A number, string, boolean or array is not an interface with members

tslang/lib/TypeScript/MLIRGenCast.cpp

@@ -1054,6 +1054,24 @@ namespace mlirgen
             {
                 return castObjectToInterface(location, value, objectType, interfaceType, genContext);
             }
+
+            // A number, string, boolean or array has no fields an interface's members could be read
+            // from: passed for an `{ kind: number }` it compiled, without a word, to a cast that
+            // lowering could not make, and the callee read garbage. An interface without members
+            // takes any value, as in TypeScript.
+            auto baseValueType = mth.stripLiteralType(valueType);
+            if (baseValueType.isIntOrIndexOrFloat()
+                || isa<mlir_ts::NumberType, mlir_ts::StringType, mlir_ts::BooleanType, mlir_ts::CharType,
+                       mlir_ts::BigIntType, mlir_ts::ArrayType, mlir_ts::ConstArrayType>(baseValueType))
+            {
+                auto interfaceInfo = getInterfaceInfoByFullName(interfaceType.getName().getValue());
+                if (interfaceInfo && interfaceInfo->getVTableSize() > 0)
+                {
+                    emitError(location) << "type '" << to_print(baseValueType) << "' can't be cast to interface '"
+                                        << to_print(interfaceType) << "': it has none of the interface's members";
+                    return mlir::failure();
+                }
+            }
         }
 
         return std::nullopt;

tslang/test/tester/CMakeLists.txt

@@ -2631,6 +2631,25 @@ foreach(call_arity_case ${call_arity_cases})
                                     FAIL_REGULAR_EXPRESSION "Stack dump|Assertion failed")
 endforeach()
 
+# A number, string, boolean or array passed where an interface with members is expected is an
+# error; it compiled to a cast lowering could not make, and the callee read garbage. An interface
+# without members still takes any value.
+foreach(interface_cast_name number string boolean array)
+    add_test(NAME test-compile-interface-cast-${interface_cast_name}
+             COMMAND $<TARGET_FILE:tslang> --emit=obj --no-default-lib -mm=none
+                     "${PROJECT_SOURCE_DIR}/test/tester/interface-cast/${interface_cast_name}.ts"
+                     -o "${CMAKE_CURRENT_BINARY_DIR}/interface-cast-${interface_cast_name}.obj")
+    set_tests_properties(test-compile-interface-cast-${interface_cast_name}
+                         PROPERTIES PASS_REGULAR_EXPRESSION "can't be cast to interface 'IKind': it has none of the interface's members"
+                                    FAIL_REGULAR_EXPRESSION "Stack dump|Assertion failed")
+endforeach()
+add_test(NAME test-compile-interface-cast-empty
+         COMMAND $<TARGET_FILE:tslang> --emit=obj --no-default-lib -mm=none
+                 "${PROJECT_SOURCE_DIR}/test/tester/interface-cast/empty.ts"
+                 -o "${CMAKE_CURRENT_BINARY_DIR}/interface-cast-empty.obj")
+set_tests_properties(test-compile-interface-cast-empty
+                     PROPERTIES FAIL_REGULAR_EXPRESSION "error:|Stack dump|Assertion failed")
+
 # An error inside a cast function the compiler generates (here: null in a union cast to string) is
 # reported where the cast is - line 6 - and not at the generated text's offset taken as a position
 # in the user's file, which put it inside the comment on line 1.

tslang/test/tester/interface-cast/array.ts

@@ -0,0 +1,11 @@
+// A value with no fields of its own passed where an interface with members is expected compiled
+// without a word, and the callee read garbage. It is an error, as in TypeScript.
+interface IKind {
+    kind: number;
+}
+
+function f(i: IKind) {
+    return i.kind;
+}
+
+print(f([1, 2]));

tslang/test/tester/interface-cast/boolean.ts

@@ -0,0 +1,11 @@
+// A value with no fields of its own passed where an interface with members is expected compiled
+// without a word, and the callee read garbage. It is an error, as in TypeScript.
+interface IKind {
+    kind: number;
+}
+
+function f(i: IKind) {
+    return i.kind;
+}
+
+print(f(true));

tslang/test/tester/interface-cast/empty.ts

@@ -0,0 +1,9 @@
+// An interface without members takes any value, as in TypeScript: this compiles.
+interface IEmpty {
+}
+
+function f(i: IEmpty) {
+    return 1;
+}
+
+print(f([1, 2]) + f(5) + f("text"));

tslang/test/tester/interface-cast/number.ts

@@ -0,0 +1,11 @@
+// A value with no fields of its own passed where an interface with members is expected compiled
+// without a word, and the callee read garbage. It is an error, as in TypeScript.
+interface IKind {
+    kind: number;
+}
+
+function f(i: IKind) {
+    return i.kind;
+}
+
+print(f(5));

tslang/test/tester/interface-cast/string.ts

@@ -0,0 +1,11 @@
+// A value with no fields of its own passed where an interface with members is expected compiled
+// without a word, and the callee read garbage. It is an error, as in TypeScript.
+interface IKind {
+    kind: number;
+}
+
+function f(i: IKind) {
+    return i.kind;
+}
+
+print(f("text"));