refactor: auto-detect lib/bs or lib/lsp by newest mtime

Both reanalyze and doc/analysis tooling now pick whichever of
lib/bs/.sourcedirs.json and lib/lsp/.sourcedirs.json was modified
most recently, so the correct build artifacts are used regardless
of whether the last build was a CLI or LSP build.

This removes the --lib-dir flag from `rescript-tools doc` and the
Cfg.libDir plumbing, since the mtime-based detection makes them
unnecessary.

Author: nojaf

analysis/reanalyze/src/Paths.ml

@@ -215,11 +215,26 @@ type cmt_scan_entry = {
 
     If missing, returns the empty list and callers should fall back to legacy behavior. *)
 
+let newerFile a b =
+  match (Sys.file_exists a, Sys.file_exists b) with
+  | true, true ->
+    let mtime_a = (Unix.stat a).st_mtime in
+    let mtime_b = (Unix.stat b).st_mtime in
+    if mtime_b > mtime_a then b else a
+  | true, false -> a
+  | false, true -> b
+  | false, false -> a
+
 let readCmtScan () =
-  let sourceDirsFile =
+  let bsFile =
     ["lib"; "bs"; ".sourcedirs.json"]
     |> List.fold_left Filename.concat runConfig.bsbProjectRoot
   in
+  let lspFile =
+    ["lib"; "lsp"; ".sourcedirs.json"]
+    |> List.fold_left Filename.concat runConfig.bsbProjectRoot
+  in
+  let sourceDirsFile = newerFile bsFile lspFile in
   let entries = ref [] in
   let read_entry (json : Ext_json_types.t) =
     match json with

analysis/src/BuildSystem.ml

@@ -40,7 +40,16 @@ let getRuntimeDir rootPath =
         None))
   | true -> Some rootPath
 
-let getLibBs path = Files.ifExists (path /+ "lib" /+ "bs")
+let getLibBs path =
+  let bs = path /+ "lib" /+ "bs" in
+  let lsp = path /+ "lib" /+ "lsp" in
+  match (Sys.file_exists bs, Sys.file_exists lsp) with
+  | true, true ->
+    let mtime path = (Unix.stat path).st_mtime in
+    if mtime lsp > mtime bs then Some lsp else Some bs
+  | true, false -> Some bs
+  | false, true -> Some lsp
+  | false, false -> None
 
 let getStdlib base =
   match getRuntimeDir base with

analysis/src/Cfg.ml

@@ -2,8 +2,6 @@ let debugFollowCtxPath = ref false
 
 let isDocGenFromCompiler = ref false
 
-let libDir : string option ref = ref None
-
 let inIncrementalTypecheckingMode =
   ref
     (try

analysis/src/Packages.ml

@@ -37,12 +37,9 @@ let newBsPackage ~rootPath =
 
   let parseRaw raw =
     let libBs =
-      match !Cfg.libDir with
-      | Some dir -> Files.ifExists (Filename.concat rootPath dir)
-      | None -> (
-        match !Cfg.isDocGenFromCompiler with
-        | true -> BuildSystem.getStdlib rootPath
-        | false -> BuildSystem.getLibBs rootPath)
+      match !Cfg.isDocGenFromCompiler with
+      | true -> BuildSystem.getStdlib rootPath
+      | false -> BuildSystem.getLibBs rootPath
     in
     match Json.parse raw with
     | Some config -> (

tools/bin/main.ml

@@ -3,10 +3,9 @@ let docHelp =
 
 Output documentation to standard output
 
-Usage: rescript-tools doc <FILE> [--lib-dir <DIR>]
+Usage: rescript-tools doc <FILE>
 
-Example: rescript-tools doc ./path/to/EntryPointLib.res
-Example: rescript-tools doc ./path/to/EntryPointLib.res --lib-dir lib/lsp|}
+Example: rescript-tools doc ./path/to/EntryPointLib.res|}
 
 let formatCodeblocksHelp =
   {|ReScript Tools
@@ -61,21 +60,13 @@ let main () =
   | "doc" :: rest -> (
     match rest with
     | ["-h"] | ["--help"] -> logAndExit (Ok docHelp)
-    | path :: args ->
+    | path :: _ ->
       (* NOTE: Internal use to generate docs from compiler *)
       let () =
         match Sys.getenv_opt "FROM_COMPILER" with
         | Some "true" -> Analysis.Cfg.isDocGenFromCompiler := true
         | _ -> ()
       in
-      let rec parseArgs = function
-        | "--lib-dir" :: dir :: remaining ->
-          Analysis.Cfg.libDir := Some dir;
-          parseArgs remaining
-        | _ :: remaining -> parseArgs remaining
-        | [] -> ()
-      in
-      parseArgs args;
       logAndExit (Tools.extractDocs ~entryPointFile:path ~debug:false)
     | _ -> logAndExit (Error docHelp))
   | "migrate" :: file :: opts -> (