Auto merge of #128440 - oli-obk:defines, r=lcnr

Add `#[define_opaques]` attribute and require it for all type-alias-impl-trait sites that register a hidden type

Instead of relying on the signature of items to decide whether they are constraining an opaque type, the opaque types that the item constrains must be explicitly listed.

A previous version of this PR used an actual attribute, but had to keep the resolved `DefId`s in a side table.

Now we just lower to fields in the AST that have no surface syntax, instead a builtin attribute macro fills in those fields where applicable.

Note that for convenience referencing opaque types in associated types from associated methods on the same impl will not require an attribute. If that causes problems `#[defines()]` can be used to overwrite the default of searching for opaques in the signature.

One wart of this design is that closures and static items do not have generics. So since I stored the opaques in the generics of functions, consts and methods, I would need to add a custom field to closures and statics to track this information. During a T-types discussion we decided to just not do this for now.

fixes #131298

7 files changed, 82 insertions, 34 deletions

diff --git a/tests/ui/consts/const-eval/ice-unhandled-type-122191.rs b/tests/ui/consts/const-eval/ice-unhandled-type-122191.rs
index a92b99976e2..75bd6f7a123 100644
--- a/tests/ui/consts/const-eval/ice-unhandled-type-122191.rs
+++ b/tests/ui/consts/const-eval/ice-unhandled-type-122191.rs
@@ -3,14 +3,20 @@ type Foo = impl Send;
 
 struct A;
 
-const VALUE: Foo = value();
-//~^ ERROR cannot find function `value` in this scope
+#[define_opaque(Foo)]
+//~^ ERROR unstable library feature
+const fn foo() -> Foo {
+    value()
+    //~^ ERROR cannot find function `value` in this scope
+}
+
+const VALUE: Foo = foo();
 
 fn test() {
     match VALUE {
         0 | 0 => {}
-//~^ ERROR mismatched types
-//~| ERROR mismatched types
+        //~^ ERROR mismatched types
+        //~| ERROR mismatched types
         _ => (),
     }
 }
diff --git a/tests/ui/consts/const-eval/ice-unhandled-type-122191.stderr b/tests/ui/consts/const-eval/ice-unhandled-type-122191.stderr
index daf0ccaa776..bcb6a80a8f2 100644
--- a/tests/ui/consts/const-eval/ice-unhandled-type-122191.stderr
+++ b/tests/ui/consts/const-eval/ice-unhandled-type-122191.stderr
@@ -1,3 +1,13 @@
+error[E0658]: use of unstable library feature `type_alias_impl_trait`: `type_alias_impl_trait` has open design concerns
+  --> $DIR/ice-unhandled-type-122191.rs:6:3
+   |
+LL | #[define_opaque(Foo)]
+   |   ^^^^^^^^^^^^^
+   |
+   = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
+   = help: add `#![feature(type_alias_impl_trait)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
 error[E0658]: `impl Trait` in type aliases is unstable
   --> $DIR/ice-unhandled-type-122191.rs:1:12
    |
@@ -9,13 +19,16 @@ LL | type Foo = impl Send;
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
 error[E0425]: cannot find function `value` in this scope
-  --> $DIR/ice-unhandled-type-122191.rs:6:20
+  --> $DIR/ice-unhandled-type-122191.rs:9:5
    |
-LL | const VALUE: Foo = value();
-   |                    ^^^^^ not found in this scope
+LL |     value()
+   |     ^^^^^ help: a constant with a similar name exists: `VALUE`
+...
+LL | const VALUE: Foo = foo();
+   | ------------------------- similarly named constant `VALUE` defined here
 
