Description

A function declared with a single return type can return multiple comma-separated values without the typechecker catching it. The codegen then emits a multi-return struct (EzMulti_foo) that was never typedef'd, causing a C compilation crash.

Reproduction

do foo() -> int {
    return 1, 2
}

do main() {
    println(foo())
}

Expected: Compile error — foo declares a single int return but returns 2 values

Actual: Typechecker passes, C compilation fails:

error: use of undeclared identifier 'EzMulti_foo'
    { EzMulti_foo _ret = (EzMulti_foo){1, 2}; ez_exit_func(); return _ret; }
      ^

Root Cause

The typechecker does not validate that the number of values in a return statement matches the number of declared return types. When a function is declared as -> int (single return), returning 1, 2 should be rejected. The codegen assumes the typechecker has validated this and emits a multi-return struct path for the comma-separated values, but no such struct was defined since the function signature only declares one return value.

Fix

In the typechecker's return statement handler, count the number of comma-separated return values and compare against the function's declared return count. If they don't match, emit an error like:

E3XXX: function 'foo' returns 1 value but return statement has 2 values