dune-configurator: respect $PKG_CONFIG

Signed-off-by: Antonio Nuno Monteiro <anmonteiro@gmail.com>

CHANGES.md

@@ -1,6 +1,9 @@
 Unreleased
 ----------
 
+- Use `$PKG_CONFIG`, when set, to find the `pkg-config` binary  (#7469, fixes
+  #2572, @anmonteiro)
+
 - Preliminary support for Coq compiled intefaces (`.vos` files) enabled via
   `(mode vos)` in `coq.theory` stanzas. This can be used in combination with
   `dune coq top` to obtain fast re-building of dependencies (with no checking

otherlibs/configurator/src/v1.ml

@@ -620,7 +620,12 @@ module Pkg_config = struct
     }
 
   let get c =
-    Option.map (which c "pkg-config") ~f:(fun pkg_config ->
+    let pkg_config_exe_name =
+      match Sys.getenv "PKG_CONFIG" with
+      | s -> s
+      | exception Not_found -> "pkg-config"
+    in
+    Option.map (which c pkg_config_exe_name) ~f:(fun pkg_config ->
         { pkg_config; configurator = c })
 
   type package_conf =

src/dune_rules/pkg_config.ml

@@ -1,5 +1,12 @@
 open Import
 
+let pkg_config_binary sctx ~dir =
+  let open Memo.O in
+  let+ env = Super_context.env_node sctx ~dir >>= Env_node.external_env in
+  match Env.get env "PKG_CONFIG" with
+  | None -> "pkg-config"
+  | Some s -> s
+
 module Query = struct
   type t =
     | Libs of string
@@ -28,7 +35,9 @@ module Query = struct
     let open Action_builder.O in
     let* bin =
       Action_builder.of_memo
-      @@ Super_context.resolve_program sctx ~loc:None ~dir "pkg-config"
+        (let open Memo.O in
+        let* pkg_config = pkg_config_binary sctx ~dir in
+        Super_context.resolve_program sctx ~loc:None ~dir pkg_config)
     in
     match bin with
     | Error _ -> Action_builder.return (default t)
@@ -42,7 +51,10 @@ end
 let gen_rule sctx ~loc ~dir query =
   let open Memo.O in
   let* bin =
-    Super_context.resolve_program sctx ~loc:(Some loc) ~dir "pkg-config"
+    let open Memo.O in
+    let* pkg_config = pkg_config_binary sctx ~dir in
+
+    Super_context.resolve_program sctx ~loc:(Some loc) ~dir pkg_config
   in
   match bin with
   | Error _ -> Memo.return @@ Error `Not_found