Faster CI: Sparse run matrix, cancel previous jobs on the same branch

.flake8

@@ -7,3 +7,6 @@ ignore =
     E712,
     # line break before binary operator
     W503
+per-file-ignores =
+    # flake8 is just plain wrong here, contradicting black
+    .github/generate-job-matrix.py:E225,E231

.github/generate-job-matrix.py

@@ -0,0 +1,206 @@
+import argparse
+import json
+import os
+import random
+import typing
+from types import SimpleNamespace
+
+from job_matrix import CombinationCollector, Compiler, Configuration
+
+
+def make_gcc_config(version: int) -> Configuration:
+    return Configuration(
+        name=f"GCC-{version}",
+        os="ubuntu-24.04",
+        compiler=Compiler(
+            type="GCC",
+            version=version,
+            cc=f"gcc-{version}",
+            cxx=f"g++-{version}",
+        ),
+        cxx_modules=False,
+        std_format_support=version >= 13,
+    )
+
+
+def make_clang_config(
+    version: int, platform: typing.Literal["x86-64", "arm64"] = "x86-64"
+) -> Configuration:
+    cfg = SimpleNamespace(
+        name=f"Clang-{version} ({platform})",
+        compiler=SimpleNamespace(
+            type="CLANG",
+            version=version,
+        ),
+        lib="libc++",
+        cxx_modules=version >= 17,
+        std_format_support=version >= 17,
+    )
+    match platform:
+        case "x86-64":
+            cfg.os = "ubuntu-22.04" if version < 17 else "ubuntu-24.04"
+            cfg.compiler.cc = f"clang-{version}"
+            cfg.compiler.cxx = f"clang++-{version}"
+        case "arm64":
+            cfg.os = "macos-14"
+            pfx = f"/opt/homebrew/opt/llvm@{version}/bin"
+            cfg.compiler.cc = f"{pfx}/clang"
+            cfg.compiler.cxx = f"{pfx}/clang++"
+        case _:
+            raise KeyError(f"Unsupported platform {platform!r} for Clang")
+    ret = cfg
+    ret.compiler = Compiler(**vars(cfg.compiler))
+    return Configuration(**vars(ret))
+
+
+def make_apple_clang_config(version: int) -> Configuration:
+    ret = Configuration(
+        name=f"Apple Clang {version}",
+        os="macos-13",
+        compiler=Compiler(
+            type="APPLE_CLANG",
+            version=f"{version}.0",
+            cc="clang",
+            cxx="clang++",
+        ),
+        cxx_modules=False,
+        std_format_support=False,
+    )
+    return ret
+
+
+def make_msvc_config(release: str, version: int) -> Configuration:
+    ret = Configuration(
+        name=f"MSVC {release}",
+        os="windows-2022",
+        compiler=Compiler(
+            type="MSVC",
+            version=version,
+            cc="",
+            cxx="",
+        ),
+        cxx_modules=False,
+        std_format_support=True,
+    )
+    return ret
+
+
+configs = {
+    c.name: c
+    for c in [make_gcc_config(ver) for ver in [12, 13, 14]]
+    + [
+        make_clang_config(ver, platform)
+        for ver in [16, 17, 18]
+        for platform in ["x86-64", "arm64"]
+        # arm64 runners are expensive; only consider one version
+        if ver == 18 or platform != "arm64"
+    ]
+    + [make_apple_clang_config(ver) for ver in [15]]
+    + [make_msvc_config(release="14.4", version=194)]
+}
+
+full_matrix = dict(
+    config=list(configs.values()),
+    std=[20, 23],
+    formatting=["std::format", "fmtlib"],
+    contracts=["none", "gsl-lite", "ms-gsl"],
+    build_type=["Release", "Debug"],
+)
+
+
+def main():
+    parser = argparse.ArgumentParser()
