add --fix support to cargo-clippy

src/main.rs

@@ -58,13 +58,38 @@ where
 {
     let mut args = vec!["check".to_owned()];
 
+    let mut fix = false;
+    let mut unstable_options = false;
+
     for arg in old_args.by_ref() {
-        if arg == "--" {
-            break;
+        match arg.as_str() {
+            "--fix" => {
+                fix = true;
+                continue;
+            },
+            "--" => break,
+            // Cover -Zunstable-options and -Z unstable-options
+            s if s.ends_with("unstable-options") => unstable_options = true,
+            _ => {},
         }
+
         args.push(arg);
     }
 
+    if fix {
+        if unstable_options {
+            args[0] = "fix".to_owned();
+        } else {
+            panic!("Usage of `--fix` requires `-Z unstable-options`");
+        }
+    }
+
+    let path_env = if unstable_options {
+        "RUSTC_WORKSPACE_WRAPPER"
+    } else {
+        "RUSTC_WRAPPER"
+    };
+
     let clippy_args: String = old_args.map(|arg| format!("{}__CLIPPY_HACKERY__", arg)).collect();
 
     let mut path = std::env::current_exe()
@@ -96,7 +121,7 @@ where
 
     let exit_status = std::process::Command::new("cargo")
         .args(&args)
-        .env("RUSTC_WRAPPER", path)
+        .env(path_env, path)
         .env("CLIPPY_ARGS", clippy_args)
         .envs(target_dir)
         .spawn()