bjoernager/rust
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Make const panic!("..") work in Rust 2021.

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During const eval, this replaces calls to core::panicking::panic_fmt and
std::panicking::being_panic_fmt with a call to a new const fn:
core::panicking::const_panic_fmt. That function uses
fmt::Arguments::as_str() to get the str and calls panic_str with that
instead.

panic!() invocations with formatting arguments are still not accepted,
as the creation of such a fmt::Arguments cannot be done in constant
functions right now.
This commit is contained in:
Mara Bos 2021-07-06 12:38:26 +00:00
parent eba3228b2a
commit f827d3e285
8 changed files with 53 additions and 11 deletions
Download patch file Download diff file Expand all files Collapse all files

37
compiler/rustc_mir/src/const_eval/machine.rs
View file

@ -30,7 +30,7 @@ impl<'mir, 'tcx> InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>> {
&mut self,
instance: ty::Instance<'tcx>,
args: &[OpTy<'tcx>],
) -> InterpResult<'tcx> {
) -> InterpResult<'tcx, Option<ty::Instance<'tcx>>> {
let def_id = instance.def_id();
if Some(def_id) == self.tcx.lang_items().panic_fn()
|| Some(def_id) == self.tcx.lang_items().panic_str()
@ -43,10 +43,25 @@ impl<'mir, 'tcx> InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>> {
let msg = Symbol::intern(self.read_str(&msg_place)?);
let span = self.find_closest_untracked_caller_location();
let (file, line, col) = self.location_triple_for_span(span);
Err(ConstEvalErrKind::Panic { msg, file, line, col }.into())
} else {
Ok(())
return Err(ConstEvalErrKind::Panic { msg, file, line, col }.into());
} else if Some(def_id) == self.tcx.lang_items().panic_fmt()
|| Some(def_id) == self.tcx.lang_items().begin_panic_fmt()
{
// For panic_fmt, call const_panic_fmt instead.
if let Some(const_panic_fmt) = self.tcx.lang_items().const_panic_fmt() {
return Ok(Some(
ty::Instance::resolve(
*self.tcx,
ty::ParamEnv::reveal_all(),
const_panic_fmt,
self.tcx.intern_substs(&[]),
)
.unwrap()
.unwrap(),
));
}
}
Ok(None)
}
}
@ -223,7 +238,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
fn find_mir_or_eval_fn(
ecx: &mut InterpCx<'mir, 'tcx, Self>,
instance: ty::Instance<'tcx>,
mut instance: ty::Instance<'tcx>,
_abi: Abi,
args: &[OpTy<'tcx>],
_ret: Option<(&PlaceTy<'tcx>, mir::BasicBlock)>,
@ -241,10 +256,14 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
if !ecx.tcx.has_attr(def.did, sym::default_method_body_is_const) {
// Some functions we support even if they are non-const -- but avoid testing
// that for const fn!
ecx.hook_panic_fn(instance, args)?;
// We certainly do *not* want to actually call the fn
// though, so be sure we return here.
throw_unsup_format!("calling non-const function `{}`", instance)
if let Some(new_instance) = ecx.hook_panic_fn(instance, args)? {
// We call another const fn instead.
instance = new_instance;
} else {
// We certainly do *not* want to actually call the fn
// though, so be sure we return here.
throw_unsup_format!("calling non-const function `{}`", instance)
}
}
}
}

2
compiler/rustc_mir/src/transform/check_consts/mod.rs
View file

@ -77,6 +77,8 @@ pub fn is_lang_panic_fn(tcx: TyCtxt<'tcx>, def_id: DefId) -> bool {
Some(def_id) == tcx.lang_items().panic_fn()
|| Some(def_id) == tcx.lang_items().panic_str()
|| Some(def_id) == tcx.lang_items().begin_panic_fn()
|| Some(def_id) == tcx.lang_items().panic_fmt()
|| Some(def_id) == tcx.lang_items().begin_panic_fmt()
}
pub fn rustc_allow_const_fn_unstable(