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isaacg1 opened this issue Feb 21, 2021 · 1 comment · Fixed by #82364
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Incorrect help text when if and else differ by reference #82361

isaacg1 opened this issue Feb 21, 2021 · 1 comment · Fixed by #82364
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@osa1
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A-suggestion-diagnostics Area: Suggestions generated by the compiler applied by `cargo fix` C-bug Category: This is a bug. D-invalid-suggestion Diagnostics: A structured suggestion resulting in incorrect code. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@isaacg1
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isaacg1 commented Feb 21, 2021 •
edited by rustbot
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I tried this code:

fn main() {
    if true {
        1
    } else {
        &1
    };
}

I expected to see this happen: I expected that the help text would give syntactically correct code, or that there would be no help text.

Instead, this happened:

help: consider dereferencing the borrow
  |
4 |     } else *{
5 |         &1
6 |     };
  |

The provided code snippet is not valid - it tries to deference the else-block, which is impossible. Better would be to put the * inside the else-block.

Meta

rustc --version --verbose:

rustc 1.52.0-nightly (83b30a639 2021-02-20)
binary: rustc
commit-hash: 83b30a639d5abd1270ade35d9bd92271f5a5ba18
commit-date: 2021-02-20
host: x86_64-unknown-linux-gnu
release: 1.52.0-nightly
LLVM version: 11.0.1

Also occurs on stable, 1.50.0.
@isaacg1 isaacg1 added the C-bug Category: This is a bug. label Feb 21, 2021
@osa1
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osa1 commented Feb 21, 2021

@rustbot claim

I have a fix for this bug + an improvement. Gotta got for now but will submit the PR later today.

@osa1 osa1 mentioned this issue Feb 21, 2021
Merged
@jonas-schievink jonas-schievink added A-suggestion-diagnostics Area: Suggestions generated by the compiler applied by `cargo fix` D-invalid-suggestion Diagnostics: A structured suggestion resulting in incorrect code. labels Feb 21, 2021
Dylan-DPC-zz pushed a commit to Dylan-DPC-zz/rust that referenced this issue Feb 24, 2021
@Dylan-DPC
Rollup merge of rust-lang#82364 - osa1:issue82361, r=estebank
92fd02d 
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 rust-lang#82361

---

r? `@estebank`
Dylan-DPC-zz pushed a commit to Dylan-DPC-zz/rust that referenced this issue Feb 24, 2021
@Dylan-DPC
Rollup merge of rust-lang#82364 - osa1:issue82361, r=estebank
b0458bc 
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 rust-lang#82361

---

r? ``@estebank``
@estebank estebank added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Feb 24, 2021
Dylan-DPC-zz pushed a commit to Dylan-DPC-zz/rust that referenced this issue Feb 24, 2021
@Dylan-DPC
Rollup merge of rust-lang#82364 - osa1:issue82361, r=estebank
3feed61 
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 rust-lang#82361

---

r? ```@estebank```
Dylan-DPC-zz pushed a commit to Dylan-DPC-zz/rust that referenced this issue Feb 25, 2021
@Dylan-DPC
Rollup merge of rust-lang#82364 - osa1:issue82361, r=estebank
12ea0f6 
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 rust-lang#82361

---

r? ````@estebank````
@bors bors closed this as completed in fa74d48 Feb 25, 2021
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A-suggestion-diagnostics Area: Suggestions generated by the compiler applied by `cargo fix` C-bug Category: This is a bug. D-invalid-suggestion Diagnostics: A structured suggestion resulting in incorrect code. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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Improve error msgs when found type is deref of expected
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@osa1 @estebank @jonas-schievink @isaacg1