linker: undefined symbol `_IError_None___index` on FreeBSD/clang

[medvednikov]

Description

Multiple bug reports from FreeBSD (clang) fail at link time with:

error: undefined symbol: _IError_None___index

IError_None is the builtin none implementor of the IError interface, and ___index is the interface type-table index entry. In normal builds this is emitted as a compile-time enum constant, e.g.:

enum { _IError_None___index = 1 };

An undefined symbol at link time for something that should be a compile-time enum constant indicates that a reference to it survived in one translation unit while its definition was either not emitted or stripped — i.e. a likely dead-code-elimination / -skip-unused or interface type-table codegen ordering problem. It may be FreeBSD/clang-specific.

Occurrences

• 5 reports, all FreeBSD / clang.
• Generated C file basename: hello_world (likely a generic placeholder; the triggering program source was not captured by the bug reporter).

Repro status

Not reproduced. On a normal build the none__ builtin const reliably registers None__ as an IError implementor, so _IError_None___index is always defined (enum { _IError_None___index = 1 };) — a plain fn main(){ println('hello world') } links fine, with the enum present. The specific source / build flags that drop the definition while keeping the reference are still needed.

Anyone who can attach the V program (and exact v flags) that produced this would help isolate it. Most likely candidates to probe: programs that use IError/none/optionals together with indexing, built with -skip-unused, on FreeBSD.

Environment

• V 0.5.1
• FreeBSD, clang

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