use 'opam --version' to get the opam version (instead of reading env)

Author: samoht

.travis-docker.sh

@@ -5,7 +5,7 @@ echo -en "travis_fold:start:prepare.ci\r"
 default_user=ocaml
 default_branch=master
 default_hub_user=ocaml
-default_opam_version=1.2.0
+default_opam_version=2.0.0
 
 fork_user=${FORK_USER:-$default_user}
 fork_branch=${FORK_BRANCH:-$default_branch}

src/ci_opam.ml

@@ -61,7 +61,12 @@ let revdep_run = list (getenv_default "REVDEPS" "")
 let opam_lint = fuzzy_bool_of_string (getenv_default "OPAM_LINT" "true")
 
 (* opam version *)
-let opam_version = getenv_default "OPAM_VERSION" "2.0.0"
+let opam_version =
+  let raw = ?|> "opam --version" in
+  match if String.length raw <= 1 then '?' else raw.[0] with
+  | '2' -> `V2
+  | '1' -> `V1
+  | _   -> failwith (raw ^ ": invalid opam version")
 
 (* other variables *)
 let extra_deps = list (getenv_default "EXTRA_DEPS" "")
@@ -252,8 +257,8 @@ with_fold "Prepare" (fun () ->
     in
 
     (if opam_lint then match opam_version with
-        | "2.0.0" -> ?|~ "opam lint %s --warn=-21-32-48" opam
-        | _       -> ?|~ "opam lint %s" opam);
+        | `V2 -> ?|~ "opam lint %s --warn=-21-32-48" opam
+        | _   -> ?|~ "opam lint %s" opam);
     let pins = lint_pins pkg pins in
     List.iter pin pins;
     ?|  "eval $(opam config env)";