compiler/rustc_mir_build/src/thir/constant.rs

   1 use rustc_ast as ast;
   2 use rustc_middle::mir::interpret::{LitToConstError, LitToConstInput};
   3 use rustc_middle::ty::{self, ParamEnv, ScalarInt, TyCtxt};
   4 use rustc_span::DUMMY_SP;
   5
   6 pub(crate) fn lit_to_const<'tcx>(
   7     tcx: TyCtxt<'tcx>,
   8     lit_input: LitToConstInput<'tcx>,
   9 ) -> Result<ty::Const<'tcx>, LitToConstError> {
  10     let LitToConstInput { lit, ty, neg } = lit_input;
  11
  12     let trunc = |n| {
  13         let param_ty = ParamEnv::reveal_all().and(ty);
  14         let width = tcx
  15             .layout_of(param_ty)
  16             .map_err(|_| {
  17                 LitToConstError::Reported(tcx.sess.delay_span_bug(
  18                     DUMMY_SP,
  19                     format!("couldn't compute width of literal: {:?}", lit_input.lit),
  20                 ))
  21             })?
  22             .size;
  23         trace!("trunc {} with size {} and shift {}", n, width.bits(), 128 - width.bits());
  24         let result = width.truncate(n);
  25         trace!("trunc result: {}", result);
  26
  27         Ok(ScalarInt::try_from_uint(result, width)
  28             .unwrap_or_else(|| bug!("expected to create ScalarInt from uint {:?}", result)))
  29     };
  30
  31     let valtree = match (lit, &ty.kind()) {
  32         (ast::LitKind::Str(s, _), ty::Ref(_, inner_ty, _)) if inner_ty.is_str() => {
  33             let str_bytes = s.as_str().as_bytes();
  34             ty::ValTree::from_raw_bytes(tcx, str_bytes)
  35         }
  36         (ast::LitKind::ByteStr(data, _), ty::Ref(_, inner_ty, _))
  37             if matches!(inner_ty.kind(), ty::Slice(_)) =>
  38         {
  39             let bytes = data as &[u8];
  40             ty::ValTree::from_raw_bytes(tcx, bytes)
  41         }
  42         (ast::LitKind::ByteStr(data, _), ty::Ref(_, inner_ty, _)) if inner_ty.is_array() => {
  43             let bytes = data as &[u8];
  44             ty::ValTree::from_raw_bytes(tcx, bytes)
  45         }
  46         (ast::LitKind::Byte(n), ty::Uint(ty::UintTy::U8)) => {
  47             ty::ValTree::from_scalar_int((*n).into())
  48         }
  49         (ast::LitKind::Int(n, _), ty::Uint(_)) | (ast::LitKind::Int(n, _), ty::Int(_)) => {
  50             let scalar_int =
  51                 trunc(if neg { (*n as i128).overflowing_neg().0 as u128 } else { *n })?;
  52             ty::ValTree::from_scalar_int(scalar_int)
  53         }
  54         (ast::LitKind::Bool(b), ty::Bool) => ty::ValTree::from_scalar_int((*b).into()),
  55         (ast::LitKind::Char(c), ty::Char) => ty::ValTree::from_scalar_int((*c).into()),
  56         (ast::LitKind::Err, _) => {
  57             return Err(LitToConstError::Reported(
  58                 tcx.sess.delay_span_bug(DUMMY_SP, "encountered LitKind::Err during mir build"),
  59             ));
  60         }
  61         _ => return Err(LitToConstError::TypeError),
  62     };
  63
  64     Ok(tcx.mk_const(valtree, ty))
  65 }