Improve parsing errors and suggestions for bad if statements
#97474
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oof yea, nonsense code, but should still parse and compile. I liked how the parser code actually got more readable with your changes. Anyway, I think we should merge this as is, but since it affects what code is accepted, cc @rust-lang/wg-diagnostics @rust-lang/compiler for visibility. Will merge this next week unless there are complaints. I think this is a minor bugfix that reverts a previous accidental breaking change, so we don't need to MCP this for any team. |
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☔ The latest upstream changes (presumably #97497) made this pull request unmergeable. Please resolve the merge conflicts. |
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@oli-obk this is ready to r+, I think! |
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@bors r+ |
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📌 Commit d1ba2d2 has been approved by |
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…r=oli-obk
Improve parsing errors and suggestions for bad `if` statements
1. Parses `if {}` as `if <err> {}` (block-like conditions that are missing a "then" block), and `if true && {}` as `if true && <err> {}` (unfinished binary operation), which is a more faithful recovery and leads to better typeck errors later on.
1. Points out the span of the condition if we don't see a "then" block after it, to help the user understand what is being parsed as a condition (and by elimination, what isn't).
1. Allow `if cond token else { }` to be fixed properly to `if cond { token } else { }`.
1. Fudge with the error messages a bit. This is somewhat arbitrary and I can revert my rewordings if they're useless.
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Also this PR addresses a strange parsing regression (1.20 -> 1.21) where we chose to reject this piece of code somewhat arbitrarily, even though we should parse it fine:
```rust
fn main() {
if { if true { return } else { return }; } {}
}
```
For context, all of these other expressions parse correctly:
```rust
fn main() {
if { if true { return } else { return } } {}
if { return; } {}
if { return } {}
if { return if true { } else { }; } {}
}
```
The parser used a heuristic to determine if the "the parsed `if` condition makes sense as a condition" that did like a one-expr-deep reachability analysis. This should not be handled by the parser though.
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☀️ Test successful - checks-actions |
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Finished benchmarking commit (ddb6cc8): comparison url. Instruction countThis benchmark run did not return any relevant results for this metric. Max RSS (memory usage)Results
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If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf. @rustbot label: -perf-regression Footnotes |
…, r=fee1-dead Remove an unused parser function (`Expr::returns`) I removed the only usage in rust-lang#97474
if {}asif <err> {}(block-like conditions that are missing a "then" block), andif true && {}asif true && <err> {}(unfinished binary operation), which is a more faithful recovery and leads to better typeck errors later on.if cond token else { }to be fixed properly toif cond { token } else { }.Also this PR addresses a strange parsing regression (1.20 -> 1.21) where we chose to reject this piece of code somewhat arbitrarily, even though we should parse it fine:
For context, all of these other expressions parse correctly:
The parser used a heuristic to determine if the "the parsed
ifcondition makes sense as a condition" that did like a one-expr-deep reachability analysis. This should not be handled by the parser though.