Add more detail to type inference error

When encountering code where type inference fails, add more actionable
information:

```
fn main() {
    let foo = Vec::new();
}
```

```
error[E0282]: type annotations needed for `std::vec::Vec<_>`
  --> $DIR/vector-no-ann.rs:2:16
   |
LL |     let foo = Vec::new();
   |         ---   ^^^^^^^^ cannot infer type for `T`
   |         |
   |         consider giving `foo` the type `std::vec::Vec<_>` with the type parameter `T` specified
```

We still need to modify type printing to optionally accept a
`TypeVariableTable` in order to properly print `std::vec::Vec<T>`.

CC #25633.

2 files changed, 3 insertions, 3 deletions

diff --git a/src/test/ui/methods/method-ambig-one-trait-unknown-int-type.rs b/src/test/ui/methods/method-ambig-one-trait-unknown-int-type.rs
index 590e98dc353..e33f23c64db 100644
--- a/src/test/ui/methods/method-ambig-one-trait-unknown-int-type.rs
+++ b/src/test/ui/methods/method-ambig-one-trait-unknown-int-type.rs
@@ -22,7 +22,7 @@ impl Foo for Vec<isize> {
 fn m1() {
     // we couldn't infer the type of the vector just based on calling foo()...
     let mut x = Vec::new();
-    //~^ ERROR type annotations needed [E0282]
+    //~^ ERROR type annotations needed
     x.foo();
 }
 
diff --git a/src/test/ui/methods/method-ambig-one-trait-unknown-int-type.stderr b/src/test/ui/methods/method-ambig-one-trait-unknown-int-type.stderr
index 063a4865b19..bae675526bd 100644
--- a/src/test/ui/methods/method-ambig-one-trait-unknown-int-type.stderr
+++ b/src/test/ui/methods/method-ambig-one-trait-unknown-int-type.stderr
@@ -1,10 +1,10 @@
-error[E0282]: type annotations needed
+error[E0282]: type annotations needed for `std::vec::Vec<_>`
   --> $DIR/method-ambig-one-trait-unknown-int-type.rs:24:17
    |
 LL |     let mut x = Vec::new();
    |         -----   ^^^^^^^^ cannot infer type for `T`
    |         |
-   |         consider giving `x` a type
+   |         consider giving `x` the type `std::vec::Vec<_>` with the type parameter `T` specified
 
 error[E0308]: mismatched types
   --> $DIR/method-ambig-one-trait-unknown-int-type.rs:33:20