Always use RevealAll for const eval queries

Author: oli-obk

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

@@ -225,17 +225,10 @@ pub fn eval_to_const_value_raw_provider<'tcx>(
     tcx: TyCtxt<'tcx>,
     key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
 ) -> ::rustc_middle::mir::interpret::EvalToConstValueResult<'tcx> {
-    // see comment in eval_to_allocation_raw_provider for what we're doing here
-    if key.param_env.reveal() == Reveal::All {
-        let mut key = key;
-        key.param_env = key.param_env.with_user_facing();
-        match tcx.eval_to_const_value_raw(key) {
-            // try again with reveal all as requested
-            Err(ErrorHandled::TooGeneric(_)) => {}
-            // deduplicate calls
-            other => return other,
-        }
-    }
+    // Const eval always happens in Reveal::All mode in order to be able to use the hidden types of
+    // opaque types. This is needed for trivial things like `size_of`, but also for using associated
+    // types that are not specified in the opaque type.
+    assert_eq!(key.param_env.reveal(), Reveal::All);
 
     // We call `const_eval` for zero arg intrinsics, too, in order to cache their value.
     // Catch such calls and evaluate them instead of trying to load a constant's MIR.
@@ -265,24 +258,11 @@ pub fn eval_to_allocation_raw_provider<'tcx>(
     tcx: TyCtxt<'tcx>,
     key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
 ) -> ::rustc_middle::mir::interpret::EvalToAllocationRawResult<'tcx> {
-    // Because the constant is computed twice (once per value of `Reveal`), we are at risk of
-    // reporting the same error twice here. To resolve this, we check whether we can evaluate the
-    // constant in the more restrictive `Reveal::UserFacing`, which most likely already was
-    // computed. For a large percentage of constants that will already have succeeded. Only
-    // associated constants of generic functions will fail due to not enough monomorphization
-    // information being available.
-
-    // In case we fail in the `UserFacing` variant, we just do the real computation.
-    if key.param_env.reveal() == Reveal::All {
-        let mut key = key;
-        key.param_env = key.param_env.with_user_facing();
-        match tcx.eval_to_allocation_raw(key) {
-            // try again with reveal all as requested
-            Err(ErrorHandled::TooGeneric(_)) => {}
-            // deduplicate calls
-            other => return other,
-        }
-    }
+    // Const eval always happens in Reveal::All mode in order to be able to use the hidden types of
+    // opaque types. This is needed for trivial things like `size_of`, but also for using associated
+    // types that are not specified in the opaque type.
+
+    assert_eq!(key.param_env.reveal(), Reveal::All);
     if cfg!(debug_assertions) {
         // Make sure we format the instance even if we do not print it.
         // This serves as a regression test against an ICE on printing.

compiler/rustc_middle/src/mir/interpret/queries.rs

@@ -145,7 +145,7 @@ impl<'tcx> TyCtxt<'tcx> {
     ) -> EvalToConstValueResult<'tcx> {
         // Const-eval shouldn't depend on lifetimes at all, so we can erase them, which should
         // improve caching of queries.
-        let inputs = self.erase_regions(param_env.and(cid));
+        let inputs = self.erase_regions(param_env.with_reveal_all_normalized(self).and(cid));
         if let Some(span) = span {
             // The query doesn't know where it is being invoked, so we need to fix the span.
             self.at(span).eval_to_const_value_raw(inputs).map_err(|e| e.with_span(span))
@@ -164,7 +164,7 @@ impl<'tcx> TyCtxt<'tcx> {
     ) -> EvalToValTreeResult<'tcx> {
         // Const-eval shouldn't depend on lifetimes at all, so we can erase them, which should
         // improve caching of queries.
-        let inputs = self.erase_regions(param_env.and(cid));
+        let inputs = self.erase_regions(param_env.with_reveal_all_normalized(self).and(cid));
         debug!(?inputs);
         if let Some(span) = span {
             // The query doesn't know where it is being invoked, so we need to fix the span.

tests/ui/associated-consts/issue-24949-assoc-const-static-recursion-impl.stderr

@@ -9,11 +9,6 @@ note: ...which requires simplifying constant for the type system `IMPL_REF_BAR`.
    |
 LL | const IMPL_REF_BAR: u32 = GlobalImplRef::BAR;
    | ^^^^^^^^^^^^^^^^^^^^^^^
-note: ...which requires simplifying constant for the type system `IMPL_REF_BAR`...
-  --> $DIR/issue-24949-assoc-const-static-recursion-impl.rs:7:1
-   |
-LL | const IMPL_REF_BAR: u32 = GlobalImplRef::BAR;
-   | ^^^^^^^^^^^^^^^^^^^^^^^
 note: ...which requires const-evaluating + checking `IMPL_REF_BAR`...
   --> $DIR/issue-24949-assoc-const-static-recursion-impl.rs:7:27
    |

tests/ui/associated-consts/issue-24949-assoc-const-static-recursion-trait-default.stderr

