TBD: Split this? Fixes for no-dangling-path

differential/src/bin/pruned_trace.rs

@@ -0,0 +1,36 @@
+//! Prints the dangling-path-free differential trace for a fuzzer input, from
+//! the real crate.
+//!
+//!     pruned_trace <input-file>      # or read the bytes from stdin
+//!
+//! `lean/.lake/build/bin/pruned-oracle` prints the same trace from
+//! `PrunedModel`; `lean/pruned_differential.py` runs both and diffs them.
+//!
+//! `--check` needs no oracle: it asserts the zipper invariants after every
+//! operation and, at the end of the run, that the write target contains no
+//! dangling path -- which is the whole claim this harness's operation subset
+//! makes.  See `differential::pruned`.
+
+use differential::pruned::run;
+use differential::serve;
+
+fn main() {
+    let args: Vec<String> = std::env::args().skip(1).collect();
+    let check = args.iter().any(|a| a == "--check");
+    // Resident mode: one process, many inputs over stdin.  See `serve`.
+    if args.iter().any(|a| a == "--server") {
+        serve(check, run);
+        return;
+    }
+    let file = args.iter().find(|a| !a.starts_with("--")).cloned();
+    let bytes: Vec<u8> = match file {
+        Some(p) => std::fs::read(p).expect("cannot read input"),
+        None => {
+            use std::io::Read;
+            let mut v = Vec::new();
+            std::io::stdin().read_to_end(&mut v).unwrap();
+            v
+        }
+    };
+    print!("{}", run(&bytes, check));
+}

differential/src/lib.rs

@@ -8,9 +8,14 @@
 //! * [`server`] is the resident-process protocol the driver speaks.
 //! * [`repro`] turns an input back into standalone `pathmap` calls.
 //! * [`act`] is the `ArenaCompactTree` read source behind `act_trace`.
+//! * [`pruned`] is a second, smaller harness: the subset of the API that
+//!   cannot leave a dangling path, checked against `lean/PrunedModel` and
+//!   driven by `lean/pruned_differential.py`.  See its module docs for why it
+//!   is not `harness` with a flag.
 
 pub mod act;
 pub mod harness;
+pub mod pruned;
 pub mod repro;
 pub mod server;