[CI test] Turn rustc-dev-guide into a subtree

[Kobzol]

This is a test PR to check what happens if we move rustc-dev-guide into a subtree. This move was discussed on Zulip.

Used instructions from https://gist.github.com/Nikita240/0c98cea8f53a15e69699cd8bc40657c4. More specifically, ran:

DIR=src/doc/rustc-dev-guide

git submodule status ${DIR}
# b21d99b770f9aceb0810c843847c52f86f45d2ed
git submodule deinit ${DIR}
git rm -r --cached ${DIR}
rm -rf ${DIR}
git commit -m"Removed ${DIR}"
git subtree add -P src/doc/rustc-dev-guide https://github.com/rust-lang/rustc-dev-guide b21d99b770f9aceb0810c843847c52f86f45d2ed

r? @jieyouxu

[ehuss]

Before merging this, can you please coordinate with me to get the automation and such ready?
Also, it would be good to know who will be responsible for keeping this in sync.

[Kobzol]

I probably do not intend to merge this PR 😁 It's mostly just for testing and discussions. Once we figure out the right way forward and prepare the automation, I'll probably create another one.

[ehuss]

You might also want to update the RustcGuide test step to not require a submodule. I don't know if that test step is actually functional right now, since it currently is unused. But might as well fix that just in case someone wants to get it working again.

(Or just remove RustcGuide, I don't know how likely it is anyone will be using it in the future. 🤷 )

[Kobzol]

Yeah, I did that in the last few commits, forgot to push them before. The RustcGuide step was completely useless before, it was using a mdbook linkcheck command that hasn't existed for a while.

I added a doc src/doc/rustc-dev-guide step, but when the linkchecker runs on it, it fails, because rustc-dev-guide currently disables its linkchecker due to some bugs :/

[rust-log-analyzer]

The job x86_64-gnu-llvm-18 failed! Check out the build log: (web) (plain)

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

#16 exporting to docker image format
#16 sending tarball 27.8s done
#16 DONE 40.7s
##[endgroup]
Setting extra environment values for docker:  --env ENABLE_GCC_CODEGEN=1 --env GCC_EXEC_PREFIX=/usr/lib/gcc/
[CI_JOB_NAME=x86_64-gnu-llvm-18]
debug: `DISABLE_CI_RUSTC_IF_INCOMPATIBLE` configured.
---
sccache: Starting the server...
##[group]Configure the build
configure: processing command line
configure: 
configure: build.configure-args := ['--build=x86_64-unknown-linux-gnu', '--llvm-root=/usr/lib/llvm-18', '--enable-llvm-link-shared', '--set', 'rust.randomize-layout=true', '--set', 'rust.thin-lto-import-instr-limit=10', '--enable-verbose-configure', '--enable-sccache', '--disable-manage-submodules', '--enable-locked-deps', '--enable-cargo-native-static', '--set', 'rust.codegen-units-std=1', '--set', 'dist.compression-profile=balanced', '--dist-compression-formats=xz', '--set', 'rust.lld=false', '--disable-dist-src', '--release-channel=nightly', '--enable-debug-assertions', '--enable-overflow-checks', '--enable-llvm-assertions', '--set', 'rust.verify-llvm-ir', '--set', 'rust.codegen-backends=llvm,cranelift,gcc', '--set', 'llvm.static-libstdcpp', '--enable-new-symbol-mangling']
configure: target.x86_64-unknown-linux-gnu.llvm-config := /usr/lib/llvm-18/bin/llvm-config
configure: llvm.link-shared     := True
configure: rust.randomize-layout := True
configure: rust.thin-lto-import-instr-limit := 10
---
  Downloaded boml v0.3.1
   Compiling boml v0.3.1
   Compiling y v0.1.0 (/checkout/compiler/rustc_codegen_gcc/build_system)
    Finished `release` profile [optimized] target(s) in 3.94s
     Running `/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-codegen/x86_64-unknown-linux-gnu/release/y test --use-system-gcc --use-backend gcc --out-dir /checkout/obj/build/x86_64-unknown-linux-gnu/stage1-tools/cg_gcc --release --mini-tests --std-tests`
Using system GCC
[BUILD] example
[AOT] mini_core_hello_world
/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-tools/cg_gcc/mini_core_hello_world
abc
---
Doc path: /checkout/obj/build/x86_64-unknown-linux-gnu/doc/edition-guide/index.html
Rustbook (x86_64-unknown-linux-gnu) - style-guide
Doc path: /checkout/obj/build/x86_64-unknown-linux-gnu/doc/style-guide/index.html
Rustbook (x86_64-unknown-linux-gnu) - rustc-dev-guide
[2024-12-10T16:27:34Z WARN  mdbook::preprocess::cmd] The command wasn't found, is the "mermaid" preprocessor installed?
[2024-12-10T16:27:34Z WARN  mdbook::preprocess::cmd]  Command: mdbook-mermaid
[2024-12-10T16:27:34Z WARN  mdbook::preprocess::cmd] The command wasn't found, is the "toc" preprocessor installed?
[2024-12-10T16:27:34Z WARN  mdbook::preprocess::cmd]  Command: mdbook-toc
[2024-12-10T16:27:35Z WARN  mdbook::preprocess::cmd] The command wasn't found, is the "mermaid" preprocessor installed?
[2024-12-10T16:27:35Z WARN  mdbook::preprocess::cmd]  Command: mdbook-mermaid
[2024-12-10T16:27:35Z WARN  mdbook::preprocess::cmd] The command wasn't found, is the "toc" preprocessor installed?
[2024-12-10T16:27:35Z WARN  mdbook::preprocess::cmd]  Command: mdbook-toc
*** WARNING: linkcheck temporarily disabled due to bugs ***
Command has failed. Rerun with -v to see more details.
  local time: Tue Dec 10 16:27:35 UTC 2024
  network time: Tue, 10 Dec 2024 16:27:39 GMT
##[error]Process completed with exit code 1.
Post job cleanup.

[bors]

☔ The latest upstream changes (presumably #134492) made this pull request unmergeable. Please resolve the merge conflicts.

[Kobzol]

Closing in favour of #134907.