Get rid of unique ids in SVG files.

This commit makes the following assumptions:
- SVG unique ids add a significant amount of noise to "git diff" outputs
- SVG unique ids are only necessary when embedding multiple SVG files
  inside the same HTML page
- even then, it was apparently necessary to further suffix style names
- SVG snapshots are embedded only in the HTML report
- SVG unique ids are kinda hard to control due to the "distance" between
  pytest and the function that actually generates them:
  1. pytest_textual_snapshot.snap_compare.<locals>.compare()
  2. textual._doc.take_svg_screenshot()
  3. App.export_screenshot()
  4. rich.Console.export_svg(... unique_id=None)

This change introduces:
- normalization of persisted SVG snapshots by stripping their ids;
- individualization of embedded SVG pictures by randomizing their ids.

Consequently:
- this change does not require to regenerate existing snapshots;
- future snapshots will not contain unique ids;
- snapshots with ids can coexist with id-less snapshots;
- conflict between embedded SVG styles is extremely unlikely despite the
  removal of style name suffixes.

Author: xavierog

pytest_textual_snapshot.py

@@ -10,6 +10,7 @@
 from operator import attrgetter
 from os import PathLike
 from pathlib import Path, PurePath
+from random import random
 from tempfile import mkdtemp
 from typing import Any, Awaitable, Union, Optional, Callable, Iterable, TYPE_CHECKING
 
@@ -33,6 +34,18 @@ class SVGImageExtension(SingleFileSnapshotExtension):
     _file_extension = "svg"
     _write_mode = WriteMode.TEXT
 
+    def _read_snapshot_data_from_location(self, *args, **kwargs) -> Optional["SerializableData"]:
+        """Normalize SVG data right after they are loaded from persistent storage."""
+        data = super()._read_snapshot_data_from_location(*args, **kwargs)
+        if data is not None:
+            data = normalize_svg(data)
+        return data
+
+    def serialize(self, *args, **kwargs) -> "SerializedData":
+        """Normalize SVG data before they get compared against a snapshot and
+        before they get persisted to storage."""
+        return normalize_svg(super().serialize(*args, **kwargs))
+
 
 class TemporaryDirectory:
     """A temporary that survives forking.
@@ -71,10 +84,14 @@ class PseudoApp:
     console: PseudoConsole
 
 
-def rename_styles(svg: str, suffix: str) -> str:
-    """Rename style names to prevent clashes when combined in HTML report."""
-    return re.sub(r"terminal-(\d+)-r(\d+)", rf"terminal-\1-r\2-{suffix}", svg)
+def individualize_svg(svg: str, unique_id: Optional[str] = None) -> str:
+    """Inject a random id, à la rich.Console.export_svg()."""
+    unique_id = str(int(random() * 1e10)) if unique_id is None else unique_id
+    return re.sub(r"\bterminal(?:-\d+)?-([\w-]+)", rf"terminal-{unique_id}-\1", svg)
 
+def normalize_svg(svg: str) -> str:
+    """Strip the unique id generated by rich.Console.export_svg()."""
+    return re.sub(r"\bterminal-\d+-([\w-]+)", r"terminal-\1", svg)
 
 def pytest_addoption(parser):
     parser.addoption(
@@ -301,8 +318,8 @@ def retrieve_svg_diffs(
             n += 1
             diffs.append(
                 SvgSnapshotDiff(
-                    snapshot=rename_styles(str(expect_svg_text), f"exp{n}"),
-                    actual=rename_styles(svg_text, f"act{n}"),
+                    snapshot=individualize_svg(str(expect_svg_text)),
+                    actual=individualize_svg(svg_text),
                     test_name=name,
                     path=full_path,
                     line_number=line_index + 1,