Rollup merge of #93412 - fee1-dead:improve-rustdoc-const-bounds, r=GuillaumeGomez

Improve rustdoc const bounds

 - Rustdoc no longer displays `~const` in trait bounds, because it currently means nothing for stable users, and because we still haven't decided on the final syntax yet.
 - Rustdoc will hide trait bounds where the trait is `Drop` AND it is `~const`, i.e. `~const Drop` bounds because it has no effect on stable users as well.
 - Because of additional logic that hides the whole `where` statement where it consists of `~const Drop` bounds (so it doesn't display `struct Foo<T>() where ;` like that), bounds that have no trait e.g. `where [T; N+1]: ;` are also hidden.

Cherry-picked from #92433.

2 files changed, 61 insertions, 1 deletions

diff --git a/src/test/rustdoc/const-generics/generic_const_exprs.rs b/src/test/rustdoc/const-generics/generic_const_exprs.rs
index 35036a89360..215ee228eb8 100644
--- a/src/test/rustdoc/const-generics/generic_const_exprs.rs
+++ b/src/test/rustdoc/const-generics/generic_const_exprs.rs
@@ -3,5 +3,5 @@
 #![allow(incomplete_features)]
 // make sure that `ConstEvaluatable` predicates dont cause rustdoc to ICE #77647
 // @has foo/struct.Ice.html '//pre[@class="rust struct"]' \
-//      'pub struct Ice<const N: usize> where [(); N + 1]: ;'
+//      'pub struct Ice<const N: usize>;'
 pub struct Ice<const N: usize> where [(); N + 1]:;
diff --git a/src/test/rustdoc/rfc-2632-const-trait-impl.rs b/src/test/rustdoc/rfc-2632-const-trait-impl.rs
new file mode 100644
index 00000000000..2adf69f6514
--- /dev/null
+++ b/src/test/rustdoc/rfc-2632-const-trait-impl.rs
@@ -0,0 +1,60 @@
+// Test that we do not currently display `~const` in rustdoc
+// as that syntax is currently provisional; `~const Drop` has
+// no effect on stable code so it should be hidden as well.
+//
+// To future blessers: make sure that `const_trait_impl` is
+// stabilized when changing `@!has` to `@has`, and please do
+// not remove this test.
+#![feature(const_trait_impl)]
+#![crate_name = "foo"]
+
+pub struct S<T>(T);
+
+// @!has foo/trait.Tr.html '//pre[@class="rust trait"]/code/a[@class="trait"]' '~const'
+// @!has - '//pre[@class="rust trait"]/code/a[@class="trait"]' 'Drop'
+// @has - '//pre[@class="rust trait"]/code/a[@class="trait"]' 'Clone'
+// @!has - '//pre[@class="rust trait"]/code/span[@class="where"]' '~const'
+// @!has - '//pre[@class="rust trait"]/code/span[@class="where"]' 'Drop'
+// @has - '//pre[@class="rust trait"]/code/span[@class="where"]' ': Clone'
+pub trait Tr<T> {
+    // @!has - '//div[@id="method.a"]/h4[@class="code-header"]' '~const'
+    // @!has - '//div[@id="method.a"]/h4[@class="code-header"]/a[@class="trait"]' 'Drop'
+    // @has - '//div[@id="method.a"]/h4[@class="code-header"]/a[@class="trait"]' 'Clone'
+    // @!has - '//div[@id="method.a"]/h4[@class="code-header"]/span[@class="where"]' '~const'
+    // @!has - '//div[@id="method.a"]/h4[@class="code-header"]/span[@class="where fmt-newline"]' 'Drop'
+    // @has - '//div[@id="method.a"]/h4[@class="code-header"]/span[@class="where fmt-newline"]' ': Clone'
+    #[default_method_body_is_const]
+    fn a<A: ~const Drop + ~const Clone>() where Option<A>: ~const Drop + ~const Clone {}
+}
+
+// @!has - '//section[@id="impl-Tr%3CT%3E"]/h3[@class="code-header in-band"]' '~const'
+// @!has - '//section[@id="impl-Tr%3CT%3E"]/h3[@class="code-header in-band"]/a[@class="trait"]' 'Drop'
+// @has - '//section[@id="impl-Tr%3CT%3E"]/h3[@class="code-header in-band"]/a[@class="trait"]' 'Clone'
+// @!has - '//section[@id="impl-Tr%3CT%3E"]/h3[@class="code-header in-band"]/span[@class="where"]' '~const'
+// @!has - '//section[@id="impl-Tr%3CT%3E"]/h3[@class="code-header in-band"]/span[@class="where fmt-newline"]' 'Drop'
+// @has - '//section[@id="impl-Tr%3CT%3E"]/h3[@class="code-header in-band"]/span[@class="where fmt-newline"]' ': Clone'
+impl<T: ~const Drop + ~const Clone> const Tr<T> for T where Option<T>: ~const Drop + ~const Clone {
+    fn a<A: ~const Drop + ~const Clone>() where Option<A>: ~const Drop + ~const Clone {}
+}
+
+// @!has foo/fn.foo.html '//pre[@class="rust fn"]/code/a[@class="trait"]' '~const'
+// @!has - '//pre[@class="rust fn"]/code/a[@class="trait"]' 'Drop'
+// @has - '//pre[@class="rust fn"]/code/a[@class="trait"]' 'Clone'
+// @!has - '//pre[@class="rust fn"]/code/span[@class="where fmt-newline"]' '~const'
+// @!has - '//pre[@class="rust fn"]/code/span[@class="where fmt-newline"]' 'Drop'
+// @has - '//pre[@class="rust fn"]/code/span[@class="where fmt-newline"]' ': Clone'
+pub const fn foo<F: ~const Drop + ~const Clone>() where Option<F>: ~const Drop + ~const Clone {
+    F::a()
+}
+
+impl<T> S<T> {
+    // @!has foo/struct.S.html '//section[@id="method.foo"]/h4[@class="code-header"]' '~const'
+    // @!has - '//section[@id="method.foo"]/h4[@class="code-header"]/a[@class="trait"]' 'Drop'
+    // @has - '//section[@id="method.foo"]/h4[@class="code-header"]/a[@class="trait"]' 'Clone'
+    // @!has - '//section[@id="method.foo"]/h4[@class="code-header"]/span[@class="where"]' '~const'
+    // @!has - '//section[@id="method.foo"]/h4[@class="code-header"]/span[@class="where fmt-newline"]' 'Drop'
+    // @has - '//section[@id="method.foo"]/h4[@class="code-header"]/span[@class="where fmt-newline"]' ': Clone'
+    pub const fn foo<B: ~const Drop + ~const Clone>() where B: ~const Drop + ~const Clone {
+        B::a()
+    }
+}