Auto merge of #91549 - fee1-dead:const_env, r=spastorino

Eliminate ConstnessAnd again

Closes #91489.
Closes #89432.

Reverts #91491.
Reverts #89450.

r? `@spastorino`

src/test/ui/consts/not_const_clusure_in_const.rs

@@ -1,9 +0,0 @@
-// run-pass
-
-const _FOO: fn() -> String = || "foo".into();
-
-pub fn bar() -> fn() -> String {
-    || "bar".into()
-}
-
-fn main(){}

src/test/ui/consts/try-operator.rs

@@ -0,0 +1,23 @@
+// run-pass
+
+#![feature(try_trait_v2)]
+#![feature(const_trait_impl)]
+#![feature(const_try)]
+#![feature(const_convert)]
+
+fn main() {
+    const fn result() -> Result<bool, ()> {
+        Err(())?;
+        Ok(true)
+    }
+
+    const FOO: Result<bool, ()> = result();
+    assert_eq!(Err(()), FOO);
+
+    const fn option() -> Option<()> {
+        None?;
+        Some(())
+    }
+    const BAR: Option<()> = option();
+    assert_eq!(None, BAR);
+}

src/test/ui/infinite/infinite-struct.stderr

@@ -19,7 +19,7 @@ LL | struct Take(Take);
    | ^^^^^^^^^^^^^^^^^^
    |
    = note: ...which immediately requires computing drop-check constraints for `Take` again
-   = note: cycle used when computing dropck types for `Canonical { max_universe: U0, variables: [], value: ParamEnvAnd { param_env: ParamEnv { caller_bounds: [], reveal: UserFacing }, value: Take } }`
+   = note: cycle used when computing dropck types for `Canonical { max_universe: U0, variables: [], value: ParamEnvAnd { param_env: ParamEnv { caller_bounds: [], reveal: UserFacing, constness: NotConst }, value: Take } }`
 
 error: aborting due to 2 previous errors
 

src/test/ui/infinite/infinite-tag-type-recursion.stderr

@@ -18,7 +18,7 @@ LL | enum MList { Cons(isize, MList), Nil }
    | ^^^^^^^^^^
    |
    = note: ...which immediately requires computing drop-check constraints for `MList` again
-   = note: cycle used when computing dropck types for `Canonical { max_universe: U0, variables: [], value: ParamEnvAnd { param_env: ParamEnv { caller_bounds: [], reveal: UserFacing }, value: MList } }`
+   = note: cycle used when computing dropck types for `Canonical { max_universe: U0, variables: [], value: ParamEnvAnd { param_env: ParamEnv { caller_bounds: [], reveal: UserFacing, constness: NotConst }, value: MList } }`
 
 error: aborting due to 2 previous errors
 

src/test/ui/issues/issue-91489.rs

@@ -0,0 +1,40 @@
+// check-pass
+
+// regression test for #91489
+
+use std::borrow::Borrow;
+use std::borrow::Cow;
+
+pub struct VariantType {}
+pub struct VariantTy {}
+
+impl Borrow<VariantTy> for VariantType {
+    fn borrow(&self) -> &VariantTy {
+        unimplemented!()
+    }
+}
+
+impl ToOwned for VariantTy {
+    type Owned = VariantType;
+    fn to_owned(&self) -> VariantType {
+        unimplemented!()
+    }
+}
+
+impl VariantTy {
+    pub fn as_str(&self) -> () {}
+}
+
+// the presence of this was causing all attempts to call `as_str` on
+// `Cow<'_, VariantTy>, including in itself, to not find the method
+static _TYP: () = {
+    let _ = || {
+        // should be found
+        Cow::Borrowed(&VariantTy {}).as_str();
+    };
+};
+
+fn main() {
+    // should be found
+    Cow::Borrowed(&VariantTy {}).as_str()
+}

src/test/ui/rfc-2632-const-trait-impl/assoc-type.rs

@@ -1,6 +1,5 @@
 // FIXME(fee1-dead): this should have a better error message
 #![feature(const_trait_impl)]
-
 struct NonConstAdd(i32);
 
 impl std::ops::Add for NonConstAdd {

src/test/ui/rfc-2632-const-trait-impl/assoc-type.stderr

@@ -1,12 +1,12 @@
 error[E0277]: cannot add `NonConstAdd` to `NonConstAdd`
-  --> $DIR/assoc-type.rs:19:16
+  --> $DIR/assoc-type.rs:18:16
    |
 LL |     type Bar = NonConstAdd;
    |                ^^^^^^^^^^^ no implementation for `NonConstAdd + NonConstAdd`
    |
    = help: the trait `Add` is not implemented for `NonConstAdd`
 note: required by a bound in `Foo::Bar`
-  --> $DIR/assoc-type.rs:15:15
+  --> $DIR/assoc-type.rs:14:15
    |
 LL |     type Bar: ~const std::ops::Add;
    |               ^^^^^^^^^^^^^^^^^^^^ required by this bound in `Foo::Bar`

src/test/ui/rfc-2632-const-trait-impl/non-const-op-in-closure-in-const.rs

@@ -0,0 +1,18 @@
+// check-pass
+
+#![feature(const_trait_impl)]
+#![feature(const_fn_trait_bound)]
+
+trait Convert<T> {
+    fn to(self) -> T;
+}
+
+impl<A, B> const Convert<B> for A where B: ~const From<A> {
+    fn to(self) -> B {
+        B::from(self)
+    }
+}
+
+const FOO: fn() -> String = || "foo".to();
+
+fn main() {}