Auto merge of #100315 - compiler-errors:norm-ct-in-proj, r=lcnr

Keep going if normalized projection has unevaluated consts in `QueryNormalizer`

#100312 was the wrong approach, I think this is the right one.

When normalizing a type, if we see that it's a projection, we currently defer to `tcx.normalize_projection_ty`, which normalizes the projections away but doesn't touch the unevaluated constants. So now we just continue to fold the type if it has unevaluated constants so we make sure to evaluate those too, if we can.

Fixes #100217
Fixes #83972
Fixes #84669
Fixes #86710
Fixes #82268
Fixes #73298

compiler/rustc_trait_selection/src/traits/query/normalize.rs

@@ -266,7 +266,15 @@ impl<'cx, 'tcx> FallibleTypeFolder<'tcx> for QueryNormalizer<'cx, 'tcx> {
                 debug!("QueryNormalizer: result = {:#?}", result);
                 debug!("QueryNormalizer: obligations = {:#?}", obligations);
                 self.obligations.extend(obligations);
-                Ok(result.normalized_ty)
+
+                let res = result.normalized_ty;
+                // `tcx.normalize_projection_ty` may normalize to a type that still has
+                // unevaluated consts, so keep normalizing here if that's the case.
+                if res != ty && res.has_type_flags(ty::TypeFlags::HAS_CT_PROJECTION) {
+                    Ok(res.try_super_fold_with(self)?)
+                } else {
+                    Ok(res)
+                }
             }
 
             ty::Projection(data) => {
@@ -305,18 +313,27 @@ impl<'cx, 'tcx> FallibleTypeFolder<'tcx> for QueryNormalizer<'cx, 'tcx> {
                 debug!("QueryNormalizer: result = {:#?}", result);
                 debug!("QueryNormalizer: obligations = {:#?}", obligations);
                 self.obligations.extend(obligations);
-                Ok(crate::traits::project::PlaceholderReplacer::replace_placeholders(
+
+                let res = crate::traits::project::PlaceholderReplacer::replace_placeholders(
                     infcx,
                     mapped_regions,
                     mapped_types,
                     mapped_consts,
                     &self.universes,
                     result.normalized_ty,
-                ))
+                );
+                // `tcx.normalize_projection_ty` may normalize to a type that still has
+                // unevaluated consts, so keep normalizing here if that's the case.
+                if res != ty && res.has_type_flags(ty::TypeFlags::HAS_CT_PROJECTION) {
+                    Ok(res.try_super_fold_with(self)?)
+                } else {
+                    Ok(res)
+                }
             }
 
             _ => ty.try_super_fold_with(self),
         })()?;
+
         self.cache.insert(ty, res);
         Ok(res)
     }

src/test/ui/const-generics/generic_const_exprs/issue-100217.rs

@@ -0,0 +1,42 @@
+// build-pass
+
+#![allow(incomplete_features)]
+#![feature(generic_const_exprs)]
+
+trait TraitOne {
+    const MY_NUM: usize;
+    type MyErr: std::fmt::Debug;
+
+    fn do_one_stuff(arr: [u8; Self::MY_NUM]) -> Result<(), Self::MyErr>;
+}
+
+trait TraitTwo {
+    fn do_two_stuff();
+}
+
+impl<O: TraitOne> TraitTwo for O
+where
+    [(); Self::MY_NUM]:,
+{
+    fn do_two_stuff() {
+        O::do_one_stuff([5; Self::MY_NUM]).unwrap()
+    }
+}
+
+struct Blargotron;
+
+#[derive(Debug)]
+struct ErrTy<const N: usize>([(); N]);
+
+impl TraitOne for Blargotron {
+    const MY_NUM: usize = 3;
+    type MyErr = ErrTy<{ Self::MY_NUM }>;
+
+    fn do_one_stuff(_arr: [u8; Self::MY_NUM]) -> Result<(), Self::MyErr> {
+        Ok(())
+    }
+}
+
+fn main() {
+    Blargotron::do_two_stuff();
+}

src/test/ui/const-generics/generic_const_exprs/issue-73298.rs

@@ -0,0 +1,23 @@
+// build-pass
+
+#![allow(incomplete_features)]
+#![feature(generic_const_exprs)]
+
+use std::convert::AsMut;
+use std::default::Default;
+
+trait Foo: Sized {
+    type Baz: Default + AsMut<[u8]>;
+    fn bar() {
+        Self::Baz::default().as_mut();
+    }
+}
+
+impl Foo for () {
+    type Baz = [u8; 1 * 1];
+    //type Baz = [u8; 1];
+}
+
+fn main() {
+    <() as Foo>::bar();
+}

