check if reason is installed before checking for rebuild

Summary: This gives a better error message when `rebuild` is missing.

Reviewed By: jberdine

Differential Revision: D3528761

fbshipit-source-id: b5be810

configure.ac

@@ -183,8 +183,6 @@ AC_PROG_OCAMLLEX
 AC_ASSERT_PROG([ocamllex], [$OCAMLLEX])
 AC_PROG_OCAMLYACC
 AC_ASSERT_PROG([ocamlyacc], [$OCAMLYACC])
-AC_CHECK_TOOL([REBUILD], [rebuild], [no])
-AC_ASSERT_PROG([rebuild], [$REBUILD])
 AC_ASSERT_OCAML_PKG([atdgen], [], [1.6.0])
 AC_ASSERT_OCAML_PKG([biniou])
 AC_ASSERT_OCAML_PKG([camlzip], [zip])
@@ -193,6 +191,10 @@ AC_ASSERT_OCAML_PKG([extlib], [], [1.5.4])
 AC_ASSERT_OCAML_PKG([oUnit], [], [2.0.0])
 AC_ASSERT_OCAML_PKG([reason])
 AC_ASSERT_OCAML_PKG([yojson])
+# check for rebuild after checking for Reason since `rebuild` is normally provided by Reason. This
+# way if Reason is missing we get a more helpful error message and not "rebuild not found".
+AC_CHECK_TOOL([REBUILD], [rebuild], [no])
+AC_ASSERT_PROG([rebuild], [$REBUILD])
 
 if test "x$enable_java_analyzers" = "xyes"; then
   AC_CHECK_TOOL([JAVA], [java], [no])

m4/ac_assert_ocaml_pkg.m4

@@ -30,12 +30,12 @@ AC_DEFUN([AC_ASSERT_OCAML_PKG],
     has_pkg=$AS_TR_SH[OCAML_PKG_$1]
     pkg=$1
     version=
-    AS_IF([test "x$3" = "x"], [dnl
+    AS_IF([test "x$3" != "x"], [dnl
       version=" version $3"
     ])
   ])
   AS_IF([test "$has_pkg" = "no"], [dnl
-    AC_MSG_ERROR([missing dependency: $pkg$version.
+    AC_MSG_ERROR([missing OCaml dependency: $pkg$version
 
 If you are using opam, please run