docs: Fix Python package dependencies for sphinx

The docs build was depending on the top level "python.install" that
pip installs all Pigweed python packages. This CL removes that and
insteads adds them to python_deps. This will improve build times
slightly and remove the dependency on having a bootstrapped
environment working to run the docs build.

Change-Id: I08e85a81531faa40f46b09b48414e8799731c426
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/215852
Commit-Queue: Anthony DiGirolamo <tonymd@google.com>
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
Reviewed-by: Wyatt Hepler <hepler@google.com>

docs/BUILD.gn

@@ -356,10 +356,10 @@ pw_doc_gen("docs") {
     ":third_party_docs",
     "$dir_pigweed/kudzu:docs",
     "$dir_pigweed/seed:seeds",
-    "$dir_pw_env_setup:python.install",
   ]
 
-  # Required to set the PYTHONPATH so automodule, autoclass or autofunction RST
-  # directives work.
-  python_metadata_deps = [ "$dir_pw_env_setup:core_pigweed_python_packages" ]
+  # Extra Python deps are required to set the PYTHONPATH so
+  # automodule, autoclass or autofunction RST directives work in
+  # sphinx.
+  python_deps = [ "$dir_pw_env_setup:core_pigweed_python_packages" ]
 }

pw_docgen/docs.gni

@@ -77,10 +77,17 @@ template("pw_doc_group") {
 #
 # Args:
 #   deps: List of pw_doc_group targets.
-#   python_metadata_deps: Python-related dependencies that are only used as deps
-#                         for generating Python package metadata list, not the
-#                         overall documentation generation. This should rarely
-#                         be used by non-Pigweed code.
+#   python_deps: Additional Python package dependencies that must be
+#                fully built before sphinx can run. This will set the
+#                PYTHONPATH when sphinx is run so automodule,
+#                autoclass or autofunction RST directives work for
+#                in-tree pw_python_package targets.
+#   python_metadata_deps: Python-related dependencies that are only
+#                         used as deps for generating Python package
+#                         metadata list, not the overall documentation
+#                         generation. This only modifies PYTHONPATH so
+#                         sphinx can import in-tree Python files. This
+#                         should rarely be used by non-Pigweed code.
 #   sources: Top-level documentation .rst source files.
 #   conf: Configuration script (conf.py) for Sphinx.
 #   output_directory: Path to directory to which HTML output is rendered.
@@ -148,8 +155,16 @@ template("pw_doc_gen") {
       python_deps = [ "$dir_pw_docgen/py" ]
       deps = [ ":$_metadata_file_target" ]
 
-      # Required to set the PYTHONPATH for any automodule/class/function RST
-      # directives.
+      # Additional Python deps that may be required for sphinx to run
+      # successfully. These deps will be fully built.
+      if (defined(invoker.python_deps)) {
+        python_deps += invoker.python_deps
+      }
+
+      # Required to set the PYTHONPATH for any automodule, autoclass,
+      # and autofunction RST directives. These deps will have their
+      # in-tree directories added to PYTHONPATH only. They will not be
+      # generated or built in the out directory first.
       python_metadata_deps = [ "$dir_pw_docgen/py" ]
       if (defined(invoker.python_metadata_deps)) {
         python_metadata_deps += invoker.python_metadata_deps

pw_metric/py/BUILD.gn

@@ -31,6 +31,7 @@ pw_python_package("py") {
   python_deps = [
     "$dir_pw_rpc/py",
     "$dir_pw_tokenizer/py",
+    "..:metric_service_proto.python",
   ]
   python_test_deps = [ "$dir_pw_metric:metric_service_proto.python" ]
   pylintrc = "$dir_pigweed/.pylintrc"