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nicer autodiff error handling #142842

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nicer autodiff error handling #142842

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5967598
make autodiff checks more helpful
ZuseZ4 Jun 26, 2025
17ab75b
verify that our fat-lto check works
ZuseZ4 Jun 26, 2025
3610d7c
verify that our rlib check works
ZuseZ4 Jun 27, 2025
d2406fc
add span information to autodiff compile time errors
ZuseZ4 Jul 1, 2025
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7 changes: 5 additions & 2 deletions compiler/rustc_ast/src/expand/autodiff_attrs.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,8 @@
use std::fmt::{self, Display, Formatter};
use std::str::FromStr;

use rustc_span::Span;

use crate::expand::{Decodable, Encodable, HashStable_Generic};
use crate::ptr::P;
use crate::{Ty, TyKind};
Expand Down Expand Up @@ -85,6 +87,7 @@ pub struct AutoDiffItem {
/// The name of the function being generated
pub target: String,
pub attrs: AutoDiffAttrs,
pub span: Span,
}

#[derive(Clone, Eq, PartialEq, Encodable, Decodable, Debug, HashStable_Generic)]
Expand Down Expand Up @@ -276,8 +279,8 @@ impl AutoDiffAttrs {
!matches!(self.mode, DiffMode::Error | DiffMode::Source)
}

pub fn into_item(self, source: String, target: String) -> AutoDiffItem {
AutoDiffItem { source, target, attrs: self }
pub fn into_item(self, source: String, target: String, span: Span) -> AutoDiffItem {
AutoDiffItem { source, target, attrs: self, span }
}
}

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5 changes: 3 additions & 2 deletions compiler/rustc_codegen_ssa/src/back/write.rs
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Expand Up @@ -419,11 +419,12 @@ fn generate_lto_work<B: ExtraBackendMethods>(
} else {
if !autodiff.is_empty() {
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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

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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.

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

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

let dcx = cgcx.create_dcx();
let span = autodiff[0].span;
if cgcx.crate_types.contains(&CrateType::Rlib) {
dcx.handle().emit_fatal(AutodiffLibraryBuild {});
dcx.handle().span_fatal(AutodiffLibraryBuild { span });
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This needs to stay `emit_fatal, unsure what span_fatal does

}
if cgcx.lto != Lto::Fat {
dcx.handle().emit_fatal(AutodiffWithoutLto {});
dcx.handle().emit_fatal(AutodiffWithoutLto { span });
}
}
assert!(needs_fat_lto.is_empty());
Expand Down
10 changes: 8 additions & 2 deletions compiler/rustc_codegen_ssa/src/errors.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -39,11 +39,17 @@ pub(crate) struct CguNotRecorded<'a> {

#[derive(Diagnostic)]
#[diag(codegen_ssa_autodiff_without_lto)]
pub struct AutodiffWithoutLto;
pub struct AutodiffWithoutLto {
#[primary_span]
pub span: Span,
}

#[derive(Diagnostic)]
#[diag(codegen_ssa_autodiff_lib_unsupported)]
pub struct AutodiffLibraryBuild;
pub struct AutodiffLibraryBuild {
#[primary_span]
pub span: Span,
}

#[derive(Diagnostic)]
#[diag(codegen_ssa_unknown_reuse_kind)]
Expand Down
5 changes: 3 additions & 2 deletions compiler/rustc_monomorphize/src/partitioning/autodiff.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -120,15 +120,16 @@ pub(crate) fn find_autodiff_source_functions<'tcx>(
None => continue,
};

debug!("source_id: {:?}", inst.def_id());
let source_def_id = inst.def_id();
debug!("source_id: {:?}", source_def_id);
let fn_ty = inst.ty(tcx, ty::TypingEnv::fully_monomorphized());
assert!(fn_ty.is_fn());
adjust_activity_to_abi(tcx, fn_ty, &mut input_activities);
let symb = symbol_name_for_instance_in_crate(tcx, inst.clone(), LOCAL_CRATE);

let mut new_target_attrs = target_attrs.clone();
new_target_attrs.input_activity = input_activities;
let itm = new_target_attrs.into_item(symb, target_symbol);
let itm = new_target_attrs.into_item(symb, target_symbol, tcx.def_span(source_def_id));
autodiff_items.push(itm);
}

Expand Down
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