Simplify Config::track_state.

This is a callback used to track otherwise untracked state. It was added
in #116731 for Clippy. (It was originally named `hash_untracked_state`,
and examples in the rustc-dev-guide still use that name.) The
`StableHasher` argument is unused, and probably has never been used.
There is a FIXME comment pointing this out, which was added more than a
year ago.

This commit removes the `StableHasher` callback argument. This also
removes the need for `Options::untracked_state_hash`.

compiler/rustc_interface/src/interface.rs

@@ -6,7 +6,6 @@
 use rustc_codegen_ssa::traits::CodegenBackend;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::jobserver::{self, Proxy};
-use rustc_data_structures::stable_hasher::StableHasher;
 use rustc_errors::{DiagCtxtHandle, ErrorGuaranteed};
 use rustc_lint::LintStore;
 use rustc_middle::ty;
@@ -339,11 +338,7 @@ pub struct Config {
     /// This is a callback to track otherwise untracked state used by the caller.
     ///
     /// You can write to `sess.env_depinfo` and `sess.file_depinfo` to track env vars and files.
-    /// To track any other state you can write to the given hasher. If the hash changes between
-    /// runs the incremental cache will be cleared.
-    ///
-    /// The hashing functionality has no known user. FIXME should this be removed?
-    pub track_state: Option<Box<dyn FnOnce(&Session, &mut StableHasher) + Send>>,
+    pub track_state: Option<Box<dyn FnOnce(&Session) + Send>>,
 
     /// This is a callback from the driver that is called when we're registering lints;
     /// it is called during lint loading when we have the LintStore in a non-shared state.
@@ -468,9 +463,7 @@ pub fn run_compiler<R: Send>(config: Config, f: impl FnOnce(&Compiler) -> R + Se
             }
 
             if let Some(track_state) = config.track_state {
-                let mut hasher = StableHasher::new();
-                track_state(&sess, &mut hasher);
-                sess.opts.untracked_state_hash = hasher.finish()
+                track_state(&sess);
             }
 
             // Even though the session holds the lint store, we can't build the

compiler/rustc_session/src/config.rs

@@ -1419,7 +1419,6 @@ fn default() -> Options {
             target_triple: TargetTuple::from_tuple(host_tuple()),
             test: false,
             incremental: None,
-            untracked_state_hash: Default::default(),
             unstable_opts,
             prints: Vec::new(),
             cg: Default::default(),
@@ -2770,7 +2769,6 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
         target_triple,
         test,
         incremental,
-        untracked_state_hash: Default::default(),
         unstable_opts,
         prints,
         cg,

compiler/rustc_session/src/options.rs

@@ -332,10 +332,6 @@ pub struct Options {
         /// If `Some`, enable incremental compilation, using the given
         /// directory to store intermediate results.
         incremental: Option<PathBuf> [UNTRACKED],
-        /// Set based on the result of the `Config::track_state` callback
-        /// for custom drivers to invalidate the incremental cache.
-        #[rustc_lint_opt_deny_field_access("should only be used via `Config::track_state`")]
-        untracked_state_hash: Hash64 [TRACKED_NO_CRATE_HASH],
 
         unstable_opts: UnstableOptions [SUBSTRUCT] { TARGET_MODIFIER: UnstableOptions(UnstableOptionsTargetModifiers) },
         prints: Vec<PrintRequest> [UNTRACKED],

src/doc/rustc-dev-guide/examples/rustc-interface-example.rs

@@ -50,7 +50,7 @@ fn main() {
         make_codegen_backend: None,
         expanded_args: Vec::new(),
         ice_file: None,
-        hash_untracked_state: None,
+        track_state: None,
         using_internal_features: &rustc_driver::USING_INTERNAL_FEATURES,
     };
     rustc_interface::run_compiler(config, |compiler| {
@@ -72,4 +72,4 @@ fn main() {
             }
         });
     });
-}
+}

src/doc/rustc-dev-guide/examples/rustc-interface-getting-diagnostics.rs

@@ -78,7 +78,7 @@ fn main() {
         make_codegen_backend: None,
         expanded_args: Vec::new(),
         ice_file: None,
-        hash_untracked_state: None,
+        track_state: None,
         using_internal_features: &rustc_driver::USING_INTERNAL_FEATURES,
     };
     rustc_interface::run_compiler(config, |compiler| {
@@ -97,4 +97,4 @@ fn main() {
     buffer.lock().unwrap().iter().for_each(|diagnostic| {
         println!("{diagnostic:#?}");
     });
-}
+}

src/tools/clippy/src/driver.rs

@@ -121,7 +121,7 @@ struct RustcCallbacks {
 impl rustc_driver::Callbacks for RustcCallbacks {
     fn config(&mut self, config: &mut interface::Config) {
         let clippy_args_var = self.clippy_args_var.take();
-        config.track_state = Some(Box::new(move |sess, _hasher| {
+        config.track_state = Some(Box::new(move |sess| {
             track_clippy_args(sess, clippy_args_var.as_deref());
         }));
         config.extra_symbols = sym::EXTRA_SYMBOLS.into();
@@ -138,7 +138,7 @@ fn config(&mut self, config: &mut interface::Config) {
         let conf_path = clippy_config::lookup_conf_file();
         let previous = config.register_lints.take();
         let clippy_args_var = self.clippy_args_var.take();
-        config.track_state = Some(Box::new(move |sess, _hasher| {
+        config.track_state = Some(Box::new(move |sess| {
             track_clippy_args(sess, clippy_args_var.as_deref());
             track_files(sess);