Traverse upwards for single context projects

CHANGELOG.md

@@ -30,6 +30,7 @@
 - Improve option optimization for constants. https://github.com/rescript-lang/rescript/pull/7913
 - Option optimization: do not create redundant local vars. https://github.com/rescript-lang/rescript/pull/7915
 - Js output: remove superfluous newline after every `if`. https://github.com/rescript-lang/rescript/pull/7920
+- Rewatch: Traverse upwards for package resolution in single context projects. https://github.com/rescript-lang/rescript/pull/7896
 
 #### :house: Internal
 

rewatch/src/config.rs

@@ -352,7 +352,7 @@ pub fn flatten_ppx_flags(
                             let path = helpers::try_package_path(
                                 package_config,
                                 project_context,
-                                format!("{}{}{}", &package_config.name, MAIN_SEPARATOR, y).as_str(),
+                                &format!("{}{}{}", &package_config.name, MAIN_SEPARATOR, y),
                             )
                             .map(|p| p.to_string_lossy().to_string())?;
 
@@ -374,7 +374,7 @@ pub fn flatten_ppx_flags(
                         Some('.') => helpers::try_package_path(
                             package_config,
                             project_context,
-                            format!("{}{}{}", package_config.name, MAIN_SEPARATOR, &ys[0]).as_str(),
+                            &format!("{}{}{}", package_config.name, MAIN_SEPARATOR, &ys[0]),
                         )
                         .map(|p| p.to_string_lossy().to_string())?,
                         _ => helpers::try_package_path(package_config, project_context, &ys[0])

rewatch/src/helpers.rs

@@ -9,6 +9,7 @@ use std::fs::File;
 use std::io::Read;
 use std::io::{self, BufRead};
 use std::path::{Component, Path, PathBuf};
+use std::sync::{LazyLock, RwLock};
 use std::time::{SystemTime, UNIX_EPOCH};
 
 pub type StdErr = String;
@@ -31,6 +32,40 @@ pub mod emojis {
     pub static LINE_CLEAR: &str = "\x1b[2K\r";
 }
 
+// Cache existence checks for candidate node_modules paths during upward traversal.
+// Keyed by the absolute candidate path; value is the existence boolean.
+static NODE_MODULES_EXIST_CACHE: LazyLock<RwLock<ahash::AHashMap<PathBuf, bool>>> =
+    LazyLock::new(|| RwLock::new(ahash::AHashMap::new()));
+
+fn cached_path_exists(path: &Path) -> bool {
+    match NODE_MODULES_EXIST_CACHE.read() {
+        Ok(cache) => {
+            if let Some(exists) = cache.get(path) {
+                return *exists;
+            }
+        }
+        Err(poisoned) => {
+            log::warn!("NODE_MODULES_EXIST_CACHE read lock poisoned; recovering");
+            let cache = poisoned.into_inner();
+            if let Some(exists) = cache.get(path) {
+                return *exists;
+            }
+        }
+    }
+    let exists = path.exists();
+    match NODE_MODULES_EXIST_CACHE.write() {
+        Ok(mut cache) => {
+            cache.insert(path.to_path_buf(), exists);
+        }
+        Err(poisoned) => {
+            log::warn!("NODE_MODULES_EXIST_CACHE write lock poisoned; recovering");
+            let mut cache = poisoned.into_inner();
+            cache.insert(path.to_path_buf(), exists);
+        }
+    }
+    exists
+}
+
 /// This trait is used to strip the verbatim prefix from a Windows path.
 /// On non-Windows systems, it simply returns the original path.
 /// This is needed until the rescript compiler can handle such paths.
@@ -154,12 +189,63 @@ pub fn try_package_path(
     } else if path_from_root.exists() {
         Ok(path_from_root)
     } else {
+        // As a last resort, when we're in a Single project context, traverse upwards
+        // starting from the parent of the package root (package_config.path.parent().parent())
+        // and probe each ancestor's node_modules for the dependency. This covers hoisted
+        // workspace setups when building a package standalone.
+        if project_context.monorepo_context.is_none() {
+            match package_config.path.parent().and_then(|p| p.parent()) {
+                Some(start_dir) => {
+                    return find_dep_in_upward_node_modules(start_dir, package_name);
+                }
+                None => {
+                    log::debug!(
+                        "try_package_path: cannot compute start directory for upward traversal from '{}'",
+                        package_config.path.to_string_lossy()
+                    );
+                }
+            }
+        }
+
         Err(anyhow!(
             "The package \"{package_name}\" is not found (are node_modules up-to-date?)..."
         ))
     }
 }
 
