pin-depends: support proper version constraints

Fixes #13

Author: balsoft

src/opam.nix

@@ -404,7 +404,12 @@ in rec {
             // {
               inherit url;
             };
-          repo = filterOpamRepo { ${name} = null; } (makeOpamRepo path);
+          repo = (filterOpamRepo { ${name} = null; } (makeOpamRepo path)).overrideAttrs (oa: {
+            # Move the package to the proper version
+            buildCommand = oa.buildCommand + ''
+              mv "packages/${name}/$(ls "packages/${name}" | head -1)" "packages/${name}/${name}.${version}"
+            '';
+          });
         in if !hasRev && !isImpure then
           lib.warn
           "pin-depends without an explicit sha1 is not supported in pure evaluation mode; try with --impure"