Allow statement-generating braced macro invocations at the end of blocks

src/librustc/hir/lowering.rs

@@ -587,10 +587,23 @@ impl<'a> LoweringContext<'a> {
     }
 
     fn lower_block(&mut self, b: &Block) -> P<hir::Block> {
+        let mut stmts = Vec::new();
+        let mut expr = None;
+
+        if let Some((last, rest)) = b.stmts.split_last() {
+            stmts = rest.iter().map(|s| self.lower_stmt(s)).collect::<Vec<_>>();
+            let last = self.lower_stmt(last);
+            if let hir::StmtExpr(e, _) = last.node {
+                expr = Some(e);
+            } else {
+                stmts.push(last);
+            }
+        }
+
         P(hir::Block {
             id: b.id,
-            stmts: b.stmts.iter().map(|s| self.lower_stmt(s)).collect(),
-            expr: b.expr.as_ref().map(|ref x| self.lower_expr(x)),
+            stmts: stmts.into(),
+            expr: expr,
             rules: self.lower_block_check_mode(&b.rules),
             span: b.span,
         })

src/librustc_driver/driver.rs

@@ -763,6 +763,10 @@ pub fn phase_2_configure_and_expand<'a>(sess: &Session,
 }
 
 pub fn assign_node_ids(sess: &Session, krate: ast::Crate) -> ast::Crate {
+    use syntax::codemap::Spanned;
+    use syntax::ptr::P;
+    use syntax::util::move_map::MoveMap;
+
     struct NodeIdAssigner<'a> {
         sess: &'a Session,
     }
@@ -772,6 +776,27 @@ pub fn assign_node_ids(sess: &Session, krate: ast::Crate) -> ast::Crate {
             assert_eq!(old_id, ast::DUMMY_NODE_ID);
             self.sess.next_node_id()
         }
+
+        fn fold_block(&mut self, block: P<ast::Block>) -> P<ast::Block> {
+            block.map(|mut block| {
+                block.id = self.new_id(block.id);
+
+                let stmt = block.stmts.pop();
+                block.stmts = block.stmts.move_flat_map(|s| self.fold_stmt(s).into_iter());
+                if let Some(Spanned { node: ast::StmtKind::Expr(expr, _), span }) = stmt {
+                    let expr = self.fold_expr(expr);
+                    let id = expr.id;
+                    block.stmts.push(Spanned {
+                        span: span,
+                        node: ast::StmtKind::Expr(expr, id)
+                    });
+                } else if let Some(stmt) = stmt {
+                    block.stmts.extend(self.fold_stmt(stmt));
+                }
+
+                block
+            })
+        }
     }
 
     let krate = time(sess.time_passes(),

src/librustc_driver/pretty.rs

@@ -657,8 +657,10 @@ impl fold::Folder for ReplaceBodyWithLoop {
     fn fold_block(&mut self, b: P<ast::Block>) -> P<ast::Block> {
         fn expr_to_block(rules: ast::BlockCheckMode, e: Option<P<ast::Expr>>) -> P<ast::Block> {
             P(ast::Block {
-                expr: e,
-                stmts: vec![],
+                stmts: e.map(|e| codemap::Spanned {
+                    span: e.span,
+                    node: ast::StmtKind::Expr(e, ast::DUMMY_NODE_ID),
+                }).into_iter().collect(),
                 rules: rules,
                 id: ast::DUMMY_NODE_ID,
                 span: codemap::DUMMY_SP,

src/libsyntax/ast.rs

@@ -528,9 +528,6 @@ impl PartialEq for MetaItemKind {
 pub struct Block {
     /// Statements in a block
     pub stmts: Vec<Stmt>,
-    /// An expression at the end of the block
-    /// without a semicolon, if any
-    pub expr: Option<P<Expr>>,
     pub id: NodeId,
     /// Distinguishes between `unsafe { ... }` and `{ ... }`
     pub rules: BlockCheckMode,
@@ -803,7 +800,7 @@ pub enum StmtKind {
     /// Could be an item or a local (let) binding:
     Decl(P<Decl>, NodeId),
 
-    /// Expr without trailing semi-colon (must have unit type):
+    /// Expr without trailing semi-colon
     Expr(P<Expr>, NodeId),
 
     /// Expr with trailing semi-colon (may have any type):

src/libsyntax/ext/build.rs

@@ -87,6 +87,7 @@ pub trait AstBuilder {
 
     // statements
     fn stmt_expr(&self, expr: P<ast::Expr>) -> ast::Stmt;
+    fn stmt_semi(&self, expr: P<ast::Expr>) -> ast::Stmt;
     fn stmt_let(&self, sp: Span, mutbl: bool, ident: ast::Ident, ex: P<ast::Expr>) -> ast::Stmt;
     fn stmt_let_typed(&self,
                       sp: Span,
@@ -98,12 +99,8 @@ pub trait AstBuilder {
     fn stmt_item(&self, sp: Span, item: P<ast::Item>) -> ast::Stmt;
 
