Add "better" edition handling on lint-docs tool

Author: spastorino

compiler/rustc_lint_defs/src/builtin.rs

@@ -3803,7 +3803,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```rust,compile_fail
+    /// ```rust,edition2018,compile_fail
     /// #![deny(rust_2021_incompatible_or_patterns)]
     ///
     /// macro_rules! match_any {
@@ -3843,7 +3843,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```rust,compile_fail
+    /// ```rust,edition2018,compile_fail
     /// #![deny(rust_2021_prelude_collisions)]
     ///
     /// trait Foo {

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

@@ -441,10 +441,19 @@ 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(&"edition2015") {
+        if options.contains(&"edition2024") {
+            cmd.arg("--edition=2024");
+        } 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 {
-            cmd.arg("--edition=2018");
+            // defaults to latest edition
+            cmd.arg("--edition=2021");
         }
         cmd.arg("--error-format=json");
         cmd.arg("--target").arg(self.rustc_target);