[flow] Fix Windows path separator mismatches in File_key and flowconfig expansion (#9402)

Summary:

Normalize directory separators to '/' in File_key suffixes at creation time (strip_project_root, lib_file_of_absolute) so that file keys are always '/'-based regardless of platform. This fixes the Graph.NodeNotFound crash when loading Linux-generated saved state on Windows, where '\'-based local file keys failed to match '/'-based saved state keys.

Also normalize separators in expand_project_root_token_as_relative so that flowconfig directives like module.system.node.root_relative_dirname with <PROJECT_ROOT> prefixes produce '/'-based paths, matching the now-normalized File_key suffixes. Without this, Files.is_prefix would append '\' on Windows while suffixes use '/', breaking root-relative module resolution.

Fix Files.is_prefix to append '/' instead of Filename.dir_sep when the prefix lacks a trailing separator. Previously, is_prefix would append '\' on Windows, which failed to match the now '/'-based File_key suffixes — breaking scoped root-relative module resolution (e.g., the `config_module_system_node_root_relative_dirnames` test).


Both normalizations are no-ops on Unix.

Changelog: [internal]

Differential Revision: D102285839

Author: panagosg7

rust_port/crates/flow_common/src/files.rs

@@ -908,11 +908,12 @@ pub fn expand_project_root_token(root: &Path, s: &str) -> String {
 
 pub fn expand_project_root_token_as_relative(s: &str) -> String {
     let s = s.replace(PROJECT_ROOT_TOKEN, "");
-    if s.starts_with('/') || s.starts_with('\\') {
+    let s = if s.starts_with('/') || s.starts_with('\\') {
         s[1..].to_string()
     } else {
         s
-    }
+    };
+    normalize_filename_dir_sep(&s).into_owned()
 }
 
 pub fn expand_builtin_root_token(flowlib_dir: &Path, s: &str) -> String {

rust_port/crates/flow_parser/src/file_key.rs

@@ -317,12 +317,14 @@ fn relative_path_from(root: &str, path: &str) -> String {
     result.join("/")
 }
 
+// The result always uses '/' separators for cross-platform consistency
+// (saved state generated on Linux must work on Windows and vice versa).
 pub fn strip_project_root(path: &str) -> String {
     let guard = PROJECT_ROOT.read().unwrap();
     match guard.as_deref() {
         Some(root) => {
             if let Some(stripped) = path.strip_prefix(root) {
-                stripped.to_string()
+                normalize_dir_sep_with(std::path::MAIN_SEPARATOR, stripped)
             } else if !is_relative(path) {
                 relative_path_from(root, path)
             } else {
@@ -437,7 +439,9 @@ impl FileKey {
         let guard = FLOWLIB_ROOT.read().unwrap();
         let suffix = match guard.as_deref() {
             Some(fl) if !fl.is_empty() && path.starts_with(fl) => {
-                format!("{}{}", FLOWLIB_MARKER, strip_prefix(fl, path))
+                let stripped =
+                    normalize_dir_sep_with(std::path::MAIN_SEPARATOR, strip_prefix(fl, path));
+                format!("{}{}", FLOWLIB_MARKER, stripped)
             }
             _ => {
                 drop(guard);

src/common/files.ml

@@ -379,6 +379,7 @@ type file_kind =
    like a pipe, socket or device. If `path` is a symbolic link, then it returns
    the type of the target of the symlink, and the target's real path. *)
 let kind_of_path dirent path =
+  let long_path = Sys_utils.win_long_path path in
   try
     let open Dirent in
     let open Unix in
@@ -387,11 +388,11 @@ let kind_of_path dirent path =
     | DT_DIR -> Dir (path, false)
     | DT_LNK
     | DT_UNKNOWN ->
-      (match (Sys_utils.lstat path).st_kind with
+      (match (Sys_utils.lstat long_path).st_kind with
       | S_REG -> Reg path
       | S_LNK ->
         (try
-           match (stat path).st_kind with
+           match (stat long_path).st_kind with
            | S_REG -> Reg (realpath_ path)
            | S_DIR -> Dir (realpath_ path, true)
            | _ -> Other
@@ -406,13 +407,6 @@ let kind_of_path dirent path =
     | DT_SOCK ->
       Other
   with
-  | Unix.Unix_error (Unix.ENOENT, _, _) when Sys.win32 && String.length path >= 248 ->
-    StatError
-      (Utils_js.spf
-         "On Windows, paths must be less than 248 characters for directories and 260 characters for files. This path has %d characters. Skipping %s"
-         (String.length path)
-         path
-      )
   | Unix.Unix_error (e, _, _) ->
     StatError (Utils_js.spf "Skipping %s: %s\n%!" path (Unix.error_message e))
 
