Cache project config on demand (rescript-lang#1000)

* cache project config on demand

* e2e for the new cache mode

* only look up project files etc when needed

* comment

* Revert "only look up project files etc when needed"

This reverts commit bc71f76.

* remove now irrelevant comment

* changelog

* conditionally

* rename

* replace instead of add

CHANGELOG.md

@@ -18,6 +18,10 @@
 
 ## 1.52.0
 
+#### :rocket: New Feature
+
+- Experimental support for caching the project config to reduce latency. https://github.com/rescript-lang/rescript-vscode/pull/1000
+
 #### :bug: Bug Fix
 
 - Fix highlighting of other languages being affected by rescript-vscode. https://github.com/rescript-lang/rescript-vscode/pull/973

analysis/bin/main.ml

@@ -110,6 +110,23 @@ let main () =
         path line col
   in
   match args with
+  | [_; "cache-project"; rootPath] -> (
+    Cfg.readProjectConfigCache := false;
+    let uri = Uri.fromPath rootPath in
+    match Packages.getPackage ~uri with
+    | Some package -> Cache.cacheProject package
+    | None -> print_endline "\"ERR\"")
+  | [_; "cache-delete"; rootPath] -> (
+    Cfg.readProjectConfigCache := false;
+    let uri = Uri.fromPath rootPath in
+    match Packages.findRoot ~uri (Hashtbl.create 0) with
+    | Some (`Bs rootPath) -> (
+      match BuildSystem.getLibBs rootPath with
+      | None -> print_endline "\"ERR\""
+      | Some libBs ->
+        Cache.deleteCache (Cache.targetFileFromLibBs libBs);
+        print_endline "\"OK\"")
+    | _ -> print_endline "\"ERR: Did not find root \"")
   | [_; "completion"; path; line; col; currentFile] ->
     printHeaderInfo path line col;
     Commands.completion ~debug ~path

analysis/src/Cache.ml

@@ -0,0 +1,41 @@
+open SharedTypes
+
+type cached = {
+  projectFiles: FileSet.t;
+  dependenciesFiles: FileSet.t;
+  pathsForModule: (file, paths) Hashtbl.t;
+}
+
+let writeCache filename (data : cached) =
+  let oc = open_out_bin filename in
+  Marshal.to_channel oc data [];
+  close_out oc
+
+let readCache filename =
+  if !Cfg.readProjectConfigCache && Sys.file_exists filename then
+    try
+      let ic = open_in_bin filename in
+      let data : cached = Marshal.from_channel ic in
+      close_in ic;
+      Some data
+    with _ -> None
+  else None
+
+let deleteCache filename = try Sys.remove filename with _ -> ()
+
+let targetFileFromLibBs libBs = Filename.concat libBs ".project-files-cache"
+
+let cacheProject (package : package) =
+  let cached =
+    {
+      projectFiles = package.projectFiles;
+      dependenciesFiles = package.dependenciesFiles;
+      pathsForModule = package.pathsForModule;
+    }
+  in
+  match BuildSystem.getLibBs package.rootPath with
+  | None -> print_endline "\"ERR\""
+  | Some libBs ->
+    let targetFile = targetFileFromLibBs libBs in
+    writeCache targetFile cached;
+    print_endline "\"OK\""

analysis/src/Cfg.ml

@@ -9,3 +9,11 @@ let inIncrementalTypecheckingMode =
        | "true" -> true
        | _ -> false
      with _ -> false)
+
+let readProjectConfigCache =
+  ref
+    (try
+       match Sys.getenv "RESCRIPT_PROJECT_CONFIG_CACHE" with
+       | "true" -> true
+       | _ -> false
+     with _ -> false)