare default as unreachable, making sure that all cases were handled.
+  void DefaultUnreachable(
+      const char *message = "Fell off the end of a type-switch") {
+    if (!foundMatch)
+      llvm_unreachable(message);
+  }
+
 private:
   /// A flag detailing if we have already found a match.
   bool foundMatch = false;

llvm/unittests/ADT/TypeSwitchTest.cpp

@@ -114,3 +114,31 @@ TEST(TypeSwitchTest, CasesOptional) {
   EXPECT_EQ(std::nullopt, translate(DerivedC()));
   EXPECT_EQ(-1, translate(DerivedD()));
 }
+
+TEST(TypeSwitchTest, DefaultUnreachableWithValue) {
+  auto translate = [](auto value) {
+    return TypeSwitch<Base *, int>(&value)
+        .Case([](DerivedA *) { return 0; })
+        .DefaultUnreachable("Unhandled type");
+  };
+  EXPECT_EQ(0, translate(DerivedA()));
+
+#if defined(GTEST_HAS_DEATH_TEST) && !defined(NDEBUG)
+  EXPECT_DEATH((void)translate(DerivedD()), "Unhandled type");
+#endif
+}
+
+TEST(TypeSwitchTest, DefaultUnreachableWithVoid) {
+  auto translate = [](auto value) {
+    int result = -1;
+    TypeSwitch<Base *>(&value)
+        .Case([&result](DerivedA *) { result = 0; })
+        .DefaultUnreachable("Unhandled type");
+    return result;
+  };
+  EXPECT_EQ(0, translate(DerivedA()));
+
+#if defined(GTEST_HAS_DEATH_TEST) && !defined(NDEBUG)
+  EXPECT_DEATH((void)translate(DerivedD()), "Unhandled type");
+#endif
+}