Auto merge of #44866 - mdevlamynck:impl-trait, r=eddyb

First step toward implementing impl Trait in argument position

First step implementing #44721.

Add a flag to hir and ty TypeParameterDef and raise an error when using
explicit type parameters when calling a function using impl Trait in
argument position.

I don't know if there is a procedure to add an error code so I just took an available code. Is that ok ?

r? @nikomatsakis

1 files changed, 38 insertions, 0 deletions

diff --git a/src/test/compile-fail/synthetic-param.rs b/src/test/compile-fail/synthetic-param.rs
new file mode 100644
index 00000000000..a9762e383fe
--- /dev/null
+++ b/src/test/compile-fail/synthetic-param.rs
@@ -0,0 +1,38 @@
+// Copyright 2015 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(generic_param_attrs, rustc_attrs)]
+
+fn func<#[rustc_synthetic] T>(_: T) {}
+
+struct Foo;
+
+impl Foo {
+    pub fn func<#[rustc_synthetic] T>(_: T) {}
+}
+
+struct Bar<S> {
+    t: S
+}
+
+impl<S> Bar<S> {
+    pub fn func<#[rustc_synthetic] T>(_: T) {}
+}
+
+fn main() {
+    func::<u8>(42); //~ ERROR cannot provide explicit type parameters
+    func(42); // Ok
+
+    Foo::func::<u8>(42); //~ ERROR cannot provide explicit type parameters
+    Foo::func(42); // Ok
+
+    Bar::<i8>::func::<u8>(42); //~ ERROR cannot provide explicit type parameters
+    Bar::<i8>::func(42); // Ok
+}