refactor if so that the "then type" is an expression

src/librustc/cfg/construct.rs

@@ -195,7 +195,7 @@ fn expr(&mut self, expr: &hir::Expr, pred: CFGIndex) -> CFGIndex {
                 //   [..expr..]
                 //
                 let cond_exit = self.expr(&cond, pred);                // 1
-                let then_exit = self.block(&then, cond_exit);          // 2
+                let then_exit = self.expr(&then, cond_exit);          // 2
                 self.add_ast_node(expr.id, &[cond_exit, then_exit])      // 3,4
             }
 
@@ -215,7 +215,7 @@ fn expr(&mut self, expr: &hir::Expr, pred: CFGIndex) -> CFGIndex {
                 //   [..expr..]
                 //
                 let cond_exit = self.expr(&cond, pred);                // 1
-                let then_exit = self.block(&then, cond_exit);          // 2
+                let then_exit = self.expr(&then, cond_exit);          // 2
                 let else_exit = self.expr(&otherwise, cond_exit);      // 3
                 self.add_ast_node(expr.id, &[then_exit, else_exit])      // 4, 5
             }

src/librustc/hir/intravisit.rs

@@ -960,7 +960,7 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr) {
         }
         ExprIf(ref head_expression, ref if_block, ref optional_else) => {
             visitor.visit_expr(head_expression);
-            visitor.visit_block(if_block);
+            visitor.visit_expr(if_block);
             walk_list!(visitor, visit_expr, optional_else);
         }
         ExprWhile(ref subexpression, ref block, ref opt_sp_name) => {

src/librustc/hir/lowering.rs

@@ -1856,7 +1856,10 @@ fn lower_expr(&mut self, e: &Expr) -> hir::Expr {
                     }
                 });
 
-                hir::ExprIf(P(self.lower_expr(cond)), self.lower_block(blk, None), else_opt)
+                let then_blk = self.lower_block(blk, None);
+                let then_expr = self.expr_block(then_blk, ThinVec::new());
+
+                hir::ExprIf(P(self.lower_expr(cond)), P(then_expr), else_opt)
             }
             ExprKind::While(ref cond, ref body, opt_ident) => {
                 self.with_loop_scope(e.id, |this|

src/librustc/hir/mod.rs

@@ -994,7 +994,7 @@ pub enum Expr_ {
     /// An `if` block, with an optional else block
     ///
     /// `if expr { block } else { expr }`
-    ExprIf(P<Expr>, P<Block>, Option<P<Expr>>),
+    ExprIf(P<Expr>, P<Expr>, Option<P<Expr>>),
     /// A while loop, with an optional label
     ///
     /// `'label: while expr { block }`

src/librustc/hir/print.rs

@@ -1036,7 +1036,7 @@ fn print_else(&mut self, els: Option<&hir::Expr>) -> io::Result<()> {
                         word(&mut self.s, " else if ")?;
                         self.print_expr(&i)?;
                         space(&mut self.s)?;
-                        self.print_block(&then)?;
+                        self.print_expr(&then)?;
                         self.print_else(e.as_ref().map(|e| &**e))
                     }
                     // "final else"
@@ -1058,13 +1058,13 @@ fn print_else(&mut self, els: Option<&hir::Expr>) -> io::Result<()> {
 
     pub fn print_if(&mut self,
                     test: &hir::Expr,
-                    blk: &hir::Block,
+                    blk: &hir::Expr,
                     elseopt: Option<&hir::Expr>)
                     -> io::Result<()> {
         self.head("if")?;
         self.print_expr(test)?;
         space(&mut self.s)?;
-        self.print_block(blk)?;
+        self.print_expr(blk)?;
         self.print_else(elseopt)
     }
 

src/librustc/middle/expr_use_visitor.rs

@@ -414,9 +414,9 @@ pub fn walk_expr(&mut self, expr: &hir::Expr) {
                 self.consume_exprs(exprs);
             }
 
