Fix cc rs flag if supported

[Kobzol]

Found in https://rust-lang.zulipchat.com/#narrow/channel/326414-t-infra.2Fbootstrap/topic/weird.20code.20in.20fill_target_compiler/with/604588655.

When cc-rs checks if a compiler flag is supported, it tries to read out_dir to generate the source file in. However, when this option is not set, then the check silently fails and the flag is considered to be unsupported. Since we didn't set out_dir, all such added flags were simply ignored.

Normally, it reads OUT_DIR, which is fine if cc-rs is used within a build script. But if it is used elsewhere, then this is a pretty gnarly footgun in cc-rs, because the failure is completely silent. CC @madsmtm or @NobodyXu in case you have thoughts on that :)

r? @bjorn3

[bjorn3]

Thanks!

@bors r+

[rust-bors]

📌 Commit 1bc29dc has been approved by bjorn3

It is now in the queue for this repository.

[rust-bors]

💔 Test for b946733 failed: CI. Failed job:

• auto - x86_64-gnu-distcheck (web logs, enhanced plaintext logs)

[Kobzol]

@bors try jobs=x86_64-gnu-distcheck

[NobodyXu]

Thanks, I've opened an issue #1765, I think this is something we should fix.

We could use a tempfile instead for it

[ChrisDenton]

Thanks, I've opened an issue #1765

I think you meant rust-lang/cc-rs#1765 😉

[rust-bors]

☀️ Try build successful (CI)
Build commit: d269546 (d269546b8320f5f3255b5c7e6268def1a4808374)
Base parent: 4008bbd (4008bbdf34b583ce44a467043aae3703afc0a76f)

[Kobzol]

@bors r=bjorn3

Let's try again.

[rust-bors]

📌 Commit d59253e has been approved by bjorn3

It is now in the queue for this repository.

[rust-log-analyzer]

The job dist-various-2 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

[RUSTC-TIMING] gimli test:false 4.980
[RUSTC-TIMING] object test:false 5.597
error: linking with `rust-lld` failed: exit status: 1
  |
  = note:  "rust-lld" "-flavor" "gnu" "--version-script=<sysroot>-std/x86_64-unknown-fuchsia/dist/deps/rustcXNjUCX/list" "--no-undefined-version" "--build-id" "--hash-style=gnu" "-z" "max-page-size=4096" "-z" "now" "-z" "start-stop-visibility=hidden" "-z" "rodynamic" "-z" "separate-loadable-segments" "-z" "rel" "--pack-dyn-relocs=relr" "<sysroot>-std/x86_64-unknown-fuchsia/dist/deps/rustcXNjUCX/symbols.o" "<1 object files omitted>" "<sysroot>-std/x86_64-unknown-fuchsia/dist/deps/rustcXNjUCX/rmeta.o" "<1 object files omitted>" "--as-needed" "-Bdynamic" "-lzircon" "-lfdio" "-lzircon" "-Bstatic" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-fuchsia/dist/deps/{libpanic_unwind-417f7c4656763808,libaddr2line-921ac66b5bf3d0d2,libgimli-9d9a783454891b12,libcfg_if-a4e68cb521965acf,libobject-636d5dbf6958baf9,libmemchr-dd2b00b4863e493e,librustc_demangle-104c0bb3c5349d29,libstd_detect-d8dda86d8d03dfaf,libhashbrown-14a49224ea05c02f,librustc_std_workspace_alloc-7db94a9d0457fcfc,libminiz_oxide-bac93a2793c027e7,libadler2-be784218a0c195f9,libunwind-272440eb5552bb3a}.rlib" "-lunwind" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-fuchsia/dist/deps/{liblibc-7362514cf8f5457e,librustc_std_workspace_core-09b73d79dacb536a,liballoc-b42f5928c0c535c8,libcore-c34ffc106f1167b3,libcompiler_builtins-c42c07b16414db0d}.rlib" "-Bdynamic" "-lc" "-lfdio" "-L" "<sysroot>-std/x86_64-unknown-fuchsia/dist/deps/rustcXNjUCX/raw-dylibs" "--eh-frame-hdr" "-z" "noexecstack" "-L" "/usr/local/core-linux-amd64-fuchsia-sdk/arch/x64/sysroot/lib" "-L" "/usr/local/core-linux-amd64-fuchsia-sdk/arch/x64/lib" "-L" "<sysroot>-std/x86_64-unknown-fuchsia/dist/build/compiler_builtins-421932536528bcee/out" "-L" "<sysroot>/lib/rustlib/x86_64-unknown-fuchsia/lib" "-o" "<sysroot>-std/x86_64-unknown-fuchsia/dist/deps/libstd-4e7987ff6682ad78.so" "-shared" "-soname=libstd-4e7987ff6682ad78.so" "-O1" "-gz" "--sysroot=/usr/local/core-linux-amd64-fuchsia-sdk/arch/x64/sysroot"
  = note: some arguments are omitted. use `--verbose` to show all linker arguments
  = note: rust-lld: error: unknown argument '-gz'
          

[RUSTC-TIMING] std test:false 17.271

[rust-bors]

💔 Test for b417acf failed: CI. Failed job:

• auto - dist-various-2 (web logs, enhanced plaintext logs)

[Kobzol]

Sigh, now we have to fix the fallout of whoever knows how long the flags weren't applied by mistake 😆

[bjorn3]

I think the probe needs to be done with the C compiled told to use rust-lld if we will use rust-lld for the actual build. Separately to actually get compressed debuginfo as intended, we have to install zlib in all containers.