Add rustdoc tests for generic const items

Author: fmease

Diff for: tests/rustdoc/generic-const-items.rs

@@ -0,0 +1,38 @@
+#![feature(generic_const_items)]
+#![allow(incomplete_features)]
+
+// @has 'generic_const_items/constant.K.html'
+// @has - '//*[@class="rust item-decl"]//code' \
+// "pub const K<'a, T: 'a + Copy, const N: usize>: Option<[T; N]> \
+// where \
+//     String: From<T>;"
+pub const K<'a, T: 'a + Copy, const N: usize>: Option<[T; N]> = None
+where
+    String: From<T>;
+
+// @has generic_const_items/trait.Trait.html
+pub trait Trait<T: ?Sized> {
+    // @has - '//*[@id="associatedconstant.C"]' \
+    // "const C<'a>: &'a T \
+    // where \
+    //     T: 'a + Eq"
+    const C<'a>: &'a T
+    where
+        T: 'a + Eq;
+}
+
+pub struct Implementor;
+
+// @has generic_const_items/struct.Implementor.html
+// @has - '//h3[@class="code-header"]' 'impl Trait<str> for Implementor'
+impl Trait<str> for Implementor {
+    // @has - '//*[@id="associatedconstant.C"]' \
+    // "const C<'a>: &'a str = \"C\" \
+    // where \
+    //     str: 'a"
+    const C<'a>: &'a str = "C"
+    // In real code we could've left off this bound but adding it explicitly allows us to test if
+    // we render where-clauses on associated consts inside impl blocks correctly.
+    where
+        str: 'a;
+}

Diff for: tests/rustdoc/inline_cross/auxiliary/generic-const-items.rs

@@ -0,0 +1,22 @@
+#![feature(generic_const_items)]
+#![allow(incomplete_features)]
+
+pub const K<'a, T: 'a + Copy, const N: usize>: Option<[T; N]> = None
+where
+    String: From<T>;
+
+pub trait Trait<T: ?Sized> {
+    const C<'a>: &'a T
+    where
+        T: 'a + Eq;
+}
+
+pub struct Implementor;
+
+impl Trait<str> for Implementor {
+    const C<'a>: &'a str = "C"
+    // In real code we could've left off this bound but adding it explicitly allows us to test if
+    // we render where-clauses on associated consts inside impl blocks correctly.
+    where
+        str: 'a;
+}

Diff for: tests/rustdoc/inline_cross/generic-const-items.rs

@@ -0,0 +1,26 @@
+#![crate_name = "user"]
+
+// aux-crate:generic_const_items=generic-const-items.rs
+// edition:2021
+
+// @has 'user/constant.K.html'
+// @has - '//*[@class="rust item-decl"]//code' \
+// "pub const K<'a, T: 'a + Copy, const N: usize>: Option<[T; N]> \
+// where \
+//     String: From<T>;"
+pub use generic_const_items::K;
+
+// @has user/trait.Trait.html
+// @has - '//*[@id="associatedconstant.C"]' \
+// "const C<'a>: &'a T \
+// where \
+//     T: 'a + Eq"
+pub use generic_const_items::Trait;
+
+// @has user/struct.Implementor.html
+// @has - '//h3[@class="code-header"]' 'impl Trait<str> for Implementor'
+// @has - '//*[@id="associatedconstant.C"]' \
+// "const C<'a>: &'a str = \"C\" \
+// where \
+//     str: 'a"
+pub use generic_const_items::Implementor;