Always use RevealAll for const eval queries

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
    |

tests/ui/consts/recursive-zst-static.unleash.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
    |

tests/ui/consts/write-to-static-mut-in-static.stderr

@@ -5,17 +5,12 @@ LL | pub static mut B: () = unsafe { A = 1; };
    |                                 ^^^^^ modifying a static's initial value from another static's initializer
 
 error[E0391]: cycle detected when const-evaluating + checking `C`
-  --> $DIR/write-to-static-mut-in-static.rs:5:1
-   |
-LL | pub static mut C: u32 = unsafe { C = 1; 0 };
-   | ^^^^^^^^^^^^^^^^^^^^^
-   |
-note: ...which requires const-evaluating + checking `C`...
   --> $DIR/write-to-static-mut-in-static.rs:5:34
    |
 LL | pub static mut C: u32 = unsafe { C = 1; 0 };
    |                                  ^^^^^
-   = note: ...which again requires const-evaluating + checking `C`, completing the cycle
+   |
+   = note: ...which immediately requires const-evaluating + checking `C` again
 note: cycle used when linting top-level module
   --> $DIR/write-to-static-mut-in-static.rs:1:1
    |

tests/ui/impl-trait/in-ctfe/array-len-size-of.rs

@@ -0,0 +1,16 @@
+//! Check that const eval can use the size of opaque types.
+// check-pass
+use std::mem;
+fn returns_opaque() -> impl Sized {
+    0u8
+}
+
+struct NamedOpaqueType {
+    data: [mem::MaybeUninit<u8>; size_of_fut(returns_opaque)],
+}
+
+const fn size_of_fut<FUT>(x: fn() -> FUT) -> usize {
+    mem::size_of::<FUT>()
+}
+
+fn main() {}

tests/ui/impl-trait/in-ctfe/array-len.rs

@@ -0,0 +1,22 @@
+//! Check that array lengths can observe associated types of opaque types
+// check-pass
+trait MyTrait: Copy {
+    const ASSOC: usize;
+}
+
+impl MyTrait for u8 {
+    const ASSOC: usize = 32;
+}
+
+const fn yeet() -> impl MyTrait {
+    0u8
+}
+
+const fn output<T: MyTrait>(_: T) -> usize {
+    <T as MyTrait>::ASSOC
+}
+
+fn main() {
+    let x = [0u8; output(yeet())];
+    println!("{:?}", x);
+}

tests/ui/impl-trait/in-ctfe/enum-discr.rs

@@ -0,0 +1,26 @@
+//! check that const eval can observe associated types of opaque types.
+// check-pass
+trait MyTrait: Copy {
+    const ASSOC: usize;
+}
+
+impl MyTrait for u8 {
+    const ASSOC: usize = 32;
+}
+
+const fn yeet() -> impl MyTrait {
+    0u8
+}
+
+const fn output<T: MyTrait>(_: T) -> usize {
+    <T as MyTrait>::ASSOC
+}
+
+#[repr(usize)]
+enum Foo {
+    Bar = output(yeet()),
+}
+
+fn main() {
+    println!("{}", Foo::Bar as usize);
+}

tests/ui/impl-trait/in-ctfe/fully_monomorphic_const_eval.rs

@@ -0,0 +1,29 @@
+//! This test ensures that we do look at the hidden types of
+//! opaque types during const eval in order to obtain the exact type
+//! of associated types.
+
+// check-pass
+
+trait MyTrait: Copy {
+    const ASSOC: usize;
+}
+
+impl MyTrait for u8 {
+    const ASSOC: usize = 32;
+}
+
+const fn yeet() -> impl MyTrait {
+    0u8
+}
+
+const fn output<T: MyTrait>(_: T) -> usize {
+    <T as MyTrait>::ASSOC
+}
+
+struct Foo<'a>(&'a ());
+const NEED_REVEAL_ALL: usize = output(yeet());
+
+fn promote_div() -> &'static usize {
+    &(10 / NEED_REVEAL_ALL)
+}
+fn main() {}

tests/ui/impl-trait/in-ctfe/match-arm-exhaustive.rs

@@ -0,0 +1,24 @@
+//! Check that pattern matching can observe the hidden type of opaque types.
+// check-pass
+trait MyTrait: Copy {
+    const ASSOC: u8;
+}
+
+impl MyTrait for () {
+    const ASSOC: u8 = 0;
+}
+
+const fn yeet() -> impl MyTrait {}
+
+const fn output<T: MyTrait>(_: T) -> u8 {
+    <T as MyTrait>::ASSOC
+}
+
+const CT: u8 = output(yeet());
+
+fn main() {
+    match 0 {
+        CT => (),
+        1.. => (),
+    }
+}

tests/ui/impl-trait/transmute/in-defining-scope.rs

@@ -0,0 +1,14 @@
+// This causes a query cycle due to using `Reveal::All`,
+// in #119821 const eval was changed to always use `Reveal::All`
+//
+// See that PR for more details.
+use std::mem::transmute;
+fn foo() -> impl Sized {
+    //~^ ERROR cycle detected when computing type of
+    unsafe {
+        transmute::<_, u8>(foo());
+    }
+    0u8
+}
+
+fn main() {}

tests/ui/impl-trait/transmute/in-defining-scope.stderr

@@ -0,0 +1,29 @@
+error[E0391]: cycle detected when computing type of `foo::{opaque#0}`
+  --> $DIR/in-defining-scope.rs:6:13
+   |
+LL | fn foo() -> impl Sized {
+   |             ^^^^^^^^^^
+   |
+note: ...which requires computing type of opaque `foo::{opaque#0}`...
+  --> $DIR/in-defining-scope.rs:6:13
+   |
+LL | fn foo() -> impl Sized {
+   |             ^^^^^^^^^^
+note: ...which requires type-checking `foo`...
+  --> $DIR/in-defining-scope.rs:6:1
+   |
+LL | fn foo() -> impl Sized {
+   | ^^^^^^^^^^^^^^^^^^^^^^
+   = note: ...which requires computing layout of `foo::{opaque#0}`...
+   = note: ...which requires normalizing `foo::{opaque#0}`...
+   = note: ...which again requires computing type of `foo::{opaque#0}`, completing the cycle
+note: cycle used when checking that `foo::{opaque#0}` is well-formed
+  --> $DIR/in-defining-scope.rs:6:13
+   |
+LL | fn foo() -> impl Sized {
+   |             ^^^^^^^^^^
+   = 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
+
+For more information about this error, try `rustc --explain E0391`.

tests/ui/impl-trait/transmute/outside-of-defining-scope.rs

@@ -0,0 +1,12 @@
+//! Check that typeck can observe the size of an opaque type.
+// check-pass
+use std::mem::transmute;
+fn foo() -> impl Sized {
+    0u8
+}
+
+fn main() {
+    unsafe {
+        transmute::<_, u8>(foo());
+    }
+}