Incorrect help text when `if` and `else` differ by reference #82361

isaacg1 · 2021-02-21T07:47:09Z

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.

The text was updated successfully, but these errors were encountered:

osa1 · 2021-02-21T09:23:08Z

@rustbot claim

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

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`

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``

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```

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````

isaacg1 added the C-bug Category: This is a bug. label Feb 21, 2021

rustbot assigned osa1 Feb 21, 2021

osa1 mentioned this issue Feb 21, 2021

Improve error msgs when found type is deref of expected #82364

Merged

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

estebank added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Feb 24, 2021

bors closed this as completed in fa74d48 Feb 25, 2021

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Incorrect help text when `if` and `else` differ by reference #82361

Incorrect help text when `if` and `else` differ by reference #82361

isaacg1 commented Feb 21, 2021 •

edited by rustbot

Loading

osa1 commented Feb 21, 2021

Incorrect help text when if and else differ by reference #82361

Incorrect help text when if and else differ by reference #82361

Comments

isaacg1 commented Feb 21, 2021 • edited by rustbot Loading

Meta

osa1 commented Feb 21, 2021

Incorrect help text when `if` and `else` differ by reference #82361

Incorrect help text when `if` and `else` differ by reference #82361

isaacg1 commented Feb 21, 2021 •

edited by rustbot

Loading