src/librustc_mir/build/expr/as_constant.rs

   1 //! See docs in build/expr/mod.rs
   2
   3 use crate::build::Builder;
   4 use crate::hair::*;
   5 use rustc::mir::*;
   6 use rustc::ty::CanonicalUserTypeAnnotation;
   7
   8 impl<'a, 'tcx> Builder<'a, 'tcx> {
   9     /// Compile `expr`, yielding a compile-time constant. Assumes that
  10     /// `expr` is a valid compile-time constant!
  11     pub fn as_constant<M>(&mut self, expr: M) -> Constant<'tcx>
  12     where
  13         M: Mirror<'tcx, Output = Expr<'tcx>>,
  14     {
  15         let expr = self.hir.mirror(expr);
  16         self.expr_as_constant(expr)
  17     }
  18
  19     fn expr_as_constant(&mut self, expr: Expr<'tcx>) -> Constant<'tcx> {
  20         let this = self;
  21         let Expr {
  22             ty,
  23             temp_lifetime: _,
  24             span,
  25             kind,
  26         } = expr;
  27         match kind {
  28             ExprKind::Scope {
  29                 region_scope: _,
  30                 lint_level: _,
  31                 value,
  32             } => this.as_constant(value),
  33             ExprKind::Literal { literal, user_ty } => {
  34                 let user_ty = user_ty.map(|user_ty| {
  35                     this.canonical_user_type_annotations.push(CanonicalUserTypeAnnotation {
  36                         span,
  37                         user_ty,
  38                         inferred_ty: ty,
  39                     })
  40                 });
  41                 assert_eq!(literal.ty, ty);
  42                 Constant {
  43                     span,
  44                     user_ty,
  45                     literal,
  46                 }
  47             },
  48             ExprKind::StaticRef { literal, .. } => {
  49                 Constant {
  50                     span,
  51                     user_ty: None,
  52                     literal,
  53                 }
  54             }
  55             _ => span_bug!(span, "expression is not a valid constant {:?}", kind),
  56         }
  57     }
  58 }