feat(mypy): centralize mypy.ini and update templates

> [!note]
> This is step one of a multi-step process. The work done here is outlined below.
Additional steps (to be completed in other PRs) include:
> * generate the **generated packages**
> * generate and/or post process **hybrid packages**

This work:
* Adds a centralized `mypy.ini` file at the root of the repository.
* Updates GAPIC generator templates to omit local `mypy.ini` and dynamically resolve the root config via a `MYPY_CONFIG_FILE` constant.

> [!note]
> Work on strictly handwritten libraries is outside the scope of this PR and can be found here: #17409

Author: chalmerlowe

mypy.ini

@@ -0,0 +1,100 @@
+[mypy]
+namespace_packages = True
+ignore_missing_imports = False
+
+# Helps mypy navigate the "google" namespace more reliably in 3.10+
+explicit_package_bases = True
+
+# Performance: reuse results from previous runs to speed up "nox"
+incremental = True
+
+exclude = (?x)(
+    (^|/)third_party/
+  | (^|/)tests/unit/resources/
+  | (^|/)tests/unit/gapic/
+  )
+
+
+# ==============================================================================
+# GLOBAL THIRD-PARTY & SHARED LIBRARY IGNORES
+# ==============================================================================
+
+[mypy-anywidget]
+ignore_missing_imports = True
+
+[mypy-cloudpickle.*]
+ignore_missing_imports = True
+
+[mypy-flask]
+ignore_missing_imports = True
+
+[mypy-google.auth.*]
+ignore_missing_imports = True
+
+[mypy-google.cloud.bigtable]
+ignore_missing_imports = True
+
+[mypy-google.cloud.pubsub]
+ignore_missing_imports = True
+
+[mypy-google.colab]
+ignore_missing_imports = True
+
+[mypy-google.iam.*]
+ignore_missing_imports = True
+
+[mypy-google.longrunning.*]
+ignore_missing_imports = True
+
+[mypy-google.oauth2.*]
+ignore_missing_imports = True
+
+[mypy-google.protobuf.*]
+ignore_missing_imports = True
+
+[mypy-google.rpc.*]
+ignore_missing_imports = True
+
+[mypy-google.type.*]
+ignore_missing_imports = True
+
+[mypy-grpc.*]
+ignore_missing_imports = True
+
+[mypy-ibis.*]
+ignore_missing_imports = True
+
+[mypy-ipywidgets]
+ignore_missing_imports = True
+
+[mypy-proto.*]
+ignore_missing_imports = True
+
+[mypy-pyarrow.*]
+ignore_missing_imports = True
+
+[mypy-pydata_google_auth]
+ignore_missing_imports = True
+
+[mypy-pytest]
+ignore_missing_imports = True
+
+[mypy-pytz]
+ignore_missing_imports = True
+
+
+# ==============================================================================
+# PACKAGE-SPECIFIC OVERRIDES & EXCEPTIONS
+# ==============================================================================
+
+# --- google-cloud-bigtable ---
+[mypy-google.cloud.bigtable.*]
+ignore_errors = True
+
+[mypy-google.cloud.bigtable.data.*]
+check_untyped_defs = True
+warn_unreachable = True
+disallow_any_generics = True
+ignore_errors = False
+
+

packages/gapic-generator/gapic/ads-templates/mypy.ini.j2

@@ -3,9 +3,13 @@
 {% block content %}
 
 import os
+import pathlib
 
 import nox  # type: ignore
 
+CURRENT_DIRECTORY = pathlib.Path(__file__).parent.absolute()
+MYPY_CONFIG_FILE = str(CURRENT_DIRECTORY.parent.parent / "mypy.ini")
+
 
 # TODO(https://github.com/googleapis/gapic-generator-python/issues/2450):
 # Add tests for Python 3.15 alpha1
@@ -44,6 +48,7 @@ def mypy(session):
     session.install('.')
     session.run(
         'mypy',
+        f"--config-file={MYPY_CONFIG_FILE}",
         {% if api.naming.module_namespace %}
         '{{ api.naming.module_namespace[0] }}',
         {% else %}

packages/gapic-generator/gapic/ads-templates/noxfile.py.j2

@@ -40,6 +40,8 @@ DEFAULT_PYTHON_VERSION = "3.14"
 PREVIEW_PYTHON_VERSION = "3.14"
 
 CURRENT_DIRECTORY = pathlib.Path(__file__).parent.absolute()
+# Path to the centralized mypy configuration file at the repository root.
+MYPY_CONFIG_FILE = str(CURRENT_DIRECTORY.parent.parent / "mypy.ini")
 
 LOWER_BOUND_CONSTRAINTS_FILE = CURRENT_DIRECTORY / "constraints.txt"
 PACKAGE_NAME = "{{ api.naming.warehouse_package_name }}"
@@ -96,6 +98,7 @@ def mypy(session):
     session.install(".")
     session.run(
         "mypy",
+        f"--config-file={MYPY_CONFIG_FILE}",
         "-p",
         {% if api.naming.module_namespace %}
         "{{ api.naming.module_namespace[0] }}",

packages/gapic-generator/gapic/templates/mypy.ini.j2

@@ -114,8 +114,9 @@ def _overwrite_golden_impl(ctx):
     golden_update_script_content = """
     cd ${{BUILD_WORKSPACE_DIRECTORY}}
     # Filename pattern-based removal is needed to preserve the BUILD.bazel file.
-    find tests/integration/goldens/{api_name}/ -name \\*.py-type f -delete
+    find tests/integration/goldens/{api_name}/ -name \\*.py -type f -delete
     find tests/integration/goldens/{api_name}/ -name \\*.json -type f -delete
+    find tests/integration/goldens/{api_name}/ -name \\*.ini -type f -delete
     unzip -ao {goldens_output_zip} -d tests/integration/goldens/{api_name}
     """.format(
         goldens_output_zip = goldens_output_zip.path,

packages/gapic-generator/gapic/templates/noxfile.py.j2

@@ -47,6 +47,8 @@
 PREVIEW_PYTHON_VERSION = "3.14"
 
 CURRENT_DIRECTORY = pathlib.Path(__file__).parent.absolute()
+# Path to the centralized mypy configuration file at the repository root.
+MYPY_CONFIG_FILE = str(CURRENT_DIRECTORY.parent.parent / "mypy.ini")
 
 LOWER_BOUND_CONSTRAINTS_FILE = CURRENT_DIRECTORY / "constraints.txt"
 PACKAGE_NAME = "google-cloud-asset"
@@ -103,6 +105,7 @@ def mypy(session):
     session.install(".")
     session.run(
         "mypy",
+        f"--config-file={MYPY_CONFIG_FILE}",
         "-p",
         "google",
         "--check-untyped-defs",

packages/gapic-generator/rules_python_gapic/test/integration_test.bzl

@@ -47,6 +47,8 @@
 PREVIEW_PYTHON_VERSION = "3.14"
 
 CURRENT_DIRECTORY = pathlib.Path(__file__).parent.absolute()
+# Path to the centralized mypy configuration file at the repository root.
+MYPY_CONFIG_FILE = str(CURRENT_DIRECTORY.parent.parent / "mypy.ini")
 
 LOWER_BOUND_CONSTRAINTS_FILE = CURRENT_DIRECTORY / "constraints.txt"
 PACKAGE_NAME = "google-iam-credentials"
@@ -103,6 +105,7 @@ def mypy(session):
     session.install(".")
     session.run(
         "mypy",
+        f"--config-file={MYPY_CONFIG_FILE}",
         "-p",
         "google",
         "--check-untyped-defs",