rust-lang · jakubadamw · Aug 9, 2026
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -2929,12 +2929,26 @@ impl<'a> Parser<'a> {
         // parentheses in what should have been a tuple pattern; return a
         // suggestion-enhanced error here rather than choking on the comma later.
         let comma_span = self.token.span;
+        // `EitherTupleOrPipe` is only ever used for the pattern of a `match` arm, which has to be
+        // followed by either a `=>` or an `if` guard. Take a snapshot so that we can rewind to the
+        // comma if neither of those follows the comma-separated list.
+        let snapshot = (rt == CommaRecoveryMode::EitherTupleOrPipe)
+            .then(|| self.create_snapshot_for_diagnostic());
         self.bump();
         if let Err(err) = self.skip_pat_list() {
             // We didn't expect this to work anyway; we just wanted to advance to the
             // end of the comma-sequence so we know the span to suggest parenthesizing.
             err.cancel();
         }
+        if let Some(snapshot) = snapshot
+            && self.token != token::FatArrow
+            && !self.token.is_keyword(kw::If)
+        {
+            // Neither parenthesising the patterns nor joining them with `|` would give the arm a
+            // body, so the comma is far more likely to stand in for a missing `=> <body>`.
+            self.restore_snapshot(snapshot);
+            return Ok(());
+        }
         let seq_span = lo.to(self.prev_token.span);
         let mut err = self.dcx().struct_span_err(comma_span, "unexpected `,` in pattern");
         err.multipart_suggestion(

diff --git a/compiler/rustc_parse/src/parser/pat.rs b/compiler/rustc_parse/src/parser/pat.rs
@@ -73,6 +73,8 @@ pub enum RecoverColon {
 #[derive(PartialEq, Copy, Clone)]
 pub enum CommaRecoveryMode {
     LikelyTuple,
+    /// Only used for the pattern of a `match` arm, which the recovery relies on: it gives up when
+    /// the comma-separated list is not followed by the `=>` or the guard of an arm.
     EitherTupleOrPipe,
 }
 

diff --git a/tests/ui/feature-gates/feature-gate-never_patterns.rs b/tests/ui/feature-gates/feature-gate-never_patterns.rs
@@ -31,7 +31,7 @@ fn main() {
     match Some(0) {
         None => {}
         Some(_),
-        //~^ ERROR unexpected `,` in pattern
+        //~^ ERROR `match` arm with no body
     }
     match Some(0) {
         None => {}
@@ -59,6 +59,7 @@ fn main() {
 
     // Check that the gate operates even behind `cfg`.
     match Some(0) {
+        //~^ ERROR non-exhaustive patterns: `Some(_)` not covered
         None => {}
         #[cfg(false)]
         Some(_)

diff --git a/tests/ui/feature-gates/feature-gate-never_patterns.stderr b/tests/ui/feature-gates/feature-gate-never_patterns.stderr
@@ -1,19 +1,3 @@
-error: unexpected `,` in pattern
-  --> $DIR/feature-gate-never_patterns.rs:33:16
-   |
-LL |         Some(_),
-   |                ^
-   |
-help: try adding parentheses to match on a tuple...
-   |
-LL |         (Some(_),)
-   |         +        +
-help: ...or a vertical bar to match on alternatives
-   |
-LL -         Some(_),
-LL +         Some(_) |
-   |
-
 error[E0658]: `!` patterns are experimental
   --> $DIR/feature-gate-never_patterns.rs:8:24
    |
@@ -54,6 +38,17 @@ LL |             ! => {}
    = help: add `#![feature(never_patterns)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
+error: `match` arm with no body
+  --> $DIR/feature-gate-never_patterns.rs:33:9
+   |
+LL |         Some(_),
+   |         ^^^^^^^
+   |
+help: add a body after the pattern
+   |
+LL |         Some(_) => { todo!() },
+   |                 ++++++++++++++
+
 error: `match` arm with no body
   --> $DIR/feature-gate-never_patterns.rs:38:9
    |
@@ -108,7 +103,7 @@ LL |         Err(!) if false,
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
 error: `match` arm with no body
-  --> $DIR/feature-gate-never_patterns.rs:64:9
+  --> $DIR/feature-gate-never_patterns.rs:65:9
    |
 LL |         Some(_)
    |         ^^^^^^^
@@ -119,7 +114,7 @@ LL |         Some(_) => { todo!() }
    |                 ++++++++++++++
 
