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Rollup merge of #82364 - osa1:issue82361, r=estebank

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Improve error msgs when found type is deref of expected

This improves help messages in two cases:

- When expected type is `T` and found type is `&T`, we now look through blocks
  and suggest dereferencing the expression of the block, rather than the whole
  block.

- In the above case, if the expression is an `&`, we not suggest removing the
  `&` instead of adding `*`.

Both of these are demonstrated in the regression test. Before this patch the
first error in the test would be:

    error[E0308]: `if` and `else` have incompatible types
     --> test.rs:8:9
      |
    5 | /     if true {
    6 | |         a
      | |         - expected because of this
    7 | |     } else {
    8 | |         b
      | |         ^ expected `usize`, found `&usize`
    9 | |     };
      | |_____- `if` and `else` have incompatible types
      |
    help: consider dereferencing the borrow
      |
    7 |     } else *{
    8 |         b
    9 |     };
      |

Now:

    error[E0308]: `if` and `else` have incompatible types
     --> test.rs:8:9
      |
    5 | /     if true {
    6 | |         a
      | |         - expected because of this
    7 | |     } else {
    8 | |         b
      | |         ^
      | |         |
      | |         expected `usize`, found `&usize`
      | |         help: consider dereferencing the borrow: `*b`
    9 | |     };
      | |_____- `if` and `else` have incompatible types

The second error:

    error[E0308]: `if` and `else` have incompatible types
      --> test.rs:14:9
       |
    11 | /     if true {
    12 | |         1
       | |         - expected because of this
    13 | |     } else {
    14 | |         &1
       | |         ^^ expected integer, found `&{integer}`
    15 | |     };
       | |_____- `if` and `else` have incompatible types
       |
    help: consider dereferencing the borrow
       |
    13 |     } else *{
    14 |         &1
    15 |     };
       |

now:

    error[E0308]: `if` and `else` have incompatible types
      --> test.rs:14:9
       |
    11 | /     if true {
    12 | |         1
       | |         - expected because of this
    13 | |     } else {
    14 | |         &1
       | |         ^-
       | |         ||
       | |         |help: consider removing the `&`: `1`
       | |         expected integer, found `&{integer}`
    15 | |     };
       | |_____- `if` and `else` have incompatible types

Fixes #82361

---

r? ````@estebank````
This commit is contained in:
Dylan DPC 2021-02-25 14:34:04 +01:00 • committed by GitHub
commit 12ea0f6112
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5 changed files with 128 additions and 4 deletions
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24
src/test/ui/suggestions/issue-82361.fixed Normal file
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@ -0,0 +1,24 @@
// run-rustfix
fn main() {
let a: usize = 123;
let b: &usize = &a;
if true {
a
} else {
*b //~ ERROR `if` and `else` have incompatible types [E0308]
};
if true {
1
} else {
1 //~ ERROR `if` and `else` have incompatible types [E0308]
};
if true {
1
} else {
1 //~ ERROR `if` and `else` have incompatible types [E0308]
};
}

24
src/test/ui/suggestions/issue-82361.rs Normal file
View file

@ -0,0 +1,24 @@
// run-rustfix
fn main() {
let a: usize = 123;
let b: &usize = &a;
if true {
a
} else {
b //~ ERROR `if` and `else` have incompatible types [E0308]
};
if true {
1
} else {
&1 //~ ERROR `if` and `else` have incompatible types [E0308]
};
if true {
1
} else {
&mut 1 //~ ERROR `if` and `else` have incompatible types [E0308]
};
}

48
src/test/ui/suggestions/issue-82361.stderr Normal file
View file

@ -0,0 +1,48 @@
error[E0308]: `if` and `else` have incompatible types
--> $DIR/issue-82361.rs:10:9
|
LL | / if true {
LL | | a
| | - expected because of this
LL | | } else {
LL | | b
| | ^
| | |
| | expected `usize`, found `&usize`
| | help: consider dereferencing the borrow: `*b`
LL | | };
| |_____- `if` and `else` have incompatible types
error[E0308]: `if` and `else` have incompatible types
--> $DIR/issue-82361.rs:16:9
|
LL | / if true {
LL | | 1
| | - expected because of this
LL | | } else {
LL | | &1
| | -^
| | |
| | expected integer, found `&{integer}`
| | help: consider removing the `&`
LL | | };
| |_____- `if` and `else` have incompatible types
error[E0308]: `if` and `else` have incompatible types
--> $DIR/issue-82361.rs:22:9
|
LL | / if true {
LL | | 1
| | - expected because of this
LL | | } else {
LL | | &mut 1
| | -----^
| | |
| | expected integer, found `&mut {integer}`
| | help: consider removing the `&mut`
LL | | };
| |_____- `if` and `else` have incompatible types
error: aborting due to 3 previous errors
For more information about this error, try `rustc --explain E0308`.