Fix the ffi_unwind_calls lint documentation

compiler/rustc_lint_defs/src/builtin.rs

@@ -3967,14 +3967,9 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```rust,ignore (need FFI)
-    /// #![feature(ffi_unwind_calls)]
+    /// ```rust
     /// #![feature(c_unwind)]
-    ///
-    /// # mod impl {
-    /// #     #[no_mangle]
-    /// #     pub fn "C-unwind" fn foo() {}
-    /// # }
+    /// #![warn(ffi_unwind_calls)]
     ///
     /// extern "C-unwind" {
     ///     fn foo();

src/tools/lint-docs/src/lib.rs

@@ -45,6 +45,36 @@ impl Lint {
     fn check_style(&self) -> Result<(), Box<dyn Error>> {
         for &expected in &["### Example", "### Explanation", "{{produces}}"] {
             if expected == "{{produces}}" && self.is_ignored() {
+                if self.doc_contains("{{produces}}") {
+                    return Err(format!(
+                        "the lint example has `ignore`, but also contains the {{{{produces}}}} marker\n\
+                        \n\
+                        The documentation generator cannot generate the example output when the \
+                        example is ignored.\n\
+                        Manually include the sample output below the example. For example:\n\
+                        \n\
+                        /// ```rust,ignore (needs command line option)\n\
+                        /// #[cfg(widnows)]\n\
+                        /// fn foo() {{}}\n\
+                        /// ```\n\
+                        ///\n\
+                        /// This will produce:\n\
+                        /// \n\
+                        /// ```text\n\
+                        /// warning: unknown condition name used\n\
+                        ///  --> lint_example.rs:1:7\n\
+                        ///   |\n\
+                        /// 1 | #[cfg(widnows)]\n\
+                        ///   |       ^^^^^^^\n\
+                        ///   |\n\
+                        ///   = note: `#[warn(unexpected_cfgs)]` on by default\n\
+                        /// ```\n\
+                        \n\
+                        Replacing the output with the text of the example you \
+                        compiled manually yourself.\n\
+                        "
+                    ).into());
+                }
                 continue;
             }
             if !self.doc_contains(expected) {
@@ -317,10 +347,10 @@ impl<'a> LintExtractor<'a> {
                             ..,
                             &format!(
                                 "This will produce:\n\
-                            \n\
-                            ```text\n\
-                            {}\
-                            ```",
+                                \n\
+                                ```text\n\
+                                {}\
+                                ```",
                                 output
                             ),
                         );
@@ -392,37 +422,36 @@ impl<'a> LintExtractor<'a> {
             .filter(|line| line.starts_with('{'))
             .map(serde_json::from_str)
             .collect::<Result<Vec<serde_json::Value>, _>>()?;
-        match msgs
+        // First try to find the messages with the `code` field set to our lint.
+        let matches: Vec<_> = msgs
             .iter()
-            .find(|msg| matches!(&msg["code"]["code"], serde_json::Value::String(s) if s==name))
-        {
-            Some(msg) => {
-                let rendered = msg["rendered"].as_str().expect("rendered field should exist");
-                Ok(rendered.to_string())
-            }
-            None => {
-                match msgs.iter().find(
-                    |msg| matches!(&msg["rendered"], serde_json::Value::String(s) if s.contains(name)),
-                ) {
-                    Some(msg) => {
-                        let rendered = msg["rendered"].as_str().expect("rendered field should exist");
-                        Ok(rendered.to_string())
-                    }
-                    None => {
-                        let rendered: Vec<&str> =
-                            msgs.iter().filter_map(|msg| msg["rendered"].as_str()).collect();
-                        let non_json: Vec<&str> =
-                            stderr.lines().filter(|line| !line.starts_with('{')).collect();
-                        Err(format!(
-                            "did not find lint `{}` in output of example, got:\n{}\n{}",
-                            name,
-                            non_json.join("\n"),
-                            rendered.join("\n")
-                        )
-                        .into())
-                    }
-                }
+            .filter(|msg| matches!(&msg["code"]["code"], serde_json::Value::String(s) if s==name))
+            .map(|msg| msg["rendered"].as_str().expect("rendered field should exist").to_string())
+            .collect();
+        if matches.is_empty() {
+            // Some lints override their code to something else (E0566).
+            // Try to find something that looks like it could be our lint.
+            let matches: Vec<_> = msgs.iter().filter(|msg|
+                matches!(&msg["rendered"], serde_json::Value::String(s) if s.contains(name)))
+                .map(|msg| msg["rendered"].as_str().expect("rendered field should exist").to_string())
+                .collect();
+            if matches.is_empty() {
+                let rendered: Vec<&str> =
+                    msgs.iter().filter_map(|msg| msg["rendered"].as_str()).collect();
+                let non_json: Vec<&str> =
+                    stderr.lines().filter(|line| !line.starts_with('{')).collect();
+                Err(format!(
+                    "did not find lint `{}` in output of example, got:\n{}\n{}",
+                    name,
+                    non_json.join("\n"),
+                    rendered.join("\n")
+                )
+                .into())
+            } else {
+                Ok(matches.join("\n"))
             }
+        } else {
+            Ok(matches.join("\n"))
         }
     }