python-graphblas · eriknw · Jul 31, 2026 · Jul 31, 2026 · Jul 31, 2026 · Aug 4, 2026
diff --git a/graphblas/core/automethods.py b/graphblas/core/automethods.py
@@ -366,11 +366,22 @@ def __ixor__(self, other):
 
 
 # End auto-generated code
-def _main():
+def _main(base_dir=None, callblack=True):
+    # base_dir lets `scripts/autogenerate.py --check` redirect reads and writes to a
+    # scratch copy of the tree; when None we regenerate the real files in place.
+    # callblack=False keeps that check hermetic: black is optional here, and letting it
+    # run would make the scratch output depend on whether it is installed.
+    import functools
     from pathlib import Path
 
     from .utils import _autogenerate_code
 
+    if not callblack:
+        _autogenerate_code = functools.partial(_autogenerate_code, callblack=False)
+
+    if base_dir is None:
+        base_dir = Path(__file__).parent
+
     common = {
         "_name_html",
         "_nvals",
@@ -488,7 +499,7 @@ def _main():
             f'    raise TypeError(f"{name!r} not supported for {{type(self).__name__}}")\n\n'
         )
 
-    _autogenerate_code(Path(__file__), "\n".join(lines))
+    _autogenerate_code(base_dir / "automethods.py", "\n".join(lines))
 
     # Copy to scalar.py and infix.py
     lines = []
@@ -509,7 +520,7 @@ def _main():
             continue
         lines.append(f"    {name} = automethods.{name}")
 
-    thisdir = Path(__file__).parent
+    thisdir = base_dir
     infix_exclude = {"_get_value"}
 
     def get_name(line):

diff --git a/graphblas/core/infixmethods.py b/graphblas/core/infixmethods.py
@@ -320,7 +320,11 @@ def __itruediv__(self, other):
 # End auto-generated code
 
 
-def _main():
+def _main(base_dir=None, callblack=True):
+    # base_dir lets `scripts/autogenerate.py --check` redirect the write to a scratch
+    # copy of the tree; when None we regenerate infixmethods.py in place.
+    # callblack=False keeps that check hermetic: black is optional here, and letting it
+    # run would make the scratch output depend on whether it is installed.
     # Run via `python -m graphblas.core.infixmethods`
     comparisons = {
         "lt": "lt",
@@ -426,11 +430,17 @@ def _main():
         "        setattr(VectorIndexExpr, name, val)\n"
         "        setattr(MatrixIndexExpr, name, val)\n"
     )
+    import functools
     from pathlib import Path
 
     from .utils import _autogenerate_code
 
-    _autogenerate_code(Path(__file__), "\n".join(lines))
+    if not callblack:
+        _autogenerate_code = functools.partial(_autogenerate_code, callblack=False)
+
+    if base_dir is None:
+        base_dir = Path(__file__).parent
+    _autogenerate_code(base_dir / "infixmethods.py", "\n".join(lines))
 
 
 if __name__ == "__main__":

diff --git a/graphblas/tests/test_autogenerate_check.py b/graphblas/tests/test_autogenerate_check.py
@@ -0,0 +1,62 @@
+"""Guard the auto-generated code blocks against undetected drift.
+
+``test_automethods.py`` guards the *names* on the generated expression surface.
+Nothing there guards the generated *content*: hand-edit a block between the
+``# Begin auto-generated code`` / ``# End auto-generated code`` markers, or edit
+the name sets in ``automethods._main`` without rerunning the generator, and the
+on-disk blocks go stale while CI stays green.
+
+``scripts/autogenerate.py --check`` closes that gap. It regenerates every
+generated file into a scratch tree and compares each against the file on disk,
+exiting nonzero (and naming the drifted files) on any mismatch. The comparison is
+on parsed syntax, so the check needs no formatter and runs everywhere rather than
+skipping in every job that lacks one.
+
+Scope, since the two guards are easy to confuse. The generator emits from the
+literal name sets in ``automethods._main``, not by introspecting the classes, so
+adding a method to Matrix/Vector/Scalar does not change its output and cannot
+show up here. That case is ``test_automethods.py``'s: it compares the concrete
+types against the generated surface and fails when a new public attribute is
+neither auto-computed nor opted out. This module covers the other half, the
+generated files no longer matching the generator that claims to produce them.
+"""
+
+import subprocess
+import sys
+from pathlib import Path
+
+import pytest
+
+REPO_ROOT = Path(__file__).resolve().parents[2]
+AUTOGEN_SCRIPT = REPO_ROOT / "scripts" / "autogenerate.py"
+PACKAGE_LINE = "graphblas package: "
+
+
+def test_autogenerated_code_is_in_sync():
+    if not AUTOGEN_SCRIPT.exists():  # pragma: no cover (source checkout only)
+        pytest.skip("scripts/autogenerate.py not present (installed package, not a checkout)")
+    result = subprocess.run(
+        [sys.executable, str(AUTOGEN_SCRIPT), "--check"],
+        capture_output=True,
+        text=True,
+        check=False,
+    )
+    report = f"stdout:\n{result.stdout}\nstderr:\n{result.stderr}"
+    checked = [
+        line[len(PACKAGE_LINE) :].strip()
+        for line in result.stdout.splitlines()
+        if line.startswith(PACKAGE_LINE)
+    ]
+
+    # Assert the positive post-condition before the exit code. A check that ran against a
+    # different `graphblas` reports success about a tree nobody asked about: sys.path[0]
+    # for a script is the script's own directory, so that is what happens whenever an
+    # editable install points elsewhere, as in a git worktree.
+    assert checked, f"--check never reported a package, so it failed before starting.\n{report}"
+    expected = str(REPO_ROOT / "graphblas")
+    assert checked == [expected], f"--check validated {checked}, not {expected}.\n{report}"
+
+    assert result.returncode == 0, (
+        "Auto-generated code is out of date. Run `python scripts/autogenerate.py` and "
+        f"commit the result.\n{report}"
+    )