introduce lower_block_expr convenience function, and use it

Author: nikomatsakis

src/librustc/hir/lowering.rs

@@ -2708,6 +2708,13 @@ impl<'a> LoweringContext<'a> {
         })
     }
 
+    /// Lowers a block directly to an expression, presuming that it
+    /// has no attributes and is not targeted by a `break`.
+    fn lower_block_expr(&mut self, b: &Block) -> hir::Expr {
+        let block = self.lower_block(b, false);
+        self.expr_block(block, ThinVec::new())
+    }
+
     fn lower_pat(&mut self, p: &Pat) -> P<hir::Pat> {
         let node = match p.node {
             PatKind::Wild => hir::PatKind::Wild,

src/librustc/hir/lowering/expr.rs

@@ -90,10 +90,7 @@ impl LoweringContext<'_> {
             ),
             ExprKind::Async(capture_clause, closure_node_id, ref block) => {
                 self.make_async_expr(capture_clause, closure_node_id, None, block.span, |this| {
-                    this.with_new_scopes(|this| {
-                        let block = this.lower_block(block, false);
-                        this.expr_block(block, ThinVec::new())
-                    })
+                    this.with_new_scopes(|this| this.lower_block_expr(block))
                 })
             }
             ExprKind::Await(ref expr) => self.lower_expr_await(e.span, expr),
@@ -284,8 +281,7 @@ impl LoweringContext<'_> {
         let else_arm = self.arm(hir_vec![else_pat], P(else_expr));
 
         // Handle then + scrutinee:
-        let then_blk = self.lower_block(then, false);
-        let then_expr = self.expr_block(then_blk, ThinVec::new());
+        let then_expr = self.lower_block_expr(then);
         let (then_pat, scrutinee, desugar) = match cond.node {
             // `<pat> => <then>`:
             ExprKind::Let(ref pat, ref scrutinee) => {
@@ -335,8 +331,7 @@ impl LoweringContext<'_> {
         };
 
         // Handle then + scrutinee:
-        let then_blk = self.lower_block(body, false);
-        let then_expr = self.expr_block(then_blk, ThinVec::new());
+        let then_expr = self.lower_block_expr(body);
         let (then_pat, scrutinee, desugar, source) = match cond.node {
             ExprKind::Let(ref pat, ref scrutinee) => {
                 // to:

src/librustc/hir/lowering/item.rs

@@ -1071,10 +1071,7 @@ impl LoweringContext<'_> {
     }
 
     fn lower_fn_body_block(&mut self, decl: &FnDecl, body: &Block) -> hir::BodyId {
-        self.lower_fn_body(decl, |this| {
-            let body = this.lower_block(body, false);
-            this.expr_block(body, ThinVec::new())
-        })
+        self.lower_fn_body(decl, |this| this.lower_block_expr(body))
     }
 
     pub(super) fn lower_const_body(&mut self, expr: &Expr) -> hir::BodyId {
@@ -1220,8 +1217,7 @@ impl LoweringContext<'_> {
                 CaptureBy::Value, closure_id, None, body.span,
                 |this| {
                     // Create a block from the user's function body:
-                    let user_body = this.lower_block(body, false);
-                    let user_body = this.expr_block(user_body, ThinVec::new());
+                    let user_body = this.lower_block_expr(body);
 
                     // Transform into `drop-temps { <user-body> }`, an expression:
                     let desugared_span = this.mark_span_with_reason(