Further improve diagnostics for expressions in pattern position #123877

ShE3py · 2024-04-13T00:09:14Z

fn main() {
    match 'b' {
        y.0.0.1.z().f()? as u32 => {},
    }
}

Before:

error: expected one of `=>`, `@`, `if`, or `|`, found `.`
 --> src/main.rs:3:10
  |
3 |         y.0.0.1.z().f()? as u32 => {},
  |          ^ expected one of `=>`, `@`, `if`, or `|`

After:

error: expected a pattern, found an expression
 --> src/main.rs:3:9
  |
3 |         y.0.0.1.z().f()? as u32 => {},
  |         ^^^^^^^^^^^^^^^^^^^^^^^ arbitrary expressions are not allowed in patterns
  |
help: consider moving the expression to a match arm guard
  |
3 |         val if val == y.0.0.1.z().f()? as u32 => {},
  |         ~~~ +++++++++++++++++++++++++++++++++
help: consider extracting the expression into a `const`
  |
2 +     const VAL: /* Type */ = y.0.0.1.z().f()? as u32;
3 ~     match 'b' {
4 ~         VAL => {},
  |
help: consider wrapping the expression in an inline `const` (requires `#![feature(inline_const_pat)]`)
  |
3 |         const { y.0.0.1.z().f()? as u32 } => {},
  |         +++++++                         +

r? fmease
@rustbot label +A-diagnostics +A-parser +A-patterns +C-enhancement

compiler/rustc_errors/src/lib.rs

fmease · 2024-04-27T09:48:16Z

Currently vacationing for two more days, then I'm gonna review this PR.

ShE3py · 2024-04-29T08:09:37Z

Squashed the commits, I still have the let expr to do (e.g. let buf[0] = expr // remove this let) and some comments to update.

compiler/rustc_parse/src/parser/item.rs

bors · 2024-06-19T16:32:42Z

☔ The latest upstream changes (presumably #126678) made this pull request unmergeable. Please resolve the merge conflicts.

fmease

I've finished reviewing 3 out of 4 commits. Looking good so far. Gonna look at the 4th one in a sec. Sorry for taking so long ^^'

compiler/rustc_parse/src/parser/expr.rs

compiler/rustc_parse/src/parser/pat.rs

fmease · 2024-07-11T20:17:53Z

compiler/rustc_parse/src/parser/pat.rs

+ else {
+ // We got a trailing method/operator, but that wasn't an expression.
+ return None;
+ };


Nice let-else!

fmease · 2024-07-11T20:34:13Z

tests/ui/parser/recover/recover-pat-exprs.stderr

+error: expected a pattern, found an expression
+ --> $DIR/recover-pat-exprs.rs:58:9
+ |
+LL | x.sqrt() @ .. => (),
+ | ^^^^^^^^ arbitrary expressions are not allowed in patterns


Btw, if you'd like to suppress this one, we could pass a param RecoverExprInPat::{Yes, No} to parse_pat…

fmease · 2024-07-11T20:39:45Z

tests/ui/parser/recover/recover-pat-exprs.stderr

+error: expected a pattern, found an expression
+ --> $DIR/recover-pat-exprs.rs:43:10
+ |
+LL | (1 + 2) * 3 => (),
+ | ^^^^^ arbitrary expressions are not allowed in patterns
+
+error: expected a pattern, found an expression
+ --> $DIR/recover-pat-exprs.rs:43:9
+ |
+LL | (1 + 2) * 3 => (),
+ | ^^^^^^^^^^^ arbitrary expressions are not allowed in patterns


Note to self: Ah, right. If we were to reparse the tokens as an expr when failing to parse a pat (starting right before the first (), then we would only emit a single error for (1 + 2) * 3 in pat position but we don't follow this approach since that would require creating a snapshot upfront potentially in the happy path very likely incurring a perf cost (it's been a while, trying to remember all the context).

fmease · 2024-07-11T20:41:52Z

tests/ui/parser/recover/recover-pat-exprs.rs

Very nicely structured test file 👏

compiler/rustc_parse/src/parser/pat.rs

bors · 2024-07-15T22:24:29Z

☔ The latest upstream changes (presumably #127777) made this pull request unmergeable. Please resolve the merge conflicts.

compiler/rustc_parse/messages.ftl

compiler/rustc_parse/src/errors.rs

compiler/rustc_parse/messages.ftl

tests/ui/parser/bad-name.stderr

fmease · 2024-08-20T01:56:10Z

Btw, I will gladly insta-approve a PR that just contains the first two commits (a9fbb22 and f8b3046) which are independent of expr-in-pats :)

ShE3py · 2024-09-05T16:47:12Z

Btw, I will gladly insta-approve a PR that just contains the first two commits (a9fbb22 and f8b3046) which are independent of expr-in-pats :)

I was on vacation and I wanted to move some comments (i.e. 2133219), I can split now if that's desirable.

