feat(mypy): centralize mypy.ini and update templates (#17523)

> [!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

Partially resolves: #17322 🦕

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 +3,17 @@
 {% block content %}
 
 import os
+import pathlib
 
 import nox  # type: ignore
 
+CURRENT_DIRECTORY = pathlib.Path(__file__).parent.absolute()
+# Search upwards to support running nox from both monorepo packages and integration test goldens.
+MYPY_CONFIG_FILE = next(
+    (str(p / "mypy.ini") for p in CURRENT_DIRECTORY.parents if (p / "mypy.ini").exists()),
+    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 +52,7 @@ 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

@@ -38,6 +38,12 @@ DEFAULT_PYTHON_VERSION = "3.14"
 PREVIEW_PYTHON_VERSION = "3.15"
 
 CURRENT_DIRECTORY = pathlib.Path(__file__).parent.absolute()
+# Path to the centralized mypy configuration file at the repository root.
+# Search upwards to support running nox from both monorepo packages and integration test goldens.
+MYPY_CONFIG_FILE = next(
+    (str(p / "mypy.ini") for p in CURRENT_DIRECTORY.parents if (p / "mypy.ini").exists()),
+    str(CURRENT_DIRECTORY.parent.parent / "mypy.ini"),
+)
 
 if (CURRENT_DIRECTORY / "testing").exists():
     LOWER_BOUND_CONSTRAINTS_FILE = (
@@ -99,6 +105,7 @@ 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

@@ -116,6 +116,7 @@ def _overwrite_golden_impl(ctx):
     # 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 \\*.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

@@ -45,6 +45,12 @@
 PREVIEW_PYTHON_VERSION = "3.15"
 
 CURRENT_DIRECTORY = pathlib.Path(__file__).parent.absolute()
+# Path to the centralized mypy configuration file at the repository root.
+# Search upwards to support running nox from both monorepo packages and integration test goldens.
+MYPY_CONFIG_FILE = next(
+    (str(p / "mypy.ini") for p in CURRENT_DIRECTORY.parents if (p / "mypy.ini").exists()),
+    str(CURRENT_DIRECTORY.parent.parent / "mypy.ini"),
+)
 
 if (CURRENT_DIRECTORY / "testing").exists():
     LOWER_BOUND_CONSTRAINTS_FILE = (
@@ -106,6 +112,7 @@ 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

@@ -45,6 +45,12 @@
 PREVIEW_PYTHON_VERSION = "3.15"
 
 CURRENT_DIRECTORY = pathlib.Path(__file__).parent.absolute()
+# Path to the centralized mypy configuration file at the repository root.
+# Search upwards to support running nox from both monorepo packages and integration test goldens.
+MYPY_CONFIG_FILE = next(
+    (str(p / "mypy.ini") for p in CURRENT_DIRECTORY.parents if (p / "mypy.ini").exists()),
+    str(CURRENT_DIRECTORY.parent.parent / "mypy.ini"),
+)
 
 if (CURRENT_DIRECTORY / "testing").exists():
     LOWER_BOUND_CONSTRAINTS_FILE = (
@@ -106,6 +112,7 @@ def mypy(session):
     session.install(".")
     session.run(
         "mypy",
+        f"--config-file={MYPY_CONFIG_FILE}",
         "-p",
         "google",
         "--check-untyped-defs",