rustc_traits/
codegen.rs
1use rustc_infer::infer::TyCtxtInferExt;
7use rustc_middle::bug;
8use rustc_middle::traits::CodegenObligationError;
9use rustc_middle::ty::{self, PseudoCanonicalInput, TyCtxt, TypeVisitableExt};
10use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
11use rustc_trait_selection::traits::{
12 ImplSource, Obligation, ObligationCause, ObligationCtxt, ScrubbedTraitError, SelectionContext,
13 Unimplemented,
14};
15use tracing::debug;
16
17pub(crate) fn codegen_select_candidate<'tcx>(
25 tcx: TyCtxt<'tcx>,
26 key: PseudoCanonicalInput<'tcx, ty::TraitRef<'tcx>>,
27) -> Result<&'tcx ImplSource<'tcx, ()>, CodegenObligationError> {
28 let PseudoCanonicalInput { typing_env, value: trait_ref } = key;
29 debug_assert_eq!(trait_ref, tcx.normalize_erasing_regions(typing_env, trait_ref));
31
32 let (infcx, param_env) = tcx.infer_ctxt().ignoring_regions().build_with_typing_env(typing_env);
35 let mut selcx = SelectionContext::new(&infcx);
36
37 let obligation_cause = ObligationCause::dummy();
38 let obligation = Obligation::new(tcx, obligation_cause, param_env, trait_ref);
39
40 let selection = match selcx.select(&obligation) {
41 Ok(Some(selection)) => selection,
42 Ok(None) => return Err(CodegenObligationError::Ambiguity),
43 Err(Unimplemented) => return Err(CodegenObligationError::Unimplemented),
44 Err(e) => {
45 bug!("Encountered error `{:?}` selecting `{:?}` during codegen", e, trait_ref)
46 }
47 };
48
49 debug!(?selection);
50
51 let ocx = ObligationCtxt::new(&infcx);
56 let impl_source = selection.map(|obligation| {
57 ocx.register_obligation(obligation);
58 });
59
60 let errors = ocx.select_all_or_error();
64 if !errors.is_empty() {
65 for err in errors {
69 if let ScrubbedTraitError::Cycle(cycle) = err {
70 infcx.err_ctxt().report_overflow_obligation_cycle(&cycle);
71 }
72 }
73 return Err(CodegenObligationError::Unimplemented);
74 }
75
76 let impl_source = infcx.resolve_vars_if_possible(impl_source);
77 let impl_source = tcx.erase_regions(impl_source);
78 if impl_source.has_non_region_infer() {
79 let guar = match impl_source {
84 ImplSource::UserDefined(impl_) => tcx.dcx().span_delayed_bug(
85 tcx.def_span(impl_.impl_def_id),
86 "this impl has unconstrained generic parameters",
87 ),
88 _ => unreachable!(),
89 };
90 return Err(CodegenObligationError::UnconstrainedParam(guar));
91 }
92
93 Ok(&*tcx.arena.alloc(impl_source))
94}