fix: keep one dump per exported hash record

scripts/exporter/baseline.py

@@ -123,6 +123,29 @@ class NativeFile:
         values = self.hashes(field_name)
         return values[0] if values else ""
 
+    def record_hash(self, field_name: str) -> str:
+        """One value of a record whose fields all describe one dump.
+
+        A clrmamepro rom line or a RomM entry carries a single crc, md5 and
+        sha1: taking each field's first accepted value wrote syscard2.pce
+        with the v2.0 crc (the truth's first) beside the v2.1 md5 and sha1
+        (System.dat's), a record no file satisfies. When the two sides
+        agree on the dump, the platform's record is kept whole, its value
+        chosen among those the truth accepts; a field only the truth names
+        is written when it names one value, which is then that dump's.
+        """
+        source = self._identity_source()
+        truth_values = _hash_values(self.truth or {}, field_name)
+        platform_values = _hash_values(self.platform or {}, field_name)
+        if source == "truth":
+            return truth_values[0] if truth_values else ""
+        if source == "platform" or not truth_values:
+            return platform_values[0] if platform_values else ""
+        if platform_values:
+            accepted = [v for v in platform_values if v in truth_values]
+            return (accepted or truth_values)[0]
+        return truth_values[0] if len(truth_values) == 1 else ""
+
     @property
     def required(self) -> bool:
         if self.truth is not None and self.truth.get("required") is not None:

scripts/exporter/romm_exporter.py

@@ -128,13 +128,13 @@ class Exporter(BaseExporter):
                 entry: OrderedDict[str, str] = OrderedDict()
                 # The fixture states every value as a string, size included.
                 entry["size"] = str(fe.size())
-                crc = fe.hash("crc32")
+                crc = fe.record_hash("crc32")
                 if crc:
                     entry["crc"] = crc
-                md5 = fe.hash("md5")
+                md5 = fe.record_hash("md5")
                 if md5:
                     entry["md5"] = md5
-                sha1 = fe.hash("sha1")
+                sha1 = fe.record_hash("sha1")
                 if sha1:
                     entry["sha1"] = sha1
                 output[f"{system.native_id}:{fe.name}"] = entry

scripts/exporter/systemdat_exporter.py

@@ -153,13 +153,13 @@ class Exporter(BaseExporter):
                 size = fe.size()
                 if size:
                     parts.append(f"size {size}")
-                crc = fe.hash("crc32")
+                crc = fe.record_hash("crc32")
                 if crc:
                     parts.append(f"crc {crc.upper()}")
-                md5 = fe.hash("md5")
+                md5 = fe.record_hash("md5")
                 if md5:
                     parts.append(f"md5 {md5}")
-                sha1 = fe.hash("sha1")
+                sha1 = fe.record_hash("sha1")
                 if sha1:
                     parts.append(f"sha1 {sha1}")
                 rendered.setdefault(name, f"\trom ( {' '.join(parts)} )")

tests/test_exporters.py

@@ -1352,3 +1352,40 @@ class UpstreamFidelity(unittest.TestCase):
 
 if __name__ == "__main__":
     unittest.main()
+
+
+class ARecordDescribesOneDump(unittest.TestCase):
+    """syscard2.pce: System.dat states v2.1 (crc 283b74e0, md5, sha1),
+    geargrafx accepts three crcs with v2.0's first. Field by field, the
+    export wrote v2.0's crc beside v2.1's md5 and sha1."""
+
+    def test_the_platform_record_stays_whole_when_the_truth_accepts_it(self):
+        from exporter.baseline import NativeFile
+
+        fe = NativeFile(
+            name="syscard2.pce", destination="syscard2.pce", native_system="pce",
+            platform={"crc32": "283b74e0", "md5": "3cdd6614" + "0" * 24,
+                      "sha1": "88da02e2" + "0" * 32},
+            truth={"crc32": ["52520bc6", "283b74e0", "ff2a5ec3"]},
+        )
+        self.assertEqual(fe.hash("crc32"), "52520bc6")
+        self.assertEqual(fe.record_hash("crc32"), "283b74e0")
+        self.assertEqual(fe.record_hash("md5"), "3cdd6614" + "0" * 24)
+
+    def test_a_field_only_the_truth_names_is_written_when_unambiguous(self):
+        from exporter.baseline import NativeFile
+
+        one = NativeFile(name="a", destination="a", native_system="s",
+                         platform={"crc32": "11111111"},
+                         truth={"crc32": "11111111", "md5": "a" * 32})
+        two = NativeFile(name="a", destination="a", native_system="s",
+                         platform={"crc32": "11111111"},
+                         truth={"crc32": "11111111", "md5": ["a" * 32, "b" * 32]})
+        self.assertEqual(one.record_hash("md5"), "a" * 32)
+        self.assertEqual(two.record_hash("md5"), "")
+
+    def test_single_record_writers_use_it(self):
+        for module in ("systemdat_exporter.py", "romm_exporter.py"):
+            source = (Path(__file__).resolve().parent.parent / "scripts" / "exporter" / module).read_text()
+            with self.subTest(module=module):
+                self.assertNotRegex(source, r'= fe\.hash\("(crc32|md5|sha1)"\)')