Point at argument when evaluating Path's bounds

When evaluating an `ExprKind::Call`, we first have to `check_expr` on it's
callee. When this one is a `ExprKind::Path`, we had to evaluate the bounds
introduced for its arguments, but by the time we evaluated them we no
longer had access to the argument spans. Now we special case this so
that we can point at the right place on unsatisfied bounds. This also
allows the E0277 deduplication to kick in correctly, so we now emit
fewer errors.

compiler/rustc_typeck/src/check/callee.rs

@@ -72,7 +72,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         arg_exprs: &'tcx [hir::Expr<'tcx>],
         expected: Expectation<'tcx>,
     ) -> Ty<'tcx> {
-        let original_callee_ty = self.check_expr(callee_expr);
+        let original_callee_ty = match &callee_expr.kind {
+            hir::ExprKind::Path(hir::QPath::Resolved(..) | hir::QPath::TypeRelative(..)) => self
+                .check_expr_with_expectation_and_args(
+                    callee_expr,
+                    Expectation::NoExpectation,
+                    arg_exprs,
+                ),
+            _ => self.check_expr(callee_expr),
+        };
+
         let expr_ty = self.structurally_resolved_type(call_expr.span, original_callee_ty);
 
         let mut autoderef = self.autoderef(callee_expr.span, expr_ty);

compiler/rustc_typeck/src/check/expr.rs

@@ -161,6 +161,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         &self,
         expr: &'tcx hir::Expr<'tcx>,
         expected: Expectation<'tcx>,
+    ) -> Ty<'tcx> {
+        self.check_expr_with_expectation_and_args(expr, expected, &[])
+    }
+
+    /// Same as `check_expr_with_expectation`, but allows us to pass in the arguments of a
+    /// `ExprKind::Call` when evaluating its callee when it is an `ExprKind::Path`.
+    pub(super) fn check_expr_with_expectation_and_args(
+        &self,
+        expr: &'tcx hir::Expr<'tcx>,
+        expected: Expectation<'tcx>,
+        args: &'tcx [hir::Expr<'tcx>],
     ) -> Ty<'tcx> {
         if self.tcx().sess.verbose() {
             // make this code only run with -Zverbose because it is probably slow
@@ -198,7 +209,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let old_diverges = self.diverges.replace(Diverges::Maybe);
         let old_has_errors = self.has_errors.replace(false);
 
-        let ty = ensure_sufficient_stack(|| self.check_expr_kind(expr, expected));
+        let ty = ensure_sufficient_stack(|| match &expr.kind {
+            hir::ExprKind::Path(
+                qpath @ hir::QPath::Resolved(..) | qpath @ hir::QPath::TypeRelative(..),
+            ) => self.check_expr_path(qpath, expr, args),
+            _ => self.check_expr_kind(expr, expected),
+        });
 
         // Warn for non-block expressions with diverging children.
         match expr.kind {
@@ -261,7 +277,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             ExprKind::Path(QPath::LangItem(lang_item, _)) => {
                 self.check_lang_item_path(lang_item, expr)
             }
-            ExprKind::Path(ref qpath) => self.check_expr_path(qpath, expr),
+            ExprKind::Path(ref qpath) => self.check_expr_path(qpath, expr, &[]),
             ExprKind::InlineAsm(asm) => self.check_expr_asm(asm),
             ExprKind::LlvmInlineAsm(asm) => {
                 for expr in asm.outputs_exprs.iter().chain(asm.inputs_exprs.iter()) {
@@ -481,10 +497,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         self.resolve_lang_item_path(lang_item, expr.span, expr.hir_id).1
     }
 
-    fn check_expr_path(
+    pub(crate) fn check_expr_path(
         &self,
         qpath: &'tcx hir::QPath<'tcx>,
         expr: &'tcx hir::Expr<'tcx>,
+        args: &'tcx [hir::Expr<'tcx>],
     ) -> Ty<'tcx> {
         let tcx = self.tcx;
         let (res, opt_ty, segs) =
@@ -517,16 +534,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     // We just want to check sizedness, so instead of introducing
                     // placeholder lifetimes with probing, we just replace higher lifetimes
                     // with fresh vars.
+                    let span = args.get(i).map(|a| a.span).unwrap_or(expr.span);
                     let input = self
                         .replace_bound_vars_with_fresh_vars(
-                            expr.span,
+                            span,
                             infer::LateBoundRegionConversionTime::FnCall,
                             fn_sig.input(i),
                         )
                         .0;
                     self.require_type_is_sized_deferred(
                         input,
-                        expr.span,
+                        span,
                         traits::SizedArgumentType(None),
                     );
                 }