Update lint-docs to default to Rust 2024

compiler/rustc_lint/src/builtin.rs

@@ -948,7 +948,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```rust,compile_fail
+    /// ```rust,compile_fail,edition2021
     /// #[no_mangle]
     /// const FOO: i32 = 5;
     /// ```

compiler/rustc_lint/src/impl_trait_overcaptures.rs

@@ -41,7 +41,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```rust,compile_fail
+    /// ```rust,compile_fail,edition2021
     /// # #![deny(impl_trait_overcaptures)]
     /// # use std::fmt::Display;
     /// let mut x = vec![];

compiler/rustc_lint_defs/src/builtin.rs

@@ -1424,7 +1424,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```rust,compile_fail
+    /// ```rust,compile_fail,edition2021
     /// macro_rules! foo {
     ///    () => {};
     ///    ($name) => { };
@@ -4128,7 +4128,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```rust,compile_fail
+    /// ```rust,compile_fail,edition2021
     /// #![deny(dependency_on_unit_never_type_fallback)]
     /// fn main() {
     ///     if true {

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

@@ -444,21 +444,15 @@ impl<'a> LintExtractor<'a> {
         fs::write(&tempfile, source)
             .map_err(|e| format!("failed to write {}: {}", tempfile.display(), e))?;
         let mut cmd = Command::new(self.rustc_path);
-        if options.contains(&"edition2024") {
-            cmd.arg("--edition=2024");
-            cmd.arg("-Zunstable-options");
-        } else if options.contains(&"edition2021") {
-            cmd.arg("--edition=2021");
-        } else if options.contains(&"edition2018") {
-            cmd.arg("--edition=2018");
-        } else if options.contains(&"edition2015") {
-            cmd.arg("--edition=2015");
-        } else if options.contains(&"edition") {
-            panic!("lint-docs: unknown edition");
-        } else {
+        let edition = options
+            .iter()
+            .filter_map(|opt| opt.strip_prefix("edition"))
+            .next()
             // defaults to latest edition
-            cmd.arg("--edition=2021");
-        }
+            .unwrap_or("2024");
+        cmd.arg(format!("--edition={edition}"));
+        // Just in case this is an unstable edition.
+        cmd.arg("-Zunstable-options");
         cmd.arg("--error-format=json");
         cmd.arg("--target").arg(self.rustc_target);
         if let Some(target_linker) = self.rustc_linker {