rustPlatform.buildRustPackage: Pass `env.RUSTFLAGS` only when specified or needed to fix builds by ShamrockLee · Pull Request #464707 · NixOS/nixpkgs

ShamrockLee · 2025-11-24T21:45:32Z

Prevent shadowing RUSTFLAGS-like variables with lower priorities, such as mint-mod-mamanager's CARGO_TARGET_X86_64_PC_WINDOWS_GNU_RUSTFLAGS.

Fixes #435278 (comment)

Fixes #464392

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gepbird

Thanks for the quick fix, I tested this with the previously failing build which works now :)

pkgs/build-support/rust/build-rust-package/default.nix

ShamrockLee · 2025-11-24T22:56:09Z

@gepbird I just noticed that the package is an ou-of-tree NUR package. Is the shadowing mechanism part of the package definition or part of the rustc behavior?

gepbird · 2025-11-24T23:10:54Z

@gepbird I just noticed that the package is an ou-of-tree NUR package. Is the shadowing mechanism part of the package definition or part of the rustc behavior?

I'm fairly confident it's a rustc behaviour, but I'm not sure how to fully confirm that.

The environment variable is not specific to the package, but for compiling to windows, see #139966 (comment). However in that issue it looks like people are compiling a package to only a single platform, while for mint-mod-manager most of it is compiled to x86_64-linux, and a crate gets compiled to windows. (This half cross compilation is necessary, because the binary of the package runs on Linux, but it creates a Windows DLL that will be injected to the game, which is usually running with Steam Proton.)

Caused by NixOS/nixpkgs#435278 RUSTFLAGS is now always set and overrides whatever we specify in .cargo/config.toml TODO: Keep an eye on NixOS/nixpkgs#464707 NixOS/nixpkgs#464992 and possibly revert or adjust to the new status quo in nixpkgs.

… or needed Prevent shadowing RUSTFLAGS-like variables with lower priorities, such as mint-mod-mamanager's CARGO_TARGET_X86_64_PC_WINDOWS_GNU_RUSTFLAGS Co-authored-by: Gergő Gutyina <gutyina.gergo.2@gmail.com>

ShamrockLee · 2025-11-26T23:43:57Z

Rebased from staging-next to staging and rebased onto the tip of the staging branch.

alyssais · 2025-11-28T12:35:13Z

pkgs/build-support/rust/build-rust-package/default.nix

+          ${if args ? RUSTFLAGS || isDarwinDebug then "RUSTFLAGS" else null} =
+            lib.optionalString isDarwinDebug "-C split-debuginfo=packed "
+            # Workaround the existing RUSTFLAGS specified as a list.
+            + interpolateString (args.RUSTFLAGS or "");


This is a good fix, but if you feel like putting in a bit more, even better would be not doing this in buildRustPackage to begin with — it's not the right place for it because plenty of Rust builds don't go through it. The rustc wrapper would be a much better place — it's universally used and doesn't need any environment variables to be modified.

I'm leaning toward addressing the simplification in a subsequent PR, as such change could introduce new incompatibility. (The existing change is a partial revert )

Would it be okay if we merge and backport this fix as-is?

I think it's okay, at least it shouldn't be worse than the previous situation

@ShamrockLee still feel like making that subsequent PR?

@ShamrockLee still feel like making that subsequent PR?

After looking into the buildRustPackage, I found the RUSTFLAG for buildRustPackagesituation to be quite different from GOFLAG for buildGoModule.

buildGoModule invokes cgo to build, which is also where GOFLAGS apply. We could specify the flags directly with our own flag lists (such as goBuildFlags).

buildRustPackage invokes cargo to build, but RUSTFLAGS apply to rustc (invoked by cargo). We cannot replace it with a flag list without stringifying to RUSTFLAGS first.

My suggestion was to put it in the rustc wrapper. Cargo invokes rustc through that wrapper.

nixpkgs-ci · 2025-11-30T15:05:30Z

Successfully created backport PR for staging-25.11:

[Backport staging-25.11] rustPlatform.buildRustPackage: Pass env.RUSTFLAGS only when specified or needed to fix builds #466586

…flags (NixOS#464981)" This reverts commit d2c6221. PR NixOS#464981 changed libcosmicAppHook to use the global RUSTFLAGS instead of target-specific CARGO_TARGET_*_RUSTFLAGS as a workaround for issue PR NixOS#464392. However, this broke cross-compilation for packages using the crabtime procedural macro (like cosmic-initial-setup). The root cause was that buildRustPackage was always setting env.RUSTFLAGS, which shadowed the target-specific flags. This has been fixed in commit PR NixOS#464707, which only sets RUSTFLAGS when explicitly needed. Fixes cross-compilation of cosmic-initial-setup and other cosmic packages that use crabtime proc macros. Signed-off-by: Brian McGillion <bmg.avoin@gmail.com>

