Don't expect bodyless arms if the pattern can never be a never pattern

Author: ShE3py

compiler/rustc_parse/src/parser/expr.rs

@@ -2937,7 +2937,13 @@ impl<'a> Parser<'a> {
             let is_almost_fat_arrow = TokenKind::FatArrow
                 .similar_tokens()
                 .is_some_and(|similar_tokens| similar_tokens.contains(&this.token.kind));
-            let mut result = if !is_fat_arrow && !is_almost_fat_arrow {
+
+            // this avoids the compiler saying that a `,` or `}` was expected even though
+            // the pattern isn't a never pattern (and thus an arm body is required)
+            let armless = (!is_fat_arrow && !is_almost_fat_arrow && pat.could_be_never_pattern())
+                || matches!(this.token.kind, token::Comma | token::CloseDelim(Delimiter::Brace));
+
+            let mut result = if armless {
                 // A pattern without a body, allowed for never patterns.
                 arm_body = None;
                 this.expect_one_of(&[token::Comma], &[token::CloseDelim(Delimiter::Brace)]).map(

tests/ui/half-open-range-patterns/range_pat_interactions1.rs

@@ -17,7 +17,7 @@ fn main() {
         }
         match x as i32 {
             0..5+1 => errors_only.push(x),
-            //~^ error: expected one of `,`, `=>`, `if`, `|`, or `}`, found `+`
+            //~^ error: expected one of `=>`, `if`, or `|`, found `+`
             1 | -3..0 => first_or.push(x),
             y @ (0..5 | 6) => or_two.push(y),
             y @ 0..const { 5 + 1 } => assert_eq!(y, 5),

tests/ui/half-open-range-patterns/range_pat_interactions1.stderr

@@ -1,8 +1,8 @@
-error: expected one of `,`, `=>`, `if`, `|`, or `}`, found `+`
+error: expected one of `=>`, `if`, or `|`, found `+`
   --> $DIR/range_pat_interactions1.rs:19:17
    |
 LL |             0..5+1 => errors_only.push(x),
-   |                 ^ expected one of `,`, `=>`, `if`, `|`, or `}`
+   |                 ^ expected one of `=>`, `if`, or `|`
 
 error[E0408]: variable `n` is not bound in all patterns
   --> $DIR/range_pat_interactions1.rs:10:25

tests/ui/half-open-range-patterns/range_pat_interactions2.rs

@@ -9,7 +9,7 @@ fn main() {
         match x as i32 {
             0..=(5+1) => errors_only.push(x),
             //~^ error: inclusive range with no end
-            //~| error: expected one of `,`, `=>`, `if`, `|`, or `}`, found `(`
+            //~| error: expected one of `=>`, `if`, or `|`, found `(`
             1 | -3..0 => first_or.push(x),
             y @ (0..5 | 6) => or_two.push(y),
             y @ 0..const { 5 + 1 } => assert_eq!(y, 5),

tests/ui/half-open-range-patterns/range_pat_interactions2.stderr

@@ -6,11 +6,11 @@ LL |             0..=(5+1) => errors_only.push(x),
    |
    = note: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
 
-error: expected one of `,`, `=>`, `if`, `|`, or `}`, found `(`
+error: expected one of `=>`, `if`, or `|`, found `(`
   --> $DIR/range_pat_interactions2.rs:10:17
    |
 LL |             0..=(5+1) => errors_only.push(x),
-   |                 ^ expected one of `,`, `=>`, `if`, `|`, or `}`
+   |                 ^ expected one of `=>`, `if`, or `|`
 
 error: aborting due to 2 previous errors
 

tests/ui/parser/attribute/attr-stmt-expr-attr-bad.rs

@@ -84,15 +84,15 @@ fn main() {}
 
 #[cfg(FALSE)] fn e() { match 0 { 0..=#[attr] 10 => () } }
 //~^ ERROR inclusive range with no end
-//~| ERROR expected one of `,`, `=>`, `if`, `|`, or `}`, found `#`
+//~| ERROR expected one of `=>`, `if`, or `|`, found `#`
 #[cfg(FALSE)] fn e() { match 0 { 0..=#[attr] -10 => () } }
 //~^ ERROR inclusive range with no end
-//~| ERROR expected one of `,`, `=>`, `if`, `|`, or `}`, found `#`
+//~| ERROR expected one of `=>`, `if`, or `|`, found `#`
 #[cfg(FALSE)] fn e() { match 0 { 0..=-#[attr] 10 => () } }
 //~^ ERROR unexpected token: `#`
 #[cfg(FALSE)] fn e() { match 0 { 0..=#[attr] FOO => () } }
 //~^ ERROR inclusive range with no end
-//~| ERROR expected one of `,`, `=>`, `if`, `|`, or `}`, found `#`
+//~| ERROR expected one of `=>`, `if`, or `|`, found `#`
 
