Merge pull request #18 from tweag/gb/cache_nixpkgs_package

Introduce a `data` attribute to `nixpkgs_package`

Author: mboes

README.md

@@ -81,8 +81,10 @@ nixpkgs_git_repository(name, revision)
 Make the content of a Nixpkgs package available in the Bazel workspace.
 
 ```bzl
-nixpkgs_package(name, attribute_path, nix_file, nix_file_content,
-                path, repository, build_file, build_file_content)
+nixpkgs_package(
+    name, attribute_path, nix_file, nix_file_deps, nix_file_content,
+    path, repository, build_file, build_file_content,
+)
 ```
 
 If neither `repository` or `path` are specified, `<nixpkgs>` is
@@ -123,6 +125,13 @@ recommended. The two are mutually exclusive.
         <p>A file containing an expression for a Nix derivation.</p>
       </td>
     </tr>
+    <tr>
+      <td><code>nix_file_deps</code></td>
+      <td>
+        <p><code>List of labels; optional</code></p>
+        <p>Dependencies of `nix_file` if any.</p>
+      </td>
+    </tr>
     <tr>
       <td><code>nix_file_content</code></td>
       <td>

WORKSPACE

@@ -36,3 +36,11 @@ nixpkgs_package(
   attribute_path = "hello",
   repository = "@nixpkgs",
 )
+
+nixpkgs_package(
+  name = "nix-file-deps-test",
+  nix_file = "//tests:hello.nix",
+  nix_file_deps = ["//tests:pkgname.nix"],
+  repository = "@nixpkgs",
+)
+

nixpkgs/nixpkgs.bzl

@@ -37,6 +37,13 @@ def _nixpkgs_package_impl(ctx):
   else:
     expr_args = ["-E", "import <nixpkgs> {}"]
 
+  # Introduce an artificial dependency with a bogus name on each of
+  # the nix_file_deps.
+  for dep in ctx.attr.nix_file_deps:
+    components = [c for c in [dep.workspace_root, dep.package, dep.name] if c]
+    link = '/'.join(components).replace('_', '_U').replace('/', '_S')
+    ctx.symlink(dep, link)
+
   expr_args.extend([
     "-A", ctx.attr.attribute_path
           if ctx.attr.nix_file or ctx.attr.nix_file_content
@@ -98,6 +105,7 @@ nixpkgs_package = repository_rule(
   attrs = {
     "attribute_path": attr.string(),
     "nix_file": attr.label(allow_single_file = [".nix"]),
+    "nix_file_deps": attr.label_list(),
     "nix_file_content": attr.string(),
     "path": attr.string(),
     "repository": attr.label(),

tests/BUILD

@@ -12,4 +12,5 @@ package(default_testonly = 1)
     "attribute-test",
     "expr-attribute-test",
     "nix-file-test",
+    "nix-file-deps-test",
 ]]

tests/hello.nix

@@ -0,0 +1,3 @@
+with import ./pkgname.nix;
+let pkgs = import <nixpkgs> {}; in builtins.getAttr pkgname pkgs
+

tests/pkgname.nix

@@ -0,0 +1 @@
+{ pkgname = "hello"; }