…flags" This reverts commit d2c6221. This is no longer needed in staging due to the proper fix #464707 having been merged

…flags" This reverts commit d2c6221. This is no longer needed in staging due to the proper fix #464707 having been merged (cherry picked from commit ea27ed7)

…flags (NixOS#464981)" This reverts commit d2c6221. PR NixOS#464981 changed libcosmicAppHook to use the global RUSTFLAGS instead of target-specific CARGO_TARGET_*_RUSTFLAGS as a workaround for issue PR NixOS#464392. However, this broke cross-compilation for packages using the crabtime procedural macro (like cosmic-initial-setup). The root cause was that buildRustPackage was always setting env.RUSTFLAGS, which shadowed the target-specific flags. This has been fixed in commit PR NixOS#464707, which only sets RUSTFLAGS when explicitly needed. Fixes cross-compilation of cosmic-initial-setup and other cosmic packages that use crabtime proc macros. Signed-off-by: Brian McGillion <bmg.avoin@gmail.com>

ShamrockLee requested a review from gepbird November 24, 2025 21:46

gepbird reviewed Nov 24, 2025

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ShamrockLee requested a review from a team November 25, 2025 05:49

This was referenced Nov 26, 2025

buildRustPackage: only set RUSTFLAGS if non-empty #464992

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cosmic-comp: crash durring startup #464392

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ShamrockLee force-pushed the build-rust-package-rustflags-unshadow branch from 3dfd0be to 947fda0 Compare November 26, 2025 20:24

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gepbird requested a review from HeitorAugustoLN November 26, 2025 21:42

nixpkgs-ci bot added the 12.approvals: 1 This PR was reviewed and approved by one person. label Nov 26, 2025

ShamrockLee marked this pull request as ready for review November 26, 2025 22:43

nixpkgs-ci bot requested review from winterqt and zowoq November 26, 2025 22:51

rustPlatform.buildRustPackage: Pass env.RUSTFLAGS only when specified…

978d298

… or needed Prevent shadowing RUSTFLAGS-like variables with lower priorities, such as mint-mod-mamanager's CARGO_TARGET_X86_64_PC_WINDOWS_GNU_RUSTFLAGS Co-authored-by: Gergő Gutyina <gutyina.gergo.2@gmail.com>

ShamrockLee force-pushed the build-rust-package-rustflags-unshadow branch from 947fda0 to 978d298 Compare November 26, 2025 23:40

ShamrockLee changed the base branch from staging-next to staging November 26, 2025 23:40

nixpkgs-ci bot closed this Nov 26, 2025

nixpkgs-ci bot reopened this Nov 26, 2025

HeitorAugustoLN approved these changes Nov 28, 2025

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nixpkgs-ci bot removed the 12.approvals: 1 This PR was reviewed and approved by one person. label Nov 28, 2025

nixpkgs-ci bot added the 12.approvals: 2 This PR was reviewed and approved by two persons. label Nov 28, 2025

alyssais reviewed Nov 28, 2025

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Aleksanaa mentioned this pull request Nov 28, 2025

Build failure: cosmic-initial-setup (cross compilation) #465948

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alyssais added this pull request to the merge queue Nov 30, 2025

Merged via the queue into NixOS:staging with commit 1a1526e Nov 30, 2025
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nixpkgs-ci bot mentioned this pull request Nov 30, 2025

[Backport staging-25.11] rustPlatform.buildRustPackage: Pass env.RUSTFLAGS only when specified or needed to fix builds #466586

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github-actions bot added the 8.has: port to stable This PR already has a backport to the stable release. label Nov 30, 2025

brianmcgillion mentioned this pull request Dec 1, 2025

COSMIC Beta 8 #465945

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brianmcgillion mentioned this pull request Dec 5, 2025

COSMIC beta 9 #467552

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Pandapip1 mentioned this pull request Dec 5, 2025

Revert "libcosmicAppHook: use RUSTFLAGS instead of platform specific flags" #468250

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github-merge-queue bot pushed a commit that referenced this pull request Dec 6, 2025

Revert "libcosmicAppHook: use RUSTFLAGS instead of platform specific …

ea27ed7

…flags" This reverts commit d2c6221. This is no longer needed in staging due to the proper fix #464707 having been merged

nekowinston mentioned this pull request Dec 9, 2025

Build failure: vimPlugins.nvim-spectre #464899

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brianmcgillion mentioned this pull request Dec 11, 2025

COSMIC stable #469745

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whispersofthedawn mentioned this pull request Jan 8, 2026

treewide: prepare Rust packages for structuredAttrs by putting variables in env #472376

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