I’ve reverted the “error reducing” for parse_pat_tuple_or_parens so as not to edit the stashing methods;

fn main() {
    let Some((1 + 2) * 3) = None::<i32>;
}

error: expected a pattern, found an expression
 --> src/main.rs:2:14
  |
2 |     let Some((1 + 2) * 3) = None::<i32>;
  |              ^^^^^^^^^^^ arbitrary expressions are not allowed in patterns

error: expected a pattern, found an expression
 --> src/main.rs:2:15
  |
2 |     let Some((1 + 2) * 3) = None::<i32>;
  |               ^^^^^ arbitrary expressions are not allowed in patterns

It's somewhat verbose, but that can be improved in a follow-up.

I wonder if the match arm guard suggestions should be moved to another PR? Tracking issue #129967 will move the guard from the match arm to the pattern, so it might be best to wait for guard_patterns's implementation's PR to be merged before adding guard suggestions.

@rustbot ready

nnethercote · 2024-09-05T21:15:19Z

compiler/rustc_parse/src/parser/pat.rs

+ /// Called by [`Parser::parse_stmt_without_recovery`], used to add statement-aware subdiagnostics to the errors stashed
+ /// by [`Parser::maybe_recover_trailing_expr`].
+ pub(super) fn maybe_augment_stashed_expr_in_pats_with_suggestions(&mut self, stmt: &Stmt) {
+ if self.dcx().has_errors().is_none() {


Can you use has_stashed_diagnostic for a more precise test?

It requires the exact span which I don't have, and there's no

fn has_stashed_diagnostics(self: &DiagCtxtInner) -> bool { !self.stashed_diagnostics.is_empty() }

So it's kinda the best I can do without modifying the stashing API.

compiler/rustc_errors/src/lib.rs

bors · 2024-09-08T01:46:59Z

☔ The latest upstream changes (presumably #130091) made this pull request unmergeable. Please resolve the merge conflicts.

fmease

Tracking issue #129967 will move the guard from the match arm to the pattern, so it might be best to wait for guard_patterns's implementation's PR to be merged before adding guard suggestions.

I see what you're getting at but erm, I'd rather merge this first. This PR is a lot older and will immediately affect diagnostics. We don't know how long it will take for the initial guard-pattern PR to get to a ready state and merged. Also, it shouldn't be that hard to update this code, I think.

I'll bors-approve after a rebase. Thanks a lot for your patience! I took way too long for this

ShE3py · 2024-09-18T21:08:22Z

@rustbot ready

fmease · 2024-09-18T23:46:04Z

@bors r+

bors · 2024-09-18T23:46:06Z

📌 Commit db09345 has been approved by fmease

It is now in the queue for this repository.

bors · 2024-09-19T00:36:36Z

⌛ Testing commit db09345 with merge df7f778...

bors · 2024-09-19T03:28:25Z

☀️ Test successful - checks-actions
Approved by: fmease
Pushing df7f778 to master...

rust-timer · 2024-09-19T04:44:25Z

Finished benchmarking commit (df7f778): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

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	mean	range	count
Regressions ❌ (primary)	0.9%	[0.9%, 0.9%]	1
Regressions ❌ (secondary)	2.2%	[2.1%, 2.2%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.9%	[0.9%, 0.9%]	1

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Results (secondary -2.3%)

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	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.3%	[-2.4%, -2.2%]	4
All ❌✅ (primary)	-	-	0

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Bootstrap: 766.835s -> 767.849s (0.13%)
Artifact size: 341.29 MiB -> 341.34 MiB (0.02%)

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ShE3py commented Apr 13, 2024

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Fix substitution parts having a shifted underline in some cases #124370

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fmease mentioned this pull request Sep 14, 2024

Fix Parser::break_up_float's right span #130349

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ShE3py added 2 commits September 18, 2024 20:37

Recover more expressions in patterns

c204721

Add suggestions for expressions in patterns

db09345

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Implement Guard Patterns #129996

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Further improve diagnostics for expressions in pattern position #121697

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Further improve diagnostics for expressions in pattern position #123877

Further improve diagnostics for expressions in pattern position #123877

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Further improve diagnostics for expressions in pattern position #123877

Further improve diagnostics for expressions in pattern position #123877

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