Add reanalyze-server with transparent delegation (#8127)

* Add reanalyze-server with transparent delegation

- Implement reanalyze-server subcommand that maintains reactive state
- Add reanalyze-server-request client for IPC via Unix socket
- **Transparent delegation**: Regular 'reanalyze' calls automatically use
  the server if running on default socket (/tmp/rescript-reanalyze.sock)
- Works with unmodified VS Code extension - just start the server manually
- Create comprehensive test harness with clean warmup/benchmark phases
- Color-coded logging: [BUILD], [SERVER], [REACTIVE], [STANDALONE], [EDIT]
- Test scenarios: add dead code (+1 issue), make dead code live (-1 issue)
- Results: 2.5x speedup (small project), 10x+ speedup (benchmark)

Usage:
  # Start server (once, in background)
  rescript-editor-analysis reanalyze-server --cwd /path/to/project -- -config -ci -json

  # Now regular reanalyze calls automatically use the server:
  rescript-editor-analysis reanalyze -config -ci -json

Signed-Off-By: Cristiano Calcagno <cristiano.calcagno@gmail.com>

* reformat

* Add detailed request stats to reanalyze-server

- Log request number, timing, issues, dead/live counts, files processed/cached
- Pass file_stats through runAnalysis to capture processing statistics
- Use locally created mutable stats record instead of global state
- Stats show files processed (new or modified) vs cached (unchanged)

* reanalyze-server: project-root socket + cleanup

- Default socket lives in project root and is discovered by walking up to rescript.json/bsconfig.json

- Use relative socket name to avoid macOS unix socket path length limits

- Unlink socket on exit and on common termination signals

- Update reanalyze README with VS Code (-json) usage

* Extract reanalyze server into dedicated module

Move server/IPC/socket-path logic into ReanalyzeServer.ml and keep Reanalyze.ml focused on analysis.

* reanalyze: add reactive server under rescript-tools

- reanalyze-server runs editor-mode (-json) with no args

- reanalyze delegates to server only for -json

- update reanalyze tests/harness to use rescript-tools

Signed-off-by: Cristiano Calcagno <cristianoc@users.noreply.github.com>

* changelog: mention reanalyze-server

Signed-off-by: Cristiano Calcagno <cristianoc@users.noreply.github.com>

* reanalyze-server: compact heap after each request, simplify mem output

- Run Gc.compact() after every request to keep memory stable (~257MB)
- Simplify server output to just show live heap: 'mem: 257.0MB'
- Add opt-out via RESCRIPT_REANALYZE_SERVER_SKIP_COMPACT=1 env var

* Reanalyze: support rewatch monorepos via root .sourcedirs.json cmt_scan

- Extend rewatch to emit version:2 .sourcedirs.json with explicit cmt_scan (build roots + scan dirs) for root-level monorepo builds.
- Update reanalyze (editor invocation: rescript-tools reanalyze -json) to prefer cmt_scan when present, with legacy single-project fallback.
- Ensure deterministic output ordering by sorting .cmt/.cmti entries in the cmt_scan path.

Tests: make test-analysis
Signed-off-by: Cristiano Calcagno <cristianoc@users.noreply.github.com>

---------

Signed-off-by: Cristiano Calcagno <cristiano.calcagno@gmail.com>
Signed-off-by: Cristiano Calcagno <cristianoc@users.noreply.github.com>

Author: cristianoc

CHANGELOG.md

@@ -21,6 +21,8 @@
 - Add support for Set, Map, WeakSet and WeakMap to `@unboxed`. https://github.com/rescript-lang/rescript/pull/8009
 - Reanalyze: add reactive incremental analysis (`-reactive`, `-runs`, `-churn`) and Mermaid pipeline dumping (`-mermaid`). https://github.com/rescript-lang/rescript/pull/8092
 
+- Reanalyze: add `reanalyze-server` (long-lived server) with transparent delegation for `rescript-tools reanalyze -json`. https://github.com/rescript-lang/rescript/pull/8127
+
 #### :bug: Bug fix
 
