[ASDAlexander77]

Problem

An error inside a cast function the compiler generates was reported at a position that has nothing to do with the code:

// An error inside the cast function the compiler generates for a union was reported at the
// ...
function text(x: number | string | null): string {
    const s: string = x;          // the actual problem (null isn't a string)

generated_cast.ts:1:59: error: can't cast from 'null' to 'string' in 'strict null mode'
// An error inside the cast function the compiler generates for a union was reported at the

Issue 6 of docs/bugs/native-ts-graphics-findings.md shows the same thing: its first error points into the comment on line 1.

Cause

castFromUnion and castPrimitiveTypeFromAny build a generic __cast function from source text, parse it with overwriteLoc set to the call site, and then call it. The guard that set overwriteLoc was scoped to the parse only. The body is generated later, inside mlirGenCallExpression, when the call instantiates it. By then overwriteLoc was unknown again, so loc() mapped the generated text's offsets onto the user's source file.

Fix

Keep the guard alive until the call has instantiated the function, at both sites. With --di, parsePartialStatements already strips the debug metadata from overwriteLoc, and that stripped value is what stays in effect.

Testing

• New test-compile-diagnostic-location-generated-cast (error-text test, like the call-arity ones): it requires generated_cast.ts:6:23: error: can't cast from 'null' to 'string' and fails on generated_cast.ts:1:. The current release prints 1:59.
• A program that goes through both generated casts successfully (any to number, number | string to string) runs the same with no flags, --di, --di --opt, and as a --di exe.
• Full ctest: 3914/3914 pass.

🤖 Generated with Claude Code