 error: `match` arm with no body
-  --> $DIR/feature-gate-never_patterns.rs:70:9
+  --> $DIR/feature-gate-never_patterns.rs:71:9
    |
 LL |         Some(_) if false
    |         ^^^^^^^^^^^^^^^^
@@ -135,6 +130,25 @@ error: a guard on a never pattern will never be run
 LL |         Err(!) if false,
    |                   ^^^^^ help: remove this guard
 
-error: aborting due to 13 previous errors
+error[E0004]: non-exhaustive patterns: `Some(_)` not covered
+  --> $DIR/feature-gate-never_patterns.rs:61:11
+   |
+LL |     match Some(0) {
+   |           ^^^^^^^ pattern `Some(_)` not covered
+   |
+note: `Option<i32>` defined here
+  --> $SRC_DIR/core/src/option.rs:LL:COL
+  ::: $SRC_DIR/core/src/option.rs:LL:COL
+   |
+   = note: not covered
+   = note: the matched value is of type `Option<i32>`
+help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
+   |
+LL ~         None => {},
+LL +         Some(_) => todo!()
+   |
+
+error: aborting due to 14 previous errors
 
-For more information about this error, try `rustc --explain E0658`.
+Some errors have detailed explanations: E0004, E0658.
+For more information about an error, try `rustc --explain E0004`.
diff --git a/tests/ui/parser/match-arm-without-body.rs b/tests/ui/parser/match-arm-without-body.rs
@@ -13,18 +13,26 @@ fn main() {
         _ => {}
         //~^ ERROR expected one of
     }
+    match Some(false) {
+        Some(_),
+        //~^ ERROR `match` arm with no body
+        //~| HELP add a body after the pattern
+    }
+    // The comma is only taken for a missing body when parenthesising the patterns (or joining
+    // them with `|`) wouldn't give the arm a body either.
     match Some(false) {
         Some(_),
         //~^ ERROR unexpected `,` in pattern
         //~| HELP try adding parentheses to match on a tuple
         //~| HELP or a vertical bar to match on alternative
+        _ => {}
     }
     match Some(false) {
         Some(_),
         //~^ ERROR unexpected `,` in pattern
         //~| HELP try adding parentheses to match on a tuple
         //~| HELP or a vertical bar to match on alternative
-        _ => {}
+        None if true => {}
     }
     match Some(false) {
         Some(_) if true

diff --git a/tests/ui/parser/match-arm-without-body.stderr b/tests/ui/parser/match-arm-without-body.stderr
@@ -7,23 +7,27 @@ LL |         _ => {}
    |         ^ unexpected token
 
 error: unexpected `,` in pattern
-  --> $DIR/match-arm-without-body.rs:17:16
+  --> $DIR/match-arm-without-body.rs:24:16
    |
 LL |         Some(_),
    |                ^
    |
 help: try adding parentheses to match on a tuple...
    |
-LL |         (Some(_),)
-   |         +        +
+LL ~         (Some(_),
+LL |
+LL |
+LL |
+LL ~         _) => {}
+   |
 help: ...or a vertical bar to match on alternatives
    |
 LL -         Some(_),
 LL +         Some(_) |
    |
 
