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Merged
merged 7 commits into from
Sep 17, 2025
Merged

Detect attempt to use var-args in closure #146581

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9405e76
Detect attempt to use var-args in closure
estebank Sep 15, 2025
0e290e4
Silence inference error on `PatKind::Err`
estebank Sep 15, 2025
a84c8de
Fix existing test
estebank Sep 15, 2025
c916e88
fmt
estebank Sep 16, 2025
ed85f98
remove redundant test
estebank Sep 16, 2025
8306a2f
Reword note
estebank Sep 16, 2025
e9270e3
Detect top-level `...` in argument type
estebank Sep 16, 2025
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1 change: 1 addition & 0 deletions compiler/rustc_parse/messages.ftl
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Original file line number Diff line number Diff line change
Expand Up @@ -189,6 +189,7 @@ parse_dotdotdot = unexpected token: `...`
parse_dotdotdot_rest_pattern = unexpected `...`
.label = not a valid pattern
.suggestion = for a rest pattern, use `..` instead of `...`
.note = C-variadic type `...` is not allowed here

parse_double_colon_in_bound = expected `:` followed by trait or lifetime
.suggestion = use single colon
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4 changes: 3 additions & 1 deletion compiler/rustc_parse/src/errors.rs
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Expand Up @@ -2723,7 +2723,9 @@ pub(crate) struct DotDotDotRestPattern {
#[label]
pub span: Span,
#[suggestion(style = "verbose", code = "", applicability = "machine-applicable")]
pub suggestion: Span,
pub suggestion: Option<Span>,
#[note]
pub var_args: Option<()>,
}

#[derive(Diagnostic)]
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27 changes: 19 additions & 8 deletions compiler/rustc_parse/src/parser/pat.rs
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Expand Up @@ -756,7 +756,7 @@ impl<'a> Parser<'a> {
self.bump(); // `..`
PatKind::Rest
} else if self.check(exp!(DotDotDot)) && !self.is_pat_range_end_start(1) {
self.recover_dotdotdot_rest_pat(lo)
self.recover_dotdotdot_rest_pat(lo, expected)
} else if let Some(form) = self.parse_range_end() {
self.parse_pat_range_to(form)? // `..=X`, `...X`, or `..X`.
} else if self.eat(exp!(Bang)) {
Expand Down Expand Up @@ -886,16 +886,27 @@ impl<'a> Parser<'a> {

/// Recover from a typoed `...` pattern that was encountered
/// Ref: Issue #70388
fn recover_dotdotdot_rest_pat(&mut self, lo: Span) -> PatKind {
fn recover_dotdotdot_rest_pat(&mut self, lo: Span, expected: Option<Expected>) -> PatKind {
// A typoed rest pattern `...`.
self.bump(); // `...`

// The user probably mistook `...` for a rest pattern `..`.
self.dcx().emit_err(DotDotDotRestPattern {
span: lo,
suggestion: lo.with_lo(lo.hi() - BytePos(1)),
});
PatKind::Rest
if let Some(Expected::ParameterName) = expected {
// We have `...` in a closure argument, likely meant to be var-arg, which aren't
// supported in closures (#146489).
PatKind::Err(self.dcx().emit_err(DotDotDotRestPattern {
span: lo,
suggestion: None,
var_args: Some(()),
}))
} else {
// The user probably mistook `...` for a rest pattern `..`.
self.dcx().emit_err(DotDotDotRestPattern {
span: lo,
suggestion: Some(lo.with_lo(lo.hi() - BytePos(1))),
var_args: None,
});
PatKind::Rest
}
}

/// Try to recover the more general form `intersect ::= $pat_lhs @ $pat_rhs`.
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10 changes: 8 additions & 2 deletions compiler/rustc_trait_selection/src/error_reporting/infer/need_type_info.rs
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Expand Up @@ -4,7 +4,7 @@ use std::path::PathBuf;

use rustc_errors::codes::*;
use rustc_errors::{Diag, IntoDiagArg};
use rustc_hir as hir;
use rustc_hir::{self as hir, PatKind};
use rustc_hir::def::{CtorOf, DefKind, Namespace, Res};
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_hir::intravisit::{self, Visitor};
Expand Down Expand Up @@ -512,7 +512,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
type_name: ty_to_string(self, ty, def_id),
});
}
InferSourceKind::ClosureArg { insert_span, ty } => {
InferSourceKind::ClosureArg { insert_span, ty, .. } => {
infer_subdiags.push(SourceKindSubdiag::LetLike {
span: insert_span,
name: String::new(),
Expand Down Expand Up @@ -652,6 +652,10 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
}),
};
*err.long_ty_path() = long_ty_path;
if let InferSourceKind::ClosureArg { kind: PatKind::Err(_), .. } = kind {
// We will have already emitted an error about this pattern.
err.downgrade_to_delayed_bug();
Comment on lines +657 to +658
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@lcnr lcnr Sep 15, 2025 •
edited
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hmm, surprised we don't have a way to silence a lint by passing in an ErrorGuaranteed. We could then do

        if let InferSourceKind::ClosureArg { kind: PatKind::Err(guar), .. } = kind {
            err.silence_via_error_guaranteed(guar);
        }
}

though maybe even better... change this function to return Result<Diag, ErrorGuaranteed> and avoid creating a diagnostic at all edit: seems annoying to do 😅

