Auto merge of #97177 - oli-obk:const-stability, r=davidtwco

Implement proper stability check for const impl Trait, fall back to unstable const when undeclared

Continuation of #93960

`@jhpratt` it looks to me like the test was simply not testing for the failure you were looking for? Your checks actually do the right thing for const traits?

16 files changed, 161 insertions, 127 deletions

diff --git a/src/librustdoc/clean/inline.rs b/src/librustdoc/clean/inline.rs
index 1b6658bb4ca..e7b966758d6 100644
--- a/src/librustdoc/clean/inline.rs
+++ b/src/librustdoc/clean/inline.rs
@@ -344,7 +344,7 @@ pub(crate) fn build_impl(
             }
 
             if let Some(stab) = tcx.lookup_stability(did) {
-                if stab.level.is_unstable() && stab.feature == sym::rustc_private {
+                if stab.is_unstable() && stab.feature == sym::rustc_private {
                     return;
                 }
             }
@@ -373,7 +373,7 @@ pub(crate) fn build_impl(
             }
 
             if let Some(stab) = tcx.lookup_stability(did) {
-                if stab.level.is_unstable() && stab.feature == sym::rustc_private {
+                if stab.is_unstable() && stab.feature == sym::rustc_private {
                     return;
                 }
             }
diff --git a/src/librustdoc/clean/types.rs b/src/librustdoc/clean/types.rs
index 3123ece3773..a832d03a501 100644
--- a/src/librustdoc/clean/types.rs
+++ b/src/librustdoc/clean/types.rs
@@ -632,7 +632,7 @@ impl Item {
         self.stability(tcx).as_ref().and_then(|s| {
             let mut classes = Vec::with_capacity(2);
 
-            if s.level.is_unstable() {
+            if s.is_unstable() {
                 classes.push("unstable");
             }
 
diff --git a/src/librustdoc/html/render/print_item.rs b/src/librustdoc/html/render/print_item.rs
index 12e6115e6fe..2c0b8d7bde1 100644
--- a/src/librustdoc/html/render/print_item.rs
+++ b/src/librustdoc/html/render/print_item.rs
@@ -445,10 +445,7 @@ fn extra_info_tags(item: &clean::Item, parent: &clean::Item, tcx: TyCtxt<'_>) ->
 
     // The "rustc_private" crates are permanently unstable so it makes no sense
     // to render "unstable" everywhere.
-    if item
-        .stability(tcx)
-        .as_ref()
-        .map(|s| s.level.is_unstable() && s.feature != sym::rustc_private)
+    if item.stability(tcx).as_ref().map(|s| s.is_unstable() && s.feature != sym::rustc_private)
         == Some(true)
     {
         tags += &tag_html("unstable", "", "Experimental");
diff --git a/src/test/ui/consts/rustc-impl-const-stability.rs b/src/test/ui/consts/rustc-impl-const-stability.rs
index e3fda57548e..0c18efa0a02 100644
--- a/src/test/ui/consts/rustc-impl-const-stability.rs
+++ b/src/test/ui/consts/rustc-impl-const-stability.rs
@@ -1,19 +1,18 @@
-// build-pass
+// check-pass
 
 #![crate_type = "lib"]
 #![feature(staged_api)]
 #![feature(const_trait_impl)]
 #![stable(feature = "foo", since = "1.0.0")]
 
-
 #[stable(feature = "potato", since = "1.27.0")]
 pub struct Data {
-    _data: u128
+    _data: u128,
 }
 
 #[stable(feature = "potato", since = "1.27.0")]
+#[rustc_const_unstable(feature = "data_foo", issue = "none")]
 impl const Default for Data {
-    #[rustc_const_unstable(feature = "data_foo", issue = "none")]
     fn default() -> Data {
         Data { _data: 42 }
     }
diff --git a/src/test/ui/rfc-2632-const-trait-impl/auxiliary/staged-api.rs b/src/test/ui/rfc-2632-const-trait-impl/auxiliary/staged-api.rs
index 80e61ab0a9e..19e9006094b 100644
--- a/src/test/ui/rfc-2632-const-trait-impl/auxiliary/staged-api.rs
+++ b/src/test/ui/rfc-2632-const-trait-impl/auxiliary/staged-api.rs
@@ -1,5 +1,4 @@
 #![feature(const_trait_impl)]
-
 #![feature(staged_api)]
 #![stable(feature = "rust1", since = "1.0.0")]
 
@@ -13,9 +12,7 @@ pub trait MyTrait {
 pub struct Unstable;
 
