Expose OpamState.contents_of_variable to resolve opam variables

src/client/opamConfigCommand.ml

@@ -185,34 +185,11 @@ let set var value =
     OpamFile.Dot_config.write config_f
       (OpamFile.Dot_config.set config var newval)
 
-let quick_lookup v =
-  if OpamVariable.Full.is_global v then (
-    let var = OpamVariable.Full.variable v in
-    let root = OpamStateConfig.(!r.root_dir) in
-    let switch = OpamStateConfig.(!r.current_switch) in
-    let config_f = OpamPath.Switch.global_config root switch in
-    let config = OpamFile.Dot_config.read config_f in
-    match OpamState.get_env_var v with
-    | Some _ as c -> c
-    | None ->
-      if OpamVariable.to_string var = "switch" then
-        Some (S (OpamSwitch.to_string switch))
-      else
-        OpamFile.Dot_config.variable config var
-  ) else
-    None
-
 let variable v =
-  log "config-variable";
-  let contents =
-    match quick_lookup v with
-    | Some c -> c
-    | None   ->
-      let t = OpamState.load_state "config-variable"
-          OpamStateConfig.(!r.current_switch) in
-      OpamFilter.ident_value (OpamState.filter_env t) ~default:(S "#undefined")
-        (OpamFilter.ident_of_var v)
-  in
+  let t = lazy (
+    OpamState.load_state "config-variable" OpamStateConfig.(!r.current_switch)
+  ) in
+  let contents = OpamState.contents_of_variable t v in
   OpamConsole.msg "%s\n" (OpamVariable.string_of_variable_contents contents)
 
 let setup user global =

src/state/opamState.ml

@@ -944,6 +944,32 @@ let consistent_available_field t opam =
   OpamFilter.eval_to_bool ~default:false (filter_env ~opam t)
     (OpamFile.OPAM.available opam)
 
+let quick_var_lookup v =
+  if OpamVariable.Full.is_global v then (
+    let var = OpamVariable.Full.variable v in
+    let root = OpamStateConfig.(!r.root_dir) in
+    let switch = OpamStateConfig.(!r.current_switch) in
+    let config_f = OpamPath.Switch.global_config root switch in
+    let config = OpamFile.Dot_config.read config_f in
+    match get_env_var v with
+    | Some _ as c -> c
+    | None ->
+      if OpamVariable.to_string var = "switch" then
+        Some (S (OpamSwitch.to_string switch))
+      else
+        OpamFile.Dot_config.variable config var
+  ) else
+    None
+
+let contents_of_variable t v =
+  log "config-variable";
+  match quick_var_lookup v with
+  | Some c -> c
+  | None   ->
+    let env = filter_env (Lazy.force t) in
+    let default = S "#undefined" in
+    OpamFilter.ident_value env ~default (OpamFilter.ident_of_var v)
+
 (* List the packages which do fulfil the compiler and OS constraints *)
 let available_packages t =
   let filter nv =

src/state/opamState.mli

@@ -165,6 +165,12 @@ val filter_env:
   ?local_variables:((variable_contents option) OpamVariable.Map.t) ->
   state -> full_variable -> variable_contents option
 
+(** [contents_of_variable t v] resolves the variable [v] using the
+    (lazy) state [t]. First check in the environment for overwrites,
+    then use an heuristic to avoid read the global state and then use
+    {!filter_env}. Return ["#undefined"] if [v] is not defined.*)
+val contents_of_variable: state Lazy.t -> full_variable -> variable_contents
+
 (** {2 Helpers} *)
 
 (** Return the OPAM file for the given package *)