Make the libstd build script smaller

[bjorn3]

Of all sysroot crates currently only compiler_builtins, miniz_oxide and std require a build script. compiler_builtins uses to conditionally enable certain features and possibly compile a C version (source), miniz_oxide only uses it to detect if liballoc is supported as the MSRV is 1.34.0 instead of the 1.36.0 which stabilized liballoc (source). std now only uses it to enable freebsd12 when the RUST_STD_FREEBSD_12_ABI env var is set, to determine if restricted-std should be set, to set the STD_ENV_ARCH env var identical to CARGO_CFG_TARGET_ARCH, and to unconditionally enable backtrace_in_libstd.

If all build scripts were to be removed, it would be possible for rustc to completely compile it's own sysroot. It currently requires a rustc version that already has an available libstd to compile the build scripts. If rustc can completely compile it's own sysroot, rustbuild could be simplified to not forcefully use the bootstrap compiler for build scripts.

@rustbot modify labels: +T-compiler +libs-impl

[rustbot]

Error: Label libs-impl can only be set by Rust team members

Please let @rust-lang/release know if you're having trouble with this bot.

[rust-highfive]

r? @KodrAus

(rust_highfive has picked a reviewer for you, use r? to override)

[bjorn3]

@rustbot modify labels: +T-compiler

[KodrAus]

r? @scottmcm

[tesuji]

Cc @joshtriplett because of the change to how libc linked.

[scottmcm]

Sorry, this is code I've never seen before and I have no experience in how these things are built, so I don't feel qualified to review this. I'll head to zulip and see if triage knows a better reviewer...

[jyn514]

@bjorn3 can you explain why the rustc-link-lib lines aren't necessary?

[Mark-Simulacrum]

r? @Mark-Simulacrum

I'm probably a goodish reviewer here, or at least will be able to forward if needed.

[jyn514]

@bjorn3 can you explain why the rustc-link-lib lines aren't necessary?

Oh I missed that you used explicit link(name) below, ignore me.

[Mark-Simulacrum]

This seems correct to me. That said, I would not anticipate us removing the build script support from rustbuild in the near future, it seems unlikely for that to be all that beneficial and the work to remove build scripts in comparison seems quite high. That said, the changes here seem reasonable and like they improve the quality of the code in question a little.

@bors r+ rollup=never for easier bisection

[bors]

📌 Commit 89db5d03c6adcaad3e6564280c2db65d1397a294 has been approved by Mark-Simulacrum

[bjorn3]

That said, I would not anticipate us removing the build script support from rustbuild in the near future, it seems unlikely for that to be all that beneficial and the work to remove build scripts in comparison seems quite high.

It is nice to have, but I don't think it is worth the effort either. At least for now. Maybe miniz_oxide will remove the build script in a future release and maybe cargo will get native support for the remaining usages of the build script of libstd, but then the compiler_builtins use case will still be hard to do without a build script.

[bors]

⌛ Testing commit 89db5d03c6adcaad3e6564280c2db65d1397a294 with merge cab1b85235027c97ae850618bba022dc518c922a...

[bors]

💔 Test failed - checks-actions

[Mark-Simulacrum]

r=me with commits squashed

[bjorn3]

splat

@bors r=Mark-Simulacrum

[bors]

📌 Commit 6f3872a has been approved by Mark-Simulacrum

[bors]

⌛ Testing commit 6f3872a with merge 45b36722bf32c27018e6c2c3e91d9a40cdc17732...

[rust-log-analyzer]

Your PR failed (pretty log, raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

[command]/usr/bin/git submodule foreach --recursive git config --local --name-only --get-regexp 'http\.https\:\/\/github\.com\/\.extraheader' && git config --local --unset-all 'http.https://github.com/.extraheader' || :
[command]/usr/bin/git config --local http.https://github.com/.extraheader AUTHORIZATION: basic ***
##[endgroup]
##[group]Fetching the repository
[command]/usr/bin/git -c protocol.version=2 fetch --no-tags --prune --progress --no-recurse-submodules --depth=2 origin +45b36722bf32c27018e6c2c3e91d9a40cdc17732:refs/remotes/origin/auto

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @rust-lang/infra. (Feature Requests)

[bors]

💔 Test failed - checks-actions

[bjorn3]

Spurious network error:

Err:1 http://azure.archive.ubuntu.com/ubuntu bionic/main amd64 python3-setuptools all 39.0.1-2
  Could not connect to azure.archive.ubuntu.com:80 (52.147.219.192), connection timed out
E: Failed to fetch http://azure.archive.ubuntu.com/ubuntu/pool/main/p/python-setuptools/python3-setuptools_39.0.1-2_all.deb  Could not connect to azure.archive.ubuntu.com:80 (52.147.219.192), connection timed out
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?

@bors retry

[bors]

⌛ Testing commit 6f3872a with merge 54508a2...

[bors]

☀️ Test successful - checks-actions
Approved by: Mark-Simulacrum
Pushing 54508a2 to master...