+fn find_dep_in_upward_node_modules(start_dir: &Path, package_name: &str) -> anyhow::Result<PathBuf> {
+    log::debug!(
+        "try_package_path: falling back to upward traversal for '{}' starting at '{}'",
+        package_name,
+        start_dir.to_string_lossy()
+    );
+
+    let mut current = Some(start_dir);
+    while let Some(dir) = current {
+        let candidate = package_path(dir, package_name);
+        log::debug!("try_package_path: checking '{}'", candidate.to_string_lossy());
+        if cached_path_exists(&candidate) {
+            log::debug!(
+                "try_package_path: found '{}' at '{}' via upward traversal",
+                package_name,
+                candidate.to_string_lossy()
+            );
+            return Ok(candidate);
+        }
+        current = dir.parent();
+    }
+    log::debug!(
+        "try_package_path: no '{}' found during upward traversal from '{}'",
+        package_name,
+        start_dir.to_string_lossy()
+    );
+    Err(anyhow!(
+        "try_package_path: upward traversal did not find '{}' starting at '{}'",
+        package_name,
+        start_dir.to_string_lossy()
+    ))
+}
+
 pub fn get_abs_path(path: &Path) -> PathBuf {
     let abs_path_buf = PathBuf::from(path);
 

rewatch/testrepo/package.json

@@ -16,7 +16,8 @@
       "packages/file-casing-no-namespace",
       "packages/pure-dev",
       "packages/with-ppx",
-      "packages/nohoist"
+      "packages/nohoist",
+      "packages/standalone"
     ],
     "nohoist": [
       "rescript-bun"
@@ -26,11 +27,11 @@
     "rescript": "12.0.0-beta.1"
   },
   "scripts": {
-    "build": "../target/release/rewatch build .",
+    "build": "../target/release/rescript build .",
     "build:rescript": "rescript legacy build",
-    "watch": "../target/release/rewatch watch .",
+    "watch": "../target/release/rescript watch .",
     "watch:rescript": "rescript legacy watch",
-    "clean": "../target/release/rewatch clean .",
+    "clean": "../target/release/rescript clean .",
     "clean:rescript": "rescript clean"
   }
 }

rewatch/testrepo/packages/standalone/package.json

@@ -0,0 +1,7 @@
+{
+    "name": "@testrepo/standalone",
+    "version": "1.0.0",
+    "dependencies": {
+        "@testrepo/dep01": "*"
+    }
+}

rewatch/testrepo/packages/standalone/rescript.json

@@ -0,0 +1,13 @@
+{
+    "name": "standalone",
+    "sources": {
+        "dir": "src",
+        "subdirs": true
+    },
+    "package-specs": {
+        "module": "es6",
+        "in-source": true
+    },
+    "suffix": ".mjs",
+    "dependencies": ["@testrepo/dep01"]
+}

rewatch/testrepo/packages/standalone/src/Standalone.mjs

@@ -0,0 +1,13 @@
+// Generated by ReScript, PLEASE EDIT WITH CARE
+
+import * as Dep01 from "@testrepo/dep01/src/Dep01.mjs";
+
+function standalone() {
+  Dep01.log();
+  console.log("standalone");
+}
+
+export {
+  standalone,
+}
+/* Dep01 Not a pure module */

rewatch/testrepo/packages/standalone/src/Standalone.res

@@ -0,0 +1,4 @@
+let standalone = () => {
+    Dep01.log()
+    Js.log("standalone")
+}

rewatch/testrepo/yarn.lock

@@ -164,6 +164,14 @@ __metadata:
   languageName: unknown
   linkType: soft
 
+"@testrepo/standalone@workspace:packages/standalone":
+  version: 0.0.0-use.local
+  resolution: "@testrepo/standalone@workspace:packages/standalone"
+  dependencies:
+    "@testrepo/dep01": "npm:*"
+  languageName: unknown
+  linkType: soft
+
 "@testrepo/with-dev-deps@workspace:packages/with-dev-deps":
   version: 0.0.0-use.local
   resolution: "@testrepo/with-dev-deps@workspace:packages/with-dev-deps"

rewatch/tests/compile.sh

@@ -34,6 +34,21 @@ else
   exit 1
 fi
 
+# Build from standalone package folder using `rescript build`
+bold "Test: Standalone package can build via rescript from package folder"
+pushd ./packages/standalone > /dev/null
+error_output=$("../../$REWATCH_EXECUTABLE" build 2>&1)
+if [ $? -eq 0 ];
+then
+  success "Standalone package built"
+else
+  error "Error building standalone package"
+  printf "%s\n" "$error_output" >&2
+  popd > /dev/null
+  exit 1
+fi
+popd > /dev/null
+
 node ./packages/main/src/Main.mjs > ./packages/main/src/output.txt
 
 mv ./packages/main/src/Main.res ./packages/main/src/Main2.res