compiler/rustc_ast_lowering/src/block.rs

   1 use crate::{ImplTraitContext, ImplTraitPosition, LoweringContext};
   2 use rustc_ast::{Block, BlockCheckMode, Local, LocalKind, Stmt, StmtKind};
   3 use rustc_hir as hir;
   4 use rustc_session::parse::feature_err;
   5 use rustc_span::sym;
   6
   7 use smallvec::SmallVec;
   8
   9 impl<'a, 'hir> LoweringContext<'a, 'hir> {
  10     pub(super) fn lower_block(
  11         &mut self,
  12         b: &Block,
  13         targeted_by_break: bool,
  14     ) -> &'hir hir::Block<'hir> {
  15         self.arena.alloc(self.lower_block_noalloc(b, targeted_by_break))
  16     }
  17
  18     pub(super) fn lower_block_noalloc(
  19         &mut self,
  20         b: &Block,
  21         targeted_by_break: bool,
  22     ) -> hir::Block<'hir> {
  23         let (stmts, expr) = self.lower_stmts(&b.stmts);
  24         let rules = self.lower_block_check_mode(&b.rules);
  25         let hir_id = self.lower_node_id(b.id);
  26         hir::Block { hir_id, stmts, expr, rules, span: self.lower_span(b.span), targeted_by_break }
  27     }
  28
  29     fn lower_stmts(
  30         &mut self,
  31         mut ast_stmts: &[Stmt],
  32     ) -> (&'hir [hir::Stmt<'hir>], Option<&'hir hir::Expr<'hir>>) {
  33         let mut stmts = SmallVec::<[hir::Stmt<'hir>; 8]>::new();
  34         let mut expr = None;
  35         while let [s, tail @ ..] = ast_stmts {
  36             match s.kind {
  37                 StmtKind::Local(ref local) => {
  38                     let hir_id = self.lower_node_id(s.id);
  39                     let local = self.lower_local(local);
  40                     self.alias_attrs(hir_id, local.hir_id);
  41                     let kind = hir::StmtKind::Local(local);
  42                     let span = self.lower_span(s.span);
  43                     stmts.push(hir::Stmt { hir_id, kind, span });
  44                 }
  45                 StmtKind::Item(ref it) => {
  46                     stmts.extend(self.lower_item_ref(it).into_iter().enumerate().map(
  47                         |(i, item_id)| {
  48                             let hir_id = match i {
  49                                 0 => self.lower_node_id(s.id),
  50                                 _ => self.next_id(),
  51                             };
  52                             let kind = hir::StmtKind::Item(item_id);
  53                             let span = self.lower_span(s.span);
  54                             hir::Stmt { hir_id, kind, span }
  55                         },
  56                     ));
  57                 }
  58                 StmtKind::Expr(ref e) => {
  59                     let e = self.lower_expr(e);
  60                     if tail.is_empty() {
  61                         expr = Some(e);
  62                     } else {
  63                         let hir_id = self.lower_node_id(s.id);
  64                         self.alias_attrs(hir_id, e.hir_id);
  65                         let kind = hir::StmtKind::Expr(e);
  66                         let span = self.lower_span(s.span);
  67                         stmts.push(hir::Stmt { hir_id, kind, span });
  68                     }
  69                 }
  70                 StmtKind::Semi(ref e) => {
  71                     let e = self.lower_expr(e);
  72                     let hir_id = self.lower_node_id(s.id);
  73                     self.alias_attrs(hir_id, e.hir_id);
  74                     let kind = hir::StmtKind::Semi(e);
  75                     let span = self.lower_span(s.span);
  76                     stmts.push(hir::Stmt { hir_id, kind, span });
  77                 }
  78                 StmtKind::Empty => {}
  79                 StmtKind::MacCall(..) => panic!("shouldn't exist here"),
  80             }
  81             ast_stmts = &ast_stmts[1..];
  82         }
  83         (self.arena.alloc_from_iter(stmts), expr)
  84     }
  85
  86     fn lower_local(&mut self, l: &Local) -> &'hir hir::Local<'hir> {
  87         let ty = l.ty.as_ref().map(|t| {
  88             self.lower_ty(t, &mut ImplTraitContext::Disallowed(ImplTraitPosition::Variable))
  89         });
  90         let init = l.kind.init().map(|init| self.lower_expr(init));
  91         let hir_id = self.lower_node_id(l.id);
  92         let pat = self.lower_pat(&l.pat);
  93         let els = if let LocalKind::InitElse(_, els) = &l.kind {
  94             if !self.tcx.features().let_else {
  95                 feature_err(
  96                     &self.tcx.sess.parse_sess,
  97                     sym::let_else,
  98                     l.span,
  99                     "`let...else` statements are unstable",
 100                 )
 101                 .emit();
 102             }
 103             Some(self.lower_block(els, false))
 104         } else {
 105             None
 106         };
 107         let span = self.lower_span(l.span);
 108         let source = hir::LocalSource::Normal;
 109         self.lower_attrs(hir_id, &l.attrs);
 110         self.arena.alloc(hir::Local { hir_id, ty, pat, init, els, span, source })
 111     }
 112
 113     fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
 114         match *b {
 115             BlockCheckMode::Default => hir::BlockCheckMode::DefaultBlock,
 116             BlockCheckMode::Unsafe(u) => {
 117                 hir::BlockCheckMode::UnsafeBlock(self.lower_unsafe_source(u))
 118             }
 119         }
 120     }
 121 }