tests: add Python 3.15 pre-release testing (googleapis#17517)

Towards b/525422520
Fixes googleapis#16215

Author: parthea

.github/workflows/gapic-generator-tests.yml

@@ -18,7 +18,13 @@ env:
   SHOWCASE_VERSION: 0.35.0
   PROTOC_VERSION: 3.20.2
   LATEST_STABLE_PYTHON: 3.14
-  ALL_PYTHON: "['3.10', '3.11', '3.12', '3.13', '3.14']"
+  PRERELEASE_PYTHON: 3.15
+  ALL_PYTHON: "['3.10', '3.11', '3.12', '3.13', '3.14', '3.15']"
+  TRIMMED_PYTHON: "['3.10', '3.14', '3.15']"
+  # Workaround: Allows libcst to compile on Python 3.15+ while PyO3 catches up
+  # Can be removed once libcst releases a version with native Python 3.15 wheels
+  # Follow https://github.com/Instagram/LibCST/issues/1445 for updates.
+  PYO3_USE_ABI3_FORWARD_COMPATIBILITY: "1"
 
 jobs:
   check_changes:
@@ -47,6 +53,8 @@ jobs:
     outputs:
       all_python: ${{ env.ALL_PYTHON }}
       latest_stable_python: ${{ env.LATEST_STABLE_PYTHON }}
+      prerelease_python: ${{ env.PRERELEASE_PYTHON }}
+      trimmed_python: $${{ env.TRIMMED_PYTHON }}
     steps:
       - run: echo "Initializing config for gapic-generator"
 
@@ -65,6 +73,12 @@ jobs:
         uses: actions/setup-python@v6
         with:
           python-version: "${{ matrix.python }}"
+          allow-prereleases: true
+          # Caches compiled wheels locally to prevent building heavy libraries 
+          # such as grpcio, which we build from scratch on every run for Python 3.15+.
+          # Follow https://github.com/grpc/grpc/issues/41010 for updates.
+          cache: 'pip'
+          cache-dependency-path: '**/requirements*.txt'
       - name: Install System Deps & Protoc
         run: |
           sudo apt-get update && sudo apt-get install -y curl pandoc unzip
@@ -132,10 +146,16 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v6
-      - name: Set up Python
+      - name: Set up Python ${{ needs.python_config.outputs.prerelease_python }}
         uses: actions/setup-python@v6
         with:
-          python-version: ${{ needs.python_config.outputs.latest_stable_python }}
+          python-version: ${{ needs.python_config.outputs.prerelease_python }}
+          allow-prereleases: true
+          # Caches compiled wheels locally to prevent building heavy libraries 
+          # such as grpcio, which we build from scratch on every run for Python 3.15+.
+          # Follow https://github.com/grpc/grpc/issues/41010 for updates.
+          cache: 'pip'
+          cache-dependency-path: '**/requirements*.txt'
       - name: Install System Deps
         run: sudo apt-get update && sudo apt-get install -y pandoc
       - name: Run Goldens (Prerelease)
@@ -150,15 +170,20 @@ jobs:
     needs: python_config
     strategy:
       matrix:
-        python: ["3.10", "3.14"]
+        python: ${{ fromJSON(needs.python_config.outputs.trimmed_python) }}
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v6
       - name: Set up Python
         uses: actions/setup-python@v6
         with:
           python-version: ${{ matrix.python }}
-      # This fixes the Pandoc error
+          allow-prereleases: true
+          # Caches compiled wheels locally to prevent building heavy libraries 
+          # such as grpcio, which we build from scratch on every run for Python 3.15+.
+          # Follow https://github.com/grpc/grpc/issues/41010 for updates.
+          cache: 'pip'
+          cache-dependency-path: '**/requirements*.txt'
       - name: Install System Deps & Protoc
         run: |
           sudo apt-get update && sudo apt-get install -y curl pandoc unzip

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

@@ -30,14 +30,12 @@ ALL_PYTHON = [
     "3.12",
     "3.13",
     "3.14",
+    "3.15",
 ]
 
 DEFAULT_PYTHON_VERSION = "3.14"
 
-# TODO(https://github.com/googleapis/gapic-generator-python/issues/2450):
-# Switch this to Python 3.15 alpha1
-# https://peps.python.org/pep-0790/
-PREVIEW_PYTHON_VERSION = "3.14"
+PREVIEW_PYTHON_VERSION = "3.15"
 
 CURRENT_DIRECTORY = pathlib.Path(__file__).parent.absolute()
 
@@ -567,7 +565,7 @@ def prerelease_deps(session, protobuf_implementation):
     )
 
 
-@nox.session(python=DEFAULT_PYTHON_VERSION)
+@nox.session(python=PREVIEW_PYTHON_VERSION)
 @nox.parametrize(
     "protobuf_implementation",
     ["python", "upb"],

packages/gapic-generator/gapic/templates/testing/constraints-3.15.txt.j2

@@ -0,0 +1,21 @@
+{% from '_pypi_packages.j2' import pypi_packages %}
+# We use the constraints file for the latest Python version
+# (currently this file) to check that the latest
+# major versions of dependencies are supported in setup.py.
+# List all library dependencies and extras in this file.
+# Require the latest major version be installed for each dependency.
+# e.g., if setup.py has "google-cloud-foo >= 1.14.0, < 2.0.0",
+# Then this file should have google-cloud-foo>=1
+google-api-core>=2
+google-auth>=2
+grpcio>=1
+proto-plus>=1
+protobuf>=7
+{% for package_tuple, package_info in pypi_packages.items() %}
+{# Quick check to make sure `package_info.package_name` is not the package being generated so we don't circularly include this package in its own constraints file. #}
+{% if api.naming.warehouse_package_name != package_info.package_name %}
+{% if api.requires_package(package_tuple) %}
+{{ package_info.package_name }}>={{ (package_info.upper_bound.split(".")[0] | int) - 1 }}
+{% endif %}
+{% endif %}
+{% endfor %}

packages/gapic-generator/noxfile.py

@@ -50,9 +50,10 @@
     "3.12",
     "3.13",
     "3.14",
+    "3.15",
 )
 
