github/gen-matrix.py: use all-pairs coverage instead of full cartesian

Switch the regular_test matrix from itertools.product to allpairspy's
AllPairs over compiler x standard x mode. With 4 compilers, 2 standards
and 2 modes the regular grid drops from 24 items to 8 while still
exercising every pair of parameter values at least once.

'dev' is no longer crossed against every compiler / standard; it gets
a single one-off entry pinned to clang++-22 / C++23, alongside the
existing DPDK, cxx-modules, and fuzz one-offs.

The script gets a PEP 723 inline-metadata block and a uv shebang
('#!/usr/bin/env -S uv run --script') so it can declare its single
dependency (allpairspy) without polluting a global Python environment.
Runs under Python 3.10 and newer.

tests-matrix.gold is regenerated: 12 jobs total (8 regular + 4 one-offs).

Author: travisdowns

.github/workflows/gen-matrix.py

@@ -1,21 +1,33 @@
-#!/usr/bin/env python3
+#!/usr/bin/env -S uv run --script
+# /// script
+# requires-python = ">=3.10"
+# dependencies = [
+#   "allpairspy",
+# ]
+# ///
 """
 Generate the regular_test include: matrix for tests.yaml.
 
-Computes the Cartesian product of compilers × standards × modes for
-regular builds, then appends special-purpose jobs (dpdk, cxx-modules,
-fuzz) so that tests.yaml has a single job definition for all of them.
-Everything outside the marked region is left untouched.
+Uses all-pairs (pairwise) coverage over compiler x standard x mode for
+the regular builds, plus an explicit list of special-purpose jobs
+(dpdk, cxx-modules, fuzz). All-pairs guarantees that every pair of
+parameter values is exercised by at least one job, with far fewer
+combinations than the full cartesian product (12 vs 24 for our 4x2x3
+matrix). Everything outside the marked region of tests.yaml is left
+untouched.
 
 Usage:
-    python3 .github/workflows/gen-matrix.py
+    .github/workflows/gen-matrix.py
     git diff .github/workflows/tests.yaml
 """
 
-import itertools
+from __future__ import annotations
+
 import pathlib
 from typing import Any
 
+from allpairspy import AllPairs
+
 HERE = pathlib.Path(__file__).parent
 TESTS_YAML = HERE / "tests.yaml"
 
@@ -29,7 +41,7 @@
     + [f"g++-{v}"   for v in GCC_VERSIONS]
 )
 STANDARDS: list[int] = [20, 23]
-MODES: list[str] = ["dev", "debug", "release"]
+MODES: list[str] = ["debug", "release"]
 
 # Markers that bracket the managed region inside tests.yaml.
 BEGIN_TAG = "# This include block is AUTOGENERATED"
@@ -39,6 +51,11 @@
 # Items only set enable-ccache when overriding the default (test.yaml treats
 # absent/empty as enabled).
 SPECIAL_ITEMS: list[dict[str, Any]] = [
+    {
+        "compiler": "clang++-22",
+        "standard": 23,
+        "mode": "dev",
+    },
     {
         "compiler": "clang++-22",
         "standard": 23,
@@ -86,8 +103,8 @@ def _format_item(item: dict[str, Any], indent: str) -> str:
 
 def generate() -> list[dict[str, Any]]:
     regular: list[dict[str, Any]] = [
-        {"compiler": c, "standard": s, "mode": m}
-        for c, s, m in itertools.product(COMPILERS, STANDARDS, MODES)
+        {"compiler": compiler, "standard": standard, "mode": mode}
+        for compiler, standard, mode in AllPairs([COMPILERS, STANDARDS, MODES])
     ]
     return regular + SPECIAL_ITEMS
 

.github/workflows/tests-matrix.gold

@@ -1,27 +1,12 @@
 Fuzz Tests
 Test (clang++-19, C++20, debug)
-Test (clang++-19, C++20, dev)
-Test (clang++-19, C++20, release)
-Test (clang++-19, C++23, debug)
-Test (clang++-19, C++23, dev)
 Test (clang++-19, C++23, release)
-Test (clang++-22, C++20, debug)
-Test (clang++-22, C++20, dev)
 Test (clang++-22, C++20, release)
 Test (clang++-22, C++23, debug)
 Test (clang++-22, C++23, dev)
-Test (clang++-22, C++23, release)
 Test (g++-14, C++20, debug)
-Test (g++-14, C++20, dev)
-Test (g++-14, C++20, release)
-Test (g++-14, C++23, debug)
-Test (g++-14, C++23, dev)
 Test (g++-14, C++23, release)
-Test (g++-16, C++20, debug)
-Test (g++-16, C++20, dev)
 Test (g++-16, C++20, release)
 Test (g++-16, C++23, debug)
-Test (g++-16, C++23, dev)
-Test (g++-16, C++23, release)
 Test with C++20 modules enabled
 Test with DPDK enabled

.github/workflows/tests.yaml

@@ -22,30 +22,15 @@ jobs:
         # This include block is AUTOGENERATED, do not edit by hand
         # instead edit + re-run .github/workflows/gen-matrix.py
         include:
-          - {compiler: clang++-19, standard: 20, mode: dev}
           - {compiler: clang++-19, standard: 20, mode: debug}
-          - {compiler: clang++-19, standard: 20, mode: release}
-          - {compiler: clang++-19, standard: 23, mode: dev}
-          - {compiler: clang++-19, standard: 23, mode: debug}
-          - {compiler: clang++-19, standard: 23, mode: release}
-          - {compiler: clang++-22, standard: 20, mode: dev}
-          - {compiler: clang++-22, standard: 20, mode: debug}
-          - {compiler: clang++-22, standard: 20, mode: release}
-          - {compiler: clang++-22, standard: 23, mode: dev}
           - {compiler: clang++-22, standard: 23, mode: debug}
-          - {compiler: clang++-22, standard: 23, mode: release}
-          - {compiler: g++-14, standard: 20, mode: dev}
-          - {compiler: g++-14, standard: 20, mode: debug}
-          - {compiler: g++-14, standard: 20, mode: release}
-          - {compiler: g++-14, standard: 23, mode: dev}
-          - {compiler: g++-14, standard: 23, mode: debug}
           - {compiler: g++-14, standard: 23, mode: release}
-          - {compiler: g++-16, standard: 20, mode: dev}
-          - {compiler: g++-16, standard: 20, mode: debug}
           - {compiler: g++-16, standard: 20, mode: release}
-          - {compiler: g++-16, standard: 23, mode: dev}
           - {compiler: g++-16, standard: 23, mode: debug}
-          - {compiler: g++-16, standard: 23, mode: release}
+          - {compiler: g++-14, standard: 20, mode: debug}
+          - {compiler: clang++-22, standard: 20, mode: release}
+          - {compiler: clang++-19, standard: 23, mode: release}
+          - {compiler: clang++-22, standard: 23, mode: dev}
           - {compiler: clang++-22, standard: 23, mode: release, enables: --enable-dpdk, options: "--cook dpdk --dpdk-machine corei7-avx", label: "Test with DPDK enabled"}
           - {compiler: clang++-22, standard: 23, mode: debug, enables: --enable-cxx-modules, enable-ccache: false, label: "Test with C++20 modules enabled"}
           - {compiler: clang++-22, standard: 23, mode: fuzz, test-args: "-- -R 'Seastar.fuzz.'", label: "Fuzz Tests"}