Add core config var OPAMERRLOGLEN to control error output

I also pushed the default from 10 to 12. Closes #2111

src/core/opamCoreConfig.ml

@@ -26,6 +26,7 @@ type t = {
   lock_retries: int;
   log_dir: string;
   keep_log_dir: bool;
+  errlog_length: int;
 }
 
 type 'a options_fun =
@@ -39,6 +40,7 @@ type 'a options_fun =
   ?lock_retries:int ->
   ?log_dir:string ->
   ?keep_log_dir:bool ->
+  ?errlog_length:int ->
   unit -> 'a
 
 let default = {
@@ -55,6 +57,7 @@ let default = {
      let base = Printf.sprintf "opam-%s-%d" user (Unix.getpid()) in
      Filename.(concat (get_temp_dir_name ()) base));
   keep_log_dir = false;
+  errlog_length = 12;
 }
 
 let setk k t
@@ -68,6 +71,7 @@ let setk k t
     ?lock_retries
     ?log_dir
     ?keep_log_dir
+    ?errlog_length
     ()
   =
   let (+) x opt = match opt with Some x -> x | None -> x in
@@ -82,6 +86,7 @@ let setk k t
     lock_retries = t.lock_retries + lock_retries;
     log_dir = t.log_dir + log_dir;
     keep_log_dir = t.keep_log_dir + keep_log_dir;
+    errlog_length = t.errlog_length + errlog_length;
   }
 
 let set t = setk (fun x -> x) t

src/core/opamCoreConfig.mli

@@ -38,6 +38,8 @@ type t = private {
   (** Where to store log and temporary files (output from commands...) *)
   keep_log_dir : bool;
   (** Whether to cleanup temporary and log files on exit *)
+  errlog_length : int;
+  (** The number of log lines displayed on process error. 0 for all *)
 }
 
 type 'a options_fun =
@@ -51,6 +53,7 @@ type 'a options_fun =
   ?lock_retries:int ->
   ?log_dir:string ->
   ?keep_log_dir:bool ->
+  ?errlog_length:int ->
   unit -> 'a
 
 val default : t

src/core/opamProcess.ml

@@ -466,7 +466,6 @@ let cleanup ?(force=false) r =
   if force || (not (OpamConsole.debug ()) && is_success r) then
     List.iter safe_unlink r.r_cleanup
 
-let log_limit = 10
 let log_line_limit = 5 * 80
 let truncate_str = "[...]"
 
@@ -481,7 +480,6 @@ let truncate_line str =
 (* Take the last [n] elements of [l] (trying to keep an unindented header line
    for context, like diff) *)
 let truncate l =
-  let l = List.rev l in
   let unindented s =
     String.length s > 0 && s.[0] <> ' ' && s.[0] <> '\t'
   in
@@ -495,7 +493,9 @@ let truncate l =
        with Not_found -> truncate_str :: truncate_line x :: acc)
     | x::r -> cut (n-1) (truncate_line x :: acc) r
   in
-  cut log_limit [] l
+  let len = OpamCoreConfig.(!r.errlog_length) in
+  if len <= 0 then l
+  else cut len [] (List.rev l)
 
 let string_of_result ?(color=`yellow) r =
   let b = Buffer.create 2048 in

src/core/opamStd.ml

@@ -876,6 +876,7 @@ module Config = struct
       ?lock_retries:(env_int "LOCKRETRIES")
       ?log_dir:(env_string "LOGS")
       ?keep_log_dir:(env_bool "KEEPLOGS")
+      ?errlog_length:(env_int "ERRLOGLEN")
       ()
 end