     // blocks
-    fn block(&self, span: Span, stmts: Vec<ast::Stmt>,
-             expr: Option<P<ast::Expr>>) -> P<ast::Block>;
+    fn block(&self, span: Span, stmts: Vec<ast::Stmt>) -> P<ast::Block>;
     fn block_expr(&self, expr: P<ast::Expr>) -> P<ast::Block>;
-    fn block_all(&self, span: Span,
-                 stmts: Vec<ast::Stmt>,
-                 expr: Option<P<ast::Expr>>) -> P<ast::Block>;
 
     // expressions
     fn expr(&self, span: Span, node: ast::ExprKind) -> P<ast::Expr>;
@@ -508,6 +505,10 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
     }
 
     fn stmt_expr(&self, expr: P<ast::Expr>) -> ast::Stmt {
+        respan(expr.span, ast::StmtKind::Expr(expr, ast::DUMMY_NODE_ID))
+    }
+
+    fn stmt_semi(&self, expr: P<ast::Expr>) -> ast::Stmt {
         respan(expr.span, ast::StmtKind::Semi(expr, ast::DUMMY_NODE_ID))
     }
 
@@ -556,30 +557,24 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         P(respan(sp, ast::StmtKind::Decl(P(decl), ast::DUMMY_NODE_ID)))
     }
 
-    fn block(&self, span: Span, stmts: Vec<ast::Stmt>,
-             expr: Option<P<Expr>>) -> P<ast::Block> {
-        self.block_all(span, stmts, expr)
-    }
-
     fn stmt_item(&self, sp: Span, item: P<ast::Item>) -> ast::Stmt {
         let decl = respan(sp, ast::DeclKind::Item(item));
         respan(sp, ast::StmtKind::Decl(P(decl), ast::DUMMY_NODE_ID))
     }
 
     fn block_expr(&self, expr: P<ast::Expr>) -> P<ast::Block> {
-        self.block_all(expr.span, Vec::new(), Some(expr))
-    }
-    fn block_all(&self,
-                 span: Span,
-                 stmts: Vec<ast::Stmt>,
-                 expr: Option<P<ast::Expr>>) -> P<ast::Block> {
-            P(ast::Block {
-               stmts: stmts,
-               expr: expr,
-               id: ast::DUMMY_NODE_ID,
-               rules: BlockCheckMode::Default,
-               span: span,
-            })
+        self.block(expr.span, vec![Spanned {
+            span: expr.span,
+            node: ast::StmtKind::Expr(expr, ast::DUMMY_NODE_ID),
+        }])
+    }
+    fn block(&self, span: Span, stmts: Vec<ast::Stmt>) -> P<ast::Block> {
+        P(ast::Block {
+           stmts: stmts,
+           id: ast::DUMMY_NODE_ID,
+           rules: BlockCheckMode::Default,
+           span: span,
+        })
     }
 
     fn expr(&self, span: Span, node: ast::ExprKind) -> P<ast::Expr> {
@@ -948,14 +943,14 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
                     ids: Vec<ast::Ident>,
                     stmts: Vec<ast::Stmt>)
                     -> P<ast::Expr> {
-        self.lambda(span, ids, self.block(span, stmts, None))
+        self.lambda(span, ids, self.block(span, stmts))
     }
     fn lambda_stmts_0(&self, span: Span, stmts: Vec<ast::Stmt>) -> P<ast::Expr> {
-        self.lambda0(span, self.block(span, stmts, None))
+        self.lambda0(span, self.block(span, stmts))
     }
     fn lambda_stmts_1(&self, span: Span, stmts: Vec<ast::Stmt>,
                       ident: ast::Ident) -> P<ast::Expr> {
-        self.lambda1(span, self.block(span, stmts, None), ident)
+        self.lambda1(span, self.block(span, stmts), ident)
     }
 
     fn arg(&self, span: Span, ident: ast::Ident, ty: P<ast::Ty>) -> ast::Arg {

src/libsyntax/ext/expand.rs

@@ -636,23 +636,14 @@ pub fn expand_block(blk: P<Block>, fld: &mut MacroExpander) -> P<Block> {
 
