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

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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

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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

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isaacg1 commented Feb 21, 2021 • edited by rustbot Loading

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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

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