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I guess the rationale for downgrade_to_delayed_bug itself not taking an ErrorGuarantee is because itself is kind of an error guarantee already :)

The guarantee is more critical for anything that could cause a binary to be emitted otherwise.

}
err
}
}
Expand All @@ -673,6 +677,7 @@ enum InferSourceKind<'tcx> {
ClosureArg {
insert_span: Span,
ty: Ty<'tcx>,
kind: PatKind<'tcx>,
},
GenericArg {
insert_span: Span,
Expand Down Expand Up @@ -1197,6 +1202,7 @@ impl<'a, 'tcx> Visitor<'tcx> for FindInferSourceVisitor<'a, 'tcx> {
kind: InferSourceKind::ClosureArg {
insert_span: param.pat.span.shrink_to_hi(),
ty: param_ty,
kind: param.pat.kind,
},
})
}
Expand Down
3 changes: 1 addition & 2 deletions tests/ui/c-variadic/no-closure.rs
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Expand Up @@ -8,8 +8,7 @@ const F: extern "C" fn(...) = |_: ...| {};

fn foo() {
let f = |...| {};
//~^ ERROR: `..` patterns are not allowed here
//~| ERROR: unexpected `...`
//~^ ERROR: unexpected `...`

let f = |_: ...| {};
//~^ ERROR C-variadic type `...` may not be nested inside another type
Expand Down
18 changes: 3 additions & 15 deletions tests/ui/c-variadic/no-closure.stderr
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Expand Up @@ -10,26 +10,14 @@ error: unexpected `...`
LL | let f = |...| {};
| ^^^ not a valid pattern
|
help: for a rest pattern, use `..` instead of `...`
|
LL - let f = |...| {};
LL + let f = |..| {};
|
= note: C-variadic type `...` is not allowed here

error[E0743]: C-variadic type `...` may not be nested inside another type
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existing, but what does "may not be nested inside another type" mean here 😅

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Could we just emit the error like using ... in normal fn:

error: `...` is not supported for non-extern functions
 --> src/lib.rs:3:8
  |
3 | fn foo(_: ...) {}
  |        ^^^^^^
  |
  = help: only `extern "C"` and `extern "C-unwind"` functions may have a C variable argument list

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@estebank estebank Sep 16, 2025 •
edited
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The reason this error triggers is because it is emitted by parse_ty_common, which was likely meant to catch uses like Vec<...>, but we didn't bother special casing the top-level case. It'll be hard to handle that in parse_ty_common because that doesn't know whether it is a top-level type being parsed, so it would have to be specially handled elsewhere. I'll look into it as a follow up.

Edit: scratch that. Curiosity got the best of me and fixed it quickly.

--> $DIR/no-closure.rs:14:17
--> $DIR/no-closure.rs:13:17
|
LL | let f = |_: ...| {};
| ^^^

error: `..` patterns are not allowed here
--> $DIR/no-closure.rs:10:14
|
LL | let f = |...| {};
| ^^^
|
= note: only allowed in tuple, tuple struct, and slice patterns

error: aborting due to 4 previous errors
error: aborting due to 3 previous errors

For more information about this error, try `rustc --explain E0743`.
10 changes: 10 additions & 0 deletions tests/ui/closures/varargs-in-closure-isnt-supported.rs
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@@ -0,0 +1,10 @@
// var-args are not supported in closures, ensure we don't misdirect people (#146489)
#![feature(c_variadic)]

unsafe extern "C" fn thats_not_a_pattern(mut ap: ...) -> u32 {
let mut lol = |...| (); //~ ERROR: unexpected `...`
unsafe { ap.arg::<u32>() } //~^ NOTE: C-variadic type `...` is not allowed here
//~| NOTE: not a valid pattern
}

fn main() {}
10 changes: 10 additions & 0 deletions tests/ui/closures/varargs-in-closure-isnt-supported.stderr
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@@ -0,0 +1,10 @@
error: unexpected `...`
--> $DIR/varargs-in-closure-isnt-supported.rs:5:20
|
LL | let mut lol = |...| ();
| ^^^ not a valid pattern
|
= note: C-variadic type `...` is not allowed here

error: aborting due to 1 previous error

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