Move a const-prop-lint specific hack from mir interpret to const-prop-lint and make it fallible

Author: oli-obk

compiler/rustc_const_eval/src/interpret/operand.rs

@@ -612,14 +612,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         span: Option<Span>,
         layout: Option<TyAndLayout<'tcx>>,
     ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
-        // FIXME(const_prop): normalization needed b/c const prop lint in
-        // `mir_drops_elaborated_and_const_checked`, which happens before
-        // optimized MIR. Only after optimizing the MIR can we guarantee
-        // that the `RevealAll` pass has happened and that the body's consts
-        // are normalized, so any call to resolve before that needs to be
-        // manually normalized.
-        let val = self.tcx.normalize_erasing_regions(self.param_env, *val);
-        match val {
+        match *val {
             mir::ConstantKind::Ty(ct) => {
                 let ty = ct.ty();
                 let valtree = self.eval_ty_constant(ct, span)?;

compiler/rustc_middle/src/ty/normalize_erasing_regions.rs

@@ -193,9 +193,9 @@ impl<'tcx> NormalizeAfterErasingRegionsFolder<'tcx> {
         let arg = self.param_env.and(arg);
 
         self.tcx.try_normalize_generic_arg_after_erasing_regions(arg).unwrap_or_else(|_| bug!(
-                "Failed to normalize {:?}, maybe try to call `try_normalize_erasing_regions` instead",
-                arg.value
-            ))
+            "Failed to normalize {:?}, maybe try to call `try_normalize_erasing_regions` instead",
+            arg.value
+        ))
     }
 }
 

compiler/rustc_mir_transform/src/const_prop_lint.rs

@@ -284,7 +284,15 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
             return None;
         }
 
-        self.use_ecx(source_info, |this| this.ecx.eval_mir_constant(&c.literal, Some(c.span), None))
+        // Normalization needed b/c const prop lint runs in
+        // `mir_drops_elaborated_and_const_checked`, which happens before
+        // optimized MIR. Only after optimizing the MIR can we guarantee
+        // that the `RevealAll` pass has happened and that the body's consts
+        // are normalized, so any call to resolve before that needs to be
+        // manually normalized.
+        let val = self.tcx.try_normalize_erasing_regions(self.param_env, c.literal).ok()?;
+
+        self.use_ecx(source_info, |this| this.ecx.eval_mir_constant(&val, Some(c.span), None))
     }
 
     /// Returns the value, if any, of evaluating `place`.

tests/ui/mir/issue-109743.rs

@@ -0,0 +1,51 @@
+// build-pass
+// compile-flags: --crate-type=lib
+
+use std::marker::PhantomData;
+
+pub trait StreamOnce {
+    type Token;
+}
+
+impl StreamOnce for &str {
+    type Token = ();
+}
+
+pub trait Parser<Input: StreamOnce> {
+    type PartialState: Default;
+    fn parse_mode(&self, _state: &Self::PartialState) {}
+    fn parse_mode_impl() {}
+}
+
+pub fn parse_bool<'a>() -> impl Parser<&'a str> {
+    pub struct TokensCmp<C, Input>
+    where
+        Input: StreamOnce,
+    {
+        _cmp: C,
+        _marker: PhantomData<Input>,
+    }
+
+    impl<Input, C> Parser<Input> for TokensCmp<C, Input>
+    where
+        C: FnMut(Input::Token),
+        Input: StreamOnce,
+    {
+        type PartialState = ();
+    }
+
+    TokensCmp { _cmp: |_| (), _marker: PhantomData }
+}
+
+pub struct ParseBool;
+
+impl<'a> Parser<&'a str> for ParseBool
+where
+    &'a str: StreamOnce,
+{
+    type PartialState = ();
+
+    fn parse_mode_impl() {
+        parse_bool().parse_mode(&Default::default())
+    }
+}