@@ -9,11 +9,6 @@ note: ...which requires simplifying constant for the type system `DEFAULT_REF_BA
    |
 LL | const DEFAULT_REF_BAR: u32 = <GlobalDefaultRef>::BAR;
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^
-note: ...which requires simplifying constant for the type system `DEFAULT_REF_BAR`...
-  --> $DIR/issue-24949-assoc-const-static-recursion-trait-default.rs:11:1
-   |
-LL | const DEFAULT_REF_BAR: u32 = <GlobalDefaultRef>::BAR;
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^
 note: ...which requires const-evaluating + checking `DEFAULT_REF_BAR`...
   --> $DIR/issue-24949-assoc-const-static-recursion-trait-default.rs:11:30
    |

tests/ui/associated-consts/issue-24949-assoc-const-static-recursion-trait.stderr

@@ -9,11 +9,6 @@ note: ...which requires simplifying constant for the type system `TRAIT_REF_BAR`
    |
 LL | const TRAIT_REF_BAR: u32 = <GlobalTraitRef>::BAR;
    | ^^^^^^^^^^^^^^^^^^^^^^^^
-note: ...which requires simplifying constant for the type system `TRAIT_REF_BAR`...
-  --> $DIR/issue-24949-assoc-const-static-recursion-trait.rs:7:1
-   |
-LL | const TRAIT_REF_BAR: u32 = <GlobalTraitRef>::BAR;
-   | ^^^^^^^^^^^^^^^^^^^^^^^^
 note: ...which requires const-evaluating + checking `TRAIT_REF_BAR`...
   --> $DIR/issue-24949-assoc-const-static-recursion-trait.rs:7:28
    |

tests/ui/consts/const-eval/const-eval-query-stack.stderr

@@ -7,7 +7,6 @@ LL | const X: i32 = 1 / 0;
 query stack during panic:
 #0 [eval_to_allocation_raw] const-evaluating + checking `X`
 #1 [eval_to_const_value_raw] simplifying constant for the type system `X`
-#2 [eval_to_const_value_raw] simplifying constant for the type system `X`
-#3 [lint_mod] linting top-level module
-#4 [analysis] running analysis passes on this crate
+#2 [lint_mod] linting top-level module
+#3 [analysis] running analysis passes on this crate
 end of query stack

tests/ui/consts/const-size_of-cycle.stderr

@@ -7,11 +7,6 @@ LL |     bytes: [u8; std::mem::size_of::<Foo>()]
 note: ...which requires const-evaluating + checking `Foo::bytes::{constant#0}`...
   --> $DIR/const-size_of-cycle.rs:4:17
    |
-LL |     bytes: [u8; std::mem::size_of::<Foo>()]
-   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^
-note: ...which requires const-evaluating + checking `Foo::bytes::{constant#0}`...
-  --> $DIR/const-size_of-cycle.rs:4:17
-   |
 LL |     bytes: [u8; std::mem::size_of::<Foo>()]
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: ...which requires computing layout of `Foo`...

tests/ui/consts/issue-36163.stderr

@@ -20,11 +20,17 @@ note: ...which requires const-evaluating + checking `A`...
 LL | const A: isize = Foo::B as isize;
    |                  ^^^^^^^^^^^^^^^
    = note: ...which again requires simplifying constant for the type system `Foo::B::{constant#0}`, completing the cycle
-note: cycle used when simplifying constant for the type system `Foo::B::{constant#0}`
-  --> $DIR/issue-36163.rs:4:9
+note: cycle used when collecting item types in top-level module
+  --> $DIR/issue-36163.rs:1:1
    |
-LL |     B = A,
-   |         ^
+LL | / const A: isize = Foo::B as isize;
+LL | |
+LL | | enum Foo {
+LL | |     B = A,
+LL | | }
+LL | |
+LL | | fn main() {}
+   | |____________^
    = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
 
 error: aborting due to 1 previous error

tests/ui/consts/issue-44415.stderr

@@ -7,11 +7,6 @@ LL |     bytes: [u8; unsafe { intrinsics::size_of::<Foo>() }],
 note: ...which requires const-evaluating + checking `Foo::bytes::{constant#0}`...
   --> $DIR/issue-44415.rs:6:17
    |
-LL |     bytes: [u8; unsafe { intrinsics::size_of::<Foo>() }],
-   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-note: ...which requires const-evaluating + checking `Foo::bytes::{constant#0}`...
-  --> $DIR/issue-44415.rs:6:17
-   |
 LL |     bytes: [u8; unsafe { intrinsics::size_of::<Foo>() }],
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: ...which requires computing layout of `Foo`...

tests/ui/consts/recursive-zst-static.default.stderr

@@ -1,15 +1,10 @@
 error[E0391]: cycle detected when const-evaluating + checking `FOO`
-  --> $DIR/recursive-zst-static.rs:10:1
-   |
-LL | static FOO: () = FOO;
-   | ^^^^^^^^^^^^^^
-   |
-note: ...which requires const-evaluating + checking `FOO`...
   --> $DIR/recursive-zst-static.rs:10:18
    |
 LL | static FOO: () = FOO;
    |                  ^^^
-   = note: ...which again requires const-evaluating + checking `FOO`, completing the cycle
+   |
+   = note: ...which immediately requires const-evaluating + checking `FOO` again
 note: cycle used when linting top-level module
   --> $DIR/recursive-zst-static.rs:10:1
    |