test: pin graph.json invariance across checkout folder, rebuild and line endings

Seven bugs of one shape (#4152, #4154, #4156, #4164, #4180, #4182, #4188) were each
found by diffing two builds of the same tree by hand: a checkout path leaking into an
id, a rebuild writing a different graph than the first build, CRLF ids differing from
LF, an edge to a node that is never declared. Each fix got its own narrow test, so the
next extractor or write-path change can bring the same class back unseen.

tests/test_graph_invariance.py builds the whole tests/fixtures corpus (every extractor)
through the real CLI, --no-cluster and clustered, and checks: two folders give the same
graph, the checkout path appears nowhere in graph.json, a rebuild of the unchanged tree
changes nothing, LF and CRLF give the same graph, and every raw edge endpoint is declared.
On 0.9.79 the three checks those fixes cover fail; on 0.9.80 all 12 pass in about 20 s.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01B8gwEpjajiWHVW3c9smuKf

tests/test_graph_invariance.py

@@ -0,0 +1,147 @@
+"""The same source tree must give the same graph.json, however it is built.
+
+Each test builds the whole ``tests/fixtures`` corpus (every language graphify
+ships an extractor for) two ways that must not matter, through the real CLI,
+and compares every node and edge with all attributes:
+
+- two checkouts in different folders (no checkout path in any id or edge),
+- a cold build and a rebuild of the unchanged tree,
+- an LF checkout and a CRLF checkout of the same files,
+- and, for the raw ``--no-cluster`` output, every edge endpoint is a declared node.
+
+Bugs of this shape were found one at a time by diffing builds by hand (#4152,
+#4154, #4156, #4164, #4180, #4182, #4188); this pins the invariants for every
+extractor at once, so a new extractor or a change to the write paths cannot
+silently break them.
+"""
+from __future__ import annotations
+
+import json
+import os
+import shutil
+import subprocess
+import sys
+from collections import Counter
+from pathlib import Path
+
+import pytest
+
+FIXTURES = Path(__file__).parent / "fixtures"
+# Attributes that are not a function of the source tree: community ids are
+# assigned by clustering and are compared elsewhere (#3761).
+_UNSTABLE_KEYS = frozenset({"community", "community_name"})
+
+
+def _copy(src: Path, dst: Path, *, crlf: bool = False) -> Path:
+    shutil.copytree(src, dst, ignore=shutil.ignore_patterns("graphify-out"))
+    if crlf:
+        for path in dst.rglob("*"):
+            if not path.is_file():
+                continue
+            data = path.read_bytes()
+            if b"\0" in data:
+                continue
+            try:
+                data.decode("utf-8")
+            except UnicodeDecodeError:
+                continue
+            path.write_bytes(data.replace(b"\r\n", b"\n").replace(b"\n", b"\r\n"))
+    return dst
+
+
+def _build(root: Path, *, cluster: bool) -> dict:
+    """Build ``root`` with the CLI and return graph.json, parsed, plus its raw text under ``"__text__"``."""
+    args = [sys.executable, "-m", "graphify", "update", str(root), "--force"]
+    if not cluster:
+        args.append("--no-cluster")
+    env = dict(os.environ, PYTHONHASHSEED="0", PYTHONIOENCODING="utf-8")
+    result = subprocess.run(args, cwd=root, env=env, capture_output=True, text=True)
+    assert result.returncode == 0, result.stderr[-2000:]
+    text = (root / "graphify-out" / "graph.json").read_text(encoding="utf-8")
+    graph = json.loads(text)
+    graph["__text__"] = text
+    return graph
+
+
+def _links(graph: dict) -> list[dict]:
+    return graph.get("links", graph.get("edges", []))
+
+
+def _canonical(graph: dict) -> tuple[Counter, Counter]:
+    def key(item: dict) -> str:
+        return json.dumps({k: v for k, v in item.items() if k not in _UNSTABLE_KEYS}, sort_keys=True)
+    return Counter(key(n) for n in graph["nodes"]), Counter(key(e) for e in _links(graph))
+
+
+def _assert_same(a: dict, b: dict, what: str) -> None:
+    keys_a = set(a) - {"__text__", "built_at_commit"}
+    keys_b = set(b) - {"__text__", "built_at_commit"}
+    assert keys_a == keys_b, f"{what} changed graph.json's top-level keys: {sorted(keys_a ^ keys_b)}"
+    nodes_a, edges_a = _canonical(a)
+    nodes_b, edges_b = _canonical(b)
+    only = {
+        "nodes only in the first": list((nodes_a - nodes_b).elements())[:5],
+        "nodes only in the second": list((nodes_b - nodes_a).elements())[:5],
+        "edges only in the first": list((edges_a - edges_b).elements())[:5],
+        "edges only in the second": list((edges_b - edges_a).elements())[:5],
+    }
+    assert not any(only.values()), f"{what} changed graph.json: " + json.dumps(only, indent=1)[:4000]
+
+
+@pytest.fixture(scope="module", params=[False, True], ids=["no_cluster", "clustered"])
+def builds(request, tmp_path_factory) -> dict:
+    cluster = request.param
+    base = tmp_path_factory.mktemp("invariance_clustered" if cluster else "invariance_raw")
+    first = _copy(FIXTURES, base / "alice_home" / "proj")
+    second = _copy(FIXTURES, base / "bob_elsewhere" / "checkout" / "proj")
+    crlf = _copy(FIXTURES, base / "crlf_checkout" / "proj", crlf=True)
+    cold = _build(first, cluster=cluster)
+    return {
+        "cluster": cluster,
+        "cold": cold,
+        "other_folder": _build(second, cluster=cluster),
+        "rebuilt": _build(first, cluster=cluster),
+        "crlf": _build(crlf, cluster=cluster),
+    }
+
+
+def test_fixture_corpus_is_not_trivial(builds):
+    # Guard against a silently empty build making every comparison pass.
+    assert len(builds["cold"]["nodes"]) > 500
+    assert len(_links(builds["cold"])) > 500
+
+
+def test_checkout_folder_does_not_change_the_graph(builds):
+    _assert_same(builds["cold"], builds["other_folder"], "moving the checkout to another folder")
+
+
+def test_graph_never_contains_the_checkout_path(builds):
+    for graph in (builds["cold"], builds["rebuilt"], builds["other_folder"]):
+        lowered = graph["__text__"].lower()
+        assert "alice_home" not in lowered and "bob_elsewhere" not in lowered, (
+            "graph.json embeds the checkout path: "
+            + str([
+                item.get("id") or (item.get("source"), item.get("target"))
+                for item in graph["nodes"] + _links(graph)
+                if "alice_home" in json.dumps(item).lower() or "bob_elsewhere" in json.dumps(item).lower()
+            ][:10])
+        )
+
+
+def test_rebuilding_an_unchanged_tree_changes_nothing(builds):
+    _assert_same(builds["cold"], builds["rebuilt"], "rebuilding the unchanged tree")
+
+
+def test_line_endings_do_not_change_the_graph(builds):
+    _assert_same(builds["cold"], builds["crlf"], "converting every text file to CRLF")
+
+
+def test_every_edge_endpoint_is_a_declared_node(builds):
+    for graph in (builds["cold"], builds["rebuilt"]):
+        declared = {n["id"] for n in graph["nodes"]}
+        undeclared = [
+            (e.get("relation"), e.get("source"), e.get("target"))
+            for e in _links(graph)
+            if e.get("source") not in declared or e.get("target") not in declared
+        ]
+        assert undeclared == [], f"edges with an undeclared endpoint: {undeclared[:10]}"