A switch case of another kind of primitive is an error

tslang/lib/TypeScript/MLIRGenImpl.h

@@ -4615,6 +4615,26 @@ class MLIRGenImpl
             EXIT_IF_FAILED_OR_NO_VALUE(result)
             caseValue = V(result);
 
+            // a case of another kind of primitive than the switch's (`switch (5) { case "a": }`)
+            // can never match: the cast made one out of the other instead
+            auto primitiveKind = [&](mlir::Type type) {
+                auto baseType = mth.getBaseType(type);
+                if (mth.isNumericType(baseType)) return 1;
+                if (isa<mlir_ts::StringType>(baseType)) return 2;
+                if (isa<mlir_ts::BooleanType>(baseType)) return 3;
+                if (isa<mlir_ts::BigIntType>(baseType)) return 4;
+                return 0;
+            };
+
+            auto switchKind = primitiveKind(switchValue.getType());
+            auto caseKind = primitiveKind(caseValue.getType());
+            if (switchKind && caseKind && switchKind != caseKind)
+            {
+                emitError(loc(caseExpr)) << "Type '" << to_print(caseValue.getType()) << "' is not comparable to type '"
+                                         << to_print(switchValue.getType()) << "'";
+                return mlir::failure();
+            }
+
             auto switchValueEffective = switchValue;
             auto actualCaseType = mth.stripLiteralType(caseValue.getType());
             if (switchValue.getType() != actualCaseType)

tslang/test/tester/CMakeLists.txt

@@ -2719,6 +2719,16 @@ add_test(NAME test-compile-integer-literal-truncation-quiet
 set_tests_properties(test-compile-integer-literal-truncation-quiet
                      PROPERTIES FAIL_REGULAR_EXPRESSION "warning:|error:|Stack dump|Assertion failed")
 
+# A switch's case of another kind of primitive (a string for a number) is an error, as it can never
+# match: the switch's value was cast to the case's type instead.
+add_test(NAME test-compile-diagnostic-location-switch-case-type
+         COMMAND $<TARGET_FILE:tslang> --emit=obj --no-default-lib -mm=none
+                 "${PROJECT_SOURCE_DIR}/test/tester/diagnostic-location/switch_case_type.ts"
+                 -o "${CMAKE_CURRENT_BINARY_DIR}/diagnostic-location-switch-case-type.obj")
+set_tests_properties(test-compile-diagnostic-location-switch-case-type
+                     PROPERTIES PASS_REGULAR_EXPRESSION "switch_case_type\\.ts:8:14: error: Type '\"a\"' is not comparable to type '5'"
+                                FAIL_REGULAR_EXPRESSION "Stack dump|Assertion failed|switch_case_type\\.ts:7:")
+
 # A store to an indexed Ref<T> (`bytes[i] = x`) names the form that stores, `Deref(bytes[i]) = x`,
 # instead of "saving to constant object".
 add_test(NAME test-compile-ref-index-store

tslang/test/tester/diagnostic-location/switch_case_type.ts

@@ -0,0 +1,10 @@
+// A case of another kind of primitive than the switch's could never match: the number was made
+// a string to compare, with no error.
+
+function main() {
+    const n = 5;
+    switch (n) {
+        case 5: print("five"); break;
+        case "a": print("a"); break;
+    }
+}