@@ -1031,10 +1025,13 @@ let expand_project_root_token_as_absolute ~root =
 
 let expand_project_root_token_as_relative str =
   let s = str |> Str.split_delim project_root_token |> String.concat "" in
-  if String.length s > 0 && (s.[0] = '/' || s.[0] = '\\') then
-    String.sub s 1 (String.length s - 1)
-  else
-    s
+  let s =
+    if String.length s > 0 && (s.[0] = '/' || s.[0] = '\\') then
+      String.sub s 1 (String.length s - 1)
+    else
+      s
+  in
+  Sys_utils.normalize_filename_dir_sep s
 
 let expand_builtin_root_token ~flowlib_dir =
   let flowlib_dir_str = File_path.to_string flowlib_dir |> Sys_utils.normalize_filename_dir_sep in

src/hack_forked/utils/disk/disk.ml

@@ -13,8 +13,24 @@ exception Rename_target_already_exists of string
 
 exception Rename_target_dir_not_empty of string
 
+let win_long_path path =
+  if Sys.win32
+     && String.length path >= 248
+     && not (String.length path >= 4
+             && path.[0] = '\\'
+             && path.[1] = '\\'
+             && path.[2] = '?'
+             && path.[3] = '\\')
+  then
+    let backslashed =
+      String.map (fun c -> if c = '/' then '\\' else c) path
+    in
+    "\\\\?\\" ^ backslashed
+  else
+    path
+
 let cat (filename : string) : string =
-  let ic = open_in_bin filename in
+  let ic = open_in_bin (win_long_path filename) in
   let len =
     try in_channel_length ic with
     | Sys_error _ -> 0

src/hack_forked/utils/sys/sys_utils.ml

@@ -301,6 +301,30 @@ let lstat path =
   else
     path
 
+(** On Windows, prepend the \\?\ extended-length path prefix to absolute
+    paths that approach the 260-char MAX_PATH limit. This lifts the limit
+    to ~32k chars. The prefix requires backslash separators and a fully
+    resolved path (no . or .. segments). No-op on non-Windows platforms
+    and on short paths. *)
+let win_long_path =
+  if not Sys.win32 then
+    fun path -> path
+  else
+    fun path ->
+      if String.length path >= 248
+         && not (String.length path >= 4
+                 && path.[0] = '\\'
+                 && path.[1] = '\\'
+                 && path.[2] = '?'
+                 && path.[3] = '\\')
+      then
+        let backslashed =
+          String.map (fun c -> if c = '/' then '\\' else c) path
+        in
+        "\\\\?\\" ^ backslashed
+      else
+        path
+
 (** Converts platform-specific directory separators to / *)
 let normalize_filename_dir_sep =
   let dir_sep_char = Filename.dir_sep.[0] in

src/parser/file_key.ml

@@ -272,12 +272,15 @@ let relative_path_from ?(dir_sep = Filename.dir_sep) root path =
    compute a relative path from the root — this ensures all suffixes are
    portable relative paths, which is critical for saved state portability
    across machines with different root paths.
-   If the root has not been set yet, returns the path unchanged. *)
+   If the root has not been set yet, returns the path unchanged.
+   The result always uses '/' separators for cross-platform consistency
+   (saved state generated on Linux must work on Windows and vice versa). *)
 let strip_project_root path =
   match !project_root with
   | Some root ->
     if String.starts_with ~prefix:root path then
-      String.sub path (String.length root) (String.length path - String.length root)
+      normalize_dir_sep
+        (String.sub path (String.length root) (String.length path - String.length root))
     else if not (Filename.is_relative path) then
       relative_path_from root path
     else
@@ -296,7 +299,7 @@ let resource_file_of_absolute path = ResourceFile (strip_project_root path)
 let lib_file_of_absolute path =
   match !flowlib_root with
   | Some fl when String.length fl > 0 && String.starts_with ~prefix:fl path ->
-    LibFile (flowlib_marker ^ strip_prefix fl path)
+    LibFile (flowlib_marker ^ normalize_dir_sep (strip_prefix fl path))
   | _ -> LibFile (strip_project_root path)
 
 module For_tests = struct

src/parsing/parsing_service_js.ml

@@ -581,4 +581,8 @@ let ensure_parsed ~reader options workers files =
       workers
       next
   in
-  Lwt.return (FilenameSet.union changed not_found)
+  if not (FilenameSet.is_empty not_found) then
+    Hh_logger.info
+      "ensure_parsed: %d files not found on disk (skipping — will be cleaned up during reparse)"
+      (FilenameSet.cardinal not_found);
+  Lwt.return changed

src/services/module/module_js.ml

@@ -581,7 +581,9 @@ module Node = struct
         let applicable =
           Base.Option.value_map
             applicable_dirname_opt
-            ~f:(fun prefix -> Files.is_prefix prefix (File_key.suffix importing_file))
+            ~f:(fun prefix ->
+              let suffix = File_key.suffix importing_file in
+              suffix = prefix || String.starts_with ~prefix:(prefix ^ "/") suffix)
             ~default:true
         in
         if applicable then