Description

Calling type_of() with a struct type name (e.g., type_of(Foo)) silently returns "unknown" at runtime instead of producing a compile-time error. Per the standard, type_of() accepts a value, not a type name. Passing a type name should be rejected by the typechecker.

Reproduction

const Foo struct {
    name string
}

do main() {
    println(type_of(Foo))
}

Expected: Compile error — type_of() expects a value, not a type name

Actual: Compiles and prints unknown

Root Cause

The typechecker does not validate that the argument to type_of() is a value expression. When a bare struct type name is passed, it resolves as TK_UNKNOWN in the typetable. The codegen then falls through to the default branch in emit_builtin_call() (~line 2448 in codegen.c):

const char *tn = t ? type_name(t) : "unknown";
emitf(cg, "ez_string_lit(\"%s\")", tn);

This silently emits "unknown" instead of the compiler catching the mistake.

Fix

Add a typechecker validation in the type_of handling block (~line 2678 in typechecker.c). When the argument is a NODE_LABEL that resolves to a struct or enum type name (not a variable), emit a new error code:

E3xxx: type_of() expects a value, not a type name; use type_of(instance) instead

Register the new code in error_codes.h under the E3xxx (type errors) section and run ./scripts/generate_errors.sh.

Notes

This same class of bug (passing a type name where a value is expected) may affect other builtins like len(), copy(), etc. Those should be audited separately but are out of scope for this issue.