rustc: missing standard library documentation

[alois31]

Nixpkgs version

• Unstable (25.05)

Describe the bug

Since somewhere in staging-next 2025-03-03, the standard library documentation is missing from rustc.doc.

Steps to reproduce

Run the commands:

nix-build -A rustc.doc
stat result-doc/share/doc/docs/html/std

The following error appears (because the documentation is not there):

stat: cannot statx 'result-doc/share/doc/docs/html/std': No such file or directory

Expected behaviour

The documentation exists.

Screenshots

No response

Relevant log output

Additional context

Before the merge of staging-next 2025-03-03, the documentation was present as expected.

System metadata

• system: "x86_64-linux"
• host os: Linux 6.14.5, NixOS, 25.05 (Warbler), 25.05pre796699.dda3dcd3fe03
• multi-user?: yes
• sandbox: yes
• version: nix-env (Lix, like Nix) 2.93.0 System type: x86_64-linux Additional system types: i686-linux, x86_64-v1-linux, x86_64-v2-linux, x86_64-v3-linux Features: gc, signed-caches System configuration file: /etc/nix/nix.conf User configuration files: [censored] Store directory: /nix/store State directory: /nix/var/nix Data directory: /nix/store/jdb3zwjn0l2gabmb3r01mr8sk5mfgxa6-lix-2.94.0-pre-20250509_dcb0a97000d5/share
• nixpkgs: /nix/store/x5q273wlnbk6dzk3r85vqxx7wpd071qm-nixpkgs

Notify maintainers

@Havvy @figsoda @Mic92 @tjni @winterqt @zowoq

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[alyssais]

Interesting — I can confirm that the std docs have disappeared (probably due to 1.85.0) update, but it also looks all the Rust documentation is being installed into an odd location — it should be share/doc/rust, not share/doc/docs.

[alyssais]

I have bisected the missing std documentation to #382166 (not the 1.85.0 update). @niklaskorz could you have a look? Wondering if something has gone wrong with your patch — is it now not generating the std documentation at all, rather than just skipping it for no_std targets?

[winterqt]

I wonder if it's related to the Rust patch itself? I remember seeing some weird stuff related to logs in my last rustc build, let me see...

(oops I realized Alyssa already brought that up)

[niklaskorz]

Looking into it, sorry for the trouble!

Edit: The std docs are definitely built, but I haven't yet figured out why they do not find their way into the output when the patch is enabled. Still digging.

Edit 2: My current suspicion is that the docs are installed once for each target, and each docs installation removes the previous target's docs from the output. BPF being the last target to perform this uninstall + install procedure, the rustc.doc output is left with no alloc or std docs (as the BPF targets contain neither).

From the logs:

rustc> Dist rust-docs-1.86.0-aarch64-apple-darwin
rustc> 	finished in 5.713 seconds
rustc> Installing stage2 docs (aarch64-apple-darwin)
rustc> install: creating uninstall script at /nix/store/b7zqhjyx4zzcv4pyrc577d3s4hjawvxk-rustc-1.86.0/lib/rustlib/uninstall.sh
rustc> install: installing component 'rust-docs'
rustc>
rustc>     rust docs installed.
rustc>
rustc> Dist rust-docs-1.86.0-wasm32-unknown-unknown
rustc> 	finished in 5.061 seconds
rustc> Installing stage2 docs (wasm32-unknown-unknown)
rustc> install: uninstalling component 'rust-docs'
rustc> install: creating uninstall script at /nix/store/b7zqhjyx4zzcv4pyrc577d3s4hjawvxk-rustc-1.86.0/lib/rustlib/uninstall.sh
rustc> install: installing component 'rust-docs'
rustc>
rustc>     rust docs installed.
rustc>
rustc> Dist rust-docs-1.86.0-wasm32v1-none
rustc> 	finished in 0.384 seconds
rustc> Installing stage2 docs (wasm32v1-none)
rustc> install: uninstalling component 'rust-docs'
rustc> install: creating uninstall script at /nix/store/b7zqhjyx4zzcv4pyrc577d3s4hjawvxk-rustc-1.86.0/lib/rustlib/uninstall.sh
rustc> install: installing component 'rust-docs'
rustc>
rustc>     rust docs installed.
rustc>
rustc> Dist rust-docs-1.86.0-bpfel-unknown-none
rustc> 	finished in 0.332 seconds
rustc> Installing stage2 docs (bpfel-unknown-none)
rustc> install: uninstalling component 'rust-docs'
rustc> install: creating uninstall script at /nix/store/b7zqhjyx4zzcv4pyrc577d3s4hjawvxk-rustc-1.86.0/lib/rustlib/uninstall.sh
rustc> install: installing component 'rust-docs'
rustc>
rustc>     rust docs installed.
rustc>
rustc> Dist rust-docs-1.86.0-bpfeb-unknown-none
rustc> 	finished in 0.332 seconds
rustc> Installing stage2 docs (bpfeb-unknown-none)
rustc> install: uninstalling component 'rust-docs'
rustc> install: creating uninstall script at /nix/store/b7zqhjyx4zzcv4pyrc577d3s4hjawvxk-rustc-1.86.0/lib/rustlib/uninstall.sh
rustc> install: installing component 'rust-docs'
rustc>
rustc>     rust docs installed.

[niklaskorz]

Moving the targetPlatform's triple to the end of the target list makes the install step use its docs (instead of the bpf target docs):

diff --git a/pkgs/development/compilers/rust/rustc.nix b/pkgs/development/compilers/rust/rustc.nix
index 263feaa61704..660db1ba32a9 100644
--- a/pkgs/development/compilers/rust/rustc.nix
+++ b/pkgs/development/compilers/rust/rustc.nix
@@ -153,11 +153,8 @@ stdenv.mkDerivation (finalAttrs: {
       # std is built for all platforms in --target.
       "--target=${
         concatStringsSep "," (
-          [
-            stdenv.targetPlatform.rust.rustcTargetSpec
-          ]
           # Other targets that don't need any extra dependencies to build.
-          ++ optionals (!fastCross) [
+          optionals (!fastCross) [
             "wasm32-unknown-unknown"
             "wasm32v1-none"
             "bpfel-unknown-none"
@@ -175,6 +172,9 @@ stdenv.mkDerivation (finalAttrs: {
           ++ optionals (stdenv.hostPlatform != stdenv.targetPlatform && !fastCross) [
             stdenv.hostPlatform.rust.rustcTargetSpec
           ]
+          ++ [
+            stdenv.targetPlatform.rust.rustcTargetSpec
+          ]
         )
       }"

As we use the install step from upstream's Makefile (and thus deeper down, upstream's boostrap.py installl scripts), I think this merits an upstream bug report. I'm not sure what the correct behavior should be for upstream, so I hope this will start a bit of discussion upstream with a satisfactory outcome for all parties. Until then, the best we can do is move the targetPlatform's triple to the end of the list because at least for nixpkgs, this is what end users would most likely expect to receive when building rustc.doc.

[niklaskorz]

@alyssais What action would you recommend with regards to the nearing NixOS 25.05 release? Moving stdenv.targetPlatform.rust.rustcTargetSpec to the end of the targets list should be harmless, but before I create a staging PR (which would then have to be backported to 25.05), I'd like to hear your opinion. I doubt we'll hear back from upstream before the release of 25.05.

[alyssais]

Sounds good to me.