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Provide structured suggestion for type mismatch in loop #118072

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merged 1 commit into from Dec 3, 2023

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estebank
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@estebank estebank commented Nov 19, 2023

We currently provide only a help message, this PR introduces the last two structured suggestions instead:

error[E0308]: mismatched types
  --> $DIR/issue-98982.rs:2:5
   |
LL |   fn foo() -> i32 {
   |               --- expected `i32` because of return type
LL | /     for i in 0..0 {
LL | |         return i;
LL | |     }
   | |_____^ expected `i32`, found `()`
   |
note: the function expects a value to always be returned, but loops might run zero times
  --> $DIR/issue-98982.rs:2:5
   |
LL |     for i in 0..0 {
   |     ^^^^^^^^^^^^^ this might have zero elements to iterate on
LL |         return i;
   |         -------- if the loop doesn't execute, this value would never get returned
help: return a value for the case when the loop has zero elements to iterate on
   |
LL ~     }
LL ~     /* `i32` value */
   |
help: otherwise consider changing the return type to account for that possibility
   |
LL ~ fn foo() -> Option<i32> {
LL |     for i in 0..0 {
LL ~         return Some(i);
LL ~     }
LL ~     None
   |

Fix #98982.

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rustbot commented Nov 19, 2023

r? @cjgillot

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@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Nov 19, 2023
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Did you forget part of the commit?

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@cjgillot I apparently had not staged the changes I wanted 😅

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bors commented Nov 22, 2023

☔ The latest upstream changes (presumably #118143) made this pull request unmergeable. Please resolve the merge conflicts.

We currently provide only a `help` message, this PR introduces the last
two structured suggestions instead:

```
error[E0308]: mismatched types
  --> $DIR/issue-98982.rs:2:5
   |
LL |   fn foo() -> i32 {
   |               --- expected `i32` because of return type
LL | /     for i in 0..0 {
LL | |         return i;
LL | |     }
   | |_____^ expected `i32`, found `()`
   |
note: the function expects a value to always be returned, but loops might run zero times
  --> $DIR/issue-98982.rs:2:5
   |
LL |     for i in 0..0 {
   |     ^^^^^^^^^^^^^ this might have zero elements to iterate on
LL |         return i;
   |         -------- if the loop doesn't execute, this value would never get returned
help: return a value for the case when the loop has zero elements to iterate on
   |
LL ~     }
LL ~     /* `i32` value */
   |
help: otherwise consider changing the return type to account for that possibility
   |
LL ~ fn foo() -> Option<i32> {
LL |     for i in 0..0 {
LL ~         return Some(i);
LL ~     }
LL ~     None
   |
```

Fix rust-lang#98982.
LL | for i in 0..0 {
LL | if n < 0 {
LL ~ return Some(i);
LL | } else if n < 10 {
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The indentation looks weird.

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I just saw, preexisting.

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cjgillot commented Dec 3, 2023

@bors r+

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bors commented Dec 3, 2023

📌 Commit 45efb8e has been approved by cjgillot

It is now in the queue for this repository.

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Dec 3, 2023
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bors commented Dec 3, 2023

⌛ Testing commit 45efb8e with merge d12dc74...

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bors commented Dec 3, 2023

☀️ Test successful - checks-actions
Approved by: cjgillot
Pushing d12dc74 to master...

@bors bors added the merged-by-bors This PR was explicitly merged by bors. label Dec 3, 2023
@bors bors merged commit d12dc74 into rust-lang:master Dec 3, 2023
12 checks passed
@rustbot rustbot added this to the 1.76.0 milestone Dec 3, 2023
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Finished benchmarking commit (d12dc74): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

mean range count
Regressions ❌
(primary)
- - 0
Regressions ❌
(secondary)
- - 0
Improvements ✅
(primary)
-2.7% [-2.7%, -2.7%] 1
Improvements ✅
(secondary)
- - 0
All ❌✅ (primary) -2.7% [-2.7%, -2.7%] 1

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

mean range count
Regressions ❌
(primary)
- - 0
Regressions ❌
(secondary)
2.4% [2.2%, 2.7%] 8
Improvements ✅
(primary)
- - 0
Improvements ✅
(secondary)
-3.0% [-3.6%, -2.7%] 6
All ❌✅ (primary) - - 0

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 673.68s -> 673.016s (-0.10%)
Artifact size: 314.11 MiB -> 314.11 MiB (-0.00%)

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Detect type mismatch due to loop that might never iterate
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