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//! See docs in build/expr/mod.rs
use crate::build::Builder;
use crate::hair::*;
use rustc::mir::*;
use rustc::ty::CanonicalUserTypeAnnotation;
impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
/// Compile `expr`, yielding a compile-time constant. Assumes that
/// `expr` is a valid compile-time constant!
pub fn as_constant<M>(&mut self, expr: M) -> Constant<'tcx>
where
M: Mirror<'tcx, Output = Expr<'tcx>>,
{
let expr = self.hir.mirror(expr);
self.expr_as_constant(expr)
}
fn expr_as_constant(&mut self, expr: Expr<'tcx>) -> Constant<'tcx> {
let this = self;
let Expr {
ty,
temp_lifetime: _,
span,
kind,
} = expr;
match kind {
ExprKind::Scope {
region_scope: _,
lint_level: _,
value,
} => this.as_constant(value),
ExprKind::Literal { literal, user_ty } => {
let user_ty = user_ty.map(|user_ty| {
this.canonical_user_type_annotations.push(CanonicalUserTypeAnnotation {
span,
user_ty,
inferred_ty: ty,
})
});
Constant {
span,
ty,
user_ty,
literal,
}
},
_ => span_bug!(span, "expression is not a valid constant {:?}", kind),
}
}
}
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