[log] log to toplevel log file in infer subprocesses

Summary:
This makes it much easier to read infer logs coming from these subprocesses
that use a sub-results dir.

Reviewed By: jberdine

Differential Revision: D5777783

fbshipit-source-id: f074536

infer/src/base/Config.ml

@@ -412,6 +412,8 @@ let os_type = match Sys.os_type with "Win32" -> Win32 | "Cygwin" -> Cygwin | _ -
     directory of the initial invocation of infer. *)
 let resolve = Utils.filename_to_absolute ~root:CLOpt.init_work_dir
 
+let infer_top_results_dir_env_var = "INFER_TOP_RESULTS_DIR"
+
 let infer_inside_maven_env_var = "INFER_INSIDE_MAVEN"
 
 let maven = CLOpt.is_env_var_set infer_inside_maven_env_var
@@ -1742,6 +1744,8 @@ let config_file =
    -> find (Sys.getcwd ()) |> Option.map ~f:(fun dir -> dir ^/ CommandDoc.inferconfig_file)
 
 let post_parsing_initialization command_opt =
+  if CommandLineOption.is_originator then
+    Unix.putenv ~key:infer_top_results_dir_env_var ~data:!results_dir ;
   ( match !version with
   | `Full
    -> (* TODO(11791235) change back to stdout once buck integration is fixed *)

infer/src/base/Config.mli

@@ -133,6 +133,8 @@ val incremental_procs : bool
 
 val infer_py_argparse_error_exit_code : int
 
+val infer_top_results_dir_env_var : string
+
 val initial_analysis_time : float
 
 val ivar_attributes : string

infer/src/base/Logging.ml

@@ -270,8 +270,14 @@ let setup_log_file () =
       ()
   | _, `Console
    -> let fmt, chan, preexisting_logfile =
-        (* assumes Config.results_dir exists already *)
-        let logfile_path = Config.results_dir ^/ Config.log_file in
+        let results_dir =
+          (* if invoked in a sub-dir (e.g., in Buck integrations), log inside the original log
+              file *)
+          Sys.getenv Config.infer_top_results_dir_env_var
+          |> Option.value ~default:Config.results_dir
+        in
+        (* assumes the results dir exists already *)
+        let logfile_path = results_dir ^/ Config.log_file in
         let preexisting_logfile = PVariant.( = ) (Sys.file_exists logfile_path) `Yes in
         let chan = Pervasives.open_out_gen [Open_append; Open_creat] 0o666 logfile_path in
         let file_fmt =