Auto merge of #48709 - tinaun:issue48703, r=nikomatsakis

remove erroneous error message when checking impl trait params

fixes #48703

src/librustc_typeck/check/method/confirm.rs

@@ -310,7 +310,7 @@ impl<'a, 'gcx, 'tcx> ConfirmContext<'a, 'gcx, 'tcx> {
         // variables.
         let method_generics = self.tcx.generics_of(pick.item.def_id);
         let mut fn_segment = Some((segment, method_generics));
-        self.fcx.check_path_parameter_count(self.span, &mut fn_segment, true);
+        self.fcx.check_path_parameter_count(self.span, &mut fn_segment, true, false);
 
         // Create subst for early-bound lifetime parameters, combining
         // parameters from the type and those from the method.

src/librustc_typeck/check/mod.rs

@@ -4809,9 +4809,9 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         // variables. If the user provided some types, we may still need
         // to add defaults. If the user provided *too many* types, that's
         // a problem.
-        self.check_path_parameter_count(span, &mut type_segment, false);
-        self.check_path_parameter_count(span, &mut fn_segment, false);
-        self.check_impl_trait(span, &mut fn_segment);
+        let supress_mismatch = self.check_impl_trait(span, &mut fn_segment);
+        self.check_path_parameter_count(span, &mut type_segment, false, supress_mismatch);
+        self.check_path_parameter_count(span, &mut fn_segment, false, supress_mismatch);
 
         let (fn_start, has_self) = match (type_segment, fn_segment) {
             (_, Some((_, generics))) => {
@@ -4964,7 +4964,8 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
     fn check_path_parameter_count(&self,
                                   span: Span,
                                   segment: &mut Option<(&hir::PathSegment, &ty::Generics)>,
-                                  is_method_call: bool) {
+                                  is_method_call: bool,
+                                  supress_mismatch_error: bool) {
         let (lifetimes, types, infer_types, bindings) = segment.map_or(
             (&[][..], &[][..], true, &[][..]),
             |(s, _)| s.parameters.as_ref().map_or(
@@ -5004,7 +5005,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
             // type parameters, we force instantiate_value_path to
             // use inference variables instead of the provided types.
             *segment = None;
-        } else if types.len() < required_len && !infer_types {
+        } else if types.len() < required_len && !infer_types && !supress_mismatch_error {
             let expected_text = count_type_params(required_len);
             let actual_text = count_type_params(types.len());
             struct_span_err!(self.tcx.sess, span, E0089,
@@ -5071,10 +5072,11 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
     /// Report error if there is an explicit type parameter when using `impl Trait`.
     fn check_impl_trait(&self,
                         span: Span,
-                        segment: &mut Option<(&hir::PathSegment, &ty::Generics)>) {
+                        segment: &mut Option<(&hir::PathSegment, &ty::Generics)>)
+                        -> bool {
         use hir::SyntheticTyParamKind::*;
 
-        segment.map(|(path_segment, generics)| {
+        let segment = segment.map(|(path_segment, generics)| {
             let explicit = !path_segment.infer_types;
             let impl_trait = generics.types.iter()
                                            .any(|ty_param| {
@@ -5095,7 +5097,11 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
 
                 err.emit();
             }
+
+            impl_trait
         });
+
+        segment.unwrap_or(false)
     }
 
     // Resolves `typ` by a single level if `typ` is a type variable.

src/test/ui/impl-trait/universal-issue-48703.rs

@@ -0,0 +1,19 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(universal_impl_trait)]
+
+use std::fmt::Debug;
+
+fn foo<T>(x: impl Debug) { }
+
+fn main() {
+    foo::<String>('a'); //~ ERROR cannot provide explicit type parameters
+}

src/test/ui/impl-trait/universal-issue-48703.stderr

@@ -0,0 +1,9 @@
+error[E0632]: cannot provide explicit type parameters when `impl Trait` is used in argument position.
+  --> $DIR/universal-issue-48703.rs:18:5
+   |
+LL |     foo::<String>('a'); //~ ERROR cannot provide explicit type parameters
+   |     ^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0632`.