 - Fix rewatch swallowing parse warnings (%todo). https://github.com/rescript-lang/rescript/pull/8135

analysis/bin/main.ml

@@ -191,13 +191,6 @@ let main () =
     in
     Printf.printf "\"%s\"" res
   | [_; "diagnosticSyntax"; path] -> Commands.diagnosticSyntax ~path
-  | _ :: "reanalyze" :: _ ->
-    let len = Array.length Sys.argv in
-    for i = 1 to len - 2 do
-      Sys.argv.(i) <- Sys.argv.(i + 1)
-    done;
-    Sys.argv.(len - 1) <- "";
-    Reanalyze.cli ()
   | [_; "references"; path; line; col] ->
     Commands.references ~path
       ~pos:(int_of_string line, int_of_string col)

analysis/reanalyze/README.md

@@ -12,13 +12,13 @@ Dead code analysis and other experimental analyses for ReScript.
 
 ```bash
 # Run DCE analysis on current project (reads rescript.json)
-rescript-editor-analysis reanalyze -config
+rescript-tools reanalyze -config
 
 # Run DCE analysis on specific CMT directory
-rescript-editor-analysis reanalyze -dce-cmt path/to/lib/bs
+rescript-tools reanalyze -dce-cmt path/to/lib/bs
 
 # Run all analyses
-rescript-editor-analysis reanalyze -all
+rescript-tools reanalyze -all
 ```
 
 ## Performance Options
@@ -28,7 +28,7 @@ rescript-editor-analysis reanalyze -all
 Cache processed file data and skip unchanged files on subsequent runs:
 
 ```bash
-rescript-editor-analysis reanalyze -config -reactive
+rescript-tools reanalyze -config -reactive
 ```
 
 This provides significant speedup for repeated analysis (e.g., in a watch mode or service):
@@ -43,7 +43,7 @@ This provides significant speedup for repeated analysis (e.g., in a watch mode o
 Run analysis multiple times to measure cache effectiveness:
 
 ```bash
-rescript-editor-analysis reanalyze -config -reactive -timing -runs 3
+rescript-tools reanalyze -config -reactive -timing -runs 3
 ```
 
 ## CLI Flags
@@ -85,7 +85,68 @@ The reactive mode (`-reactive`) caches processed per-file results and efficientl
 2. **Subsequent runs**: Only changed files are re-processed
 3. **Unchanged files**: Return cached `file_data` immediately (no I/O or unmarshalling)
 
-This is the foundation for a persistent analysis service that can respond to file changes in milliseconds.
+This is the foundation for the **reanalyze-server** — a persistent analysis service that keeps reactive state warm across requests.
+
+## Reanalyze Server
+
+A long-lived server process that keeps reactive analysis state warm across multiple requests. This enables fast incremental analysis for editor integration.
+
+### Transparent Server Delegation
+
+When a server is running on the default socket (`<projectRoot>/.rescript-reanalyze.sock`), the regular `reanalyze` command **automatically delegates** to it. This means:
+
+1. **Start the server once** (in the background)
+2. **Use the editor normally** — all `reanalyze` calls go through the server
+3. **Enjoy fast incremental analysis** — typically 10x faster after the first run
+
+This works transparently with the VS Code extension's "Start Code Analyzer" command.
+
+### Quick Start
+
+```bash
+# From anywhere inside your project, start the server:
+rescript-tools reanalyze-server
+
+# Now any reanalyze call will automatically use the server:
+rescript-tools reanalyze -json  # → delegates to server
+```
+
+### Starting the Server
+
+```bash
+rescript-tools reanalyze-server [--socket <path>]
+```
+
+Options:
+- `--socket <path>` — Unix domain socket path (default: `<projectRoot>/.rescript-reanalyze.sock`)
+
+Examples:
+
+```bash
+# Start server with default socket (recommended)
+rescript-tools reanalyze-server \
+
+# With custom socket path
+rescript-tools reanalyze-server \
+  --socket /tmp/my-custom.sock \
+```
+
+### Behavior
+
+- **Transparent delegation**: Regular `reanalyze` calls automatically use the server if running
+- **Default socket**: `<projectRoot>/.rescript-reanalyze.sock` (used by both server and client)
+- **Socket location invariant**: socket is always in the project root; `reanalyze` may be called from anywhere inside the project
+- **Reactive mode forced**: The server always runs with `-reactive` enabled internally
+- **Same output**: stdout/stderr/exit-code match what a direct CLI invocation would produce
+- **Incremental updates**: When source files change and the project is rebuilt, subsequent requests reflect the updated analysis
+
+### Typical Workflow
+
+1. **Start server** (once, in background)
+2. **Edit source files**
+3. **Rebuild project** (`yarn build` / `rescript build`)
+4. **Use editor** — analysis requests automatically go through the server
+5. **Stop server** when done (or leave running)
 
