refactor: compute the gap report once per build

The region grouping and phase 2 of each pack and manifest called
find_undeclared_files with the same arguments: 30 reports for the 15
manifests of --all --manifest, 2.8 s, now 15 and 1.7 s. The 15 manifests
are byte-identical before and after.

scripts/generate_pack.py

@@ -546,6 +546,7 @@ def _select_variants(
     regions: list[str] | None,
     one_per_slot: bool,
     required_only: bool = False,
+    undeclared: list[dict] | None = None,
 ) -> tuple[set, list, list]:
     """Which regional and slot alternatives this pack leaves out.
 
@@ -574,6 +575,7 @@ def _select_variants(
             include_all=(source == "truth"),
             required_only=required_only,
             held_out=held,
+            undeclared=undeclared,
         )
     if regions:
         region_index = region_mod.platform_region_index(
@@ -796,9 +798,20 @@ def generate_pack(
     # dedicated extras pass with an empty seen set: it only needs group
     # membership, never destinations, and a superset of members is the safe
     # direction. Runs only when --region is given.
+    # The gap report both extras passes read, computed once: the region
+    # grouping and the core complement below ask it the same question.
+    undeclared = (
+        undeclared_report(
+            config, emulators_dir, db, emu_profiles, target_cores,
+            include_all=(source == "truth"),
+        )
+        if source != "platform" and precomputed_extras is None
+        else None
+    )
     region_drops, region_fallbacks, slot_undecidable = _select_variants(
         config, pack_systems, emulators_dir, db, base_dest, emu_profiles,
         target_cores, source, regions, one_per_slot, required_only,
+        undeclared=undeclared,
     )
 
     with _writing_pack(zip_path) as zf:
@@ -1060,6 +1073,7 @@ def generate_pack(
               _collect_emulator_extras(
                   config, emulators_dir, db, set(), base_dest, emu_profiles,
                   target_cores=target_cores, include_all=(source == "truth"),
+                  undeclared=undeclared,
               ),
               system_filter,
           )
@@ -1073,6 +1087,7 @@ def generate_pack(
               emu_profiles,
               target_cores=target_cores,
               include_all=(source == "truth"),
+              undeclared=undeclared,
           )
 
       core_count = 0
@@ -3888,6 +3903,7 @@ def _manifest_selection(
     source: str,
     required_only: bool,
     regions: list[str] | None,
+    undeclared: list[dict] | None = None,
 ) -> tuple[set[str], SelectionIndex]:
     """Destinations a region list removes, and the groups the installer replays.
 
@@ -3909,6 +3925,7 @@ def _manifest_selection(
         required_only=required_only,
         extras_out=extras,
         held_out=held,
+        undeclared=undeclared,
     )
     region_index = region_mod.platform_region_index(
         config, emu_profiles, target_cores
@@ -4100,9 +4117,18 @@ def generate_manifest(
             ),
         }
 
+    # Read by the region grouping and by phase 2 with the same arguments.
+    undeclared = (
+        undeclared_report(
+            config, emulators_dir, db, emu_profiles, target_cores,
+            include_all=(source == "truth"),
+        )
+        if source != "platform"
+        else None
+    )
     region_drops, selection = _manifest_selection(
         config, pack_systems, emulators_dir, db, base_dest, emu_profiles,
-        target_cores, source, required_only, regions,
+        target_cores, source, required_only, regions, undeclared=undeclared,
     )
 
     # Phase 1: baseline files
@@ -4296,6 +4322,7 @@ def generate_manifest(
             unplaceable=unplaceable,
             baseline_claims=baseline_claims,
             absent=absent,
+            undeclared=undeclared,
         )
     else:
         core_files = []
@@ -4802,6 +4829,7 @@ from packextras import (  # noqa: E402,F401
     emulator_region_drops,
     _emulator_region_group,
     expand_agnostic_entries,
+    undeclared_report,
 )
 
 

scripts/packextras.py

@@ -793,6 +793,26 @@ class ExtraPlacement:
         return self.slug_based and self.flat and "/" in dest
 