 #[cfg(FALSE)] fn e() { let _ = x.#![attr]foo(); }
 //~^ ERROR unexpected token: `#`

tests/ui/parser/attribute/attr-stmt-expr-attr-bad.stderr

@@ -365,11 +365,11 @@ LL | #[cfg(FALSE)] fn e() { match 0 { 0..=#[attr] 10 => () } }
    |
    = note: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
 
-error: expected one of `,`, `=>`, `if`, `|`, or `}`, found `#`
+error: expected one of `=>`, `if`, or `|`, found `#`
   --> $DIR/attr-stmt-expr-attr-bad.rs:85:38
    |
 LL | #[cfg(FALSE)] fn e() { match 0 { 0..=#[attr] 10 => () } }
-   |                                      ^ expected one of `,`, `=>`, `if`, `|`, or `}`
+   |                                      ^ expected one of `=>`, `if`, or `|`
 
 error[E0586]: inclusive range with no end
   --> $DIR/attr-stmt-expr-attr-bad.rs:88:35
@@ -379,11 +379,11 @@ LL | #[cfg(FALSE)] fn e() { match 0 { 0..=#[attr] -10 => () } }
    |
    = note: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
 
-error: expected one of `,`, `=>`, `if`, `|`, or `}`, found `#`
+error: expected one of `=>`, `if`, or `|`, found `#`
   --> $DIR/attr-stmt-expr-attr-bad.rs:88:38
    |
 LL | #[cfg(FALSE)] fn e() { match 0 { 0..=#[attr] -10 => () } }
-   |                                      ^ expected one of `,`, `=>`, `if`, `|`, or `}`
+   |                                      ^ expected one of `=>`, `if`, or `|`
 
 error: unexpected token: `#`
   --> $DIR/attr-stmt-expr-attr-bad.rs:91:39
@@ -399,11 +399,11 @@ LL | #[cfg(FALSE)] fn e() { match 0 { 0..=#[attr] FOO => () } }
    |
    = note: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
 
-error: expected one of `,`, `=>`, `if`, `|`, or `}`, found `#`
+error: expected one of `=>`, `if`, or `|`, found `#`
   --> $DIR/attr-stmt-expr-attr-bad.rs:93:38
    |
 LL | #[cfg(FALSE)] fn e() { match 0 { 0..=#[attr] FOO => () } }
-   |                                      ^ expected one of `,`, `=>`, `if`, `|`, or `}`
+   |                                      ^ expected one of `=>`, `if`, or `|`
 
 error: unexpected token: `#`
   --> $DIR/attr-stmt-expr-attr-bad.rs:97:34

tests/ui/parser/issues/issue-24375.rs

@@ -3,7 +3,7 @@ static tmp : [&'static str; 2]  = ["hello", "he"];
 fn main() {
     let z = "hello";
     match z {
-        tmp[0] => {} //~ ERROR expected one of `,`, `=>`, `@`, `if`, `|`, or `}`, found `[`
+        tmp[0] => {} //~ ERROR expected one of `=>`, `@`, `if`, or `|`, found `[`
         _ => {}
     }
 }

tests/ui/parser/issues/issue-24375.stderr

@@ -1,8 +1,8 @@
-error: expected one of `,`, `=>`, `@`, `if`, `|`, or `}`, found `[`
+error: expected one of `=>`, `@`, `if`, or `|`, found `[`
   --> $DIR/issue-24375.rs:6:12
    |
 LL |         tmp[0] => {}
-   |            ^ expected one of `,`, `=>`, `@`, `if`, `|`, or `}`
+   |            ^ expected one of `=>`, `@`, `if`, or `|`
 
 error: aborting due to 1 previous error
 

tests/ui/parser/match-arm-without-body.stderr

@@ -1,8 +1,8 @@
-error: expected one of `,`, `=>`, `if`, `|`, or `}`, found reserved identifier `_`
+error: expected one of `=>`, `if`, or `|`, found reserved identifier `_`
   --> $DIR/match-arm-without-body.rs:13:9
    |
 LL |         Some(_)
-   |                - expected one of `,`, `=>`, `if`, `|`, or `}`
+   |                - expected one of `=>`, `if`, or `|`
 LL |         _ => {}
    |         ^ unexpected token
 
@@ -44,11 +44,11 @@ LL +
 LL ~         _ => {}
    |
 
-error: expected one of `,`, `.`, `=>`, `?`, `}`, or an operator, found reserved identifier `_`
+error: expected one of `.`, `=>`, `?`, or an operator, found reserved identifier `_`
   --> $DIR/match-arm-without-body.rs:36:9
    |
 LL |         Some(_) if true
-   |                        - expected one of `,`, `.`, `=>`, `?`, `}`, or an operator
+   |                        - expected one of `.`, `=>`, `?`, or an operator
 LL |         _ => {}
    |         ^ unexpected token