fix: let cargo decide freshness for scripts with path dependencies

src/main.rs

@@ -313,6 +313,14 @@ struct InputAction {
     */
     force_compile: bool,
 
+    /**
+    Does the manifest declare path dependencies?
+
+    Their sources are invisible to the mtime freshness check below, so cargo
+    must decide whether a rebuild is needed (issue #122).
+    */
+    has_path_dependencies: bool,
+
     /// Execute the compiled binary?
     execute: bool,
 
@@ -409,7 +417,13 @@ impl InputAction {
             }
         };
 
-        if matches!(self.build_kind, BuildKind::Normal) && !self.force_compile {
+        // A script with path dependencies must not be served from the binary
+        // cache without consulting cargo: this mtime comparison cannot see
+        // changes in the dependency sources (issue #122).
+        if matches!(self.build_kind, BuildKind::Normal)
+            && !self.force_compile
+            && !self.has_path_dependencies
+        {
             match fs::File::open(&built_binary_path) {
                 Ok(built_binary_file) => {
                     // When possible, use creation time instead of modified time as cargo may copy
@@ -538,6 +552,8 @@ fn decide_action_for(
         toolchain_version.clone(),
     )?;
 
+    let has_path_dependencies = manifest::has_path_dependencies(&mani_str)?;
+
     // Forcibly override some flags based on build kind.
     let debug = match args.build_kind {
         BuildKind::Normal => args.debug,
@@ -548,6 +564,7 @@ fn decide_action_for(
     Ok(InputAction {
         cargo_output: args.cargo_output,
         force_compile: args.force,
+        has_path_dependencies,
         execute: !args.gen_pkg_only,
         pkg_path,
         script_path,

src/manifest.rs

@@ -1294,6 +1294,54 @@ fn merge_manifest(
 /**
 Given a Cargo manifest, attempts to rewrite relative file paths to absolute ones, allowing the manifest to be relocated.
 */
+/// Dependency keys whose `path` values point at a local directory.
+const DEPENDENCY_PATH_KEYS: &[&[&str]] = &[
+    &["build-dependencies", "*", "path"],
+    &["dependencies", "*", "path"],
+    &["dev-dependencies", "*", "path"],
+    &["target", "*", "dependencies", "*", "path"],
+];
+
+/**
+Does the manifest declare any path dependencies?
+
+The sources of a path dependency never invalidate a cached binary: the cache
+freshness check compares only the script file and generated manifest mtimes.
+Builds with path dependencies must therefore let cargo decide whether a
+rebuild is needed (issue #122).
+*/
+pub fn has_path_dependencies(mani: &str) -> MainResult<bool> {
+    let mani: toml::value::Table = toml::from_str(mani).map_err(|e| {
+        MainError::Tag(
+            "could not parse embedded manifest".into(),
+            Box::new(MainError::Other(Box::new(e))),
+        )
+    })?;
+
+    let mut mani = toml::Value::Table(mani);
+    let mut has_paths = false;
+    for path in DEPENDENCY_PATH_KEYS {
+        iterate_toml_mut_path(&mut mani, path, &mut |v| {
+            if v.is_str() {
+                has_paths = true;
+            }
+            Ok(())
+        })?;
+    }
+    Ok(has_paths)
+}
+
+#[test]
+fn test_has_path_dependencies() {
+    assert!(!has_path_dependencies("[package]\nname = \"x\"\n").unwrap());
+    assert!(!has_path_dependencies("[dependencies]\nserde = \"1\"\n").unwrap());
+    assert!(has_path_dependencies("[dependencies]\nfoo = { path = \"../foo\" }\n").unwrap());
+    assert!(has_path_dependencies(
+        "[target.'cfg(unix)'.dependencies]\nfoo = { path = \"../foo\" }\n"
+    )
+    .unwrap());
+}
+
 fn fix_manifest_paths(mani: toml::value::Table, base: &Path) -> MainResult<toml::value::Table> {
     // Values that need to be rewritten:
     let paths: &[&[&str]] = &[

tests/scripts/path-dependency-cache.expected

@@ -0,0 +1,2 @@
+value = v1
+value = v2

tests/scripts/path-dependency-cache.script

@@ -0,0 +1,37 @@
+#!/bin/sh
+set -e -u
+
+# https://unix.stackexchange.com/questions/30091/fix-or-alternative-for-mktemp-in-os-x
+mytmpdir=$(mktemp -d 2>/dev/null || mktemp -d -t 'mytmpdir')
+
+cd "$mytmpdir"
+
+mkdir -p dep/src
+cat > dep/Cargo.toml <<'EOF'
+[package]
+name = "rspathdep"
+version = "0.1.0"
+edition = "2021"
+EOF
+
+printf 'pub const VALUE: &str = "v1";\n' > dep/src/lib.rs
+
+cat > script.rs <<'EOF'
+#!/usr/bin/env rust-script
+//! ```cargo
+//! [dependencies]
+//! rspathdep = { path = "dep" }
+//! ```
+fn main() {
+    println!("value = {}", rspathdep::VALUE);
+}
+EOF
+
+rust-script script.rs
+
+# Modify the path dependency: the next run has to notice and rebuild it.
+# The sleep guards against coarse filesystem mtime granularity.
+sleep 1
+printf 'pub const VALUE: &str = "v2";\n' > dep/src/lib.rs
+
+rust-script script.rs