Rollup merge of rust-lang#84029 - drahnr:master, r=petrochenkov

add `track_path::path` fn for usage in `proc_macro`s

Adds a way to declare a dependency on external files without including them, to either re-trigger the build of a file as well as covering the use case of including dependencies within the `rustc` invocation, such that tools like `sccache`/`cachepot` are able to handle references to external files which are not included.

Ref rust-lang#73921

Author: JohnTitor

proc_macro/src/bridge/mod.rs

@@ -55,6 +55,7 @@ macro_rules! with_api {
             FreeFunctions {
                 fn drop($self: $S::FreeFunctions);
                 fn track_env_var(var: &str, value: Option<&str>);
+                fn track_path(path: &str);
             },
             TokenStream {
                 fn drop($self: $S::TokenStream);

proc_macro/src/lib.rs

@@ -1234,3 +1234,17 @@ pub mod tracked_env {
         value
     }
 }
+
+/// Tracked access to additional files.
+#[unstable(feature = "track_path", issue = "73921")]
+pub mod tracked_path {
+
+    /// Track a file explicitly.
+    ///
+    /// Commonly used for tracking asset preprocessing.
+    #[unstable(feature = "track_path", issue = "73921")]
+    pub fn path<P: AsRef<str>>(path: P) {
+        let path: &str = path.as_ref();
+        crate::bridge::client::FreeFunctions::track_path(path);
+    }
+}