 error[E0308]: mismatched types
-  --> $DIR/ice-unhandled-type-122191.rs:11:9
+  --> $DIR/ice-unhandled-type-122191.rs:17:9
    |
 LL | type Foo = impl Send;
    |            --------- the expected opaque type
@@ -27,14 +40,14 @@ LL |         0 | 0 => {}
    |
    = note: expected opaque type `Foo`
                      found type `{integer}`
-note: this item must have the opaque type in its signature in order to be able to register hidden types
-  --> $DIR/ice-unhandled-type-122191.rs:9:4
+note: this item must have a `#[define_opaque(Foo)]` attribute to be able to define hidden types
+  --> $DIR/ice-unhandled-type-122191.rs:15:4
    |
 LL | fn test() {
    |    ^^^^
 
 error[E0308]: mismatched types
-  --> $DIR/ice-unhandled-type-122191.rs:11:13
+  --> $DIR/ice-unhandled-type-122191.rs:17:13
    |
 LL | type Foo = impl Send;
    |            --------- the expected opaque type
@@ -46,13 +59,13 @@ LL |         0 | 0 => {}
    |
    = note: expected opaque type `Foo`
                      found type `{integer}`
-note: this item must have the opaque type in its signature in order to be able to register hidden types
-  --> $DIR/ice-unhandled-type-122191.rs:9:4
+note: this item must have a `#[define_opaque(Foo)]` attribute to be able to define hidden types
+  --> $DIR/ice-unhandled-type-122191.rs:15:4
    |
 LL | fn test() {
    |    ^^^^
 
-error: aborting due to 4 previous errors
+error: aborting due to 5 previous errors
 
 Some errors have detailed explanations: E0308, E0425, E0658.
 For more information about an error, try `rustc --explain E0308`.
diff --git a/tests/ui/consts/const-promoted-opaque.atomic.stderr b/tests/ui/consts/const-promoted-opaque.atomic.stderr
index b9d5cbf801a..9c0c969d586 100644
--- a/tests/ui/consts/const-promoted-opaque.atomic.stderr
+++ b/tests/ui/consts/const-promoted-opaque.atomic.stderr
@@ -1,5 +1,5 @@
-error[E0493]: destructor of `helper::Foo` cannot be evaluated at compile-time
-  --> $DIR/const-promoted-opaque.rs:28:26
+error[E0493]: destructor of `Foo` cannot be evaluated at compile-time
+  --> $DIR/const-promoted-opaque.rs:32:26
    |
 LL |     let _: &'static _ = &FOO;
    |                          ^^^ the destructor for this type cannot be evaluated in constants
@@ -8,13 +8,13 @@ LL | };
    | - value is dropped here
 
 error[E0492]: constants cannot refer to interior mutable data
-  --> $DIR/const-promoted-opaque.rs:32:19
+  --> $DIR/const-promoted-opaque.rs:36:19
    |
 LL | const BAZ: &Foo = &FOO;
    |                   ^^^^ this borrow of an interior mutable value may end up in the final value
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/const-promoted-opaque.rs:36:26
+  --> $DIR/const-promoted-opaque.rs:40:26
    |
 LL |     let _: &'static _ = &FOO;
    |            ----------    ^^^ creates a temporary value which is freed while still in use
diff --git a/tests/ui/consts/const-promoted-opaque.rs b/tests/ui/consts/const-promoted-opaque.rs
index bb33e92778a..188dacd1003 100644
--- a/tests/ui/consts/const-promoted-opaque.rs
+++ b/tests/ui/consts/const-promoted-opaque.rs
@@ -8,25 +8,29 @@
 //! hidden type of the opaque type. Thus we ended up relying on the
 //! result of our analysis to compute the result of our analysis.
 