 ## Development
 

analysis/reanalyze/src/EmitJson.ml

@@ -1,5 +1,7 @@
 let items = ref 0
-let start () = Printf.printf "["
+let start () =
+  items := 0;
+  Printf.printf "["
 let finish () = Printf.printf "\n]\n"
 let emitClose () = "\n}"
 

analysis/reanalyze/src/Paths.ml

@@ -26,13 +26,14 @@ let rec findProjectRoot ~dir =
 
 let runConfig = RunConfig.runConfig
 
-let setReScriptProjectRoot =
-  lazy
-    (runConfig.projectRoot <- findProjectRoot ~dir:(Sys.getcwd ());
-     runConfig.bsbProjectRoot <-
-       (match Sys.getenv_opt "BSB_PROJECT_ROOT" with
-       | None -> runConfig.projectRoot
-       | Some s -> s))
+let setProjectRootFromCwd () =
+  runConfig.projectRoot <- findProjectRoot ~dir:(Sys.getcwd ());
+  runConfig.bsbProjectRoot <-
+    (match Sys.getenv_opt "BSB_PROJECT_ROOT" with
+    | None -> runConfig.projectRoot
+    | Some s -> s)
+
+let setReScriptProjectRoot = lazy (setProjectRootFromCwd ())
 
 module Config = struct
   let readSuppress conf =
@@ -84,7 +85,7 @@ module Config = struct
 
   (* Read the config from rescript.json and apply it to runConfig and suppress and unsuppress *)
   let processBsconfig () =
-    Lazy.force setReScriptProjectRoot;
+    setProjectRootFromCwd ();
     let rescriptFile = Filename.concat runConfig.projectRoot rescriptJson in
     let bsconfigFile = Filename.concat runConfig.projectRoot bsconfig in
 