-NEWEST_PYTHON = ALL_PYTHON[-1]
+NEWEST_PYTHON = ALL_PYTHON[-2]
 
 
 @nox.session(python=ALL_PYTHON)

packages/gapic-generator/tests/integration/goldens/asset/noxfile.py

@@ -37,14 +37,12 @@
     "3.12",
     "3.13",
     "3.14",
+    "3.15",
 ]
 
 DEFAULT_PYTHON_VERSION = "3.14"
 
-# TODO(https://github.com/googleapis/gapic-generator-python/issues/2450):
-# Switch this to Python 3.15 alpha1
-# https://peps.python.org/pep-0790/
-PREVIEW_PYTHON_VERSION = "3.14"
+PREVIEW_PYTHON_VERSION = "3.15"
 
 CURRENT_DIRECTORY = pathlib.Path(__file__).parent.absolute()
 
@@ -559,7 +557,7 @@ def prerelease_deps(session, protobuf_implementation):
     )
 
 
-@nox.session(python=DEFAULT_PYTHON_VERSION)
+@nox.session(python=PREVIEW_PYTHON_VERSION)
 @nox.parametrize(
     "protobuf_implementation",
     ["python", "upb"],

packages/gapic-generator/tests/integration/goldens/asset/testing/constraints-3.15.txt

@@ -0,0 +1,15 @@
+# We use the constraints file for the latest Python version
+# (currently this file) to check that the latest
+# major versions of dependencies are supported in setup.py.
+# List all library dependencies and extras in this file.
+# Require the latest major version be installed for each dependency.
+# e.g., if setup.py has "google-cloud-foo >= 1.14.0, < 2.0.0",
+# Then this file should have google-cloud-foo>=1
+google-api-core>=2
+google-auth>=2
+grpcio>=1
+proto-plus>=1
+protobuf>=7
+google-cloud-access-context-manager>=0
+google-cloud-os-config>=1
+grpc-google-iam-v1>=0

packages/gapic-generator/tests/integration/goldens/credentials/noxfile.py

@@ -37,14 +37,12 @@
     "3.12",
     "3.13",
     "3.14",
+    "3.15",
 ]
 
 DEFAULT_PYTHON_VERSION = "3.14"
 
-# TODO(https://github.com/googleapis/gapic-generator-python/issues/2450):
-# Switch this to Python 3.15 alpha1
-# https://peps.python.org/pep-0790/
-PREVIEW_PYTHON_VERSION = "3.14"
+PREVIEW_PYTHON_VERSION = "3.15"
 
 CURRENT_DIRECTORY = pathlib.Path(__file__).parent.absolute()
 
@@ -559,7 +557,7 @@ def prerelease_deps(session, protobuf_implementation):
     )
 
 
-@nox.session(python=DEFAULT_PYTHON_VERSION)
+@nox.session(python=PREVIEW_PYTHON_VERSION)
 @nox.parametrize(
     "protobuf_implementation",
     ["python", "upb"],

packages/gapic-generator/tests/integration/goldens/credentials/testing/constraints-3.15.txt

@@ -0,0 +1,12 @@
+# We use the constraints file for the latest Python version
+# (currently this file) to check that the latest
+# major versions of dependencies are supported in setup.py.
+# List all library dependencies and extras in this file.
+# Require the latest major version be installed for each dependency.
+# e.g., if setup.py has "google-cloud-foo >= 1.14.0, < 2.0.0",
+# Then this file should have google-cloud-foo>=1
+google-api-core>=2
+google-auth>=2
+grpcio>=1
+proto-plus>=1
+protobuf>=7

packages/gapic-generator/tests/integration/goldens/eventarc/noxfile.py

@@ -37,14 +37,12 @@
     "3.12",
     "3.13",
     "3.14",
+    "3.15",
 ]
 
 DEFAULT_PYTHON_VERSION = "3.14"
 
-# TODO(https://github.com/googleapis/gapic-generator-python/issues/2450):
-# Switch this to Python 3.15 alpha1
-# https://peps.python.org/pep-0790/
-PREVIEW_PYTHON_VERSION = "3.14"
+PREVIEW_PYTHON_VERSION = "3.15"
 
 CURRENT_DIRECTORY = pathlib.Path(__file__).parent.absolute()
 
@@ -559,7 +557,7 @@ def prerelease_deps(session, protobuf_implementation):
     )
 
 
-@nox.session(python=DEFAULT_PYTHON_VERSION)
+@nox.session(python=PREVIEW_PYTHON_VERSION)
 @nox.parametrize(
     "protobuf_implementation",
     ["python", "upb"],

packages/gapic-generator/tests/integration/goldens/eventarc/testing/constraints-3.15.txt

@@ -0,0 +1,13 @@
+# We use the constraints file for the latest Python version
+# (currently this file) to check that the latest
+# major versions of dependencies are supported in setup.py.
+# List all library dependencies and extras in this file.
+# Require the latest major version be installed for each dependency.
+# e.g., if setup.py has "google-cloud-foo >= 1.14.0, < 2.0.0",
+# Then this file should have google-cloud-foo>=1
+google-api-core>=2
+google-auth>=2
+grpcio>=1
+proto-plus>=1
+protobuf>=7
+grpc-google-iam-v1>=0