Auto merge of #76196 - r-52:r-coverage-allow-missing-docs, r=jyn514

rustdoc: skip #[allow(missing docs)] for docs in coverage report

During the document coverage reporting with:
```bash
rustdoc something.rs -Z unstable-options --show-coverage
```

the coverage report counts code that is marked with `#[allow(missing_docs)]` for the calculation, which outputs lower numbers in the coverage report even though these parts should be ignored for the calculation.

Right now I'm not sure how this can be tested (CI)? (I verified it by hand and ran the unit tests)

r? `@jyn514`

**Reference:** Fixes #76121

3 files changed, 68 insertions, 0 deletions

diff --git a/src/test/rustdoc-ui/coverage/allow_missing_docs.rs b/src/test/rustdoc-ui/coverage/allow_missing_docs.rs
new file mode 100644
index 00000000000..c077be31b20
--- /dev/null
+++ b/src/test/rustdoc-ui/coverage/allow_missing_docs.rs
@@ -0,0 +1,41 @@
+// compile-flags:-Z unstable-options --show-coverage
+// check-pass
+
+//! Make sure to have some docs on your crate root
+
+#[allow(missing_docs)]
+pub mod mod_foo {
+    pub struct Bar;
+}
+
+/// This is a struct with a `#[allow(missing_docs)]`
+pub struct AllowTheMissingDocs {
+    #[allow(missing_docs)]
+    pub empty_str: String,
+
+    /// This has
+    #[allow(missing_docs)]
+    /// but also has documentation comments
+    pub hello: usize,
+
+    /// The doc id just to create a boilerplate comment
+    pub doc_id: Vec<u8>,
+}
+
+/// A function that has a documentation
+pub fn this_is_func() {}
+
+#[allow(missing_docs)]
+pub struct DemoStruct {
+    something: usize,
+}
+
+#[allow(missing_docs)]
+pub mod bar {
+    #[warn(missing_docs)]
+    pub struct Bar { //~ WARN
+        pub f: u32, //~ WARN
+    }
+
+    pub struct NeedsNoDocs;
+}
diff --git a/src/test/rustdoc-ui/coverage/allow_missing_docs.stderr b/src/test/rustdoc-ui/coverage/allow_missing_docs.stderr
new file mode 100644
index 00000000000..3d5b512d14d
--- /dev/null
+++ b/src/test/rustdoc-ui/coverage/allow_missing_docs.stderr
@@ -0,0 +1,20 @@
+warning: missing documentation for a struct
+  --> $DIR/allow_missing_docs.rs:36:5
+   |
+LL |     pub struct Bar {
+   |     ^^^^^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/allow_missing_docs.rs:35:12
+   |
+LL |     #[warn(missing_docs)]
+   |            ^^^^^^^^^^^^
+
+warning: missing documentation for a struct field
+  --> $DIR/allow_missing_docs.rs:37:9
+   |
+LL |         pub f: u32,
+   |         ^^^^^^^^^^
+
+warning: 2 warnings emitted
+
diff --git a/src/test/rustdoc-ui/coverage/allow_missing_docs.stdout b/src/test/rustdoc-ui/coverage/allow_missing_docs.stdout
new file mode 100644
index 00000000000..17e8ee9e23d
--- /dev/null
+++ b/src/test/rustdoc-ui/coverage/allow_missing_docs.stdout
@@ -0,0 +1,7 @@
++-------------------------------------+------------+------------+------------+------------+
+| File                                | Documented | Percentage |   Examples | Percentage |
++-------------------------------------+------------+------------+------------+------------+
+| ...i/coverage/allow_missing_docs.rs |          5 |      71.4% |          0 |       0.0% |
++-------------------------------------+------------+------------+------------+------------+
+| Total                               |          5 |      71.4% |          0 |       0.0% |
++-------------------------------------+------------+------------+------------+------------+