-//@[unit] check-pass
+pub type Foo = impl Sized;
 
-mod helper {
-    pub type Foo = impl Sized;
+#[cfg(string)]
+#[define_opaque(Foo)]
+const fn foo() -> Foo {
+    String::new()
+}
 
-    #[cfg(string)]
-    pub const FOO: Foo = String::new();
+#[cfg(atomic)]
+#[define_opaque(Foo)]
+const fn foo() -> Foo {
+    std::sync::atomic::AtomicU8::new(42)
+}
 
-    #[cfg(atomic)]
-    pub const FOO: Foo = std::sync::atomic::AtomicU8::new(42);
+#[cfg(unit)]
+#[define_opaque(Foo)]
+const fn foo() -> Foo {}
 
-    #[cfg(unit)]
-    pub const FOO: Foo = ();
-}
-use helper::*;
+const FOO: Foo = foo();
 
 const BAR: () = {
     let _: &'static _ = &FOO;
-    //[string,atomic]~^ ERROR: destructor of `helper::Foo` cannot be evaluated at compile-time
+    //[string,atomic,unit]~^ ERROR: destructor of `Foo` cannot be evaluated at compile-time
 };
 
 const BAZ: &Foo = &FOO;
@@ -34,5 +38,5 @@ const BAZ: &Foo = &FOO;
 
 fn main() {
     let _: &'static _ = &FOO;
-    //[string,atomic]~^ ERROR: temporary value dropped while borrowed
+    //[string,atomic,unit]~^ ERROR: temporary value dropped while borrowed
 }
diff --git a/tests/ui/consts/const-promoted-opaque.string.stderr b/tests/ui/consts/const-promoted-opaque.string.stderr
index 33e5f426448..847a466f21c 100644
--- a/tests/ui/consts/const-promoted-opaque.string.stderr
+++ b/tests/ui/consts/const-promoted-opaque.string.stderr
@@ -1,5 +1,5 @@
-error[E0493]: destructor of `helper::Foo` cannot be evaluated at compile-time
-  --> $DIR/const-promoted-opaque.rs:28:26
+error[E0493]: destructor of `Foo` cannot be evaluated at compile-time
+  --> $DIR/const-promoted-opaque.rs:32:26
    |
 LL |     let _: &'static _ = &FOO;
    |                          ^^^ the destructor for this type cannot be evaluated in constants
@@ -8,7 +8,7 @@ LL | };
    | - value is dropped here
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/const-promoted-opaque.rs:36:26
+  --> $DIR/const-promoted-opaque.rs:40:26
    |
 LL |     let _: &'static _ = &FOO;
    |            ----------    ^^^ creates a temporary value which is freed while still in use
diff --git a/tests/ui/consts/const-promoted-opaque.unit.stderr b/tests/ui/consts/const-promoted-opaque.unit.stderr
new file mode 100644
index 00000000000..847a466f21c
--- /dev/null
+++ b/tests/ui/consts/const-promoted-opaque.unit.stderr
@@ -0,0 +1,24 @@
+error[E0493]: destructor of `Foo` cannot be evaluated at compile-time
+  --> $DIR/const-promoted-opaque.rs:32:26
+   |
+LL |     let _: &'static _ = &FOO;
+   |                          ^^^ the destructor for this type cannot be evaluated in constants
+LL |
+LL | };
+   | - value is dropped here
+
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/const-promoted-opaque.rs:40:26
+   |
+LL |     let _: &'static _ = &FOO;
+   |            ----------    ^^^ creates a temporary value which is freed while still in use
+   |            |
+   |            type annotation requires that borrow lasts for `'static`
+LL |
+LL | }
+   | - temporary value is freed at the end of this statement
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0493, E0716.
+For more information about an error, try `rustc --explain E0493`.
diff --git a/tests/ui/consts/required-consts/collect-in-dead-fn-behind-opaque-type.rs b/tests/ui/consts/required-consts/collect-in-dead-fn-behind-opaque-type.rs
index 795e021ceb0..f333f3462c7 100644
--- a/tests/ui/consts/required-consts/collect-in-dead-fn-behind-opaque-type.rs
+++ b/tests/ui/consts/required-consts/collect-in-dead-fn-behind-opaque-type.rs
@@ -20,6 +20,7 @@ mod m {
         }
     }
 
+    #[define_opaque(NotCalledFn)]
     fn mk_not_called() -> NotCalledFn {
         not_called::<i32>
     }