Rollup merge of #114684 - compiler-errors:redundant-resolves, r=lcnr

Remove redundant calls to `resolve_vars_with_obligations`

I've been auditing the calls to `resolve_vars_with_obligations` for the new solver, and have found a few that have no effect on diagnostics. Let's just remove 'em.

Also remove a redundant `resolve_vars_with_obligations_and_mutate_fulfillment` call.

r? ``@lcnr``

compiler/rustc_hir_typeck/src/coercion.rs

@@ -1039,6 +1039,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     /// Returns false if the coercion creates any obligations that result in
     /// errors.
     pub fn can_coerce(&self, expr_ty: Ty<'tcx>, target: Ty<'tcx>) -> bool {
+        // FIXME(-Ztrait-solver=next): We need to structurally resolve both types here.
         let source = self.resolve_vars_with_obligations(expr_ty);
         debug!("coercion::can_with_predicates({:?} -> {:?})", source, target);
 

compiler/rustc_hir_typeck/src/demand.rs

@@ -260,7 +260,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         ));
         let expr = expr.peel_drop_temps();
         let cause = self.misc(expr.span);
-        let expr_ty = self.resolve_vars_with_obligations(checked_ty);
+        let expr_ty = self.resolve_vars_if_possible(checked_ty);
         let mut err = self.err_ctxt().report_mismatched_types(&cause, expected, expr_ty, e);
 
         let is_insufficiently_polymorphic =

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -85,16 +85,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     /// to get more type information.
     // FIXME(-Ztrait-solver=next): A lot of the calls to this method should
     // probably be `try_structurally_resolve_type` or `structurally_resolve_type` instead.
-    pub(in super::super) fn resolve_vars_with_obligations(&self, ty: Ty<'tcx>) -> Ty<'tcx> {
-        self.resolve_vars_with_obligations_and_mutate_fulfillment(ty, |_| {})
-    }
-
-    #[instrument(skip(self, mutate_fulfillment_errors), level = "debug", ret)]
-    pub(in super::super) fn resolve_vars_with_obligations_and_mutate_fulfillment(
-        &self,
-        mut ty: Ty<'tcx>,
-        mutate_fulfillment_errors: impl Fn(&mut Vec<traits::FulfillmentError<'tcx>>),
-    ) -> Ty<'tcx> {
+    #[instrument(skip(self), level = "debug", ret)]
+    pub(in super::super) fn resolve_vars_with_obligations(&self, mut ty: Ty<'tcx>) -> Ty<'tcx> {
         // No Infer()? Nothing needs doing.
         if !ty.has_non_region_infer() {
             debug!("no inference var, nothing needs doing");
@@ -112,7 +104,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // possible. This can help substantially when there are
         // indirect dependencies that don't seem worth tracking
         // precisely.
-        self.select_obligations_where_possible(mutate_fulfillment_errors);
+        self.select_obligations_where_possible(|_| {});
         self.resolve_vars_if_possible(ty)
     }
 

compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

@@ -950,7 +950,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         if !expected.is_unit() {
             return;
         }
-        let found = self.resolve_vars_with_obligations(found);
+        let found = self.resolve_vars_if_possible(found);
 
         let in_loop = self.is_loop(id)
             || self

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -2994,7 +2994,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // This occurs for UFCS desugaring of `T::method`, where there is no
         // receiver expression for the method call, and thus no autoderef.
         if let SelfSource::QPath(_) = source {
-            return is_local(self.resolve_vars_with_obligations(rcvr_ty));
+            return is_local(rcvr_ty);
         }
 
         self.autoderef(span, rcvr_ty).any(|(ty, _)| is_local(ty))