Disable implicit nixpkgs config file

WORKSPACE

@@ -36,7 +36,7 @@ nixpkgs_package(
 
 nixpkgs_package(
     name = "expr-test",
-    nix_file_content = "let pkgs = import <nixpkgs> {}; in pkgs.hello",
+    nix_file_content = "let pkgs = import <nixpkgs> { config = {}; }; in pkgs.hello",
     # Deliberately not @nixpkgs, to test whether explict file works.
     repositories = {"nixpkgs": "//:nixpkgs.nix"},
 )
@@ -50,7 +50,7 @@ nixpkgs_package(
 nixpkgs_package(
     name = "expr-attribute-test",
     attribute_path = "hello",
-    nix_file_content = "import <nixpkgs> {}",
+    nix_file_content = "import <nixpkgs> { config = {}; }",
     repository = "@nixpkgs",
 )
 
@@ -77,7 +77,7 @@ nixpkgs_package(
 nixpkgs_package(
     name = "extra-args-test",
     nix_file_content = """
-{ packagePath }: (import <nixpkgs> {}).${packagePath}
+{ packagePath }: (import <nixpkgs> { config = {}; }).${packagePath}
     """,
     repository = "@nixpkgs",
     nixopts = ["--argstr", "packagePath", "hello"],

nixpkgs/nixpkgs.bzl

@@ -97,7 +97,7 @@ def _nixpkgs_package_impl(repository_ctx):
     elif not repositories:
         fail(strFailureImplicitNixpkgs)
     else:
-        expr_args = ["-E", "import <nixpkgs> {}"]
+        expr_args = ["-E", "import <nixpkgs> { config = {}; }"]
 
     _symlink_nix_file_deps(repository_ctx, repository_ctx.attr.nix_file_deps)
 
@@ -185,11 +185,9 @@ def _nixpkgs_package_impl(repository_ctx):
                 # We ignore some files:
                 # - Anything in /nix/store, they are not explicit dependencies are are supposed to be immutable
                 # - Anything from .cache/bazel, only case I encountered was a local nixpkgs clone handled by bazel
-                # - .config/nixpkgs. user configuration should not impact the reproducibility of the build
                 if (
                    not line[2].startswith("'/nix/store")
                    and ".cache/bazel" not in line[2]
-                   and ".config/nixpkgs" not in line[2]
                 ):
                     filename = line[2][1:-1] # trimming quotes
 
@@ -241,6 +239,9 @@ nix_file_deps = [
     "{deps_listing}",
 ]
 
+Note: if it points to the nixpkgs global configuration file, such as ~/.config/nixpkgs/config.nix. You must force nixpkgs to not use the local configuration, by providing a `config` argument to your nixpkgs import, such as:
+
+import (nixpkgs_path) {{ config = {{}}; }};
 """.format(repo_name = repository_ctx.name,
            deps_listing = '",\n    "'.join(deps_minus_declared_deps.keys())))
 
@@ -371,7 +372,7 @@ def nixpkgs_cc_configure(
     """
     if not nix_file and not nix_file_content:
         nix_file_content = """
-          with import <nixpkgs> {}; buildEnv {
+          with import <nixpkgs> { config = {}; }; buildEnv {
             name = "bazel-cc-toolchain";
             paths = [ stdenv.cc binutils ];
           }

shell.nix

@@ -1,4 +1,4 @@
-{ pkgs ? import ./nixpkgs.nix {} }:
+{ pkgs ? import ./nixpkgs.nix { config = {}; } }:
 
 with pkgs;
 

tests/hello.nix

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

tests/nixpkgs.nix

@@ -1 +1 @@
-import <nixpkgs> {}
+import <nixpkgs> { config = {}; }

tests/output.nix

@@ -1,4 +1,4 @@
-with import <nixpkgs> {};
+with import <nixpkgs> { config = {}; };
 
 runCommand "some-output" {
   preferLocalBuild = true;