syntax: make match arms store the expr directly.

Previously `ast::Arm` was always storing a single `ast::Expr` wrapped in an
`ast::Block` (for historical reasons, AIUI), so we might as just store
that expr directly.

Closes #3085.

7 files changed, 21 insertions, 47 deletions

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index 947463d8f47..7efae9305e4 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -491,7 +491,7 @@ pub enum Decl_ {
 pub struct Arm {
     pats: Vec<@Pat> ,
     guard: Option<@Expr>,
-    body: P<Block>,
+    body: @Expr,
 }
 
 #[deriving(Clone, Eq, Encodable, Decodable, Hash)]
diff --git a/src/libsyntax/ext/build.rs b/src/libsyntax/ext/build.rs
index 34625923ea1..8296ee34c54 100644
--- a/src/libsyntax/ext/build.rs
+++ b/src/libsyntax/ext/build.rs
@@ -679,7 +679,7 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         ast::Arm {
             pats: pats,
             guard: None,
-            body: self.block_expr(expr)
+            body: expr
         }
     }
 
diff --git a/src/libsyntax/ext/deriving/primitive.rs b/src/libsyntax/ext/deriving/primitive.rs
index ecd042eb172..190f009103f 100644
--- a/src/libsyntax/ext/deriving/primitive.rs
+++ b/src/libsyntax/ext/deriving/primitive.rs
@@ -110,7 +110,7 @@ fn cs_from(name: &str, cx: &mut ExtCtxt, trait_span: Span, substr: &Substructure
                         let arm = ast::Arm {
                             pats: vec!(cx.pat_wild(span)),
                             guard: Some(guard),
-                            body: cx.block_expr(body),
+                            body: body,
                         };
 
                         arms.push(arm);
@@ -129,7 +129,7 @@ fn cs_from(name: &str, cx: &mut ExtCtxt, trait_span: Span, substr: &Substructure
             let arm = ast::Arm {
                 pats: vec!(cx.pat_wild(trait_span)),
                 guard: None,
-                body: cx.block_expr(cx.expr_none(trait_span)),
+                body: cx.expr_none(trait_span),
             };
             arms.push(arm);
 
diff --git a/src/libsyntax/fold.rs b/src/libsyntax/fold.rs
index b01ba7718ba..e5b90393e0a 100644
--- a/src/libsyntax/fold.rs
+++ b/src/libsyntax/fold.rs
@@ -117,7 +117,7 @@ pub trait Folder {
         Arm {
             pats: a.pats.map(|x| self.fold_pat(*x)),
             guard: a.guard.map(|x| self.fold_expr(x)),
-            body: self.fold_block(a.body),
+            body: self.fold_expr(a.body),
         }
     }
 
@@ -933,4 +933,3 @@ mod test {
                      ~"zz!zz((zz$zz:zz$(zz $zz:zz)zz+=>(zz$(zz$zz$zz)+)))");
     }
 }
-
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 2557af5e436..341151117f0 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -2634,16 +2634,7 @@ impl Parser {
                 self.eat(&token::COMMA);
             }
 
-            let blk = P(ast::Block {
-                view_items: Vec::new(),
-                stmts: Vec::new(),
-                expr: Some(expr),
-                id: ast::DUMMY_NODE_ID,
-                rules: DefaultBlock,
-                span: expr.span,
-            });
-
-            arms.push(ast::Arm { pats: pats, guard: guard, body: blk });
+            arms.push(ast::Arm { pats: pats, guard: guard, body: expr });
         }
         let hi = self.span.hi;
         self.bump();
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index ec8c474d194..e8c32d07c74 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -1352,38 +1352,22 @@ pub fn print_expr(s: &mut State, expr: &ast::Expr) -> io::IoResult<()> {
             }
             try!(word_space(s, "=>"));
 
-            // Extract the expression from the extra block the parser adds
-            // in the case of foo => expr
-            if arm.body.view_items.is_empty() &&
-                arm.body.stmts.is_empty() &&
-                arm.body.rules == ast::DefaultBlock &&
-                arm.body.expr.is_some()
-            {
-                match arm.body.expr {
-                    Some(expr) => {
-                        match expr.node {
-                            ast::ExprBlock(blk) => {
-                                // the block will close the pattern's ibox
-                                try!(print_block_unclosed_indent(
-                                    s, blk, indent_unit));
-                            }
-                            _ => {
-                                try!(end(s)); // close the ibox for the pattern
-                                try!(print_expr(s, expr));
-                            }
-                        }
-                        if !expr_is_simple_block(expr)
-                            && i < len - 1 {
-                            try!(word(&mut s.s, ","));
-                        }
-                        try!(end(s)); // close enclosing cbox
-                    }
-                    None => fail!()
+            match arm.body.node {
+                ast::ExprBlock(blk) => {
+                    // the block will close the pattern's ibox
+                    try!(print_block_unclosed_indent(
+                                s, blk, indent_unit));
                 }
-            } else {
-                // the block will close the pattern's ibox
-                try!(print_block_unclosed_indent(s, arm.body, indent_unit));
+                _ => {
+                    try!(end(s)); // close the ibox for the pattern
+                    try!(print_expr(s, arm.body));
+                }
+            }
+            if !expr_is_simple_block(expr)
+                && i < len - 1 {
+                try!(word(&mut s.s, ","));
             }
+            try!(end(s)); // close enclosing cbox
         }
         try!(bclose_(s, expr.span, indent_unit));
       }
diff --git a/src/libsyntax/visit.rs b/src/libsyntax/visit.rs
index 2edfd367f4e..d25d1a8cc35 100644
--- a/src/libsyntax/visit.rs
+++ b/src/libsyntax/visit.rs
@@ -765,5 +765,5 @@ pub fn walk_arm<E: Clone, V: Visitor<E>>(visitor: &mut V, arm: &Arm, env: E) {
         visitor.visit_pat(*pattern, env.clone())
     }
     walk_expr_opt(visitor, arm.guard, env.clone());
-    visitor.visit_block(arm.body, env)
+    visitor.visit_expr(arm.body, env)
 }