Suggested trait implementation ordering is now deterministic.

Author: davidtwco

src/librustc/traits/error_reporting.rs

@@ -435,13 +435,14 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     }
 
     fn report_similar_impl_candidates(&self,
-                                      impl_candidates: Vec<ty::TraitRef<'tcx>>,
+                                      mut impl_candidates: Vec<ty::TraitRef<'tcx>>,
                                       err: &mut DiagnosticBuilder)
     {
         if impl_candidates.is_empty() {
             return;
         }
 
+        let len = impl_candidates.len();
         let end = if impl_candidates.len() <= 5 {
             impl_candidates.len()
         } else {
@@ -459,10 +460,17 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             }
         });
 
+        // Sort impl candidates so that ordering is consistent for UI tests.
+        let normalized_impl_candidates = &mut impl_candidates[0..end]
+            .iter()
+            .map(normalize)
+            .collect::<Vec<String>>();
+        normalized_impl_candidates.sort();
+
         err.help(&format!("the following implementations were found:{}{}",
-                          &impl_candidates[0..end].iter().map(normalize).collect::<String>(),
-                          if impl_candidates.len() > 5 {
-                              format!("\nand {} others", impl_candidates.len() - 4)
+                          normalized_impl_candidates.join(""),
+                          if len > 5 {
+                              format!("\nand {} others", len - 4)
                           } else {
                               "".to_owned()
                           }

src/test/ui/catch/catch-bad-type.stderr

@@ -5,10 +5,10 @@ LL |         Err("")?; //~ ERROR the trait bound `i32: std::convert::From<&str>`
    |         ^^^^^^^^ the trait `std::convert::From<&str>` is not implemented for `i32`
    |
    = help: the following implementations were found:
-             <i32 as std::convert::From<u16>>
              <i32 as std::convert::From<bool>>
              <i32 as std::convert::From<i16>>
              <i32 as std::convert::From<i8>>
+             <i32 as std::convert::From<u16>>
              <i32 as std::convert::From<u8>>
    = note: required by `std::convert::From::from`
 

src/test/ui/did_you_mean/issue-21659-show-relevant-trait-impls-2.stderr

@@ -5,9 +5,9 @@ LL |     f1.foo(1usize);
    |        ^^^ the trait `Foo<usize>` is not implemented for `Bar`
    |
    = help: the following implementations were found:
-             <Bar as Foo<i8>>
              <Bar as Foo<i16>>
              <Bar as Foo<i32>>
+             <Bar as Foo<i8>>
              <Bar as Foo<u8>>
            and 2 others
 

src/test/ui/did_you_mean/issue-39802-show-5-trait-impls.stderr

@@ -5,11 +5,11 @@ LL |     Foo::<i32>::bar(&1i8); //~ ERROR is not satisfied
    |     ^^^^^^^^^^^^^^^ the trait `Foo<i32>` is not implemented for `i8`
    |
    = help: the following implementations were found:
-             <i8 as Foo<u8>>
+             <i8 as Foo<bool>>
              <i8 as Foo<u16>>
              <i8 as Foo<u32>>
              <i8 as Foo<u64>>
-             <i8 as Foo<bool>>
+             <i8 as Foo<u8>>
 note: required by `Foo::bar`
   --> $DIR/issue-39802-show-5-trait-impls.rs:12:5
    |
@@ -23,10 +23,10 @@ LL |     Foo::<i32>::bar(&1u8); //~ ERROR is not satisfied
    |     ^^^^^^^^^^^^^^^ the trait `Foo<i32>` is not implemented for `u8`
    |
    = help: the following implementations were found:
+             <u8 as Foo<bool>>
              <u8 as Foo<u16>>
              <u8 as Foo<u32>>
              <u8 as Foo<u64>>
-             <u8 as Foo<bool>>
 note: required by `Foo::bar`
   --> $DIR/issue-39802-show-5-trait-impls.rs:12:5
    |
@@ -40,10 +40,10 @@ LL |     Foo::<i32>::bar(&true); //~ ERROR is not satisfied
    |     ^^^^^^^^^^^^^^^ the trait `Foo<i32>` is not implemented for `bool`
    |
    = help: the following implementations were found:
-             <bool as Foo<u8>>
              <bool as Foo<u16>>
              <bool as Foo<u32>>
              <bool as Foo<u64>>
+             <bool as Foo<u8>>
            and 2 others
 note: required by `Foo::bar`
   --> $DIR/issue-39802-show-5-trait-impls.rs:12:5