Auto merge of rust-lang#11154 - Alexendoo:track-clippy-conf-dir, r=flip1995

Trigger a rebuild when `CLIPPY_CONF_DIR` changes

changelog: none

This is a fix for rust-lang/rust-clippy#9928 (comment), any time `CLIPPY_CONF_DIR` changes cargo will now rebuild the crate clippy is being run on, giving it a chance to lint with the (potentially) different config file

r? `@flip1995`

Author: bors

src/driver.rs

@@ -130,6 +130,13 @@ impl rustc_driver::Callbacks for ClippyCallbacks {
         config.parse_sess_created = Some(Box::new(move |parse_sess| {
             track_clippy_args(parse_sess, &clippy_args_var);
             track_files(parse_sess);
+
+            // Trigger a rebuild if CLIPPY_CONF_DIR changes. The value must be a valid string so
+            // changes between dirs that are invalid UTF-8 will not trigger rebuilds
+            parse_sess.env_depinfo.get_mut().insert((
+                Symbol::intern("CLIPPY_CONF_DIR"),
+                env::var("CLIPPY_CONF_DIR").ok().map(|dir| Symbol::intern(&dir)),
+            ));
         }));
         config.register_lints = Some(Box::new(move |sess, lint_store| {
             // technically we're ~guaranteed that this is none but might as well call anything that