Add missing_examples_doc lint

Author: phy1729

CHANGELOG.md

@@ -6622,6 +6622,7 @@ Released 2018-09-13
 [`missing_docs_in_private_items`]: https://rust-lang.github.io/rust-clippy/master/index.html#missing_docs_in_private_items
 [`missing_enforced_import_renames`]: https://rust-lang.github.io/rust-clippy/master/index.html#missing_enforced_import_renames
 [`missing_errors_doc`]: https://rust-lang.github.io/rust-clippy/master/index.html#missing_errors_doc
+[`missing_examples_doc`]: https://rust-lang.github.io/rust-clippy/master/index.html#missing_examples_doc
 [`missing_fields_in_debug`]: https://rust-lang.github.io/rust-clippy/master/index.html#missing_fields_in_debug
 [`missing_inline_in_public_items`]: https://rust-lang.github.io/rust-clippy/master/index.html#missing_inline_in_public_items
 [`missing_panics_doc`]: https://rust-lang.github.io/rust-clippy/master/index.html#missing_panics_doc

clippy_lints/src/declared_lints.rs

@@ -122,6 +122,7 @@ pub static LINTS: &[&::declare_clippy_lint::LintInfo] = &[
     crate::doc::DOC_SUSPICIOUS_FOOTNOTES_INFO,
     crate::doc::EMPTY_DOCS_INFO,
     crate::doc::MISSING_ERRORS_DOC_INFO,
+    crate::doc::MISSING_EXAMPLES_DOC_INFO,
     crate::doc::MISSING_PANICS_DOC_INFO,
     crate::doc::MISSING_SAFETY_DOC_INFO,
     crate::doc::NEEDLESS_DOCTEST_MAIN_INFO,

clippy_lints/src/doc/missing_headers.rs

@@ -1,4 +1,7 @@
-use super::{DocHeaders, MISSING_ERRORS_DOC, MISSING_PANICS_DOC, MISSING_SAFETY_DOC, UNNECESSARY_SAFETY_DOC};
+use super::{
+    DocHeaders, MISSING_ERRORS_DOC, MISSING_EXAMPLES_DOC, MISSING_PANICS_DOC, MISSING_SAFETY_DOC,
+    UNNECESSARY_SAFETY_DOC,
+};
 use clippy_utils::diagnostics::{span_lint, span_lint_and_note};
 use clippy_utils::macros::{is_panic, root_macro_call_first_node};
 use clippy_utils::res::MaybeDef;
@@ -34,6 +37,9 @@ pub fn check(
     }
 
     let span = cx.tcx.def_span(owner_id);
+    if !headers.examples {
+        span_lint(cx, MISSING_EXAMPLES_DOC, span, "docs missing `# Examples` section");
+    }
     match (headers.safety, sig.header.safety()) {
         (false, Safety::Unsafe) => span_lint(
             cx,

clippy_lints/src/doc/mod.rs

@@ -211,6 +211,33 @@ declare_clippy_lint! {
     "`pub fn` may panic without `# Panics` in doc comment"
 }
 
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks the doc comments of publicly visible functions and warns if
+    /// there is no `# Examples` section.
+    ///
+    /// ### Why is this bad?
+    /// Examples help readers better understand how and why to use the function.
+    ///
+    /// ### Examples
+    /// The following function has an `# Examples` section in its doc comment:
+    ///
+    /// ```
+    /// /// # Examples
+    /// ///
+    /// /// ```
+    /// /// assert_eq!(bikeshed_color(), "blue");
+    /// /// ```
+    /// pub fn bikeshed_color() -> &str {
+    ///     "blue"
+    /// }
+    /// ```
+    #[clippy::version = "1.92.0"]
+    pub MISSING_EXAMPLES_DOC,
+    pedantic,
+    "`pub fn` without `# Examples` in doc comment"
+}
+
 declare_clippy_lint! {
     /// ### What it does
     /// Checks for `fn main() { .. }` in doctests
@@ -721,6 +748,7 @@ impl_lint_pass!(Documentation => [
     MISSING_SAFETY_DOC,
     MISSING_ERRORS_DOC,
     MISSING_PANICS_DOC,
+    MISSING_EXAMPLES_DOC,
     NEEDLESS_DOCTEST_MAIN,
     TEST_ATTR_IN_DOCTEST,
     UNNECESSARY_SAFETY_DOC,
@@ -832,10 +860,12 @@ impl Fragments<'_> {
 }
 
 #[derive(Copy, Clone, Default)]
+#[expect(clippy::struct_excessive_bools)]
 struct DocHeaders {
     safety: bool,
     errors: bool,
     panics: bool,
+    examples: bool,
     first_paragraph_len: usize,
 }
 
@@ -1282,6 +1312,7 @@ fn check_doc<'a, Events: Iterator<Item = (pulldown_cmark::Event<'a>, Range<usize
                 headers.safety |= in_heading && trimmed_text == "Implementation Safety";
                 headers.errors |= in_heading && trimmed_text == "Errors";
                 headers.panics |= in_heading && trimmed_text == "Panics";
+                headers.examples |= in_heading && trimmed_text == "Examples";
 
                 if let Some(tags) = code {
                     if tags.rust && !tags.compile_fail && !tags.ignore {

tests/dogfood.rs

@@ -82,7 +82,16 @@ fn run_clippy_for_package(project: &str) -> bool {
 
     command.arg("--");
     command.arg("-Cdebuginfo=0"); // disable debuginfo to generate less data in the target dir
-    command.args(["-D", "clippy::all", "-D", "clippy::pedantic", "-D", "clippy::dbg_macro"]);
+    command.args([
+        "-D",
+        "clippy::all",
+        "-D",
+        "clippy::pedantic",
+        "-D",
+        "clippy::dbg_macro",
+        "-A",
+        "clippy::missing_examples_doc",
+    ]);
     if !cfg!(feature = "internal") {
         // running a clippy built without internal lints on the clippy source
         // that contains e.g. `allow(clippy::symbol_as_str)`

tests/ui/doc_examples.rs

@@ -0,0 +1,32 @@
+#![warn(clippy::missing_examples_doc)]
+
+pub fn pub_fn_missing_docs() {
+    //~^ missing_examples_doc
+    unimplemented!();
+}
+
+/// Docs without examples
+pub fn pub_fn_missing_examples() {
+    //~^ missing_examples_doc
+    unimplemented!();
+}
+
+/// Docs with examples
+///
+/// # Examples
+///
+/// ```
+/// pub_fn_missing_examples()
+/// ```
+pub fn pub_fn_with_examples() {
+    unimplemented!();
+}
+
+fn priv_fn_missing_docs() {
+    unimplemented!();
+}
+
+#[doc(hidden)]
+pub fn hidden_fn_missing_docs() {
+    unimplemented!();
+}

tests/ui/doc_examples.stderr

@@ -0,0 +1,17 @@
+error: docs missing `# Examples` section
+  --> tests/ui/doc_examples.rs:3:1
+   |
+LL | pub fn pub_fn_missing_docs() {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `-D clippy::missing-examples-doc` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::missing_examples_doc)]`
+
+error: docs missing `# Examples` section
+  --> tests/ui/doc_examples.rs:9:1
+   |
+LL | pub fn pub_fn_missing_examples() {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+