bug: Windows MSVC release build fails with unresolved libc symbols

[danielsreichenbach]

Summary

The Release Binaries workflow fails for x86_64-pc-windows-msvc with linker errors for four libc functions.

Error

From run #22211846804:

error LNK2019: unresolved external symbol gmtime_s referenced in function _ZN5rilua6stdlib2os7os_date...
error LNK2019: unresolved external symbol localtime_s referenced in function _ZN5rilua6stdlib2os7os_date...
error LNK2019: unresolved external symbol fprintf referenced in function _ZN5rilua6stdlib2io7g_write...
error LNK2019: unresolved external symbol fscanf referenced in function _ZN5rilua6stdlib2io6g_read...
fatal error LNK1120: 4 unresolved externals

Affected symbols

Symbol	File	Function
gmtime_s	src/stdlib/os.rs	os_date (UTC)
localtime_s	src/stdlib/os.rs	os_date (local)
fprintf	src/stdlib/io.rs	g_write
fscanf	src/stdlib/io.rs	g_read

Cause

The FFI declarations in src/platform.rs reference C runtime functions that require explicit linking on Windows MSVC. The CI test workflow passes because it runs cargo test on Linux, but the release binary workflow cross-compiles with --target x86_64-pc-windows-msvc where the universal C runtime (ucrt) is not linked automatically.

Possible fixes

1. Add #[link(name = "ucrt")] or #[link(name = "msvcrt")] to the FFI extern blocks on Windows
2. Use #[cfg_attr(target_env = "msvc", link(name = "ucrt"))] conditionally
3. Add a build.rs that emits cargo:rustc-link-lib=ucrt on MSVC targets

First observed

Tag v0.1.8, workflow run on 2026-02-20.