target: fix destabilising target-spec-json by davidtwco · Pull Request #151534 · rust-lang/rust

davidtwco · 2026-01-23T11:12:42Z

#150151 missed a case and didn't entirely destabilise target-spec-json - this patch corrects that.

rustbot · 2026-01-23T11:12:46Z

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This adds the `-Z json-target-spec` CLI flag to assist with using custom `.json` target spec files. `rustc` recently switched so that it requires `-Z unstable-options` when using custom spec files (rust-lang/rust#151534). This can make it rather awkward to use spec files with cargo because it then requires setting RUSTFLAGS and RUSTDOCFLAGS to pass `-Zunstable-options`. It also ends up causing some confusing error messages. Now, using `--target` with `.json` extension files generates an error that explains you need `-Zjson-target-spec`. The only thing this flag does is disable that error, and automatically passes `-Zunstable-options` with the `--target` flag. This does not 100% cover json target spec files, because they can be placed in RUST_TARGET_PATH or the sysroot, and `rustc` will automatically search for them (without the `.json` extension in the `--target` arg). The user will just need to use RUSTFLAGS/RUSTDOCFLAGS in that situation (but I expect that to be rare). The majority of this change is changing `CompileTarget::new` to take a flag if `-Zjson-target-spec` is enabled, and then threading through all the places that call it. `CompileTarget::new` is responsible for generating an error if json is used without the Z flag.

This adds the `-Z json-target-spec` CLI flag to assist with using custom `.json` target spec files. `rustc` recently switched so that it requires `-Z unstable-options` when using custom spec files (rust-lang/rust#151534). This can make it rather awkward to use spec files with cargo because it then requires setting RUSTFLAGS and RUSTDOCFLAGS to pass `-Zunstable-options`. It also ends up causing some confusing error messages. See the individual commits for more details. This ended up being a larger diff than I wanted. I'm not 100% certain this is worth it, but I think it significantly improves the experience using `.json` files, so I I'm leaning towards it. ### How to test and review this PR? Testing can be done with `rustc` built from rust-lang/rust#151534 to ensure that everything passes after that PR (including setting `CARGO_RUN_BUILD_STD_TESTS=1`).

This adds the `-Z json-target-spec` CLI flag to assist with using custom `.json` target spec files. `rustc` recently switched so that it requires `-Z unstable-options` when using custom spec files (rust-lang/rust#151534). This can make it rather awkward to use spec files with cargo because it then requires setting RUSTFLAGS and RUSTDOCFLAGS to pass `-Zunstable-options`. It also ends up causing some confusing error messages. See the individual commits for more details. This ended up being a larger diff than I wanted. I'm not 100% certain this is worth it, but I think it significantly improves the experience using `.json` files, so I I'm leaning towards it. Testing can be done with `rustc` built from rust-lang/rust#151534 to ensure that everything passes after that PR (including setting `CARGO_RUN_BUILD_STD_TESTS=1`).

davidtwco · 2026-01-26T15:01:05Z

I'm at a loss for how this could be impacting the rustdoc-gui tests

ehuss · 2026-01-26T15:26:07Z

The GUI tests have been failing frequently lately, see #93784.

chenyukang · 2026-01-27T03:28:55Z

@bors r=chenyukang

rust-bors · 2026-01-27T03:28:58Z

📌 Commit 76b6623 has been approved by chenyukang

It is now in the queue for this repository.

…json-again, r=chenyukang target: fix destabilising target-spec-json cc rust-lang#151528 rust-lang#150151 missed a case and didn't entirely destabilise target-spec-json - this patch corrects that. Closes rust-lang#71009

Rollup of 4 pull requests Successful merges: - #147436 (slice/ascii: Optimize `eq_ignore_ascii_case` with auto-vectorization) - #151390 (Reintroduce `QueryStackFrame` split.) - #151534 (target: fix destabilising target-spec-json) - #151692 (Try to reduce rustdoc GUI tests flakyness)

Zalathar · 2026-01-27T06:36:02Z

Failed in rollup in x86_64-rust-for-linux: #151722 (comment)

@bors r-

rust-bors · 2026-01-27T06:36:06Z

Commit 76b6623 has been unapproved.

Custom target specifications are unstable, but starting with Rust 1.95.0, `rustc` requires to explicitly pass `-Zunstable-options` to use them [1]: error: error loading target specification: custom targets are unstable and require `-Zunstable-options` | = help: run `rustc --print target-list` for a list of built-in targets David (Rust compiler team lead), writes: "We're destabilising custom targets to allow us to move forward with build-std without accidentally exposing functionality that we'd like to revisit prior to committing to. I'll start a thread on Zulip to discuss with the RfL team how we can come up with an alternative for them." Thus pass it. Cc: David Wood <[email protected]> Cc: Wesley Wiser <[email protected]> Cc: [email protected] # Needed in 6.12.y and later (Rust is pinned in older LTSs). Link: rust-lang/rust#151534 [1] Signed-off-by: Miguel Ojeda <[email protected]>

…stom target specs This also takes the chance to move forward the job to Linux v6.19-rc7, thus the previous workaround is not needed anymore. Link: rust-lang#151534 Signed-off-by: Miguel Ojeda <[email protected]>

ojeda · 2026-01-27T20:47:03Z

Done -- could you please cherry-pick ojeda@c8656b7?