 #[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_const_unstable(feature = "staged", issue = "none")]
+#[rustc_const_unstable(feature = "unstable", issue = "none")]
 impl const MyTrait for Unstable {
-    fn func() {
-
-    }
+    fn func() {}
 }
diff --git a/src/test/ui/rfc-2632-const-trait-impl/stability.rs b/src/test/ui/rfc-2632-const-trait-impl/stability.rs
deleted file mode 100644
index 906956f5eba..00000000000
--- a/src/test/ui/rfc-2632-const-trait-impl/stability.rs
+++ /dev/null
@@ -1,45 +0,0 @@
-#![feature(allow_internal_unstable)]
-#![feature(const_add)]
-#![feature(const_trait_impl)]
-#![feature(staged_api)]
-#![stable(feature = "rust1", since = "1.0.0")]
-
-#[stable(feature = "rust1", since = "1.0.0")]
-pub struct Int(i32);
-
-#[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_const_stable(feature = "rust1", since = "1.0.0")]
-impl const std::ops::Sub for Int {
-    type Output = Self;
-
-    fn sub(self, rhs: Self) -> Self {
-        //~^ ERROR trait methods cannot be stable const fn
-        Int(self.0 - rhs.0)
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_const_unstable(feature = "const_add", issue = "none")]
-impl const std::ops::Add for Int {
-    type Output = Self;
-
-    fn add(self, rhs: Self) -> Self {
-        Int(self.0 + rhs.0)
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_const_stable(feature = "rust1", since = "1.0.0")]
-pub const fn foo() -> Int {
-    Int(1i32) + Int(2i32)
-    //~^ ERROR not yet stable as a const fn
-}
-
-// ok
-#[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_const_unstable(feature = "bar", issue = "none")]
-pub const fn bar() -> Int {
-    Int(1i32) + Int(2i32)
-}
-
-fn main() {}
diff --git a/src/test/ui/rfc-2632-const-trait-impl/stability.stderr b/src/test/ui/rfc-2632-const-trait-impl/stability.stderr
deleted file mode 100644
index 7473b801cce..00000000000
--- a/src/test/ui/rfc-2632-const-trait-impl/stability.stderr
+++ /dev/null
@@ -1,19 +0,0 @@
-error: trait methods cannot be stable const fn
-  --> $DIR/stability.rs:15:5
-   |
-LL | /     fn sub(self, rhs: Self) -> Self {
-LL | |
-LL | |         Int(self.0 - rhs.0)
-LL | |     }
-   | |_____^
-
-error: `<Int as Add>::add` is not yet stable as a const fn
-  --> $DIR/stability.rs:34:5
-   |
-LL |     Int(1i32) + Int(2i32)
-   |     ^^^^^^^^^^^^^^^^^^^^^
-   |
-   = help: const-stable functions can only call other const-stable functions
-
-error: aborting due to 2 previous errors
-
diff --git a/src/test/ui/rfc-2632-const-trait-impl/staged-api-user-crate.rs b/src/test/ui/rfc-2632-const-trait-impl/staged-api-user-crate.rs
new file mode 100644
index 00000000000..fc0d82727b5
--- /dev/null
+++ b/src/test/ui/rfc-2632-const-trait-impl/staged-api-user-crate.rs
@@ -0,0 +1,16 @@
+// aux-build: staged-api.rs
+extern crate staged_api;
+
+use staged_api::*;
+
+// Const stability has no impact on usage in non-const contexts.
+fn non_const_context() {
+    Unstable::func();
+}
+
+const fn stable_const_context() {
+    Unstable::func();
+    //~^ ERROR cannot call non-const fn `<staged_api::Unstable as staged_api::MyTrait>::func` in constant functions
+}
+
+fn main() {}
diff --git a/src/test/ui/rfc-2632-const-trait-impl/staged-api-user-crate.stderr b/src/test/ui/rfc-2632-const-trait-impl/staged-api-user-crate.stderr
new file mode 100644
index 00000000000..61f9840e0d0
--- /dev/null
+++ b/src/test/ui/rfc-2632-const-trait-impl/staged-api-user-crate.stderr
@@ -0,0 +1,11 @@
+error[E0015]: cannot call non-const fn `<staged_api::Unstable as staged_api::MyTrait>::func` in constant functions
+  --> $DIR/staged-api-user-crate.rs:12:5
+   |
+LL |     Unstable::func();
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0015`.
diff --git a/src/test/ui/rfc-2632-const-trait-impl/staged-api.rs b/src/test/ui/rfc-2632-const-trait-impl/staged-api.rs
index 39a1b6066de..1d79f5adf93 100644
--- a/src/test/ui/rfc-2632-const-trait-impl/staged-api.rs
+++ b/src/test/ui/rfc-2632-const-trait-impl/staged-api.rs
@@ -1,9 +1,7 @@
-// revisions: stock staged
-#![cfg_attr(staged, feature(staged))]
+// revisions: stable unstable
 
