Auto merge of #13573 - y21:issue13427, r=Centri3

Don't lint unnamed consts and nested items within functions in `missing_docs_in_private_items`

With this change we no longer require doc comments for `const _: ()` items as well as nested items in functions or other bodies. In both of those cases, rustdoc generates no documentation even with `--document-private-items`.

Fixes #13427 (first commit)
Fixes #13298 (second commit)
cc https://github.com/rust-lang/rust-clippy/issues/5736#issuecomment-668524296

changelog: [`missing_docs_in_private_items`]: avoid linting in more cases where rustdoc generates no documentation

clippy_lints/src/missing_doc.rs

@@ -12,11 +12,13 @@
 use clippy_utils::source::SpanRangeExt;
 use rustc_ast::ast::{self, MetaItem, MetaItemKind};
 use rustc_hir as hir;
+use rustc_hir::def::DefKind;
 use rustc_hir::def_id::LocalDefId;
 use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_middle::ty::Visibility;
 use rustc_session::impl_lint_pass;
 use rustc_span::def_id::CRATE_DEF_ID;
+use rustc_span::symbol::kw;
 use rustc_span::{Span, sym};
 
 declare_clippy_lint! {
@@ -110,6 +112,21 @@ fn check_missing_docs_attrs(
             return;
         }
 
+        if let Some(parent_def_id) = cx.tcx.opt_parent(def_id.to_def_id())
+            && let DefKind::AnonConst
+            | DefKind::AssocConst
+            | DefKind::AssocFn
+            | DefKind::Closure
+            | DefKind::Const
+            | DefKind::Fn
+            | DefKind::InlineConst
+            | DefKind::Static { .. }
+            | DefKind::SyntheticCoroutineBody = cx.tcx.def_kind(parent_def_id)
+        {
+            // Nested item has no generated documentation, so it doesn't need to be documented.
+            return;
+        }
+
         let has_doc = attrs
             .iter()
             .any(|a| a.doc_str().is_some() || Self::has_include(a.meta()))
@@ -184,8 +201,12 @@ fn check_item(&mut self, cx: &LateContext<'tcx>, it: &'tcx hir::Item<'_>) {
                     }
                 }
             },
-            hir::ItemKind::Const(..)
-            | hir::ItemKind::Enum(..)
+            hir::ItemKind::Const(..) => {
+                if it.ident.name == kw::Underscore {
+                    note_prev_span_then_ret!(self.prev_span, it.span);
+                }
+            },
+            hir::ItemKind::Enum(..)
             | hir::ItemKind::Macro(..)
             | hir::ItemKind::Mod(..)
             | hir::ItemKind::Static(..)

tests/ui/missing_doc.rs

@@ -116,6 +116,14 @@ fn main() {}
 with_span!(span pub static FOO_PM: u32 = 0;);
 with_span!(span pub const FOO2_PM: u32 = 0;);
 
+// Don't lint unnamed constants
+const _: () = ();
+
+fn issue13298() {
+    // Rustdoc doesn't generate documentation for items within other items like fns or consts
+    const MSG: &str = "Hello, world!";
+}
+
 // issue #12197
 // Undocumented field originated inside of spanned proc-macro attribute
 /// Some dox for struct.

tests/ui/missing_doc.stderr

@@ -88,5 +88,14 @@ error: missing documentation for a function
 LL |         fn also_undocumented2() {}
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 13 previous errors
+error: missing documentation for a function
+  --> tests/ui/missing_doc.rs:122:1
+   |
+LL | / fn issue13298() {
+LL | |     // Rustdoc doesn't generate documentation for items within other items like fns or consts
+LL | |     const MSG: &str = "Hello, world!";
+LL | | }
+   | |_^
+
+error: aborting due to 14 previous errors