Split autodiff into autodiff_forward and autodiff_reverse

[Sa4dUs]

This PR splits #[autodiff] macro so #[autodiff(df, Reverse, args)] would become #[autodiff_reverse(df, args)] and #[autodiff(df, Forward, args)] would become #[autodiff_forwad(df, args)].

Pending tasks:

• Fix cannot find a built-in macro with name error.
• Update the tests to reflect the new macro structure.
• Review the implementation for better code.

[ZuseZ4]

I'd almost bet it has to do with bootstrapping, see e.g. https://github.com/rust-lang/rust/pull/129458/files#diff-ea30f57e78f3b861b784ae315b3ac31358b7cea2aa14a668084ad412de12e586
It will be removed by other people later after landing, that's probably why you didn't see it anymore when just looking at the current code for it. Ping me if that doesn't solve the issue, then I can try to play around with it locally.

[jieyouxu]

I don't remember exactly, can built-in attributes be namespaced now? E.g. #[autodiff::forward()] and #[autodiff::reverse()]. That way, only one "top-level" name would cause macro ambiguities from the built-in attribute (autodiff), instead of two.

[ZuseZ4]

I think :: looks much prettier than _. Our attribute is called rustc_autodiff and not autodiff, so I don't think there will be ambiguities either way.
@jdonszelmann is probably the right person to ask about parsing. (see the question above)

[jieyouxu]

Right sorry, I keep forgetting there's two

[ZuseZ4]

Try build/x86_64-unknown-linux-gnu/llvm/bin/clang-format compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp -i (Adjusted for all the cpp files you touched).

[Sa4dUs]

I'd say the tidy error it's because compiler/rustc_builtin_macros/messages.ftl has the message builtin_macros_autodiff_mode, but it's not being used. I still need to fix a bug when parsing the arguments (I'm assuming it's a silly mistake with an index or array boundary), and once everything works properly, I'll take care of errors and such, which I assume will need to be adjusted somehow for the new macros.

[rust-log-analyzer]

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#18 exporting to docker image format
#18 sending tarball 20.6s done
#18 DONE 28.6s
##[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-19]
[CI_JOB_NAME=x86_64-gnu-llvm-19]
debug: `DISABLE_CI_RUSTC_IF_INCOMPATIBLE` configured.
---
sccache: Listening on address 127.0.0.1:4226
##[group]Configure the build
configure: processing command line
configure: 
configure: build.configure-args := ['--build=x86_64-unknown-linux-gnu', '--llvm-root=/usr/lib/llvm-19', '--enable-llvm-link-shared', '--set', 'rust.randomize-layout=true', '--set', 'rust.thin-lto-import-instr-limit=10', '--set', 'build.print-step-timings', '--enable-verbose-tests', '--set', 'build.metrics', '--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', '--set', 'gcc.download-ci-gcc=true', '--enable-new-symbol-mangling']
configure: build.build          := x86_64-unknown-linux-gnu
configure: target.x86_64-unknown-linux-gnu.llvm-config := /usr/lib/llvm-19/bin/llvm-config
configure: llvm.link-shared     := True
configure: rust.randomize-layout := True
configure: rust.thin-lto-import-instr-limit := 10
---
3    |
4 LL | use std::autodiff::autodiff_forward;
5    |     ------------------------------- previous import of the macro `autodiff_forward` here
- ...
+ LL | extern crate my_macro;
7 LL | use my_macro::autodiff_forward; // bring `autodiff_forward` in scope
8    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^ `autodiff_forward` reimported here
9    |

13 LL | use my_macro::autodiff_forward as other_autodiff_forward; // bring `autodiff_forward` in scope
14    |                                +++++++++++++++++++++++++
15 
- error: this rustc version does not support autodiff_forward
+ error: this rustc version does not support autodiff
17   --> $DIR/visibility.rs:13:1
---
To only update this specific test, also pass `--test-args autodiff/visibility.rs`

error in revision `std_autodiff`: 1 errors occurred comparing output.
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/autodiff/visibility.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2" "--target=x86_64-unknown-linux-gnu" "--cfg" "std_autodiff" "--check-cfg" "cfg(test,FALSE,std_autodiff,no_std_autodiff)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/autodiff/visibility.std_autodiff" "-A" "unused" "-A" "internal_features" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/autodiff/visibility.std_autodiff/auxiliary" "--extern" "my_macro=/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/autodiff/visibility.std_autodiff/auxiliary/libmy_macro.so"
stdout: none
--- stderr -------------------------------
error[E0252]: the name `autodiff_forward` is defined multiple times
##[error]  --> /checkout/tests/ui/autodiff/visibility.rs:11:5
   |
LL | use std::autodiff::autodiff_forward;
   |     ------------------------------- previous import of the macro `autodiff_forward` here
LL | extern crate my_macro;
LL | use my_macro::autodiff_forward; // bring `autodiff_forward` in scope
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^ `autodiff_forward` reimported here
   |
   = note: `autodiff_forward` must be defined only once in the macro namespace of this module
help: you can use `as` to change the binding name of the import
   |
LL | use my_macro::autodiff_forward as other_autodiff_forward; // bring `autodiff_forward` in scope
   |                                +++++++++++++++++++++++++

error: this rustc version does not support autodiff
##[error]  --> /checkout/tests/ui/autodiff/visibility.rs:13:1
   |