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Auto merge of #46461 - zackmdavis:elemental_method_suggestion_jamboree, r=estebank

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type error method suggestions use whitelisted identity-like conversions

![method_jamboree_summit](https://user-images.githubusercontent.com/1076988/33523646-e5c43184-d7c0-11e7-98e5-1bff426ade86.png)

Previously, on a type mismatch (and if this wasn't preëmpted by a
higher-priority suggestion), we would look for argumentless methods
returning the expected type, and list them in a `help` note. This had two
major shortcomings: firstly, a lot of the suggestions didn't really make
sense (if you used a &str where a String was expected,
`.to_ascii_uppercase()` is probably not the solution you were hoping
for). Secondly, we weren't generating suggestions from the most useful
traits! We address the first problem with an internal
`#[rustc_conversion_suggestion]` attribute meant to mark methods that keep
the "same value" in the relevant sense, just converting the type. We
address the second problem by making `FnCtxt.probe_for_return_type` pass
the `ProbeScope::AllTraits` to `probe_op`: this would seem to be safe
because grep reveals no other callers of `probe_for_return_type`.

Also, structured suggestions are pretty and good for RLS and friends.

Unfortunately, the trait probing is still not all one would hope for: at a
minimum, we don't know how to rule out `into()` in cases where it wouldn't
actually work, and we don't know how to rule in `.to_owned()` where it
would. Issues #46459 and #46460 have been filed and are ref'd in a FIXME.

This is hoped to resolve #42929, #44672, and #45777.
This commit is contained in:
bors 2018-01-13 02:15:19 +00:00
commit 6eff103aa1
14 changed files with 147 additions and 65 deletions
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11
src/test/ui/deref-suggestion.stderr
View file

@ -2,16 +2,13 @@ error[E0308]: mismatched types
--> $DIR/deref-suggestion.rs:18:9
|
18 | foo(s); //~ ERROR mismatched types
| ^ expected struct `std::string::String`, found reference
| ^
| |
| expected struct `std::string::String`, found reference
| help: try using a conversion method: `s.to_string()`
|
= note: expected type `std::string::String`
found type `&std::string::String`
= help: here are some functions which might fulfill your needs:
- .escape_debug()
- .escape_default()
- .escape_unicode()
- .to_ascii_lowercase()
- .to_ascii_uppercase()
error[E0308]: mismatched types
--> $DIR/deref-suggestion.rs:23:10

4
src/test/ui/did_you_mean/recursion_limit_deref.stderr
View file

@ -4,11 +4,11 @@ error[E0055]: reached the recursion limit while auto-dereferencing I
62 | let x: &Bottom = &t; //~ ERROR mismatched types
| ^^ deref recursion limit reached
|
= help: consider adding a `#[recursion_limit="20"]` attribute to your crate
= help: consider adding a `#![recursion_limit="20"]` attribute to your crate
error[E0055]: reached the recursion limit while auto-dereferencing I
|
= help: consider adding a `#[recursion_limit="20"]` attribute to your crate
= help: consider adding a `#![recursion_limit="20"]` attribute to your crate
error[E0308]: mismatched types
--> $DIR/recursion_limit_deref.rs:62:22

8
src/test/ui/span/coerce-suggestions.stderr
View file

@ -6,9 +6,6 @@ error[E0308]: mismatched types
|
= note: expected type `usize`
found type `std::string::String`
= help: here are some functions which might fulfill your needs:
- .capacity()
- .len()
error[E0308]: mismatched types
--> $DIR/coerce-suggestions.rs:19:19
@ -44,7 +41,10 @@ error[E0308]: mismatched types
--> $DIR/coerce-suggestions.rs:27:9
|
27 | f = box f;
| ^^^^^ cyclic type of infinite size
| ^^^^^
| |
| cyclic type of infinite size
| help: try using a conversion method: `box f.to_string()`
error[E0308]: mismatched types
--> $DIR/coerce-suggestions.rs:31:9

2
src/test/ui/span/issue-34264.stderr
View file

@ -33,8 +33,6 @@ error[E0308]: mismatched types
|
= note: expected type `usize`
found type `&'static str`
= help: here are some functions which might fulfill your needs:
- .len()
error[E0061]: this function takes 2 parameters but 3 parameters were supplied
--> $DIR/issue-34264.rs:20:5

23
src/test/ui/suggestions/conversion-methods.rs Normal file
View file

@ -0,0 +1,23 @@
// Copyright 2017 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.
use std::path::{Path, PathBuf};
fn main() {
let _tis_an_instants_play: String = "'Tis a fond Ambush—"; //~ ERROR mismatched types
let _just_to_make_bliss: PathBuf = Path::new("/ern/her/own/surprise");
//~^ ERROR mismatched types
let _but_should_the_play: String = 2; // Perhaps surprisingly, we suggest .to_string() here
//~^ ERROR mismatched types
let _prove_piercing_earnest: Vec<usize> = &[1, 2, 3]; //~ ERROR mismatched types
}

50
src/test/ui/suggestions/conversion-methods.stderr Normal file
View file

@ -0,0 +1,50 @@
error[E0308]: mismatched types
--> $DIR/conversion-methods.rs:15:41
|
15 | let _tis_an_instants_play: String = "'Tis a fond Ambush—"; //~ ERROR mismatched types
| ^^^^^^^^^^^^^^^^^^^^^
| |
| expected struct `std::string::String`, found reference
| help: try using a conversion method: `"'Tis a fond Ambush—".to_string()`
|
= note: expected type `std::string::String`
found type `&'static str`
error[E0308]: mismatched types
--> $DIR/conversion-methods.rs:16:40
|
16 | let _just_to_make_bliss: PathBuf = Path::new("/ern/her/own/surprise");
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| |
| expected struct `std::path::PathBuf`, found reference
| help: try using a conversion method: `Path::new("/ern/her/own/surprise").to_path_buf()`
|
= note: expected type `std::path::PathBuf`
found type `&std::path::Path`
error[E0308]: mismatched types
--> $DIR/conversion-methods.rs:19:40
|
19 | let _but_should_the_play: String = 2; // Perhaps surprisingly, we suggest .to_string() here
| ^
| |
| expected struct `std::string::String`, found integral variable
| help: try using a conversion method: `2.to_string()`
|
= note: expected type `std::string::String`
found type `{integer}`
error[E0308]: mismatched types
--> $DIR/conversion-methods.rs:22:47
|
22 | let _prove_piercing_earnest: Vec<usize> = &[1, 2, 3]; //~ ERROR mismatched types
| ^^^^^^^^^^
| |
| expected struct `std::vec::Vec`, found reference
| help: try using a conversion method: `&[1, 2, 3].to_vec()`
|
= note: expected type `std::vec::Vec<usize>`
found type `&[{integer}; 3]`
error: aborting due to 4 previous errors