I tested locally with your compiler branch, let's see if it works.

…stom target specs This also takes the chance to move forward the job to Linux v6.19-rc7, thus the previous workaround is not needed anymore. Link: rust-lang#151534 Signed-off-by: Miguel Ojeda <[email protected]>

chenyukang · 2026-02-04T09:27:10Z

@bors r=chenyukang

rust-bors · 2026-02-04T09:27:13Z

📌 Commit 2a9de6b has been approved by chenyukang

It is now in the queue for this repository.

…json-again, r=chenyukang target: fix destabilising target-spec-json cc rust-lang#151528 rust-lang#150151 missed a case and didn't entirely destabilise target-spec-json - this patch corrects that. Closes rust-lang#71009

…uwer Rollup of 11 pull requests Successful merges: - #150605 (skip codegen for intrinsics with big fallback bodies if backend does not need them) - #150992 (link modifier `export-symbols`: export all global symbols from selected uptream c static libraries) - #151534 (target: fix destabilising target-spec-json) - #152088 (rustbook/README.md: add missing `)`) - #151526 (Fix autodiff codegen tests) - #151810 (citool: report debuginfo test statistics) - #152065 (Convert to inline diagnostics in `rustc_ty_utils`) - #152068 (Convert to inline diagnostics in `rustc_resolve`) - #152070 (Convert to inline diagnostics in `rustc_pattern_analysis`) - #152072 (Convert to inline diagnostics in `rustc_monomorphize`) - #152083 (Fix set_times_nofollow for directory on windows) Failed merges: - #152069 (Convert to inline diagnostics in `rustc_privacy`)

…json-again, r=chenyukang target: fix destabilising target-spec-json cc rust-lang#151528 rust-lang#150151 missed a case and didn't entirely destabilise target-spec-json - this patch corrects that. Closes rust-lang#71009

…uwer Rollup of 12 pull requests Successful merges: - #150992 (link modifier `export-symbols`: export all global symbols from selected uptream c static libraries) - #151534 (target: fix destabilising target-spec-json) - #152088 (rustbook/README.md: add missing `)`) - #151526 (Fix autodiff codegen tests) - #151810 (citool: report debuginfo test statistics) - #151952 (Revert doc attribute parsing errors to future warnings) - #152065 (Convert to inline diagnostics in `rustc_ty_utils`) - #152066 (Convert to inline diagnostics in `rustc_session`) - #152069 (Convert to inline diagnostics in `rustc_privacy`) - #152072 (Convert to inline diagnostics in `rustc_monomorphize`) - #152083 (Fix set_times_nofollow for directory on windows) - #152102 (Convert to inline diagnostics in all codegen backends) Failed merges: - #152068 (Convert to inline diagnostics in `rustc_resolve`) - #152070 (Convert to inline diagnostics in `rustc_pattern_analysis`)

Rollup merge of #151534 - davidtwco:destabilise-target-spec-json-again, r=chenyukang target: fix destabilising target-spec-json cc #151528 #150151 missed a case and didn't entirely destabilise target-spec-json - this patch corrects that. Closes #71009

rustbot assigned chenyukang Jan 23, 2026

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ehuss mentioned this pull request Jan 23, 2026

Tracking Issue for target-spec-json (flexible target specifications) #151528

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ehuss mentioned this pull request Jan 25, 2026

Add -Z json-target-spec rust-lang/cargo#16557

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target: fix destabilising target-spec-json

76b6623

davidtwco force-pushed the destabilise-target-spec-json-again branch from ad34ef3 to 76b6623 Compare January 26, 2026 12:08

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Zalathar mentioned this pull request Jan 27, 2026

Rollup of 3 pull requests #151721

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Rollup of 4 pull requests #151722

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ojeda mentioned this pull request Jan 29, 2026

Rust unstable features needed for the kernel Rust-for-Linux/linux#2

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CI: rfl: move to temporary commit to pass -Zunstable-options for cu…

2a9de6b

…stom target specs This also takes the chance to move forward the job to Linux v6.19-rc7, thus the previous workaround is not needed anymore. Link: rust-lang#151534 Signed-off-by: Miguel Ojeda <[email protected]>

davidtwco force-pushed the destabilise-target-spec-json-again branch from 84f1eda to 2a9de6b Compare January 30, 2026 13:55

rustbot added A-CI Area: Our Github Actions CI A-testsuite Area: The testsuite used to check the correctness of rustc T-infra Relevant to the infrastructure team, which will review and decide on the PR/issue. labels Jan 30, 2026

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Rollup of 9 pull requests #152093

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Rollup of 8 pull requests #152094

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Rollup of 11 pull requests #152099

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Rollup of 10 pull requests #152100

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Rollup of 12 pull requests #152104

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rust-bors bot merged commit 841c462 into rust-lang:main Feb 4, 2026
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rustbot added this to the 1.95.0 milestone Feb 4, 2026

davidtwco deleted the destabilise-target-spec-json-again branch February 5, 2026 15:30

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target: fix destabilising target-spec-json#151534

target: fix destabilising target-spec-json#151534
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davidtwco:destabilise-target-spec-json-again

davidtwco commented Jan 23, 2026 •

edited by ehuss

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davidtwco commented Jan 23, 2026 •

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