Add support for custom JSON targets when using build-std.

[c272]

Currently, when building with build-std, some library build scripts check properties of the target by inspecting the target triple at env::TARGET, which is simply set to the filename of the JSON file when using JSON target files.

This patch alters these build scripts to use env::CARGO_CFG_* to fetch target information instead, allowing JSON target files describing platforms without restricted_std to build correctly when using -Z build-std. There are some weak assertions here (for example, nintendo && newlib), however this seems at least a marginal improvement on the existing solution.

Fixes https://github.com/rust-lang/wg-cargo-std-aware/issues/60.

[rustbot]

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[Mark-Simulacrum]

To make sure I understand the problem this is solving, you have custom target spec JSON not named after the triplet for the target? E.g., it looks to me like making the file x86_64-linux-special-gnu.json would probably also make all of these build scripts work?

(Doesn't make this change a bad one but want to make sure I understand the problem)

[c272]

@Mark-Simulacrum Yes, renaming the JSON target file to include "linux" in the filename would allow the target to build (in the linked issue, the author is using mytarget.json, so none of the clauses match). The current behaviour seems a bit imprecise, for example you could currently name a target file "contour" or something similarly unrelated and catch the "nto" clause unknowingly, or have a valid target with a different filename that doesn't compile as above.

[bors]

:umbrella: The latest upstream changes (presumably #117958) made this pull request unmergeable. Please resolve the merge conflicts.

[Mark-Simulacrum]

@bors r+ rollup

This looks good to me. Thanks!

[bors]

:pushpin: Commit 797cf5927872459a00ca3a2758216c8aa89cef2b has been approved by Mark-Simulacrum

It is now in the queue for this repository.

[Mark-Simulacrum]

@bors rollup=iffy

[bors]

:hourglass: Testing commit 797cf5927872459a00ca3a2758216c8aa89cef2b with merge 0d38e40343c59c824f06b49af91b1997055aa255...

[c272]

@bors r- Still need to fix the typo, apologies.

[rust-log-analyzer]

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

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

[RUSTC-TIMING] object test:false 4.482
error: `futex_condvar::Condvar::new` is not yet stable as a const fn
   --> library/std/src/sync/condvar.rs:127:26
    |
127 |         Condvar { inner: sys::Condvar::new() }
    |
    = help: const-stable functions can only call other const-stable functions

error: `futex_mutex::Mutex::new` is not yet stable as a const fn
error: `futex_mutex::Mutex::new` is not yet stable as a const fn
   --> library/std/src/sync/mutex.rs:230:24
    |
230 |         Mutex { inner: sys::Mutex::new(), poison: poison::Flag::new(), data: UnsafeCell::new(t) }
    |
    = help: const-stable functions can only call other const-stable functions

error: `sys_common::once::futex::Once::new` is not yet stable as a const fn
error: `sys_common::once::futex::Once::new` is not yet stable as a const fn
  --> library/std/src/sync/once.rs:76:23
   |
76 |         Once { inner: sys::Once::new() }
   |                       ^^^^^^^^^^^^^^^^
   |
   = help: const-stable functions can only call other const-stable functions

error: `futex_rwlock::RwLock::new` is not yet stable as a const fn
    |
    |
161 |         RwLock { inner: sys::RwLock::new(), poison: poison::Flag::new(), data: UnsafeCell::new(t) }
    |
    = help: const-stable functions can only call other const-stable functions

[RUSTC-TIMING] std test:false 2.677

[bors]

:broken_heart: Test failed - checks-actions

[c272]

Fixed the typo, and the new patch should also fix the test failures - all linux-android targets report their OS as android and not linux, which I overlooked.

[Mark-Simulacrum]

@bors r+

[bors]

:pushpin: Commit 1ecb08409d17f08a2a52013b99fd969018e404dd has been approved by Mark-Simulacrum

It is now in the queue for this repository.

[bors]

:hourglass: Testing commit 1ecb08409d17f08a2a52013b99fd969018e404dd with merge 0cbef48150e1fab161b5fd147b57ceb3f9272a52...

[bors]

:sunny: Test successful - checks-actions Approved by: Mark-Simulacrum Pushing 0cbef48150e1fab161b5fd147b57ceb3f9272a52 to master...

[rust-timer]

Finished benchmarking commit (0cbef48150e1fab161b5fd147b57ceb3f9272a52): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	4.4%	[4.4%, 4.4%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

This benchmark run did not return any relevant results for this metric.

Binary size

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.1%	[0.1%, 0.1%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Bootstrap: 666.058s -> 668.04s (0.30%) Artifact size: 308.32 MiB -> 308.26 MiB (-0.02%)