+    #    parser.add_argument("-I","--include",nargs="+",action="append")
+    #    parser.add_argument("-X","--exclude",nargs="+",action="append")
+    parser.add_argument("--seed", type=int, default=42)
+    parser.add_argument("--preset", default=None)
+    parser.add_argument("--debug", nargs="+", default=["combinations"])
+    parser.add_argument("--suppress-output", default=False, action="store_true")
+
+    args = parser.parse_args()
+
+    rgen = random.Random(args.seed)
+
+    collector = CombinationCollector(
+        full_matrix,
+        hard_excludes=lambda e: (
+            e.formatting == "std::format" and not e.config.std_format_support
+        ),
+    )
+    match args.preset:
+        case None:
+            pass
+        case "all":
+            collector.all_combinations()
+        case "conan" | "cmake":
+            collector.all_combinations(
+                formatting="std::format",
+                contracts="gsl-lite",
+                build_type="Debug",
+                std=20,
+            )
+            collector.all_combinations(
+                filter=lambda me: not me.config.std_format_support,
+                formatting="fmtlib",
+                contracts="gsl-lite",
+                build_type="Debug",
+                std=20,
+            )
+            collector.sample_combinations(rgen=rgen, min_samples_per_value=2)
+        case "clang-tidy":
+            collector.all_combinations(config=configs["Clang-18 (x86-64)"])
+        case "freestanding":
+            # TODO For some reason Clang-18 Debug with -ffreestanding does not pass CMakeTestCXXCompiler
+            collector.all_combinations(
+                filter=lambda e: not (
+                    e.config.name.startswith("Clang-18") and e.build_type == "Debug"
+                ),
+                config=[configs[c] for c in ["GCC-14", "Clang-18 (x86-64)"]],
+                contracts="none",
+                std=23,
+            )
+        case _:
+            raise KeyError(f"Unsupported preset {args.preset!r}")
+
+    if not collector.combinations:
+        raise ValueError("No combination has been produced")
+
+    data = sorted(collector.combinations)
+
+    json_data = [e.as_json() for e in data]
+
+    output_file = os.environ.get("GITHUB_OUTPUT")
+    if not args.suppress_output:
+        if output_file:
+            print(f"Writing outputs to {output_file}")
+            with open(output_file, "wt") as fh:
+                fh.write(f"matrix={json.dumps(json_data)}")
+        else:
+            print("No output file received!")
+
+    for dbg in args.debug:
+        match dbg:
+            case "yaml":
+                import yaml
+
+                json_data = json.loads(json.dumps(json_data))
+                print(yaml.safe_dump(json_data))
+            case "json":
+                print(json.dumps(json_data, indent=4))
+            case "combinations":
+                for e in data:
+                    print(
+                        f"{e.config!s:17s}  c++{e.std:2d}  {e.formatting:11s}  {e.contracts:8s}  {e.build_type:8s}"
+                    )
+            case "counts":
+                print(f"Total combinations {len(data)}")
+                for (k, v), n in sorted(collector.per_value_counts.items()):
+                    print(f"  {k}={v}: {n}")
+            case "none":
+                pass
+            case _:
+                raise KeyError(f"Unknown debug mode {dbg!r}")
+
+
+if __name__ == "__main__":
+    main()

