feat: add flag for gapic metadata (#795)

As per the design doc, gapic metadata should not be generated by
default, and should be gated by the 'metadata' flag.

When invoking the generator via protoc, toggle the metadata flag like so:
--python_gapic_opt="metadata"

Subsequent Bazel integration is WIP.

gapic/generator/generator.py

@@ -105,11 +105,12 @@ def get_response(
                     template_name, api_schema=api_schema, opts=opts)
             )
 
-        output_files.update(
-            self._generate_samples_and_manifest(
-                api_schema, self._env.get_template(sample_templates[0]),
-            )
-        )
+        sample_output = self._generate_samples_and_manifest(
+            api_schema,
+            self._env.get_template(sample_templates[0]),
+        ) if sample_templates else {}
+
+        output_files.update(sample_output)
 
         # Return the CodeGeneratorResponse output.
         res = CodeGeneratorResponse(
@@ -233,6 +234,10 @@ def _render_template(
         answer: Dict[str, CodeGeneratorResponse.File] = OrderedDict()
         skip_subpackages = False
 
+        # Very, very special case. This flag exists to gate this one file.
+        if not opts.metadata and template_name.endswith("gapic_metadata.json.j2"):
+            return answer
+
         # Sanity check: Rendering per service and per proto would be a
         # combinatorial explosion and is almost certainly not what anyone
         # ever wants. Error colorfully on it.

gapic/utils/options.py

@@ -41,20 +41,22 @@ class Options:
     lazy_import: bool = False
     old_naming: bool = False
     add_iam_methods: bool = False
+    metadata: bool = False
     # TODO(yon-mg): should there be an enum for transport type?
     transport: List[str] = dataclasses.field(default_factory=lambda: [])
 
     # Class constants
     PYTHON_GAPIC_PREFIX: str = 'python-gapic-'
     OPT_FLAGS: FrozenSet[str] = frozenset((
+        'add-iam-methods',      # microgenerator implementation for `reroute_to_grpc_interface`
+        'lazy-import',          # requires >= 3.7
+        'metadata',             # generate GAPIC metadata JSON file
         'old-naming',           # TODO(dovs): Come up with a better comment
         'retry-config',         # takes a path
         'samples',              # output dir
-        'lazy-import',          # requires >= 3.7
-        'add-iam-methods',      # microgenerator implementation for `reroute_to_grpc_interface`
         # transport type(s) delineated by '+' (i.e. grpc, rest, custom.[something], etc?)
         'transport',
-        'warehouse-package-name'  # change the package name on PyPI
+        'warehouse-package-name',  # change the package name on PyPI
     ))
 
     @classmethod
@@ -143,6 +145,7 @@ def tweak_path(p):
             lazy_import=bool(opts.pop('lazy-import', False)),
             old_naming=bool(opts.pop('old-naming', False)),
             add_iam_methods=bool(opts.pop('add-iam-methods', False)),
+            metadata=bool(opts.pop('metadata', False)),
             # transport should include desired transports delimited by '+', e.g. transport='grpc+rest'
             transport=opts.pop('transport', ['grpc'])[0].split('+')
         )

tests/unit/generator/test_generator.py

@@ -116,6 +116,22 @@ def test_get_response_fails_invalid_file_paths():
         assert "%proto" in ex_str and "%service" in ex_str
 
 
+def test_get_response_ignore_gapic_metadata():
+    g = make_generator()
+    with mock.patch.object(jinja2.FileSystemLoader, "list_templates") as lt:
+        lt.return_value = ["gapic/gapic_metadata.json.j2"]
+        with mock.patch.object(jinja2.Environment, "get_template") as gt:
+            gt.return_value = jinja2.Template(
+                "This is not something we want to see")
+            res = g.get_response(
+                api_schema=make_api(),
+                opts=Options.build(""),
+            )
+
+            # We don't expect any files because opts.metadata is not set.
+            assert res.file == CodeGeneratorResponse().file
+
+
 def test_get_response_ignores_unwanted_transports_and_clients():
     g = make_generator()
     with mock.patch.object(jinja2.FileSystemLoader, "list_templates") as lt:

tests/unit/generator/test_options.py

@@ -14,6 +14,7 @@
 
 import os
 import pytest
+import re
 from unittest import mock
 import warnings
 
@@ -139,21 +140,24 @@ def test_options_service_config(fs):
     assert opts.retry == expected_cfg
 
 
-def test_options_lazy_import():
-    opts = Options.build('lazy-import')
-    assert opts.lazy_import
-
-
-def test_options_old_naming():
-    opts = Options.build('old-naming')
-    assert opts.old_naming
-
-
-def test_options_add_iam_methods():
-    opts = Options.build('add-iam-methods')
-    assert opts.add_iam_methods
-
-
-def test_options_warehouse_package_name():
-    opts = Options.build('warehouse-package-name')
-    assert opts.warehouse_package_name
+def test_options_bool_flags():
+    # All these options are default False.
+    # If new options violate this assumption,
+    # this test may need to be tweaked.
+    # New options should follow the dash-case/snake_case convention.
+    opt_str_to_attr_name = {
+        name: re.sub(r"-", "_", name)
+        for name in
+        ["lazy-import",
+         "old-naming",
+         "add-iam-methods",
+         "metadata",
+         "warehouse-package-name",
+         ]}
+
+    for opt, attr in opt_str_to_attr_name.items():
+        options = Options.build("")
+        assert not getattr(options, attr)
+
+        options = Options.build(opt)
+        assert getattr(options, attr)