rustc_typeck: add obligation cause code for function call

Fixes rust-lang#90285

Author: notriddle

compiler/rustc_middle/src/traits/mod.rs

@@ -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,
 

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -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,

compiler/rustc_typeck/src/check/fn_ctxt/checks.rs

@@ -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,
+                        };
                     error.obligation.cause.span = callee.span;
                 }
             }