Add the `#[derive_const]` attribute

6 files changed, 73 insertions, 2 deletions

diff --git a/src/test/ui/issues/issue-32655.stderr b/src/test/ui/issues/issue-32655.stderr
index 2d9ce430a46..5a758c7002b 100644
--- a/src/test/ui/issues/issue-32655.stderr
+++ b/src/test/ui/issues/issue-32655.stderr
@@ -2,18 +2,28 @@ error: cannot find attribute `derive_Clone` in this scope
   --> $DIR/issue-32655.rs:3:11
    |
 LL |         #[derive_Clone]
-   |           ^^^^^^^^^^^^
+   |           ^^^^^^^^^^^^ help: an attribute macro with a similar name exists: `derive_const`
 ...
 LL | foo!();
    | ------ in this macro invocation
    |
+  ::: $SRC_DIR/core/src/macros/mod.rs:LL:COL
+   |
+LL |     pub macro derive_const($item:item) {
+   |     ---------------------- similarly named attribute macro `derive_const` defined here
+   |
    = note: this error originates in the macro `foo` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: cannot find attribute `derive_Clone` in this scope
   --> $DIR/issue-32655.rs:15:7
    |
 LL |     #[derive_Clone]
-   |       ^^^^^^^^^^^^
+   |       ^^^^^^^^^^^^ help: an attribute macro with a similar name exists: `derive_const`
+   |
+  ::: $SRC_DIR/core/src/macros/mod.rs:LL:COL
+   |
+LL |     pub macro derive_const($item:item) {
+   |     ---------------------- similarly named attribute macro `derive_const` defined here
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/rfc-2632-const-trait-impl/const_derives/derive-const-gate.rs b/src/test/ui/rfc-2632-const-trait-impl/const_derives/derive-const-gate.rs
new file mode 100644
index 00000000000..348ca0ab190
--- /dev/null
+++ b/src/test/ui/rfc-2632-const-trait-impl/const_derives/derive-const-gate.rs
@@ -0,0 +1,4 @@
+#[derive_const(Default)] //~ ERROR use of unstable library feature
+pub struct S;
+
+fn main() {}
diff --git a/src/test/ui/rfc-2632-const-trait-impl/const_derives/derive-const-gate.stderr b/src/test/ui/rfc-2632-const-trait-impl/const_derives/derive-const-gate.stderr
new file mode 100644
index 00000000000..cc9bdd2715f
--- /dev/null
+++ b/src/test/ui/rfc-2632-const-trait-impl/const_derives/derive-const-gate.stderr
@@ -0,0 +1,11 @@
+error[E0658]: use of unstable library feature 'derive_const'
+  --> $DIR/derive-const-gate.rs:1:3
+   |
+LL | #[derive_const(Default)]
+   |   ^^^^^^^^^^^^
+   |
+   = help: add `#![feature(derive_const)]` to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.
diff --git a/src/test/ui/rfc-2632-const-trait-impl/const_derives/derive-const-non-const-type.rs b/src/test/ui/rfc-2632-const-trait-impl/const_derives/derive-const-non-const-type.rs
new file mode 100644
index 00000000000..92843a8a2da
--- /dev/null
+++ b/src/test/ui/rfc-2632-const-trait-impl/const_derives/derive-const-non-const-type.rs
@@ -0,0 +1,13 @@
+#![feature(derive_const)]
+
+pub struct A;
+
+impl Default for A {
+    fn default() -> A { A }
+}
+
+#[derive_const(Default)]
+pub struct S(A);
+//~^ cannot call non-const fn
+
+fn main() {}
diff --git a/src/test/ui/rfc-2632-const-trait-impl/const_derives/derive-const-non-const-type.stderr b/src/test/ui/rfc-2632-const-trait-impl/const_derives/derive-const-non-const-type.stderr
new file mode 100644
index 00000000000..d463c774e28
--- /dev/null
+++ b/src/test/ui/rfc-2632-const-trait-impl/const_derives/derive-const-non-const-type.stderr
@@ -0,0 +1,14 @@
+error[E0015]: cannot call non-const fn `<A as Default>::default` in constant functions
+  --> $DIR/derive-const-non-const-type.rs:10:14
+   |
+LL | #[derive_const(Default)]
+   |                ------- in this derive macro expansion
+LL | pub struct S(A);
+   |              ^
+   |
+   = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
+   = note: this error originates in the derive macro `Default` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+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/const_derives/derive-const-use.rs b/src/test/ui/rfc-2632-const-trait-impl/const_derives/derive-const-use.rs
new file mode 100644
index 00000000000..d1fbeac8598
--- /dev/null
+++ b/src/test/ui/rfc-2632-const-trait-impl/const_derives/derive-const-use.rs
@@ -0,0 +1,19 @@
+// check-pass
+#![feature(const_trait_impl, const_cmp, const_default_impls, derive_const)]
+
+pub struct A;
+
+impl const Default for A {
+    fn default() -> A { A }
+}
+
+impl const PartialEq for A {
+    fn eq(&self, _: &A) -> bool { true }
+}
+
+#[derive_const(Default, PartialEq)]
+pub struct S((), A);
+
+const _: () = assert!(S((), A) == S::default());
+
+fn main() {}