+#![cfg_attr(unstable, feature(unstable))] // The feature from the ./auxiliary/staged-api.rs file.
 #![feature(const_trait_impl)]
-#![allow(incomplete_features)]
-
 #![feature(staged_api)]
 #![stable(feature = "rust1", since = "1.0.0")]
 
@@ -13,27 +11,53 @@ extern crate staged_api;
 use staged_api::*;
 
 #[stable(feature = "rust1", since = "1.0.0")]
-pub struct Stable;
+pub struct Foo;
 
 #[stable(feature = "rust1", since = "1.0.0")]
-#[cfg_attr(staged, rustc_const_stable(feature = "rust1", since = "1.0.0"))]
-// ^ should trigger error with or without the attribute
-impl const MyTrait for Stable {
-    fn func() { //~ ERROR trait methods cannot be stable const fn
-
-    }
+#[cfg_attr(unstable, rustc_const_unstable(feature = "foo", issue = "none"))]
+#[cfg_attr(stable, rustc_const_stable(feature = "foo", since = "1.0.0"))]
+impl const MyTrait for Foo {
+    //[stable]~^ ERROR trait implementations cannot be const stable yet
+    fn func() {}
 }
 
+// Const stability has no impact on usage in non-const contexts.
 fn non_const_context() {
     Unstable::func();
-    Stable::func();
+    Foo::func();
 }
 
 #[unstable(feature = "none", issue = "none")]
 const fn const_context() {
     Unstable::func();
-    //[stock]~^ ERROR `<staged_api::Unstable as staged_api::MyTrait>::func` is not yet stable as a const fn
-    Stable::func();
+    // ^ This is okay regardless of whether the `unstable` feature is enabled, as this function is
+    // not const-stable.
+    Foo::func();
+    //[unstable]~^ ERROR not yet stable as a const fn
+    // ^ fails, because the `foo` feature is not active
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(unstable, rustc_const_unstable(feature = "foo", issue = "none"))]
+pub const fn const_context_not_const_stable() {
+    //[stable]~^ ERROR function has missing const stability attribute
+    Unstable::func();
+    // ^ This is okay regardless of whether the `unstable` feature is enabled, as this function is
+    // not const-stable.
+    Foo::func();
+    //[unstable]~^ ERROR not yet stable as a const fn
+    // ^ fails, because the `foo` feature is not active
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_const_stable(feature = "cheese", since = "1.0.0")]
+const fn stable_const_context() {
+    Unstable::func();
+    //[unstable]~^ ERROR not yet stable as a const fn
+    Foo::func();
+    //[unstable]~^ ERROR not yet stable as a const fn
+    const_context_not_const_stable()
+    //[unstable]~^ ERROR not yet stable as a const fn
 }
 