-            hir::ExprIf(ref cond_expr, ref then_blk, ref opt_else_expr) => {
+            hir::ExprIf(ref cond_expr, ref then_expr, ref opt_else_expr) => {
                 self.consume_expr(&cond_expr);
-                self.walk_block(&then_blk);
+                self.walk_expr(&then_expr);
                 if let Some(ref else_expr) = *opt_else_expr {
                     self.consume_expr(&else_expr);
                 }

src/librustc/middle/liveness.rs

@@ -951,7 +951,7 @@ fn propagate_through_expr(&mut self, expr: &Expr, succ: LiveNode)
             //   (  succ  )
             //
             let else_ln = self.propagate_through_opt_expr(els.as_ref().map(|e| &**e), succ);
-            let then_ln = self.propagate_through_block(&then, succ);
+            let then_ln = self.propagate_through_expr(&then, succ);
             let ln = self.live_node(expr.id, expr.span);
             self.init_from_succ(ln, else_ln);
             self.merge_from_succ(ln, then_ln, false);

src/librustc_mir/hair/cx/expr.rs

@@ -636,7 +636,7 @@ fn make_mirror_unadjusted<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
         hir::ExprIf(ref cond, ref then, ref otherwise) => {
             ExprKind::If {
                 condition: cond.to_ref(),
-                then: block::to_expr_ref(cx, then),
+                then: then.to_ref(),
                 otherwise: otherwise.to_ref(),
             }
         }

src/librustc_typeck/check/mod.rs

@@ -2739,7 +2739,7 @@ fn check_method_call(&self,
     // or if-else.
     fn check_then_else(&self,
                        cond_expr: &'gcx hir::Expr,
-                       then_blk: &'gcx hir::Block,
+                       then_expr: &'gcx hir::Expr,
                        opt_else_expr: Option<&'gcx hir::Expr>,
                        sp: Span,
                        expected: Expectation<'tcx>) -> Ty<'tcx> {
@@ -2748,7 +2748,7 @@ fn check_then_else(&self,
         self.diverges.set(Diverges::Maybe);
 
         let expected = expected.adjust_for_branches(self);
-        let then_ty = self.check_block_with_expected(then_blk, expected);
+        let then_ty = self.check_expr_with_expectation(then_expr, expected);
         let then_diverges = self.diverges.get();
         self.diverges.set(Diverges::Maybe);
 
@@ -2763,26 +2763,13 @@ fn check_then_else(&self,
             // to assign coercions to, otherwise it's () or diverging.
             expected_ty = then_ty;
             found_ty = else_ty;
-            result = if let Some(ref then) = then_blk.expr {
-                let res = self.try_find_coercion_lub(&cause, || Some(&**then),
-                                                     then_ty, else_expr, else_ty);
-
-                // In case we did perform an adjustment, we have to update
-                // the type of the block, because old trans still uses it.
-                if res.is_ok() {
-                    let adj = self.tables.borrow().adjustments.get(&then.id).cloned();
-                    if let Some(adj) = adj {
-                        self.write_ty(then_blk.id, adj.target);
-                    }
-                }
 
-                res
-            } else {
-                self.commit_if_ok(|_| {
-                    let trace = TypeTrace::types(&cause, true, then_ty, else_ty);
-                    self.lub(true, trace, &then_ty, &else_ty)
-                        .map(|ok| self.register_infer_ok_obligations(ok))
-                })
+            let coerce_to = expected.only_has_type(self).unwrap_or(then_ty);
+            result = {
+                self.try_coerce(then_expr, then_ty, coerce_to)
+                    .and_then(|t| {
+                        self.try_find_coercion_lub(&cause, || Some(then_expr), t, else_expr, else_ty)
+                    })
             };
 
             // We won't diverge unless both branches do (or the condition does).
@@ -3587,9 +3574,9 @@ fn check_expr_kind(&self,
                 tcx.mk_nil()
             }
           }
-          hir::ExprIf(ref cond, ref then_blk, ref opt_else_expr) => {
-            self.check_then_else(&cond, &then_blk, opt_else_expr.as_ref().map(|e| &**e),
-                                 expr.span, expected)
+          hir::ExprIf(ref cond, ref then_expr, ref opt_else_expr) => {
+              self.check_then_else(&cond, then_expr, opt_else_expr.as_ref().map(|e| &**e),
+                                   expr.span, expected)
           }
           hir::ExprWhile(ref cond, ref body, _) => {
             let unified = self.tcx.mk_nil();