Commit hacky script to visualise store inheritance

Use e.g. with `scripts-dev/storage_inheritance.py DataStore --show`.

scripts-dev/storage_inheritance.py

@@ -0,0 +1,180 @@
+#! /usr/bin/env python3
+import argparse
+import os
+import re
+import subprocess
+import sys
+import tempfile
+from typing import Iterable, Optional, Set
+
+import networkx
+
+
+def scrape_storage_classes() -> str:
+    """Grep the for classes ending with "Store" and extract their list of parents.
+
+    Returns the stdout from `rg` as a single string."""
+
+    # TODO: this is a big hack which assumes that each Store class has a unique name.
+    #   That assumption is wrong: there are two DirectoryStores, one in
+    #   synapse/replication/slave/storage/directory.py and the other in
+    #   synapse/storage/databases/main/directory.py
+    #   Would be nice to have a way to account for this.
+
+    return subprocess.check_output(
+        [
+            "rg",
+            "-o",
+            "--no-line-number",
+            "--no-filename",
+            "--multiline",
+            r"class .*Store\((.|\n)*?\):$",
+            "synapse",
+            "tests",
+        ],
+        cwd="/home/dmr/workspace/synapse/",
+    ).decode()
+
+
+oneline_class_pattern = re.compile(r"^class (.*)\((.*)\):$")
+opening_class_pattern = re.compile(r"^class (.*)\($")
+
+
+def load_graph(lines: Iterable[str]) -> networkx.DiGraph:
+    """Process the output of scrape_storage_classes to build an inheritance graph.
+
+    Every time a class C is created that explicitly inherits from a parent P, we add an
+    edge C -> P.
+    """
+    G = networkx.DiGraph()
+    child: Optional[str] = None
+
+    for line in lines:
+        line = line.strip()
+        if not line or line.startswith("#"):
+            continue
+        if (match := oneline_class_pattern.match(line)) is not None:
+            child, parents = match.groups()
+            for parent in parents.split(", "):
+                if "metaclass" not in parent:
+                    G.add_edge(child, parent)
+
+            child = None
+        elif (match := opening_class_pattern.match(line)) is not None:
+            (child,) = match.groups()
+        elif line == "):":
+            child = None
+        else:
+            assert child is not None, repr(line)
+            parent = line.strip(",")
+            if "metaclass" not in parent:
+                G.add_edge(child, parent)
+
+    return G
+
+
+def select_vertices_of_interest(G: networkx.DiGraph, target: Optional[str]) -> Set[str]:
+    """Find all nodes we want to visualise.
+
+    If no TARGET is given, we visualise all of G. Otherwise we visualise a given
+    TARGET, its parents, and all of their parents recursively.
+
+    Requires that G is a DAG.
+    If not None, the TARGET must belong to G.
+    """
+    assert networkx.is_directed_acyclic_graph(G)
+    if target is not None:
+        component: Set[str] = networkx.descendants(G, target)
+        component.add(target)
+    else:
+        component = set(G.nodes)
+    return component
+
+
+def generate_dot_source(G: networkx.DiGraph, nodes: Set[str]) -> str:
+    output = """\
+strict digraph {
+    rankdir="LR";
+    node [shape=box];
+
+"""
+    for (child, parent) in G.edges:
+        if child in nodes and parent in nodes:
+            output += f"   {child} -> {parent};\n"
+    output += "}\n"
+    return output
+
+
+def render_png(dot_source: str, destination: Optional[str]) -> str:
+    if destination is None:
+        handle, destination = tempfile.mkstemp()
+        os.close(handle)
+        print("Warning: writing to", destination, "which will persist", file=sys.stderr)
+
+    subprocess.run(
+        [
+            "dot",
+            "-o",
+            destination,
+            "-Tpng",
+        ],
+        input=dot_source,
+        encoding="utf-8",
+        check=True,
+    )
+    return destination
+
+
+def show_graph(location: str) -> None:
+    subprocess.run(
+        ["xdg-open", location],
+        check=True,
+    )
+
+
+def main(parser: argparse.ArgumentParser, args: argparse.Namespace) -> int:
+    if not (args.output or args.show):
+        parser.print_help(file=sys.stderr)
+        print("Must either --output or --show, or both.", file=sys.stderr)
+        return os.EX_USAGE
+
+    lines = scrape_storage_classes().split("\n")
+    G = load_graph(lines)
+    nodes = select_vertices_of_interest(G, args.target)
+    dot_source = generate_dot_source(G, nodes)
+    output_location = render_png(dot_source, args.output)
+    if args.show:
+        show_graph(output_location)
+    return os.EX_OK
+
+
+def build_parser() -> argparse.ArgumentParser:
+    parser = argparse.ArgumentParser(
+        description="Visualise the inheritance of Synapse's storage classes. Requires "
+        "ripgrep (https://github.com/BurntSushi/ripgrep) as 'rg'; graphviz "
+        "(https://graphviz.org/) for the 'dot' program; and networkx "
+        "(https://networkx.org/). Requires Python 3.8+ for the walrus"
+        "operator."
+    )
+    parser.add_argument(
+        "target",
+        nargs="?",
+        help="Show only TARGET and its ancestors. Otherwise, show the entire hierarchy.",
+    )
+    parser.add_argument(
+        "--output",
+        nargs=1,
+        help="Render inheritance graph to a png file.",
+    )
+    parser.add_argument(
+        "--show",
+        action="store_true",
+        help="Open the inheritance graph in an image viewer.",
+    )
+    return parser
+
+
+if __name__ == "__main__":
+    parser = build_parser()
+    args = parser.parse_args()
+    sys.exit(main(parser, args))