Merge pull request #179 from layus/no-registration

Make toolchain registration optional

CHANGELOG.md

@@ -8,6 +8,12 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/).
 
 [Unreleased]: https://github.com/tweag/rules_nixpkgs/compare/v0.8.0...HEAD
 
+### Added
+
+- nixpkgs_cc_configure gained a flag to disable automatic registration of the
+  toolchain it creates.
+  See [#179][#179]
+
 ## [0.8.0] - 2021-02-11
 
 [0.8.0]: https://github.com/tweag/rules_nixpkgs/compare/v0.7.0...v0.8.0

README.md

@@ -239,7 +239,7 @@ Dependencies of `nix_file` if any.
 <pre>
 nixpkgs_cc_configure(<a href="#nixpkgs_cc_configure-name">name</a>, <a href="#nixpkgs_cc_configure-attribute_path">attribute_path</a>, <a href="#nixpkgs_cc_configure-nix_file">nix_file</a>, <a href="#nixpkgs_cc_configure-nix_file_content">nix_file_content</a>, <a href="#nixpkgs_cc_configure-nix_file_deps">nix_file_deps</a>, <a href="#nixpkgs_cc_configure-repositories">repositories</a>,
                      <a href="#nixpkgs_cc_configure-repository">repository</a>, <a href="#nixpkgs_cc_configure-nixopts">nixopts</a>, <a href="#nixpkgs_cc_configure-quiet">quiet</a>, <a href="#nixpkgs_cc_configure-fail_not_supported">fail_not_supported</a>, <a href="#nixpkgs_cc_configure-exec_constraints">exec_constraints</a>,
-                     <a href="#nixpkgs_cc_configure-target_constraints">target_constraints</a>)
+                     <a href="#nixpkgs_cc_configure-target_constraints">target_constraints</a>, <a href="#nixpkgs_cc_configure-register">register</a>)
 </pre>
 
 Use a CC toolchain from Nixpkgs. No-op if not a nix-based platform.
@@ -429,6 +429,20 @@ default is <code>None</code>
 
 Constraints for the target platform.
 
+</p>
+</td>
+</tr>
+<tr id="nixpkgs_cc_configure-register">
+<td><code>register</code></td>
+<td>
+
+optional.
+default is <code>True</code>
+
+<p>
+
+bool, enabled by default, Whether to register (with `register_toolchains`) the generated toolchain and install it as the default cc_toolchain.
+
 </p>
 </td>
 </tr>

nixpkgs/nixpkgs.bzl

@@ -622,7 +622,8 @@ def nixpkgs_cc_configure(
         quiet = False,
         fail_not_supported = True,
         exec_constraints = None,
-        target_constraints = None):
+        target_constraints = None,
+        register = True):
     """Use a CC toolchain from Nixpkgs. No-op if not a nix-based platform.
 
     By default, Bazel auto-configures a CC toolchain from commands (e.g.
@@ -653,6 +654,7 @@ def nixpkgs_cc_configure(
       fail_not_supported: bool, Whether to fail if `nix-build` is not available.
       exec_constraints: Constraints for the execution platform.
       target_constraints: Constraints for the target platform.
+      register: bool, enabled by default, Whether to register (with `register_toolchains`) the generated toolchain and install it as the default cc_toolchain.
     """
 
     nixopts = list(nixopts)
@@ -727,12 +729,13 @@ def nixpkgs_cc_configure(
         target_constraints = target_constraints,
     )
 
-    maybe(
-        native.bind,
-        name = "cc_toolchain",
-        actual = "@{}//:toolchain".format(name),
-    )
-    native.register_toolchains("@{}_toolchains//:all".format(name))
+    if register:
+        maybe(
+            native.bind,
+            name = "cc_toolchain",
+            actual = "@{}//:toolchain".format(name),
+        )
+        native.register_toolchains("@{}_toolchains//:all".format(name))
 
 def _readlink(repository_ctx, path):
     return repository_ctx.path(path).realpath