.github/job_matrix.py

@@ -0,0 +1,139 @@
+import dataclasses
+import itertools
+import random
+import typing
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True, order=True)
+class Compiler:
+    type: typing.Literal["GCC", "CLANG", "APPLE_CLANG", "MSVC"]
+    version: str | int
+    cc: str
+    cxx: str
+
+
+@dataclass(frozen=True, order=True)
+class Configuration:
+    name: str
+    os: str
+    compiler: Compiler
+    cxx_modules: bool
+    std_format_support: bool
+    conan_config: str = ""
+    lib: typing.Literal["libc++", "libstdc++"] | None = None
+
+    def __str__(self):
+        return self.name
+
+
+@dataclass(frozen=True, order=True)
+class MatrixElement:
+    config: Configuration
+    std: typing.Literal[20, 23]
+    formatting: typing.Literal["std::format", "fmtlib"]
+    contracts: typing.Literal["none", "gsl-lite", "ms-gsl"]
+    build_type: typing.Literal["Release", "Debug"]
+
+    def as_json(self):
+        def dataclass_to_json(obj):
+            """Convert dataclasses to something json-serialisable"""
+            if dataclasses.is_dataclass(obj):
+                return {
+                    k: dataclass_to_json(v) for k, v in dataclasses.asdict(obj).items()
+                }
+            return obj
+
+        ret = dataclass_to_json(self)
+        # patch boolean conan configuration options
+        config = ret["config"]
+        for k in ["cxx_modules"]:
+            config[k] = "True" if config[k] else "False"
+        return ret
+
+
+class CombinationCollector:
+    """Incremental builder of MatrixElements, allowing successive selection of entries."""
+
+    def __init__(
+        self,
+        full_matrix: dict[str, list[typing.Any]],
+        *,
+        hard_excludes: typing.Callable[[MatrixElement], bool] | None = None,
+    ):
+        self.full_matrix = full_matrix
+        self.hard_excludes = hard_excludes
+        self.combinations: set[MatrixElement] = set()
+        self.per_value_counts: dict[tuple[str, typing.Any], int] = {
+            (k, v): 0 for k, options in full_matrix.items() for v in options
+        }
+
+    def _make_submatrix(self, **overrides):
+        new_matrix = dict(self.full_matrix)
+        for k, v in overrides.items():
+            if not isinstance(v, list):
+                v = [v]
+            new_matrix[k] = v
+        return new_matrix
+
+    def _add_combination(self, e: MatrixElement):
+        if e in self.combinations or (
+            self.hard_excludes is not None and self.hard_excludes(e)
+        ):
+            return
+        self.combinations.add(e)
+        # update per_value_counts
+        for k, v in vars(e).items():
+            idx = (k, v)
+            self.per_value_counts[idx] = self.per_value_counts.get(idx, 0) + 1
+
+    def all_combinations(
+        self,
+        *,
+        filter: typing.Callable[[MatrixElement], bool] | None = None,
+        **overrides,
+    ):
+        """Adds all combinations in the submatrix defined by `overrides`."""
+        matrix = self._make_submatrix(**overrides)
+        keys = tuple(matrix.keys())
+        for combination in itertools.product(*matrix.values()):
+            cand = MatrixElement(**dict(zip(keys, combination)))
+            if filter and not filter(cand):
+                continue
+            self._add_combination(cand)
+
+    def sample_combinations(
+        self,
+        *,
+        rgen: random.Random,
+        min_samples_per_value: int = 1,
+        filter: typing.Callable[[MatrixElement], bool] | None = None,
+        **overrides,
+    ):
+        """Adds samples from the submatrix defined by `overrides`,
+        ensuring each individual value appears at least n times.
+        """
+        matrix = self._make_submatrix(**overrides)
+        missing: dict[tuple[str, typing.Any], int] = {}
+        for key, options in matrix.items():
+            for value in options:
+                idx = (key, value)
+                missing[idx] = min_samples_per_value - self.per_value_counts.get(idx, 0)
+        while missing:
+            (force_key, force_option), remaining = next(iter(missing.items()))
+            if remaining <= 0:
+                missing.pop((force_key, force_option))
+                continue
+            choice = {}
+            for key, options in matrix.items():
+                choice[key] = force_option if key == force_key else rgen.choice(options)
+            cand = MatrixElement(**choice)
+            if filter and not filter(cand):
+                continue
+            self._add_combination(cand)
+            for idx in choice.items():
+                if missing.pop(idx, 0) <= 0:
+                    continue
+                remaining = min_samples_per_value - self.per_value_counts.get(idx, 0)
+                if remaining > 0:
+                    missing[idx] = remaining