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 use syntax_pos::Span;
  16
  17 impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
  18     pub fn ast_block(&mut self,
  19                      destination: &Lvalue<'tcx>,
  20                      block: BasicBlock,
  21                      ast_block: &'tcx hir::Block,
  22                      source_info: SourceInfo)
  23                      -> BlockAnd<()> {
  24         let Block { extent, span, stmts, expr, targeted_by_break } = self.hir.mirror(ast_block);
  25         self.in_scope(extent, block, move |this| {
  26             if targeted_by_break {
  27                 // This is a `break`-able block (currently only `catch { ... }`)
  28                 let exit_block = this.cfg.start_new_block();
  29                 let block_exit = this.in_breakable_scope(None, exit_block,
  30                                                          destination.clone(), |this| {
  31                     this.ast_block_stmts(destination, block, span, stmts, expr)
  32                 });
  33                 this.cfg.terminate(unpack!(block_exit), source_info,
  34                                    TerminatorKind::Goto { target: exit_block });
  35                 exit_block.unit()
  36             } else {
  37                 this.ast_block_stmts(destination, block, span, stmts, expr)
  38             }
  39         })
  40     }
  41
  42     fn ast_block_stmts(&mut self,
  43                        destination: &Lvalue<'tcx>,
  44                        mut block: BasicBlock,
  45                        span: Span,
  46                        stmts: Vec<StmtRef<'tcx>>,
  47                        expr: Option<ExprRef<'tcx>>)
  48                        -> BlockAnd<()> {
  49         let this = self;
  50
  51         // This convoluted structure is to avoid using recursion as we walk down a list
  52         // of statements. Basically, the structure we get back is something like:
  53         //
  54         //    let x = <init> in {
  55         //       expr1;
  56         //       let y = <init> in {
  57         //           expr2;
  58         //           expr3;
  59         //           ...
  60         //       }
  61         //    }
  62         //
  63         // The let bindings are valid till the end of block so all we have to do is to pop all
  64         // the let-scopes at the end.
  65         //
  66         // First we build all the statements in the block.
  67         let mut let_extent_stack = Vec::with_capacity(8);
  68         let outer_visibility_scope = this.visibility_scope;
  69         for stmt in stmts {
  70             let Stmt { span: _, kind } = this.hir.mirror(stmt);
  71             match kind {
  72                 StmtKind::Expr { scope, expr } => {
  73                     unpack!(block = this.in_scope(scope, block, |this| {
  74                         let expr = this.hir.mirror(expr);
  75                         this.stmt_expr(block, expr)
  76                     }));
  77                 }
  78                 StmtKind::Let { remainder_scope, init_scope, pattern, initializer } => {
  79                     let tcx = this.hir.tcx();
  80
  81                     // Enter the remainder scope, i.e. the bindings' destruction scope.
  82                     this.push_scope(remainder_scope);
  83                     let_extent_stack.push(remainder_scope);
  84
  85                     // Declare the bindings, which may create a visibility scope.
  86                     let remainder_span = remainder_scope.span(&tcx.hir);
  87                     let remainder_span = remainder_span.unwrap_or(span);
  88                     let scope = this.declare_bindings(None, remainder_span, &pattern);
  89
  90                     // Evaluate the initializer, if present.
  91                     if let Some(init) = initializer {
  92                         unpack!(block = this.in_scope(init_scope, block, move |this| {
  93                             // FIXME #30046                              ^~~~
  94                             this.expr_into_pattern(block, pattern, init)
  95                         }));
  96                     } else {
  97                         this.visit_bindings(&pattern, &mut |this, _, _, node, span, _| {
  98                             this.storage_live_binding(block, node, span);
  99                             this.schedule_drop_for_binding(node, span);
 100                         })
 101                     }
 102
 103                     // Enter the visibility scope, after evaluating the initializer.
 104                     if let Some(visibility_scope) = scope {
 105                         this.visibility_scope = visibility_scope;
 106                     }
 107                 }
 108             }
 109         }
 110         // Then, the block may have an optional trailing expression which is a “return” value
 111         // of the block.
 112         if let Some(expr) = expr {
 113             unpack!(block = this.into(destination, block, expr));
 114         } else {
 115             let source_info = this.source_info(span);
 116             this.cfg.push_assign_unit(block, source_info, destination);
 117         }
 118         // Finally, we pop all the let scopes before exiting out from the scope of block
 119         // itself.
 120         for extent in let_extent_stack.into_iter().rev() {
 121             unpack!(block = this.pop_scope(extent, block));
 122         }
 123         // Restore the original visibility scope.
 124         this.visibility_scope = outer_visibility_scope;
 125         block.unit()
 126     }
 127 }