rdeps-and-dev-dependencies

blog/2026-03-12-rdeps-and-dev-dependencies.md

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+---
+slug: rdeps-and-bazel-dev-dependencies
+title: Rdeps and Bazel Development Dependencies
+authors: nils
+tags: [bazel, buildozer]
+---
+
+# Rdeps and Bazel Development Dependencies
+
+## Google test wants to build with cpp17
+
+When reviving an old module that used to build googletest I encountered this error.
+Likely because I somehow lost the features setup for the code.
+
+```
+ERROR: /home/nils/gits/repo/rule/cc/test/BUILD.bazel:53:8: Compiling rule/cc/test/library_test.cpp failed: (Exit 1): gcc failed: error executing CppCompile command (from target //rule/cc/test:test_binary) external/+gcc+gcc_9.4.0_x86_64_linux_toolchain/usr/bin/gcc @bazel-out/k8-fastbuild/bin/rule/cc/test/_objs/test_binary/library_test.pic.o.params
+Remote server execution message: Action details (uncached result): https://buildbarn.example.com/browser/blobs/sha256/historical_execute_response/68a13e98d2231c8055b662fdf84735a648d5c2b074551571b41cccdd70d98f80-1309/
+In file included from external/googletest+/googletest/include/gtest/gtest-message.h:57,
+                 from external/googletest+/googletest/include/gtest/gtest-assertion-result.h:46,
+                 from external/googletest+/googletest/include/gtest/gtest.h:63,
+                 from rule/cc/test/library_test.cpp:16:
+external/googletest+/googletest/include/gtest/internal/gtest-port.h:273:2: error: #error C++ versions l
+ess than C++17 are not supported.
+  273 | #error C++ versions less than C++17 are not supported.
+      |  ^~~~~
+In file included from external/googletest+/googletest/include/gtest/gtest.h:67,
+                 from external/googletest+/googletest/src/gtest.cc:33:
+external/googletest+/googletest/include/gtest/gtest-param-test.h:483:56: error: missing template argume
+nts before '(' token
+  483 |           typename StdFunction = decltype(std::function(std::declval<Func>()))>
+      |                                                        ^
+external/googletest+/googletest/include/gtest/gtest-param-test.h:493:56: error: missing template argume
+nts before '(' token
+  493 |           typename StdFunction = decltype(std::function(std::declval<Func>()))>
+      |                                                        ^
+```
+
+While this is a run-of-the-mill error when reviving a project
+I wanted to take this opportunity to give `rdeps` and `buildozer` a spin.
+So I wouldn't have to update the BUILD files myself.
+
+## Patch googletest to use c++17 for its compilation
+
+For this example I don't pay much attention to mixing standards in one compilation.
+We should seek to make 17 the default for the entire code base.
+
+```
++single_version_override(
++    module_name = "googletest",
++    patch_cmds = [
++        """echo 'repo(features = ["-c++14", "c++17"])' > REPO.bazel"""
++    ],
++)
+```
+
+## Rdeps and Buildozer
+
+Next we must use the header, which carries the `#error`.
+So we want to update all users in our repo
+to use c++17 instead of c++14.
+
+Find all targets in the code that directly depend on googletest stuff:
+
+  $ bazel query 'rdeps(//..., @googletest//..., 1) intersect //...'
+
+Then send that to `buildozer`:
+
+  $ buildozer 'add features -c++14 c++17'
+
+## Rdeps does not work in the absence of dev dependencies
+
+```
+$ bazel query 'rdeps(//..., @googletest//..., 1) intersect //...'
+Starting local Bazel server (8.5.0) and connecting to it...
+ERROR: error loading package under directory '': error loading package '@@googletest+//googlemock/test': Unable to find package for @@[unknown repo 'rules_python' requested from @@googletest+]//python:defs.bzl: The repository '@@[unknown repo 'rules_python' requested from @@googletest+]' could not be resolved: No repository visible as '@rules_python' from repository '@@googletest+'.
+```
+
+As `rules_python` is a dev dependency
+we cannot use it from a consuming module:
+
+```
+$ bazel mod deps googletest
+<root> (rules_vcc@_)
+└───googletest@1.17.0.bcr.2
+    ├───abseil-cpp@20240116.2
+    │   └───googletest@1.17.0.bcr.2 (cycle)
+    ├───platforms@1.0.0
+    ├───re2@2025-08-12.bcr.1
+    └───rules_cc@0.2.16
+```
+
+## Patch the module file?
+
+Will not work, as this is governed by the module file in the registry:
+```
+single_version_override(
+    module_name = "googletest",
+    patch_cmds = [
+        "sed -i '/dev_dependency = "True"/d' MODULE.bazel
+    ],
+)
+```
+
+## If you have your own registry you can patch it there:
+
+We do have our own registry in our monorepo
+so I can patch it there,
+notice that this is not a patch file that is applied to the MODULE file,
+but a change of the MODULE file itself.
+
+```
+bazel_central_registry $ sed -i '/dev_dependency = True/d' registries/bcr.bazel.build/modules/googletest/1.17.0.bcr.2/MODULE.bazel
+```
+
+## Shut down Bazel to pick up the change
+
+When working with your own registry one must shut down Bazel between edits
+for the module dependency data to be updated.
+
+```
+$ bazel shutdown
+$ bazel query 'rdeps(//..., @googletest//..., 1) intersect //...'
+//rule/cc:runfiles_helper
+//rule/cc/test:test_binary
+//rule/cc/test:test_cc_legacy_shared
+```
+
+## An experimental flag to follow dev dependencies in query?
+
+It would be great if query had a flag to follow all dev dependencies.
+To make queries like this possible,
+the cost of downloading more modules than strictly necessary for a build
+is warranted by enabling Bazel's powerful query system.
+Which otherwise sadly does not work for modules with dev dependencies.