Fix enzyme build errors
After [this PR](https://github.com/rust-lang/rust/pull/136428) was merged, I switched to master and attempted building `./x.py build --stage 1 library` with the config mentioned in the enzyme rustbook but it resulted in some errors tho the config.example.toml build succeeded
The errors were re:
### 1. Use of ref in match patterns
The errors were related to match ergonomics in Rust 2024, where ref is no longer needed when matching on references. Examples:
```
error: binding modifiers may only be written when the default binding mode is `move`
--> compiler/rustc_builtin_macros/src/autodiff.rs:136:31
|
136 | Annotatable::Item(ref iitem) => {
| ^^^ binding modifier not allowed under `ref` default binding mode
|
= note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
note: matching on a reference type with a non-reference pattern changes the default binding mode
--> compiler/rustc_builtin_macros/src/autodiff.rs:136:13
|
136 | Annotatable::Item(ref iitem) => {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ this matches on type `&_`
help: remove the unnecessary binding modifier
|
136 - Annotatable::Item(ref iitem) => {
136 + Annotatable::Item(iitem) => {
|
error: binding modifiers may only be written when the default binding mode is `move`
--> compiler/rustc_builtin_macros/src/autodiff.rs:146:36
|
146 | Annotatable::AssocItem(ref assoc_item, _) => {
| ^^^ binding modifier not allowed under `ref` default binding mode
|
= note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
note: matching on a reference type with a non-reference pattern changes the default binding mode
--> compiler/rustc_builtin_macros/src/autodiff.rs:146:13
|
146 | Annotatable::AssocItem(ref assoc_item, _) => {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ this matches on type `&_`
help: remove the unnecessary binding modifier
|
146 - Annotatable::AssocItem(ref assoc_item, _) => {
146 + Annotatable::AssocItem(assoc_item, _) => {
|
error: binding modifiers may only be written when the default binding mode is `move`
--> compiler/rustc_builtin_macros/src/autodiff.rs:174:31
|
174 | ... Annotatable::Item(ref iitem) => (iitem.vis.clone(), iitem.ide...
| ^^^ binding modifier not allowed under `ref` default binding mode
|
= note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
note: matching on a reference type with a non-reference pattern changes the default binding mode
--> compiler/rustc_builtin_macros/src/autodiff.rs:174:13
|
174 | ... Annotatable::Item(ref iitem) => (iitem.vis.clone(), iitem.ident.c...
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ this matches on type `&_`
help: remove the unnecessary binding modifier
|
174 - Annotatable::Item(ref iitem) => (iitem.vis.clone(), iitem.ident.clone()),
174 + Annotatable::Item(iitem) => (iitem.vis.clone(), iitem.ident.clone()),
|
error: binding modifiers may only be written when the default binding mode is `move`
--> compiler/rustc_builtin_macros/src/autodiff.rs:175:36
|
175 | Annotatable::AssocItem(ref assoc_item, _) => {
| ^^^ binding modifier not allowed under `ref` default binding mode
|
= note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
note: matching on a reference type with a non-reference pattern changes the default binding mode
--> compiler/rustc_builtin_macros/src/autodiff.rs:175:13
|
175 | Annotatable::AssocItem(ref assoc_item, _) => {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ this matches on type `&_`
help: remove the unnecessary binding modifier
|
175 - Annotatable::AssocItem(ref assoc_item, _) => {
175 + Annotatable::AssocItem(assoc_item, _) => {
|
error: could not compile `rustc_builtin_macros` (lib) due to 4 previous errors
warning: build failed, waiting for other jobs to finish...
Build completed unsuccessfully in 0:19:39
```
### 2. the use of external C blocks without unsafe in compiler/rustc_codegen_llvm/src/llvm/enzyme_ffi.rs (I don't have the error message handy)
The first commit fixes the errors above
---
## Additional Improvement:
`@ZuseZ4` suggested we consolidate the variants under `#[cfg(llvm_enzyme)]` and `#[cfg(not(llvm_enzyme))]` by conditionally checking for `cfg!(llvm_enzyme)` instead. This way, the autodiff code is compiled but not executed avoiding such regressions
r? `@ZuseZ4`
cc: `@oli-obk`
d65f568302