[flow] Add server.max_workers.full_check flowconfig option

Summary:
We'll probably want to have lazy servers start with a smaller number of workers, but keep full checks at a higher number.

This diff adds a new flowconfig option that overrides the worker count specifically for non-lazy mode (full checks).

In lazy mode, the regular server.max_workers (or system default) is used instead.

Priority order: CLI --max-workers > server.max_workers.full_check (non-lazy only) > server.max_workers > system default.

Reviewed By: SamChou19815

Differential Revision: D95162909

fbshipit-source-id: dfe220f960a880a376796e1314d8fbf017a0d120

Author: panagosg7

src/commands/commandUtils.ml

@@ -1544,9 +1544,21 @@ let make_options
     opt_max_header_tokens = FlowConfig.max_header_tokens flowconfig;
     opt_max_seconds_for_check_per_worker = FlowConfig.max_seconds_for_check_per_worker flowconfig;
     opt_max_workers =
-      Base.Option.first_some options_flags.max_workers (FlowConfig.max_workers flowconfig)
-      |> Base.Option.value ~default:Sys_utils.nbr_procs
-      |> min Sys_utils.nbr_procs;
+      (* Priority: CLI --max-workers > server.max_workers.full_check (non-lazy only)
+         > server.max_workers > system default (nbr_procs).
+         The result is capped at nbr_procs. *)
+      (let config_max_workers =
+         if not opt_lazy_mode then
+           Base.Option.first_some
+             (FlowConfig.max_workers_full_check flowconfig)
+             (FlowConfig.max_workers flowconfig)
+         else
+           FlowConfig.max_workers flowconfig
+       in
+       Base.Option.first_some options_flags.max_workers config_max_workers
+       |> Base.Option.value ~default:Sys_utils.nbr_procs
+       |> min Sys_utils.nbr_procs
+      );
     opt_merge_timeout;
     opt_missing_module_generators = FlowConfig.missing_module_generators flowconfig;
     opt_module = FlowConfig.module_system flowconfig;

src/commands/config/flowConfig.ml

@@ -107,6 +107,7 @@ module Opts = struct
     max_header_tokens: int;
     max_seconds_for_check_per_worker: float;
     max_workers: int option;
+    max_workers_full_check: int option;
     merge_timeout: int option;
     missing_module_generators: (Str.regexp * string) list;
     module_declaration_dirnames: string list;
@@ -265,6 +266,7 @@ module Opts = struct
       max_header_tokens = 10;
       max_seconds_for_check_per_worker = 5.0;
       max_workers = None;
+      max_workers_full_check = None;
       merge_timeout = Some 100;
       missing_module_generators = [];
       module_declaration_dirnames = ["<PROJECT_ROOT>/@flowtyped"];
@@ -1271,6 +1273,9 @@ module Opts = struct
         boolean (fun opts v -> Ok { opts with saved_state_skip_version_check = v })
       );
       ("server.max_workers", uint (fun opts v -> Ok { opts with max_workers = Some v }));
+      ( "server.max_workers.full_check",
+        uint (fun opts v -> Ok { opts with max_workers_full_check = Some v })
+      );
       ( "server.max_workers.windows",
         uint (fun opts v ->
             if Sys.win32 then
@@ -2033,6 +2038,8 @@ let max_seconds_for_check_per_worker c = c.options.Opts.max_seconds_for_check_pe
 
 let max_workers c = c.options.Opts.max_workers
 
+let max_workers_full_check c = c.options.Opts.max_workers_full_check
+
 let merge_timeout c = c.options.Opts.merge_timeout
 
 let missing_module_generators c = c.options.Opts.missing_module_generators

src/commands/config/flowConfig.mli

@@ -194,6 +194,8 @@ val max_seconds_for_check_per_worker : config -> float
 
 val max_workers : config -> int option
 
+val max_workers_full_check : config -> int option
+
 val merge_timeout : config -> int option
 
 val missing_module_generators : config -> (Str.regexp * string) list