src/librustc_mir/build/block.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use build::{BlockAnd, BlockAndExtension, Builder};
  12 use hair::*;
  13 use rustc::mir::*;
  14 use rustc::hir;
  15
  16 impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
  17     pub fn ast_block(&mut self,
  18                      destination: &Lvalue<'tcx>,
  19                      mut block: BasicBlock,
  20                      ast_block: &'tcx hir::Block)
  21                      -> BlockAnd<()> {
  22         let Block { extent, span, stmts, expr } = self.hir.mirror(ast_block);
  23         self.in_scope(extent, block, move |this| {
  24             // This convoluted structure is to avoid using recursion as we walk down a list
  25             // of statements. Basically, the structure we get back is something like:
  26             //
  27             //    let x = <init> in {
  28             //       expr1;
  29             //       let y = <init> in {
  30             //           expr2;
  31             //           expr3;
  32             //           ...
  33             //       }
  34             //    }
  35             //
  36             // The let bindings are valid till the end of block so all we have to do is to pop all
  37             // the let-scopes at the end.
  38             //
  39             // First we build all the statements in the block.
  40             let mut let_extent_stack = Vec::with_capacity(8);
  41             let outer_visibility_scope = this.visibility_scope;
  42             for stmt in stmts {
  43                 let Stmt { span: _, kind } = this.hir.mirror(stmt);
  44                 match kind {
  45                     StmtKind::Expr { scope, expr } => {
  46                         unpack!(block = this.in_scope(scope, block, |this| {
  47                             let expr = this.hir.mirror(expr);
  48                             this.stmt_expr(block, expr)
  49                         }));
  50                     }
  51                     StmtKind::Let { remainder_scope, init_scope, pattern, initializer } => {
  52                         let tcx = this.hir.tcx();
  53
  54                         // Enter the remainder scope, i.e. the bindings' destruction scope.
  55                         this.push_scope(remainder_scope);
  56                         let_extent_stack.push(remainder_scope);
  57
  58                         // Declare the bindings, which may create a visibility scope.
  59                         let remainder_span = remainder_scope.span(&tcx.region_maps, &tcx.hir);
  60                         let remainder_span = remainder_span.unwrap_or(span);
  61                         let scope = this.declare_bindings(None, remainder_span, &pattern);
  62
  63                         // Evaluate the initializer, if present.
  64                         if let Some(init) = initializer {
  65                             unpack!(block = this.in_scope(init_scope, block, move |this| {
  66                                 // FIXME #30046                              ^~~~
  67                                 this.expr_into_pattern(block, pattern, init)
  68                             }));
  69                         } else {
  70                             this.visit_bindings(&pattern, &mut |this, _, _, node, span, _| {
  71                                 this.storage_live_binding(block, node, span);
  72                                 this.schedule_drop_for_binding(node, span);
  73                             })
  74                         }
  75
  76                         // Enter the visibility scope, after evaluating the initializer.
  77                         if let Some(visibility_scope) = scope {
  78                             this.visibility_scope = visibility_scope;
  79                         }
  80                     }
  81                 }
  82             }
  83             // Then, the block may have an optional trailing expression which is a “return” value
  84             // of the block.
  85             if let Some(expr) = expr {
  86                 unpack!(block = this.into(destination, block, expr));
  87             } else {
  88                 let source_info = this.source_info(span);
  89                 this.cfg.push_assign_unit(block, source_info, destination);
  90             }
  91             // Finally, we pop all the let scopes before exiting out from the scope of block
  92             // itself.
  93             for extent in let_extent_stack.into_iter().rev() {
  94                 unpack!(block = this.pop_scope(extent, block));
  95             }
  96             // Restore the original visibility scope.
  97             this.visibility_scope = outer_visibility_scope;
  98             block.unit()
  99         })
 100     }
 101 }