 // expand the elements of a block.
 pub fn expand_block_elts(b: P<Block>, fld: &mut MacroExpander) -> P<Block> {
-    b.map(|Block {id, stmts, expr, rules, span}| {
+    b.map(|Block {id, stmts, rules, span}| {
         let new_stmts = stmts.into_iter().flat_map(|x| {
             // perform pending renames and expand macros in the statement
             fld.fold_stmt(x).into_iter()
         }).collect();
-        let new_expr = expr.map(|x| {
-            let expr = {
-                let pending_renames = &mut fld.cx.syntax_env.info().pending_renames;
-                let mut rename_fld = IdentRenamer{renames:pending_renames};
-                rename_fld.fold_expr(x)
-            };
-            fld.fold_expr(expr)
-        });
         Block {
             id: fld.new_id(id),
             stmts: new_stmts,
-            expr: new_expr,
             rules: rules,
             span: span
         }

src/libsyntax/ext/quote.rs

@@ -512,10 +512,8 @@ pub fn expand_quote_matcher(cx: &mut ExtCtxt,
     let (cx_expr, tts) = parse_arguments_to_quote(cx, tts);
     let mut vector = mk_stmts_let(cx, sp);
     vector.extend(statements_mk_tts(cx, &tts[..], true));
-    let block = cx.expr_block(
-        cx.block_all(sp,
-                     vector,
-                     Some(cx.expr_ident(sp, id_ext("tt")))));
+    vector.push(cx.stmt_expr(cx.expr_ident(sp, id_ext("tt"))));
+    let block = cx.expr_block(cx.block(sp, vector));
 
     let expanded = expand_wrapper(cx, sp, cx_expr, block, &[&["syntax", "ext", "quote", "rt"]]);
     base::MacEager::expr(expanded)
@@ -765,8 +763,9 @@ fn statements_mk_tt(cx: &ExtCtxt, tt: &TokenTree, matcher: bool) -> Vec<ast::Stm
             let stmt_let_tt = cx.stmt_let(sp, true, id_ext("tt"), cx.expr_vec_ng(sp));
             let mut tts_stmts = vec![stmt_let_tt];
             tts_stmts.extend(statements_mk_tts(cx, &seq.tts[..], matcher));
-            let e_tts = cx.expr_block(cx.block(sp, tts_stmts,
-                                                   Some(cx.expr_ident(sp, id_ext("tt")))));
+            tts_stmts.push(cx.stmt_expr(cx.expr_ident(sp, id_ext("tt"))));
+            let e_tts = cx.expr_block(cx.block(sp, tts_stmts));
+
             let e_separator = match seq.separator {
                 Some(ref sep) => cx.expr_some(sp, expr_mk_token(cx, sp, sep)),
                 None => cx.expr_none(sp),
@@ -884,10 +883,8 @@ fn expand_tts(cx: &ExtCtxt, sp: Span, tts: &[TokenTree])
 
     let mut vector = mk_stmts_let(cx, sp);
     vector.extend(statements_mk_tts(cx, &tts[..], false));
-    let block = cx.expr_block(
-        cx.block_all(sp,
-                     vector,
-                     Some(cx.expr_ident(sp, id_ext("tt")))));
+    vector.push(cx.stmt_expr(cx.expr_ident(sp, id_ext("tt"))));
+    let block = cx.expr_block(cx.block(sp, vector));
 
     (cx_expr, block)
 }
@@ -901,13 +898,14 @@ fn expand_wrapper(cx: &ExtCtxt,
     let cx_expr_borrow = cx.expr_addr_of(sp, cx.expr_deref(sp, cx_expr));
     let stmt_let_ext_cx = cx.stmt_let(sp, false, id_ext("ext_cx"), cx_expr_borrow);
 
-    let stmts = imports.iter().map(|path| {
+    let mut stmts = imports.iter().map(|path| {
         // make item: `use ...;`
         let path = path.iter().map(|s| s.to_string()).collect();
         cx.stmt_item(sp, cx.item_use_glob(sp, ast::Visibility::Inherited, ids_ext(path)))
-    }).chain(Some(stmt_let_ext_cx)).collect();
+    }).chain(Some(stmt_let_ext_cx)).collect::<Vec<_>>();
+    stmts.push(cx.stmt_expr(expr));
 
