fix: keep System.dat lines indented with spaces

libretro indents 39 rom lines of System.dat with spaces. The export
read tab-indented lines only, so those left the base and came back
re-rendered at the end of their section, and one our transcription
lacked would have been deleted. Any indentation is read and kept.

scripts/exporter/systemdat_exporter.py

@@ -36,7 +36,10 @@ def _quote(name: str, quoted: frozenset[str] = frozenset()) -> str:
     return f'"{name}"' if name in quoted or any(c in name for c in ' ()') else name
 
 
-_ROM_NAME = re.compile(r'^\trom \( name ("[^"]+"|\S+)')
+# libretro indents most lines with a tab and 39 with four spaces (the Amiga
+# kickstarts, the TI-83). Read with a tab only, those lines left the base and
+# came back re-rendered, re-indented and moved to the end of their section.
+_ROM_NAME = re.compile(r'^(\s+)rom \( name ("[^"]+"|\S+)')
 
 
 def _sections(original: str) -> list[tuple[str, list[str]]]:
@@ -46,9 +49,10 @@ def _sections(original: str) -> list[tuple[str, list[str]]]:
         return []
     sections: list[tuple[str, list[str]]] = []
     for line in body.splitlines():
-        if line.startswith('\tcomment "') and line != '\tcomment "System"':
-            sections.append((line[len('\tcomment "'):].rstrip('"'), []))
-        elif line.startswith("\trom (") and sections:
+        stripped = line.lstrip()
+        if stripped.startswith('comment "') and stripped != 'comment "System"':
+            sections.append((stripped[len('comment "'):].rstrip('"'), []))
+        elif stripped.startswith("rom (") and line != stripped and sections:
             sections[-1][1].append(line)
     return sections
 
@@ -180,7 +184,11 @@ class Exporter(BaseExporter):
             body = []
             for line in roms:
                 match = _ROM_NAME.match(line)
-                body.append(rendered.pop(match.group(1), line) if match else line)
+                if match and match.group(2) in rendered:
+                    # The values are ours, the indentation stays libretro's.
+                    body.append(match.group(1) + rendered.pop(match.group(2)).lstrip("\t"))
+                else:
+                    body.append(line)
             body.extend(rendered.values())
             section(comment, body)
         for comment in sorted(ours):

tests/test_exporters.py

@@ -782,6 +782,37 @@ class RommExport(unittest.TestCase):
         self.assertTrue(all(k.startswith("psx:") for k in data))
 
 
+class SystemDatKeepsSpaceIndentedLines(unittest.TestCase):
+    """libretro indents 39 rom lines with four spaces. Read with a tab only,
+    they left the base and came back last in their section, re-indented."""
+
+    def test_order_and_indentation_survive(self):
+        amiga = "Commodore - Amiga"
+        a, b = "1" * 32, "2" * 32
+        original = (
+            'clrmamepro (\n\tname "System"\n)\n\ngame (\n\tname "System"\n'
+            '\tcomment "System"\n\n'
+            f'\tcomment "{amiga}"\n'
+            f"    rom ( name kick33180.A500 size 262144 md5 {a} )\n"
+            f"\trom ( name kick34005.A500 size 262144 md5 {b} )\n"
+            ")\n"
+        )
+        scraped = {"systems": {"commodore-amiga": {"native_id": amiga, "files": [
+            {"name": "kick33180.A500", "destination": "kick33180.A500",
+             "native_system": amiga, "md5": a, "size": 262144},
+            {"name": "kick34005.A500", "destination": "kick34005.A500",
+             "native_system": amiga, "md5": b, "size": 262144},
+        ]}}}
+        systems, report = build_native_model({"systems": {}}, scraped)
+        produced = discover_exporters()["retroarch"]().render(
+            systems, report, {"System.dat": original}, None
+        )["System.dat"]
+        body = produced[produced.index(f'comment "{amiga}"'):].splitlines()[1:3]
+        self.assertTrue(body[0].startswith("    rom ( name kick33180.A500"), body)
+        self.assertTrue(body[1].startswith("\trom ( name kick34005.A500"), body)
+        self.assertEqual(produced.count("kick33180.A500"), 1)
+
+
 class RommSizeIsNeverNone(unittest.TestCase):
     """size() is None where the truth contradicts RomM's hash without a size
     or names several sizes; str(None) went out as "None", validate() passed