[configurator] Return pkg-config error to clients of new query API.

It is very convenient for configuration tools to be able to provide a
better error message to the user when pkg-config fails.

This was suggested by @garrigue.

We take advantage of the newly [undocumented] API in 1.7.2 to modify
its return type, but this could be a problem. If so, we will have to
introduce yet another function if we want this functionality.

We also update `src/configurator/dune` to include transitive
dependencies as suggested by @rgrinberg

Signed-off-by: Emilio Jesus Gallego Arias <e+git@x80.org>

src/configurator/dune

@@ -3,5 +3,5 @@
 (library
  (name        configurator)
  (public_name dune.configurator)
- (libraries   stdune ocaml_config dune_lang)
+ (libraries   stdune ocaml_config dune_lang dune_caml)
  (flags       (:standard -safe-string (:include flags/flags.sexp))))

src/configurator/v1.ml

@@ -256,9 +256,6 @@ module Process = struct
   let run_command_ok t ?dir ?env cmd =
     (run_command t ?dir ?env cmd).exit_code = 0
 
-  let run_process_ok t ?dir ?env prog args =
-    (run_process t ?dir ?env prog args).exit_code = 0
-
   let run t ?dir ?env prog args =
     run_command t ?dir ?env (command_line prog args)
 
@@ -615,22 +612,29 @@ module Pkg_config = struct
         end
       | _ -> None
     in
-    if Process.run_process_ok c ~dir ?env t.pkg_config [expr] then
+    let pc_flags = "--print-errors" in
+    let { Process.exit_code; stderr; _ } =
+      Process.run_process c ~dir ?env t.pkg_config [pc_flags; expr] in
+    if exit_code = 0 then
       let run what =
         match String.trim (Process.run_capture_exn c ~dir ?env
                              t.pkg_config [what; package])
         with
         | "" -> []
         | s  -> String.split s ~on:' '
       in
-      Some
+      Ok
         { libs   = run "--libs"
         ; cflags = run "--cflags"
         }
     else
-      None
+      Error stderr
+
+  let query t ~package =
+    match gen_query t ~package ~expr:None with
+    | Ok p -> Some p
+    | Error _msg -> None
 
-  let query t ~package = gen_query t ~package ~expr:None
   let query_expr t ~package ~expr = gen_query t ~package ~expr:(Some expr)
 end
 

src/configurator/v1.mli

@@ -93,7 +93,14 @@ module Pkg_config : sig
      package may contain a version constraint.  For example
      "gtk+-3.0 >= 3.18".  Returns [None] if [package] is not available  *)
 
-  val query_expr : t -> package:string -> expr:string -> package_conf option
+  val query_expr : t
+    -> package:string
+    -> expr:string
+    -> (package_conf, string) Dune_caml.result
+  (** [query_expr t ~package ~expr] query pkg-config for the
+     [package]. [expr] may contain a version constraint, for example
+     "gtk+-3.0 >= 3.18". [package] should be just the name of the
+     package. Returns [Error error_msg] if [package] is not available *)
 end with type configurator := t
 
 module Flags : sig

test/blackbox-tests/test-cases/pkg-config-quoting/pkg_config.ml

@@ -1,4 +1,8 @@
+(* We'd like to use String.equal but that's OCaml >= 4.03 *)
+let not_flag x = not ("--print-errors" = x)
+
 let () =
   let args = List.tl (Array.to_list Sys.argv) in
+  let args = List.filter not_flag args in
   Format.printf "%a@."
     (Format.pp_print_list Format.pp_print_string) args

test/blackbox-tests/test-cases/pkg-config-quoting/run.t

@@ -1,6 +1,6 @@
 These tests show how various pkg-config invocations get qouted:
   $ dune build 2>&1 | awk '/run:.*bin\/pkg-config/{a=1}/stderr/{a=0}a'
-  run: $TESTCASE_ROOT/_build/install/default/bin/pkg-config gtk+-quartz-3.0
+  run: $TESTCASE_ROOT/_build/install/default/bin/pkg-config --print-errors gtk+-quartz-3.0
   -> process exited with code 0
   -> stdout:
    | gtk+-quartz-3.0
@@ -14,7 +14,7 @@ These tests show how various pkg-config invocations get qouted:
   -> stdout:
    | --libs
    | gtk+-quartz-3.0
-  run: $TESTCASE_ROOT/_build/install/default/bin/pkg-config 'gtk+-quartz-3.0 >= 3.18'
+  run: $TESTCASE_ROOT/_build/install/default/bin/pkg-config --print-errors 'gtk+-quartz-3.0 >= 3.18'
   -> process exited with code 0
   -> stdout:
    | gtk+-quartz-3.0 >= 3.18
@@ -28,7 +28,7 @@ These tests show how various pkg-config invocations get qouted:
   -> stdout:
    | --libs
    | gtk+-quartz-3.0 >= 3.18
-  run: $TESTCASE_ROOT/_build/install/default/bin/pkg-config 'gtksourceview-3.0 >= 3.18'
+  run: $TESTCASE_ROOT/_build/install/default/bin/pkg-config --print-errors 'gtksourceview-3.0 >= 3.18'
   -> process exited with code 0
   -> stdout:
    | gtksourceview-3.0 >= 3.18