nicer autodiff error handling

[ZuseZ4]

I still intend to finish #137570 by adding proper handling for library builds.
I was hoping to directly get the proper fix in, but I haven't had the time in a while, and other contributors and early testers run into this issue often enough.

[rustbot]

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[rustbot]

Some changes occurred in compiler/rustc_codegen_ssa

cc @WaffleLapkin

[oli-obk]

Please give the commit a proper commit message 😆

[ZuseZ4]

cc @Sa4dUs that should prevent your issue in the future.

[ZuseZ4]

ok, I'm happy with these two tests, let me know if you want any changes.

[oli-obk]

maybe pick a random (like the first) entry from this list and use its span so in case of a larger crate the user is aware of why this is being emitted. I could see it being confusing in case someone is adding cfgs to turn on/off autodiff and got sth wrong in the process

[ZuseZ4]

I added a span to the error, but emit_error now fails with:

thread 'coordinator' panicked at compiler/rustc_codegen_ssa/src/back/write.rs:1908:9:
assertion `left == right` failed
  left: MultiSpan { primary_spans: [Span { lo: BytePos(123), hi: BytePos(148), ctxt: #0 }], span_labels: [] }
 right: MultiSpan { primary_spans: [], span_labels: [] }
stack backtrace:

Do you have a recommendation for how to best emit the error? I had some issues to find the right function to get it to work.

[ZuseZ4]

ping @oli-obk if you by chance know the source of this error? Otherwise I can spend some more time to try it out.

[oli-obk]

I don't know this error, maybe I'll see sth if you push the changes that don't work

[rust-log-analyzer]

The job x86_64-gnu-llvm-19 failed! Check out the build log: (web) (plain enhanced) (plain)

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

 - LegacyKeyValueFormat: "ENV key=value" should be used instead of legacy "ENV key value" format (line 48)
 - LegacyKeyValueFormat: "ENV key=value" should be used instead of legacy "ENV key value" format (line 51)
 - LegacyKeyValueFormat: "ENV key=value" should be used instead of legacy "ENV key value" format (line 68)
##[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
---
[RUSTC-TIMING] rustc_hir_analysis test:false 55.549
   Compiling rustc_hir_typeck v0.0.0 (/checkout/compiler/rustc_hir_typeck)
[RUSTC-TIMING] rustc_mir_build test:false 30.404
   Compiling rustc_mir_transform v0.0.0 (/checkout/compiler/rustc_mir_transform)
error[E0277]: the trait bound `MultiSpan: From<AutodiffLibraryBuild>` is not satisfied
    --> compiler/rustc_codegen_ssa/src/back/write.rs:424:41
     |
424  |                 dcx.handle().span_fatal(AutodiffLibraryBuild { span });
     |                              ---------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `From<AutodiffLibraryBuild>` is not implemented for `MultiSpan`
     |                              |
     |                              required by a bound introduced by this call
     |
     = help: the following other types implement trait `From<T>`:
               `MultiSpan` implements `From<Vec<rustc_span::Span>>`
               `MultiSpan` implements `From<rustc_span::Span>`
     = note: required for `AutodiffLibraryBuild` to implement `Into<MultiSpan>`
note: required by a bound in `DiagCtxtHandle::<'a>::span_fatal`
    --> /checkout/compiler/rustc_errors/src/lib.rs:1272:40
     |
1272 |     pub fn span_fatal(self, span: impl Into<MultiSpan>, msg: impl Into<DiagMessage>) -> ! {
     |                                        ^^^^^^^^^^^^^^^ required by this bound in `DiagCtxtHandle::<'a>::span_fatal`

error[E0061]: this method takes 2 arguments but 1 argument was supplied
    --> compiler/rustc_codegen_ssa/src/back/write.rs:424:30
     |
424  |                 dcx.handle().span_fatal(AutodiffLibraryBuild { span });
     |                              ^^^^^^^^^^------------------------------- argument #2 is missing
     |
note: method defined here
    --> /checkout/compiler/rustc_errors/src/lib.rs:1272:12
     |
1272 |     pub fn span_fatal(self, span: impl Into<MultiSpan>, msg: impl Into<DiagMessage>) -> ! {
     |            ^^^^^^^^^^
help: provide the argument
     |
424  |                 dcx.handle().span_fatal(AutodiffLibraryBuild { span }, /* msg */);
     |                                                                      +++++++++++

Some errors have detailed explanations: E0061, E0277.
For more information about an error, try `rustc --explain E0061`.
[RUSTC-TIMING] rustc_codegen_ssa test:false 3.390

[bors]

☔ The latest upstream changes (presumably #144044) made this pull request unmergeable. Please resolve the merge conflicts.

[oli-obk]

This needs to stay `emit_fatal, unsure what span_fatal does