Rollup merge of rust-lang#49262 - oli-obk:fixed_size_array_len, r=est…

…ebank

Produce nice array lengths on a best effort basis

fixes rust-lang#49208

r? @estebank

src/librustc/traits/error_reporting.rs

@@ -443,10 +443,20 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
  } else {
  4
  };
+
+ let normalize = |candidate| self.tcx.global_tcx().infer_ctxt().enter(|ref infcx| {
+ let normalized = infcx
+ .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
+ .normalize(candidate)
+ .ok();
+ match normalized {
+ Some(normalized) => format!("\n {:?}", normalized.value),
+ None => format!("\n {:?}", candidate),
+ }
+ });
+
  err.help(&format!("the following implementations were found:{}{}",
- &impl_candidates[0..end].iter().map(|candidate| {
- format!("\n {:?}", candidate)
- }).collect::<String>(),
+ &impl_candidates[0..end].iter().map(normalize).collect::<String>(),
  if impl_candidates.len() > 5 {
  format!("\nand {} others", impl_candidates.len() - 4)
  } else {

src/librustc/ty/sty.rs

@@ -1670,7 +1670,6 @@ impl<'a, 'gcx, 'tcx> TyS<'tcx> {
 pub struct Const<'tcx> {
  pub ty: Ty<'tcx>,
 
- // FIXME(eddyb) Replace this with a miri value.
  pub val: ConstVal<'tcx>,
 }
 

src/librustc/util/ppaux.rs

@@ -1177,8 +1177,8 @@ define_print! {
  ConstVal::Value(Value::ByVal(PrimVal::Bytes(sz))) => {
  write!(f, "{}", sz)?;
  }
- ConstVal::Unevaluated(_def_id, substs) => {
- write!(f, "<unevaluated{:?}>", &substs[..])?;
+ ConstVal::Unevaluated(_def_id, _substs) => {
+ write!(f, "_")?;
  }
  _ => {
  write!(f, "{:?}", sz)?;

src/test/ui/did_you_mean/bad-assoc-ty.stderr

@@ -46,7 +46,7 @@ error[E0223]: ambiguous associated type
 LL | type A = [u8; 4]::AssocTy;
  | ^^^^^^^^^^^^^^^^ ambiguous associated type
  |
- = note: specify the type using the syntax `<[u8; <unevaluated[]>] as Trait>::AssocTy`
+ = note: specify the type using the syntax `<[u8; _] as Trait>::AssocTy`
 
 error[E0223]: ambiguous associated type
  --> $DIR/bad-assoc-ty.rs:15:10

src/test/ui/unevaluated_fixed_size_array_len.rs

@@ -0,0 +1,23 @@
+// Copyright 2018 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.
+
+// https://github.com/rust-lang/rust/issues/49208
+
+trait Foo {
+ fn foo();
+}
+
+impl Foo for [(); 1] {
+ fn foo() {}
+}
+
+fn main() {
+ <[(); 0] as Foo>::foo() //~ ERROR E0277
+}

src/test/ui/unevaluated_fixed_size_array_len.stderr

@@ -0,0 +1,17 @@
+error[E0277]: the trait bound `[(); 0]: Foo` is not satisfied
+ --> $DIR/unevaluated_fixed_size_array_len.rs:22:5
+ |
+LL | <[(); 0] as Foo>::foo() //~ ERROR E0277
+ | ^^^^^^^^^^^^^^^^^^^^^ the trait `Foo` is not implemented for `[(); 0]`
+ |
+ = help: the following implementations were found:
+ <[(); 1] as Foo>
+note: required by `Foo::foo`
+ --> $DIR/unevaluated_fixed_size_array_len.rs:14:5
+ |
+LL | fn foo();
+ | ^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.