rustc_ast_lowering/
block.rs

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1use rustc_ast::{Block, BlockCheckMode, Local, LocalKind, Stmt, StmtKind};
2use rustc_hir as hir;
3use rustc_span::sym;
4use smallvec::SmallVec;
5
6use crate::{ImplTraitContext, ImplTraitPosition, LoweringContext};
7
8impl<'a, 'hir> LoweringContext<'a, 'hir> {
9    pub(super) fn lower_block(
10        &mut self,
11        b: &Block,
12        targeted_by_break: bool,
13    ) -> &'hir hir::Block<'hir> {
14        let hir_id = self.lower_node_id(b.id);
15        self.arena.alloc(self.lower_block_noalloc(hir_id, b, targeted_by_break))
16    }
17
18    pub(super) fn lower_block_noalloc(
19        &mut self,
20        hir_id: hir::HirId,
21        b: &Block,
22        targeted_by_break: bool,
23    ) -> hir::Block<'hir> {
24        let (stmts, expr) = self.lower_stmts(&b.stmts);
25        let rules = self.lower_block_check_mode(&b.rules);
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::Let(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::Let(local);
42                    let span = self.lower_span(s.span);
43                    stmts.push(hir::Stmt { hir_id, kind, span });
44                }
45                StmtKind::Item(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(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(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 = tail;
82        }
83        (self.arena.alloc_from_iter(stmts), expr)
84    }
85
86    /// Return an `ImplTraitContext` that allows impl trait in bindings if
87    /// the feature gate is enabled, or issues a feature error if it is not.
88    fn impl_trait_in_bindings_ctxt(&self, position: ImplTraitPosition) -> ImplTraitContext {
89        if self.tcx.features().impl_trait_in_bindings() {
90            ImplTraitContext::InBinding
91        } else {
92            ImplTraitContext::FeatureGated(position, sym::impl_trait_in_bindings)
93        }
94    }
95
96    fn lower_local(&mut self, l: &Local) -> &'hir hir::LetStmt<'hir> {
97        // Let statements are allowed to have impl trait in bindings.
98        let ty = l.ty.as_ref().map(|t| {
99            self.lower_ty(t, self.impl_trait_in_bindings_ctxt(ImplTraitPosition::Variable))
100        });
101        let init = l.kind.init().map(|init| self.lower_expr(init));
102        let hir_id = self.lower_node_id(l.id);
103        let pat = self.lower_pat(&l.pat);
104        let els = if let LocalKind::InitElse(_, els) = &l.kind {
105            Some(self.lower_block(els, false))
106        } else {
107            None
108        };
109        let span = self.lower_span(l.span);
110        let source = hir::LocalSource::Normal;
111        self.lower_attrs(hir_id, &l.attrs, l.span);
112        self.arena.alloc(hir::LetStmt { hir_id, ty, pat, init, els, span, source })
113    }
114
115    fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
116        match *b {
117            BlockCheckMode::Default => hir::BlockCheckMode::DefaultBlock,
118            BlockCheckMode::Unsafe(u) => {
119                hir::BlockCheckMode::UnsafeBlock(self.lower_unsafe_source(u))
120            }
121        }
122    }
123}
rustc_ast_lowering/block.rs

rustc_ast_lowering/
block.rs
