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Unary tuples printed as (T) instead of (T,) #18426

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neuschaefer opened this issue Oct 29, 2014 · 0 comments · Fixed by #18264
Closed

Unary tuples printed as (T) instead of (T,) #18426

neuschaefer opened this issue Oct 29, 2014 · 0 comments · Fixed by #18264

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@neuschaefer
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$ cat tuple.rs
fn main() {
    let _: uint = (1u,);
}
$ rustc tuple.rs
tuple.rs:2:19: 2:24 error: mismatched types: expected `uint` but found `(uint)` (expected uint but found tuple)
tuple.rs:2     let _: uint = (1u,);
                             ^~~~~
error: aborting due to previous error
@ghost ghost mentioned this issue Oct 29, 2014
Merged
bors added a commit that referenced this issue Oct 31, 2014
@bors
auto merge of #18264 : jakub-/rust/var-ids-in-error-messages, r=nikom…
82045ca 
…atsakis

This PR aims to improve the readability of diagnostic messages that involve unresolved type variables. Currently, messages like the following:

```rust
mismatched types: expected `core::result::Result<uint,()>`, found `core::option::Option<<generic #1>>`
<anon>:6     let a: Result<uint, ()> = None;
                                       ^~~~
mismatched types: expected `&mut <generic #2>`, found `uint`
<anon>:7     f(42u);
               ^~~
```

tend to appear unapproachable to new users. [0] While specific type var IDs are valuable in
diagnostics that deal with more than one such variable, in practice many messages
only mention one. In those cases, leaving out the specific number makes the messages
slightly less terrifying.

```rust
mismatched types: expected `core::result::Result<uint, ()>`, found `core::option::Option<_>`
<anon>:6     let a: Result<uint, ()> = None;
                                       ^~~~
mismatched types: expected `&mut _`, found `uint`
<anon>:7     f(42u);
               ^~~
```

As you can see, I also tweaked the aesthetics slightly by changing type variables to use the type hole syntax _. For integer variables, the syntax used is:

```rust
mismatched types: expected `core::result::Result<uint, ()>`, found `core::option::Option<_#1i>`
<anon>:6     let a: Result<uint, ()> = Some(1);
```

and float variables:

```rust
mismatched types: expected `core::result::Result<uint, ()>`, found `core::option::Option<_#1f>`
<anon>:6     let a: Result<uint, ()> = Some(0.5);
```

[0] https://twitter.com/coda/status/517713085465772032

Closes #2632.
Closes #3404.
Closes #18426.
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Change the way type variables are printed in diagnostics
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@neuschaefer