Rollup merge of #90905 - GuillaumeGomez:empty-impl-blocks, r=jsha

Add empty impl blocks if they have documentation

Fixes https://github.com/rust-lang/rust/issues/90866.

The update for the test script is needed to count the number of impl blocks we have with only the struct. To be noted that with https://github.com/rust-lang/rust/pull/89676 merged, it wouldn't be needed (I don't know what is the status of it btw. cc ```@Mark-Simulacrum).```

It looks like this:

![Screenshot from 2021-11-14 16-51-28](https://user-images.githubusercontent.com/3050060/141689100-e57123c0-bf50-4c42-adf5-d991e169a0e4.png)

cc ```@jyn514```
r? ```@camelid```

1 files changed, 20 insertions, 0 deletions

diff --git a/src/test/rustdoc/empty-impl-block.rs b/src/test/rustdoc/empty-impl-block.rs
new file mode 100644
index 00000000000..6a2a254f63a
--- /dev/null
+++ b/src/test/rustdoc/empty-impl-block.rs
@@ -0,0 +1,20 @@
+#![crate_name = "foo"]
+
+// @has 'foo/struct.Foo.html'
+pub struct Foo;
+
+// @has - '//*[@class="docblock"]' 'Hello empty impl block!'
+// @has - '//*[@class="item-info"]' 'This impl block contains no items.'
+/// Hello empty impl block!
+impl Foo {}
+// We ensure that this empty impl block without doc isn't rendered.
+// @count - '//*[@class="impl has-srclink"]' 'impl Foo' 1
+impl Foo {}
+
+// Just to ensure that empty trait impl blocks are rendered.
+pub struct Another;
+pub trait Bar {}
+
+// @has 'foo/struct.Another.html'
+// @has - '//h3[@class="code-header in-band"]' 'impl Bar for Another'
+impl Bar for Another {}