 
+def undeclared_report(
+    config: dict,
+    emulators_dir: str,
+    db: dict,
+    emu_profiles: dict | None,
+    target_cores: set[str] | None = None,
+    include_all: bool = False,
+) -> list[dict]:
+    """The gap report _collect_emulator_extras reads, for a caller that
+    collects the extras more than once with these arguments: the region
+    grouping and the pack or manifest phase 2 each computed it in full."""
+    from verify import find_undeclared_files
+
+    return find_undeclared_files(
+        config, emulators_dir, db, emu_profiles, target_cores=target_cores,
+        include_all=include_all,
+        declared_names=platform_declarations(config, db, enrich=False),
+    )
+
+
 def _collect_emulator_extras(
     config: dict,
     emulators_dir: str,
@@ -840,8 +860,6 @@ def _collect_emulator_extras(
 
     Works for ANY platform (RetroArch, Batocera, Recalbox, etc.)
     """
-    from verify import find_undeclared_files
-
     profiles = (
         emu_profiles
         if emu_profiles is not None
@@ -858,9 +876,8 @@ def _collect_emulator_extras(
     yaml_names = platform_declarations(config, db, enrich=False)
 
     if undeclared is None:
-        undeclared = find_undeclared_files(
-            config, emulators_dir, db, emu_profiles, target_cores=target_cores,
-            include_all=include_all, declared_names=yaml_names,
+        undeclared = undeclared_report(
+            config, emulators_dir, db, emu_profiles, target_cores, include_all
         )
     # A destination two cores claim goes to the one that names its content:
     # hypseus-singe asks for gamecontrollerdb.txt by name alone and took the
@@ -1153,6 +1170,7 @@ def platform_region_groups(
     required_only: bool = False,
     extras_out: list[dict] | None = None,
     held_out: set[str] | None = None,
+    undeclared: list[dict] | None = None,
 ) -> tuple[dict[str, list[tuple[str, str]]], dict[tuple[str, str, str], str]]:
     """Group a platform's pack candidates the way region filtering reads them.
 
@@ -1165,7 +1183,9 @@ def platform_region_groups(
     withdraw from its report exactly what the builder withdraws from the pack:
     grouping the declared files here and the core extras there would let the
     two answer differently on the same request.  `extras_out` receives the
-    core extras that were grouped, for the install manifest.
+    core extras that were grouped, for the install manifest. ``undeclared``
+    is the gap report when the caller holds it (undeclared_report, with the
+    same target_cores and include_all).
     """
     groups: dict[str, list[tuple[str, str]]] = {}
     for sys_id, system in systems.items():
@@ -1199,6 +1219,7 @@ def platform_region_groups(
         include_all=include_all,
         claimants=extra_dests,
         absent=absent,
+        undeclared=undeclared,
     )
     held = {id(extra) for extra in extras}
     spellings = system_spellings(systems)

tests/test_directory_entries.py

@@ -14,6 +14,7 @@ import json
 import sys
 import tempfile
 import unittest
+from unittest import mock
 import zipfile
 from pathlib import Path
 
@@ -247,6 +248,36 @@ class PackCarriesADirectory(DirectoryFixture):
         self.assertTrue(self.EXPECTED <= dests, sorted(dests))
         json.dumps(manifest)
 
+    def test_the_gap_report_is_computed_once_per_build(self):
+        """The region grouping and phase 2 each ran find_undeclared_files with
+        the same arguments: 30 reports for 15 manifests."""
+        import verify
+
+        real = verify.find_undeclared_files
+        calls: list[int] = []
+
+        def counted(*a, **kw):
+            calls.append(1)
+            return real(*a, **kw)
+
+        profiles = self._profiles()
+        out = self.root / "counted"
+        out.mkdir()
+        with mock.patch.object(verify, "find_undeclared_files", counted):
+            builder.generate_manifest(
+                "demo", str(self.platforms), self._db(), str(self.bios),
+                str(self.platforms / "_registry.yml"),
+                emulators_dir=str(self.emulators), emu_profiles=profiles,
+                offline=True,
+            )
+            self.assertEqual(len(calls), 1)
+            builder.generate_pack(
+                "demo", str(self.platforms), self._db(), str(self.bios), str(out),
+                emulators_dir=str(self.emulators), emu_profiles=profiles,
+                offline=True, regions=["north-america"],
+            )
+        self.assertEqual(len(calls), 2)
+
     def test_an_emulator_pack_ships_the_tree(self):
         self._profiles()
         out = self.root / "emu"