 fn main() {}
diff --git a/src/test/ui/rfc-2632-const-trait-impl/staged-api.stable.stderr b/src/test/ui/rfc-2632-const-trait-impl/staged-api.stable.stderr
new file mode 100644
index 00000000000..a1aca762ef4
--- /dev/null
+++ b/src/test/ui/rfc-2632-const-trait-impl/staged-api.stable.stderr
@@ -0,0 +1,25 @@
+error: trait implementations cannot be const stable yet
+  --> $DIR/staged-api.rs:19:1
+   |
+LL | / impl const MyTrait for Foo {
+LL | |
+LL | |     fn func() {}
+LL | | }
+   | |_^
+   |
+   = note: see issue #67792 <https://github.com/rust-lang/rust/issues/67792> for more information
+
+error: function has missing const stability attribute
+  --> $DIR/staged-api.rs:42:1
+   |
+LL | / pub const fn const_context_not_const_stable() {
+LL | |
+LL | |     Unstable::func();
+LL | |     // ^ This is okay regardless of whether the `unstable` feature is enabled, as this function is
+...  |
+LL | |     // ^ fails, because the `foo` feature is not active
+LL | | }
+   | |_^
+
+error: aborting due to 2 previous errors
+
diff --git a/src/test/ui/rfc-2632-const-trait-impl/staged-api.staged.stderr b/src/test/ui/rfc-2632-const-trait-impl/staged-api.staged.stderr
deleted file mode 100644
index d2ff4ce2001..00000000000
--- a/src/test/ui/rfc-2632-const-trait-impl/staged-api.staged.stderr
+++ /dev/null
@@ -1,10 +0,0 @@
-error: trait methods cannot be stable const fn
-  --> $DIR/staged-api.rs:22:5
-   |
-LL | /     fn func() {
-LL | |
-LL | |     }
-   | |_____^
-
-error: aborting due to previous error
-
diff --git a/src/test/ui/rfc-2632-const-trait-impl/staged-api.stock.stderr b/src/test/ui/rfc-2632-const-trait-impl/staged-api.stock.stderr
deleted file mode 100644
index 91c5469bd90..00000000000
--- a/src/test/ui/rfc-2632-const-trait-impl/staged-api.stock.stderr
+++ /dev/null
@@ -1,18 +0,0 @@
-error: trait methods cannot be stable const fn
-  --> $DIR/staged-api.rs:22:5
-   |
-LL | /     fn func() {
-LL | |
-LL | |     }
-   | |_____^
-
-error: `<staged_api::Unstable as staged_api::MyTrait>::func` is not yet stable as a const fn
-  --> $DIR/staged-api.rs:34:5
-   |
-LL |     Unstable::func();
-   |     ^^^^^^^^^^^^^^^^
-   |
-   = help: add `#![feature(staged)]` to the crate attributes to enable
-
-error: aborting due to 2 previous errors
-
diff --git a/src/test/ui/rfc-2632-const-trait-impl/staged-api.unstable.stderr b/src/test/ui/rfc-2632-const-trait-impl/staged-api.unstable.stderr
new file mode 100644
index 00000000000..c38d1a81ae7
--- /dev/null
+++ b/src/test/ui/rfc-2632-const-trait-impl/staged-api.unstable.stderr
@@ -0,0 +1,42 @@
+error: `<Foo as staged_api::MyTrait>::func` is not yet stable as a const fn
+  --> $DIR/staged-api.rs:35:5
+   |
+LL |     Foo::func();
+   |     ^^^^^^^^^^^
+   |
+   = help: add `#![feature(foo)]` to the crate attributes to enable
+
+error: `<Foo as staged_api::MyTrait>::func` is not yet stable as a const fn
+  --> $DIR/staged-api.rs:47:5
+   |
+LL |     Foo::func();
+   |     ^^^^^^^^^^^
+   |
+   = help: add `#![feature(foo)]` to the crate attributes to enable
+
+error: `<staged_api::Unstable as staged_api::MyTrait>::func` is not yet stable as a const fn
+  --> $DIR/staged-api.rs:55:5
+   |
+LL |     Unstable::func();
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: const-stable functions can only call other const-stable functions
+
+error: `<Foo as staged_api::MyTrait>::func` is not yet stable as a const fn
+  --> $DIR/staged-api.rs:57:5
+   |
+LL |     Foo::func();
+   |     ^^^^^^^^^^^
+   |
+   = help: const-stable functions can only call other const-stable functions
+
+error: `const_context_not_const_stable` is not yet stable as a const fn
+  --> $DIR/staged-api.rs:59:5
+   |
+LL |     const_context_not_const_stable()
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: const-stable functions can only call other const-stable functions
+
+error: aborting due to 5 previous errors
+
diff --git a/src/test/ui/stability-attribute/missing-const-stability.rs b/src/test/ui/stability-attribute/missing-const-stability.rs
index 57e64737d0f..d89886af314 100644
--- a/src/test/ui/stability-attribute/missing-const-stability.rs
+++ b/src/test/ui/stability-attribute/missing-const-stability.rs
@@ -18,9 +18,15 @@ impl Foo {
     pub const fn bar() {} // ok because function is unstable
 }
 
-// FIXME Once #![feature(const_trait_impl)] is allowed to be stable, add a test
-// for const trait impls. Right now, a "trait methods cannot be stable const fn"
-// error is emitted. This occurs prior to the lint being tested here, such that
-// the lint cannot currently be tested on this use case.
+#[stable(feature = "stable", since = "1.0.0")]
+pub trait Bar {
+    #[stable(feature = "stable", since = "1.0.0")]
+    fn fun();
+}
+#[stable(feature = "stable", since = "1.0.0")]
+impl const Bar for Foo {
+    //~^ ERROR implementation has missing const stability attribute
+    fn fun() {}
+}
 
 fn main() {}
diff --git a/src/test/ui/stability-attribute/missing-const-stability.stderr b/src/test/ui/stability-attribute/missing-const-stability.stderr
index 7eba99a477a..6f2ade0d0ab 100644
--- a/src/test/ui/stability-attribute/missing-const-stability.stderr
+++ b/src/test/ui/stability-attribute/missing-const-stability.stderr
@@ -10,5 +10,14 @@ error: associated function has missing const stability attribute
 LL |     pub const fn foo() {}
    |     ^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 2 previous errors
+error: implementation has missing const stability attribute
+  --> $DIR/missing-const-stability.rs:27:1
+   |
+LL | / impl const Bar for Foo {
+LL | |
+LL | |     fn fun() {}
+LL | | }
+   | |_^
+
+error: aborting due to 3 previous errors