@@ -204,3 +205,72 @@ let readSourceDirs ~configSources =
       Log_.item "Types for cross-references will not be found.\n");
     dirs := readDirsFromConfig ~configSources);
   !dirs
+
+type cmt_scan_entry = {
+  build_root: string;
+  scan_dirs: string list;
+  also_scan_build_root: bool;
+}
+(** Read explicit `.cmt/.cmti` scan plan from `.sourcedirs.json`.
+
+    This is a v2 extension produced by `rewatch` to support monorepos without requiring
+    reanalyze-side package resolution.
+
+    The scan plan is a list of build roots (usually `<pkg>/lib/bs`) relative to the project root,
+    plus a list of subdirectories (relative to that build root) to scan for `.cmt/.cmti`.
+
+    If missing, returns the empty list and callers should fall back to legacy behavior. *)
+
+let readCmtScan () =
+  let sourceDirsFile =
+    ["lib"; "bs"; ".sourcedirs.json"]
+    |> List.fold_left Filename.concat runConfig.bsbProjectRoot
+  in
+  let entries = ref [] in
+  let read_entry (json : Ext_json_types.t) =
+    match json with
+    | Ext_json_types.Obj {map} -> (
+      let build_root =
+        match StringMap.find_opt map "build_root" with
+        | Some (Ext_json_types.Str {str}) -> Some str
+        | _ -> None
+      in
+      let scan_dirs =
+        match StringMap.find_opt map "scan_dirs" with
+        | Some (Ext_json_types.Arr {content = arr}) ->
+          arr |> Array.to_list
+          |> List.filter_map (fun x ->
+                 match x with
+                 | Ext_json_types.Str {str} -> Some str
+                 | _ -> None)
+        | _ -> []
+      in
+      let also_scan_build_root =
+        match StringMap.find_opt map "also_scan_build_root" with
+        | Some (Ext_json_types.True _) -> true
+        | Some (Ext_json_types.False _) -> false
+        | _ -> false
+      in
+      match build_root with
+      | Some build_root ->
+        entries := {build_root; scan_dirs; also_scan_build_root} :: !entries
+      | None -> ())
+    | _ -> ()
+  in
+  let read_cmt_scan (json : Ext_json_types.t) =
+    match json with
+    | Ext_json_types.Obj {map} -> (
+      match StringMap.find_opt map "cmt_scan" with
+      | Some (Ext_json_types.Arr {content = arr}) ->
+        arr |> Array.iter read_entry
+      | _ -> ())
+    | _ -> ()
+  in
+  if sourceDirsFile |> Sys.file_exists then (
+    let jsonOpt = sourceDirsFile |> Ext_json_parse.parse_json_from_file in
+    match jsonOpt with
+    | exception _ -> []
+    | json ->
+      read_cmt_scan json;
+      !entries |> List.rev)
+  else []

analysis/reanalyze/src/ReactiveAnalysis.ml

@@ -19,6 +19,13 @@ type all_files_result = {
 type t = (Cmt_format.cmt_infos, cmt_file_result option) ReactiveFileCollection.t
 (** The reactive collection type *)
 
+type processing_stats = {
+  mutable total_files: int;
+  mutable processed: int;
+  mutable from_cache: int;
+}
+(** Stats from a process_files call *)
+
 (** Process cmt_infos into a file result *)
 let process_cmt_infos ~config ~cmtFilePath cmt_infos : cmt_file_result option =
   let excludePath sourceFile =
@@ -75,8 +82,10 @@ let create ~config : t =
 
 (** Process all files incrementally using ReactiveFileCollection.
     First run processes all files. Subsequent runs only process changed files.
-    Uses batch processing to emit all changes as a single Batch delta. *)
-let process_files ~(collection : t) ~config:_ cmtFilePaths : all_files_result =
+    Uses batch processing to emit all changes as a single Batch delta.
+    Returns (result, stats) where stats contains processing information. *)
+let process_files ~(collection : t) ~config:_ cmtFilePaths :
+    all_files_result * processing_stats =
   Timing.time_phase `FileLoading (fun () ->
       let total_files = List.length cmtFilePaths in
       let cached_before =
@@ -90,6 +99,7 @@ let process_files ~(collection : t) ~config:_ cmtFilePaths : all_files_result =
         ReactiveFileCollection.process_files_batch collection cmtFilePaths
       in
       let from_cache = total_files - processed in
+      let stats = {total_files; processed; from_cache} in
 
       if !Cli.timing then
         Printf.eprintf
@@ -113,10 +123,11 @@ let process_files ~(collection : t) ~config:_ cmtFilePaths : all_files_result =
           | None -> ())
         collection;
 
-      {
-        dce_data_list = List.rev !dce_data_list;
-        exception_results = List.rev !exception_results;
-      })
+      ( {
+          dce_data_list = List.rev !dce_data_list;
+          exception_results = List.rev !exception_results;
+        },
+        stats ))
 
 (** Get collection length *)
 let length (collection : t) = ReactiveFileCollection.length collection