diff --git a/compiler/rustc_lint/src/builtin.rs b/compiler/rustc_lint/src/builtin.rs
index 824a1868c55df..7f60fc727f22b 100644
--- a/compiler/rustc_lint/src/builtin.rs
+++ b/compiler/rustc_lint/src/builtin.rs
@@ -426,12 +426,6 @@ impl MissingDoc {
         article: &'static str,
         desc: &'static str,
     ) {
-        // If we're building a test harness, then warning about
-        // documentation is probably not really relevant right now.
-        if cx.sess().opts.test {
-            return;
-        }
-
         // Only check publicly-visible items, using the result from the privacy pass.
         // It's an option so the crate root can also use this function (it doesn't
         // have a `NodeId`).
@@ -444,11 +438,10 @@ impl MissingDoc {
         let attrs = cx.tcx.hir().attrs(cx.tcx.local_def_id_to_hir_id(def_id));
         let has_doc = attrs.iter().any(has_doc);
         if !has_doc {
-            cx.emit_span_lint(
-                MISSING_DOCS,
-                cx.tcx.def_span(def_id),
-                BuiltinMissingDoc { article, desc },
-            );
+            let sp = cx.tcx.def_span(def_id);
+            if !sp.is_dummy() {
+                cx.emit_span_lint(MISSING_DOCS, sp, BuiltinMissingDoc { article, desc });
+            }
         }
     }
 }
diff --git a/library/alloc/src/slice.rs b/library/alloc/src/slice.rs
index 9d70487032699..8cdba166c9dff 100644
--- a/library/alloc/src/slice.rs
+++ b/library/alloc/src/slice.rs
@@ -96,6 +96,7 @@ pub(crate) mod hack {
     // We shouldn't add inline attribute to this since this is used in
     // `vec!` macro mostly and causes perf regression. See #71204 for
     // discussion and perf results.
+    #[allow(missing_docs)]
     pub fn into_vec<T, A: Allocator>(b: Box<[T], A>) -> Vec<T, A> {
         unsafe {
             let len = b.len();
@@ -105,6 +106,7 @@ pub(crate) mod hack {
     }
 
     #[cfg(not(no_global_oom_handling))]
+    #[allow(missing_docs)]
     #[inline]
     pub fn to_vec<T: ConvertVec, A: Allocator>(s: &[T], alloc: A) -> Vec<T, A> {
         T::to_vec(s, alloc)
diff --git a/library/alloc/src/string.rs b/library/alloc/src/string.rs
index bc8b7e24bf12b..05617669ed231 100644
--- a/library/alloc/src/string.rs
+++ b/library/alloc/src/string.rs
@@ -508,6 +508,7 @@ impl String {
     // NB see the slice::hack module in slice.rs for more information
     #[inline]
     #[cfg(test)]
+    #[allow(missing_docs)]
     pub fn from_str(_: &str) -> String {
         panic!("not available with cfg(test)");
     }
diff --git a/library/std/src/io/buffered/bufreader.rs b/library/std/src/io/buffered/bufreader.rs
index cf226bd28d005..035afbb8368b4 100644
--- a/library/std/src/io/buffered/bufreader.rs
+++ b/library/std/src/io/buffered/bufreader.rs
@@ -267,6 +267,7 @@ impl<R: ?Sized> BufReader<R> {
 // This is only used by a test which asserts that the initialization-tracking is correct.
 #[cfg(test)]
 impl<R: ?Sized> BufReader<R> {
+    #[allow(missing_docs)]
     pub fn initialized(&self) -> usize {
         self.buf.initialized()
     }
diff --git a/tests/ui/lint/lint-missing-doc-expect.rs b/tests/ui/lint/lint-missing-doc-expect.rs
new file mode 100644
index 0000000000000..991f65003dc26
--- /dev/null
+++ b/tests/ui/lint/lint-missing-doc-expect.rs
@@ -0,0 +1,13 @@
+// Make sure that `#[expect(missing_docs)]` is always correctly fulfilled.
+
+//@ check-pass
+//@ revisions: lib bin test
+//@ [lib]compile-flags: --crate-type lib
+//@ [bin]compile-flags: --crate-type bin
+//@ [test]compile-flags: --test
+
+#[expect(missing_docs)]
+pub fn foo() {}
+
+#[cfg(bin)]
+fn main() {}