src/librustc_mir_build/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_middle::mir::*;
   6 use rustc_middle::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     crate 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 { ty, temp_lifetime: _, span, kind } = expr;
  22         match kind {
  23             ExprKind::Scope { region_scope: _, lint_level: _, value } => this.as_constant(value),
  24             ExprKind::Literal { literal, user_ty } => {
  25                 let user_ty = user_ty.map(|user_ty| {
  26                     this.canonical_user_type_annotations.push(CanonicalUserTypeAnnotation {
  27                         span,
  28                         user_ty,
  29                         inferred_ty: ty,
  30                     })
  31                 });
  32                 assert_eq!(literal.ty, ty);
  33                 Constant { span, user_ty, literal }
  34             }
  35             ExprKind::StaticRef { literal, .. } => Constant { span, user_ty: None, literal },
  36             _ => span_bug!(span, "expression is not a valid constant {:?}", kind),
  37         }
  38     }
  39 }