Differentiate statement boundary rules for stmt vs match arm

Author: dtolnay

src/classify.rs

@@ -6,8 +6,14 @@ use crate::ty::{ReturnType, Type};
 use proc_macro2::{Delimiter, TokenStream, TokenTree};
 use std::ops::ControlFlow;
 
-pub(crate) fn requires_terminator(expr: &Expr) -> bool {
-    // see https://github.com/rust-lang/rust/blob/9a19e7604/compiler/rustc_ast/src/util/classify.rs#L7-L26
+pub(crate) fn requires_semi_to_be_stmt(expr: &Expr) -> bool {
+    match expr {
+        Expr::Macro(expr) => !expr.mac.delimiter.is_brace(),
+        _ => requires_comma_to_be_match_arm(expr),
+    }
+}
+
+pub(crate) fn requires_comma_to_be_match_arm(expr: &Expr) -> bool {
     match expr {
         Expr::If(_)
         | Expr::Match(_)

src/expr.rs

@@ -2873,7 +2873,7 @@ pub(crate) mod parsing {
                 fat_arrow_token: input.parse()?,
                 body: {
                     let body = Expr::parse_with_earlier_boundary_rule(input)?;
-                    requires_comma = classify::requires_terminator(&body);
+                    requires_comma = classify::requires_comma_to_be_match_arm(&body);
                     Box::new(body)
                 },
                 comma: {
@@ -3312,7 +3312,10 @@ pub(crate) mod printing {
                     // Ensure that we have a comma after a non-block arm, except
                     // for the last one.
                     let is_last = i == self.arms.len() - 1;
-                    if !is_last && classify::requires_terminator(&arm.body) && arm.comma.is_none() {
+                    if !is_last
+                        && classify::requires_comma_to_be_match_arm(&arm.body)
+                        && arm.comma.is_none()
+                    {
                         <Token![,]>::default().to_tokens(tokens);
                     }
                 }

src/stmt.rs

@@ -159,7 +159,7 @@ pub(crate) mod parsing {
                 }
                 let stmt = parse_stmt(input, AllowNoSemi(true))?;
                 let requires_semicolon = match &stmt {
-                    Stmt::Expr(stmt, None) => classify::requires_terminator(stmt),
+                    Stmt::Expr(stmt, None) => classify::requires_semi_to_be_stmt(stmt),
                     Stmt::Macro(stmt) => {
                         stmt.semi_token.is_none() && !stmt.mac.delimiter.is_brace()
                     }
@@ -401,7 +401,7 @@ pub(crate) mod parsing {
 
         if semi_token.is_some() {
             Ok(Stmt::Expr(e, semi_token))
-        } else if allow_nosemi.0 || !classify::requires_terminator(&e) {
+        } else if allow_nosemi.0 || !classify::requires_semi_to_be_stmt(&e) {
             Ok(Stmt::Expr(e, None))
         } else {
             Err(input.error("expected semicolon"))