🐮 Disable implicit function declaration error on clang-16 and up #43
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This happens specifically when (cross?-)compiling to > cargo b --target x86_64-pc-windows-msvc
warning: [email protected]: /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/metis-sys-0.3.1/vendor/GKlib/io.c(63,18): error: call to undeclared function 'read'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
warning: [email protected]: 63 | if ((rsize = read(fd, buf, tsize)) == -1)
warning: [email protected]: | ^
...
warning: [email protected]: /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/metis-sys-0.3.1/vendor/GKlib/io.c(84,17): error: call to undeclared function 'write'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
warning: [email protected]: 84 | if ((size = write(fd, buf, tsize)) == -1)
warning: [email protected]: | ^These functions are pretty much POSIX which Windows isn't expected to provide, but they do have it: They don't specify where |
MarijnS95
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May 22, 2025
…h Clang
When (cross?) compiling this crate to Windows (in a Rust project) using
Clang 16 or newer, we're seeing these declaration errors:
> cargo b --target x86_64-pc-windows-msvc
warning: [email protected]: /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/metis-sys-0.3.1/vendor/GKlib/io.c(63,18): error: call to undeclared function 'read'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
warning: [email protected]: 63 | if ((rsize = read(fd, buf, tsize)) == -1)
warning: [email protected]: | ^
...
warning: [email protected]: /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/metis-sys-0.3.1/vendor/GKlib/io.c(84,17): error: call to undeclared function 'write'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
warning: [email protected]: 84 | if ((size = write(fd, buf, tsize)) == -1)
warning: [email protected]: | ^
(LIHPC-Computational-Geometry/metis-rs#43 (comment))
Now it's yet unknown (we haven't checked) if older Clang had these
declarations in a header, or didn't treat this warning as error yet,
but the functions are POSIX which Windows isn't required to implement.
Fortunately they provide it but with a deprecation warning and a
recommended replacement of `_read()` (and `_write()`), but for this
`<io.h>` needs to be included:
https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/posix-read
https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/read
The same is true for `getpid()` that commit a8e7e25 ("port to vs2017")
used to provide a `win32/adapt.c/h` workaround for, but this can instead
be pulled from `<process.h>` (equally with a deprecation warning, but
we should probably address these all in a consistent manner instead
of defining a workaround). Let's take this as a starting point and go
from there.
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Starting with clang-16 GKlib fails to compile with an implicit function declaration error. Just disable the error for it as it's most friendly to library users.