src/test/ui/const-generics/generic_const_exprs/issue-82268.rs

@@ -0,0 +1,73 @@
+// build-pass
+
+#![allow(incomplete_features)]
+#![feature(generic_const_exprs)]
+
+trait Collate<Op> {
+    type Pass;
+    type Fail;
+
+    fn collate(self) -> (Self::Pass, Self::Fail);
+}
+
+impl<Op> Collate<Op> for () {
+    type Pass = ();
+    type Fail = ();
+
+    fn collate(self) -> ((), ()) {
+        ((), ())
+    }
+}
+
+trait CollateStep<X, Prev> {
+    type Pass;
+    type Fail;
+    fn collate_step(x: X, prev: Prev) -> (Self::Pass, Self::Fail);
+}
+
+impl<X, P, F> CollateStep<X, (P, F)> for () {
+    type Pass = (X, P);
+    type Fail = F;
+
+    fn collate_step(x: X, (p, f): (P, F)) -> ((X, P), F) {
+        ((x, p), f)
+    }
+}
+
+struct CollateOpImpl<const MASK: u32>;
+trait CollateOpStep {
+    type NextOp;
+    type Apply;
+}
+
+impl<const MASK: u32> CollateOpStep for CollateOpImpl<MASK>
+where
+    CollateOpImpl<{ MASK >> 1 }>: Sized,
+{
+    type NextOp = CollateOpImpl<{ MASK >> 1 }>;
+    type Apply = ();
+}
+
+impl<H, T, Op: CollateOpStep> Collate<Op> for (H, T)
+where
+    T: Collate<Op::NextOp>,
+    Op::Apply: CollateStep<H, (T::Pass, T::Fail)>,
+{
+    type Pass = <Op::Apply as CollateStep<H, (T::Pass, T::Fail)>>::Pass;
+    type Fail = <Op::Apply as CollateStep<H, (T::Pass, T::Fail)>>::Fail;
+
+    fn collate(self) -> (Self::Pass, Self::Fail) {
+        <Op::Apply as CollateStep<H, (T::Pass, T::Fail)>>::collate_step(self.0, self.1.collate())
+    }
+}
+
+fn collate<X, const MASK: u32>(x: X) -> (X::Pass, X::Fail)
+where
+    X: Collate<CollateOpImpl<MASK>>,
+{
+    x.collate()
+}
+
+fn main() {
+    dbg!(collate::<_, 5>(("Hello", (42, ('!', ())))));
+}

src/test/ui/const-generics/generic_const_exprs/issue-83972.rs

@@ -0,0 +1,38 @@
+// build-pass
+
+#![allow(incomplete_features)]
+#![feature(generic_const_exprs)]
+
+pub trait Foo {
+    fn foo(&self);
+}
+
+pub struct FooImpl<const N: usize>;
+impl<const N: usize> Foo for FooImpl<N> {
+    fn foo(&self) {}
+}
+
+pub trait Bar: 'static {
+    type Foo: Foo;
+    fn get() -> &'static Self::Foo;
+}
+
+struct BarImpl;
+impl Bar for BarImpl {
+    type Foo = FooImpl<
+        {
+            { 4 }
+        },
+    >;
+    fn get() -> &'static Self::Foo {
+        &FooImpl
+    }
+}
+
+pub fn boom<B: Bar>() {
+    B::get().foo();
+}
+
+fn main() {
+    boom::<BarImpl>();
+}

src/test/ui/const-generics/generic_const_exprs/issue-84669.rs

@@ -0,0 +1,30 @@
+// build-pass
+
+#![feature(generic_const_exprs)]
+#![allow(incomplete_features)]
+
+trait Foo {
+    type Output;
+
+    fn foo() -> Self::Output;
+}
+
+impl Foo for [u8; 3] {
+    type Output = [u8; 1 + 2];
+
+    fn foo() -> [u8; 3] {
+        [1u8; 3]
+    }
+}
+
+fn bug<const N: usize>()
+where
+    [u8; N]: Foo,
+    <[u8; N] as Foo>::Output: AsRef<[u8]>,
+{
+    <[u8; N]>::foo().as_ref();
+}
+
+fn main() {
+    bug::<3>();
+}

src/test/ui/const-generics/generic_const_exprs/issue-86710.rs

@@ -0,0 +1,73 @@
+// build-pass
+
+#![allow(incomplete_features)]
+#![feature(generic_const_exprs)]
+
+use std::marker::PhantomData;
+
+fn main() {
+    let x = FooImpl::<BarImpl<1>> { phantom: PhantomData };
+    let _ = x.foo::<BarImpl<1>>();
+}
+
+trait Foo<T>
+where
+    T: Bar,
+{
+    fn foo<U>(&self)
+    where
+        T: Operation<U>,
+        <T as Operation<U>>::Output: Bar;
+}
+
+struct FooImpl<T>
+where
+    T: Bar,
+{
+    phantom: PhantomData<T>,
+}
+
+impl<T> Foo<T> for FooImpl<T>
+where
+    T: Bar,
+{
+    fn foo<U>(&self)
+    where
+        T: Operation<U>,
+        <T as Operation<U>>::Output: Bar,
+    {
+        <<T as Operation<U>>::Output as Bar>::error_occurs_here();
+    }
+}
+
+trait Bar {
+    fn error_occurs_here();
+}
+
+struct BarImpl<const N: usize>;
+
+impl<const N: usize> Bar for BarImpl<N> {
+    fn error_occurs_here() {}
+}
+
+trait Operation<Rhs> {
+    type Output;
+}
+
+//// Part-A: This causes error.
+impl<const M: usize, const N: usize> Operation<BarImpl<M>> for BarImpl<N>
+where
+    BarImpl<{ N + M }>: Sized,
+{
+    type Output = BarImpl<{ N + M }>;
+}
+
+//// Part-B: This doesn't cause error.
+// impl<const M: usize, const N: usize> Operation<BarImpl<M>> for BarImpl<N> {
+//     type Output = BarImpl<M>;
+// }
+
+//// Part-C: This also doesn't cause error.
+// impl<const M: usize, const N: usize> Operation<BarImpl<M>> for BarImpl<N> {
+//     type Output = BarImpl<{ M }>;
+// }