 error: unexpected `,` in pattern
-  --> $DIR/match-arm-without-body.rs:23:16
+  --> $DIR/match-arm-without-body.rs:31:16
    |
 LL |         Some(_),
    |                ^
@@ -34,7 +38,7 @@ LL ~         (Some(_),
 LL |
 LL |
 LL |
-LL ~         _) => {}
+LL ~         None) if true => {}
    |
 help: ...or a vertical bar to match on alternatives
    |
@@ -43,15 +47,15 @@ LL +         Some(_) |
    |
 
 error: expected one of `.`, `=>`, `?`, or an operator, found reserved identifier `_`
-  --> $DIR/match-arm-without-body.rs:36:9
+  --> $DIR/match-arm-without-body.rs:44:9
    |
 LL |         Some(_) if true
    |                        - expected one of `.`, `=>`, `?`, or an operator
 LL |         _ => {}
    |         ^ unexpected token
 
 error: expected `,` following `match` arm
-  --> $DIR/match-arm-without-body.rs:66:15
+  --> $DIR/match-arm-without-body.rs:74:15
    |
 LL |         pat!()
    |               ^
@@ -73,7 +77,18 @@ LL |         Some(_) => { todo!() }
    |                 ++++++++++++++
 
 error: `match` arm with no body
-  --> $DIR/match-arm-without-body.rs:30:9
+  --> $DIR/match-arm-without-body.rs:17:9
+   |
+LL |         Some(_),
+   |         ^^^^^^^
+   |
+help: add a body after the pattern
+   |
+LL |         Some(_) => { todo!() },
+   |                 ++++++++++++++
+
+error: `match` arm with no body
+  --> $DIR/match-arm-without-body.rs:38:9
    |
 LL |         Some(_) if true
    |         ^^^^^^^^^^^^^^^
@@ -84,7 +99,7 @@ LL |         Some(_) if true => { todo!() }
    |                         ++++++++++++++
 
 error: `match` arm with no body
-  --> $DIR/match-arm-without-body.rs:40:9
+  --> $DIR/match-arm-without-body.rs:48:9
    |
 LL |         Some(_) if true,
    |         ^^^^^^^^^^^^^^^
@@ -95,7 +110,7 @@ LL |         Some(_) if true => { todo!() },
    |                         ++++++++++++++
 
 error: `match` arm with no body
-  --> $DIR/match-arm-without-body.rs:45:9
+  --> $DIR/match-arm-without-body.rs:53:9
    |
 LL |         Some(_) if true,
    |         ^^^^^^^^^^^^^^^
@@ -106,7 +121,7 @@ LL |         Some(_) if true => { todo!() },
    |                         ++++++++++++++
 
 error: `match` arm with no body
-  --> $DIR/match-arm-without-body.rs:51:9
+  --> $DIR/match-arm-without-body.rs:59:9
    |
 LL |         pat!()
    |         ^^^^^^
@@ -117,7 +132,7 @@ LL |         pat!() => { todo!() }
    |                ++++++++++++++
 
 error: `match` arm with no body
-  --> $DIR/match-arm-without-body.rs:56:9
+  --> $DIR/match-arm-without-body.rs:64:9
    |
 LL |         pat!(),
    |         ^^^^^^
@@ -128,7 +143,7 @@ LL |         pat!() => { todo!() },
    |                ++++++++++++++
 
 error: `match` arm with no body
-  --> $DIR/match-arm-without-body.rs:61:9
+  --> $DIR/match-arm-without-body.rs:69:9
    |
 LL |         pat!() if true,
    |         ^^^^^^^^^^^^^^
@@ -139,7 +154,7 @@ LL |         pat!() if true => { todo!() },
    |                        ++++++++++++++
 
 error: `match` arm with no body
-  --> $DIR/match-arm-without-body.rs:72:9
+  --> $DIR/match-arm-without-body.rs:80:9
    |
 LL |         pat!(),
    |         ^^^^^^
@@ -149,5 +164,5 @@ help: add a body after the pattern
 LL |         pat!() => { todo!() },
    |                ++++++++++++++
 
-error: aborting due to 13 previous errors
+error: aborting due to 14 previous errors