-    cx.expr_block(cx.block_all(sp, stmts, Some(expr)))
+    cx.expr_block(cx.block(sp, stmts))
 }
 
 fn expand_parse_call(cx: &ExtCtxt,

src/libsyntax/fold.rs

@@ -845,10 +845,9 @@ fn noop_fold_bounds<T: Folder>(bounds: TyParamBounds, folder: &mut T)
 }
 
 pub fn noop_fold_block<T: Folder>(b: P<Block>, folder: &mut T) -> P<Block> {
-    b.map(|Block {id, stmts, expr, rules, span}| Block {
+    b.map(|Block {id, stmts, rules, span}| Block {
         id: folder.new_id(id),
         stmts: stmts.move_flat_map(|s| folder.fold_stmt(s).into_iter()),
-        expr: expr.and_then(|x| folder.fold_opt_expr(x)),
         rules: rules,
         span: folder.new_span(span),
     })

src/libsyntax/parse/mod.rs

@@ -953,7 +953,6 @@ mod tests {
                                                 attrs: None,}),
                                                 ast::DUMMY_NODE_ID),
                                             span: sp(17,19)}),
-                                        expr: None,
                                         id: ast::DUMMY_NODE_ID,
                                         rules: ast::BlockCheckMode::Default, // no idea
                                         span: sp(15,21),

src/libsyntax/parse/parser.rs

@@ -3217,9 +3217,11 @@ impl<'a> Parser<'a> {
                 let body_expr = self.parse_expr()?;
                 P(ast::Block {
                     id: ast::DUMMY_NODE_ID,
-                    stmts: vec![],
                     span: body_expr.span,
-                    expr: Some(body_expr),
+                    stmts: vec![Spanned {
+                        span: body_expr.span,
+                        node: StmtKind::Expr(body_expr, ast::DUMMY_NODE_ID),
+                    }],
                     rules: BlockCheckMode::Default,
                 })
             }
@@ -4082,7 +4084,6 @@ impl<'a> Parser<'a> {
     /// Precondition: already parsed the '{'.
     fn parse_block_tail(&mut self, lo: BytePos, s: BlockCheckMode) -> PResult<'a, P<Block>> {
         let mut stmts = vec![];
-        let mut expr = None;
 
         while !self.eat(&token::CloseDelim(token::Brace)) {
             let Spanned {node, span} = if let Some(s) = self.parse_stmt_() {
@@ -4095,11 +4096,10 @@ impl<'a> Parser<'a> {
             };
             match node {
                 StmtKind::Expr(e, _) => {
-                    self.handle_expression_like_statement(e, span, &mut stmts, &mut expr)?;
+                    self.handle_expression_like_statement(e, span, &mut stmts)?;
                 }
                 StmtKind::Mac(mac, MacStmtStyle::NoBraces, attrs) => {
-                    // statement macro without braces; might be an
-                    // expr depending on whether a semicolon follows
+                    // statement macro without braces
                     match self.token {
                         token::Semi => {
                             stmts.push(Spanned {
@@ -4115,11 +4115,7 @@ impl<'a> Parser<'a> {
                             let lo = e.span.lo;
                             let e = self.parse_dot_or_call_expr_with(e, lo, attrs)?;
                             let e = self.parse_assoc_expr_with(0, LhsExpr::AlreadyParsed(e))?;
-                            self.handle_expression_like_statement(
-                                e,
-                                span,
-                                &mut stmts,
-                                &mut expr)?;
+                            self.handle_expression_like_statement(e, span, &mut stmts)?;
                         }
                     }
                 }
@@ -4133,13 +4129,6 @@ impl<'a> Parser<'a> {
                             });
                             self.bump();
                         }
-                        token::CloseDelim(token::Brace) => {
-                            // if a block ends in `m!(arg)` without
-                            // a `;`, it must be an expr
-                            expr = Some(self.mk_mac_expr(span.lo, span.hi,
-                                                         m.and_then(|x| x.node),
-                                                         attrs));
-                        }
                         _ => {
                             stmts.push(Spanned {
                                 node: StmtKind::Mac(m, style, attrs),
@@ -4165,7 +4154,6 @@ impl<'a> Parser<'a> {
 
         Ok(P(ast::Block {
             stmts: stmts,
-            expr: expr,
             id: ast::DUMMY_NODE_ID,
             rules: s,
             span: mk_sp(lo, self.last_span.hi),
@@ -4175,8 +4163,7 @@ impl<'a> Parser<'a> {
     fn handle_expression_like_statement(&mut self,
                                         e: P<Expr>,
                                         span: Span,
-                                        stmts: &mut Vec<Stmt>,
-                                        last_block_expr: &mut Option<P<Expr>>)
+                                        stmts: &mut Vec<Stmt>)
                                         -> PResult<'a, ()> {
         // expression without semicolon
         if classify::expr_requires_semi_to_be_stmt(&e) {
@@ -4202,7 +4189,6 @@ impl<'a> Parser<'a> {
                     span: span_with_semi,
                 });
             }
-            token::CloseDelim(token::Brace) => *last_block_expr = Some(e),
             _ => {
                 stmts.push(Spanned {
                     node: StmtKind::Expr(e, ast::DUMMY_NODE_ID),