1 files changed, 115 insertions, 0 deletions
diff --git a/tvix/glue/src/refscan.rs b/tvix/glue/src/refscan.rs
new file mode 100644
index 0000000000..0e0bb6c778
--- /dev/null
+++ b/tvix/glue/src/refscan.rs
@@ -0,0 +1,115 @@
+//! Simple scanner for non-overlapping, known references of Nix store paths in a
+//! given string.
+//!
+//! This is used for determining build references (see
+//! //tvix/eval/docs/build-references.md for more details).
+//!
+//! The scanner itself is using the Wu-Manber string-matching algorithm, using
+//! our fork of the `wu-mamber` crate.
+
+use std::collections::BTreeSet;
+use wu_manber::TwoByteWM;
+
+pub const STORE_PATH_LEN: usize = "/nix/store/00000000000000000000000000000000".len();
+
+/// Represents a "primed" reference scanner with an automaton that knows the set
+/// of store paths to scan for.
+pub struct ReferenceScanner<P: Ord + AsRef<[u8]>> {
+    candidates: Vec<P>,
+    searcher: Option<TwoByteWM>,
+    matches: Vec<usize>,
+}
+
+impl<P: Clone + Ord + AsRef<[u8]>> ReferenceScanner<P> {
+    /// Construct a new `ReferenceScanner` that knows how to scan for the given
+    /// candidate store paths.
+    pub fn new(candidates: Vec<P>) -> Self {
+        let searcher = if candidates.is_empty() {
+            None
+        } else {
+            Some(TwoByteWM::new(&candidates))
+        };
+
+        ReferenceScanner {
+            searcher,
+            candidates,
+            matches: Default::default(),
+        }
+    }
+
+    /// Scan the given str for all non-overlapping matches and collect them
+    /// in the scanner.
+    pub fn scan<S: AsRef<[u8]>>(&mut self, haystack: S) {
+        if haystack.as_ref().len() < STORE_PATH_LEN {
+            return;
+        }
+
+        if let Some(searcher) = &self.searcher {
+            for m in searcher.find(haystack) {
+                self.matches.push(m.pat_idx);
+            }
+        }
+    }
+
+    /// Finalise the reference scanner and return the resulting matches.
+    pub fn finalise(self) -> BTreeSet<P> {
+        self.matches
+            .into_iter()
+            .map(|idx| self.candidates[idx].clone())
+            .collect()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // The actual derivation of `nixpkgs.hello`.
+    const HELLO_DRV: &str = r#"Derive([("out","/nix/store/33l4p0pn0mybmqzaxfkpppyh7vx1c74p-hello-2.12.1","","")],[("/nix/store/6z1jfnqqgyqr221zgbpm30v91yfj3r45-bash-5.1-p16.drv",["out"]),("/nix/store/ap9g09fxbicj836zm88d56dn3ff4clxl-stdenv-linux.drv",["out"]),("/nix/store/pf80kikyxr63wrw56k00i1kw6ba76qik-hello-2.12.1.tar.gz.drv",["out"])],["/nix/store/9krlzvny65gdc8s7kpb6lkx8cd02c25b-default-builder.sh"],"x86_64-linux","/nix/store/4xw8n979xpivdc46a9ndcvyhwgif00hz-bash-5.1-p16/bin/bash",["-e","/nix/store/9krlzvny65gdc8s7kpb6lkx8cd02c25b-default-builder.sh"],[("buildInputs",""),("builder","/nix/store/4xw8n979xpivdc46a9ndcvyhwgif00hz-bash-5.1-p16/bin/bash"),("cmakeFlags",""),("configureFlags",""),("depsBuildBuild",""),("depsBuildBuildPropagated",""),("depsBuildTarget",""),("depsBuildTargetPropagated",""),("depsHostHost",""),("depsHostHostPropagated",""),("depsTargetTarget",""),("depsTargetTargetPropagated",""),("doCheck","1"),("doInstallCheck",""),("mesonFlags",""),("name","hello-2.12.1"),("nativeBuildInputs",""),("out","/nix/store/33l4p0pn0mybmqzaxfkpppyh7vx1c74p-hello-2.12.1"),("outputs","out"),("patches",""),("pname","hello"),("propagatedBuildInputs",""),("propagatedNativeBuildInputs",""),("src","/nix/store/pa10z4ngm0g83kx9mssrqzz30s84vq7k-hello-2.12.1.tar.gz"),("stdenv","/nix/store/cp65c8nk29qq5cl1wyy5qyw103cwmax7-stdenv-linux"),("strictDeps",""),("system","x86_64-linux"),("version","2.12.1")])"#;
+
+    #[test]
+    fn test_no_patterns() {
+        let mut scanner: ReferenceScanner<String> = ReferenceScanner::new(vec![]);
+
+        scanner.scan(HELLO_DRV);
+
+        let result = scanner.finalise();
+
+        assert_eq!(result.len(), 0);
+    }
+
+    #[test]
+    fn test_single_match() {
+        let mut scanner = ReferenceScanner::new(vec![
+            "/nix/store/4xw8n979xpivdc46a9ndcvyhwgif00hz-bash-5.1-p16".to_string(),
+        ]);
+        scanner.scan(HELLO_DRV);
+
+        let result = scanner.finalise();
+
+        assert_eq!(result.len(), 1);
+        assert!(result.contains("/nix/store/4xw8n979xpivdc46a9ndcvyhwgif00hz-bash-5.1-p16"));
+    }
+
+    #[test]
+    fn test_multiple_matches() {
+        let candidates = vec![
+            // these exist in the drv:
+            "/nix/store/33l4p0pn0mybmqzaxfkpppyh7vx1c74p-hello-2.12.1".to_string(),
+            "/nix/store/pf80kikyxr63wrw56k00i1kw6ba76qik-hello-2.12.1.tar.gz.drv".to_string(),
+            "/nix/store/cp65c8nk29qq5cl1wyy5qyw103cwmax7-stdenv-linux".to_string(),
+            // this doesn't:
+            "/nix/store/fn7zvafq26f0c8b17brs7s95s10ibfzs-emacs-28.2.drv".to_string(),
+        ];
+
+        let mut scanner = ReferenceScanner::new(candidates.clone());
+        scanner.scan(HELLO_DRV);
+
+        let result = scanner.finalise();
+        assert_eq!(result.len(), 3);
+
+        for c in candidates[..3].iter() {
+            assert!(result.contains(c));
+        }
+    }
+}