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rustc_typeck: add obligation cause code for function call #94036

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rustc_typeck: add obligation cause code for function call #94036

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7 changes: 7 additions & 0 deletions compiler/rustc_middle/src/traits/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -270,6 +270,13 @@ pub enum ObligationCauseCode<'tcx> {
parent_code: Lrc<ObligationCauseCode<'tcx>>,
},

FunctionCallObligation {
/// The node of the function call.
call_hir_id: hir::HirId,
/// The obligation introduced by this argument.
parent_code: Lrc<ObligationCauseCode<'tcx>>,
},

/// Error derived when matching traits/impls; see ObligationCause for more details
CompareImplConstObligation,

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12 changes: 12 additions & 0 deletions compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
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Expand Up @@ -2294,6 +2294,18 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
)
});
}
ObligationCauseCode::FunctionCallObligation { ref parent_code, .. } => {
ensure_sufficient_stack(|| {
self.note_obligation_cause_code(
err,
predicate,
param_env,
&parent_code,
obligated_types,
seen_requirements,
)
});
}
ObligationCauseCode::FunctionArgumentObligation {
arg_hir_id,
call_hir_id,
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6 changes: 6 additions & 0 deletions compiler/rustc_typeck/src/check/fn_ctxt/checks.rs
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Expand Up @@ -1137,6 +1137,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
} else if error.obligation.cause.span == call_sp {
// Make function calls point at the callee, not the whole thing.
if let hir::ExprKind::Call(callee, _) = expr.kind {
let parent_code = error.obligation.cause.clone_code();
*error.obligation.cause.make_mut_code() =
ObligationCauseCode::FunctionCallObligation {
call_hir_id: expr.hir_id,
parent_code,
};
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I'm not sure what this PR really does.
Which obligation code was previously used for this case?
Can this new code make any observable changes in tests?
Also call_hir_id is set here but never used.

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Which obligation code was previously used for this case?

That's the problem: almost any obligation code could have been previously used for this case. This code is used in any case where a function call introduces an obligation, but the obligation cannot be tracked down to a particular function parameter, so the function callee itself is used for the span.

Can this new code make any observable changes in tests?

It doesn't, no.

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That's the problem: almost any obligation code could have been previously used for this case.

Why is that a problem though?
Why is it necessary to wrap the parent obligation into something instead of using it directly? Especially if it is not observable from the outside.

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I’m not sure.

@estebank what else did you want done here?

error.obligation.cause.span = callee.span;
}
}
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