feat: extract retrobat guarded bios ini writes

emulatorLauncher writes a BIOS path into an emulator's configuration only when the file exists: string x = Path.Combine(bios, "name"); if (File.Exists(x)) ini.WriteValue(section, key, x). The extractor now records each such write as a fixed_name launcher record, with the enclosing if and early-return conditions, and a key that receives the bios folder itself as passes_path. A path reassigned before the check, or a write under a loop or an else, is not read. Generators read at 48cdc616: KegaFusion (SCD and 32X keys, GenesisBIOS given the folder), Jgenesis, MelonDS (DS), Mupen64, Project64, mGBA. The RetroBat paragraph of the Kega Fusion profile now lives in the launcher layer.
2026-10-23 20:29:06 -05:00 · 2026-10-21 10:42:09 +02:00
1 parent fd1d1b7b96
commit 448540dced
@@ -37,13 +37,6 @@ notes: |
  file names the binary fixes. Each file is opened with fopen "rb" and read
  with a fixed count, no length, checksum or header is compared.

-  RetroBat's generator writes SCDEURBIOS, SCDUSABIOS and SCDJAPBIOS as
-  bios_CD_E.bin, bios_CD_U.bin and bios_CD_J.bin, and the three 32X keys as
-  32X_G_BIOS.BIN, 32X_M_BIOS.BIN and 32X_S_BIOS.BIN in its bios folder, each
-  only when the file exists. GenesisBIOS receives the bios folder itself, so
-  the fopen fails and no TMSS ROM is loaded. The 8-bit keys are not written.
-  ref: emulatorlauncher Generators/KegaFusion.Generator.cs:99-128
-
  CDTray.raw, Cursor_8.raw, STATIC_8.RAW and gg_nor.all are looked up by name
  in an archive embedded in the executable (0x47a530), not on disk. Plugins
  (*.rpi) and the KGV1 video codec ship with the program. Fusion.ini, battery
@@ -3238,6 +3238,261 @@ launchers:
  fails_when_missing: not checked by the launcher
  depends_on_option: duck_bios
  source_ref: "emulatorLauncher/Generators/Duckstation.Generator.cs:204-209, .emulationstation/es_features.cfg:11638-11646"
+- emulator: jgenesis
+  build: standalone
+  kind: fixed_name
+  names:
+  - gba_bios.bin
+  case_insensitive: true
+  search_dir: bios
+  passes_to: "jgenesis-config.toml [game_boy_advance] bios_path, only if the file\
+    \ exists"
+  fails_when_missing: bios_path not written
+  depends_on_option: system == "game_boy_advance"
+  source_ref: "emulatorLauncher/Generators/Jgenesis.Generator.cs:257-263"
+- emulator: jgenesis
+  build: standalone
+  kind: fixed_name
+  names:
+  - bios_CD_U.bin
+  case_insensitive: true
+  search_dir: bios
+  passes_to: "jgenesis-config.toml [sega_cd] bios_path, only if the file exists"
+  fails_when_missing: bios_path not written
+  depends_on_option: system == "genesis" || system == "sega_cd" || system == "sega_32x",
+    system == "sega_cd"
+  source_ref: "emulatorLauncher/Generators/Jgenesis.Generator.cs:282-283, 317, 323-324"
+- emulator: jgenesis
+  build: standalone
+  kind: fixed_name
+  names:
+  - bios_CD_J.bin
+  case_insensitive: true
+  search_dir: bios
+  passes_to: "jgenesis-config.toml [sega_cd] jp_bios_path, only if the file exists"
+  fails_when_missing: jp_bios_path not written
+  depends_on_option: system == "genesis" || system == "sega_cd" || system == "sega_32x",
+    system == "sega_cd"
+  source_ref: "emulatorLauncher/Generators/Jgenesis.Generator.cs:282-283, 318, 325-326"
+- emulator: jgenesis
+  build: standalone
+  kind: fixed_name
+  names:
+  - bios_CD_E.bin
+  case_insensitive: true
+  search_dir: bios
+  passes_to: "jgenesis-config.toml [sega_cd] eu_bios_path, only if the file exists"
+  fails_when_missing: eu_bios_path not written
+  depends_on_option: system == "genesis" || system == "sega_cd" || system == "sega_32x",
+    system == "sega_cd"
+  source_ref: "emulatorLauncher/Generators/Jgenesis.Generator.cs:282-283, 319, 327-328"
+- emulator: kega-fusion
+  build: standalone
+  kind: fixed_name
+  names:
+  - bios_CD_E.bin
+  case_insensitive: true
+  search_dir: bios
+  passes_to: Fusion.ini SCDEURBIOS, only if the file exists
+  fails_when_missing: SCDEURBIOS not written
+  source_ref: "emulatorLauncher/Generators/KegaFusion.Generator.cs:106-108"
+- emulator: kega-fusion
+  build: standalone
+  kind: fixed_name
+  names:
+  - bios_CD_U.bin
+  case_insensitive: true
+  search_dir: bios
+  passes_to: Fusion.ini SCDUSABIOS, only if the file exists
+  fails_when_missing: SCDUSABIOS not written
+  source_ref: "emulatorLauncher/Generators/KegaFusion.Generator.cs:110-112"
+- emulator: kega-fusion
+  build: standalone
+  kind: fixed_name
+  names:
+  - bios_CD_J.bin
+  case_insensitive: true
+  search_dir: bios
+  passes_to: Fusion.ini SCDJAPBIOS, only if the file exists
+  fails_when_missing: SCDJAPBIOS not written
+  source_ref: "emulatorLauncher/Generators/KegaFusion.Generator.cs:114-116"
+- emulator: kega-fusion
+  build: standalone
+  kind: fixed_name
+  names:
+  - 32X_G_BIOS.BIN
+  case_insensitive: true
+  search_dir: bios
+  passes_to: Fusion.ini 32XM68KBIOS, only if the file exists
+  fails_when_missing: 32XM68KBIOS not written
+  source_ref: "emulatorLauncher/Generators/KegaFusion.Generator.cs:118-120"
+- emulator: kega-fusion
+  build: standalone
+  kind: fixed_name
+  names:
+  - 32X_M_BIOS.BIN
+  case_insensitive: true
+  search_dir: bios
+  passes_to: Fusion.ini 32XMSH2BIOS, only if the file exists
+  fails_when_missing: 32XMSH2BIOS not written
+  source_ref: "emulatorLauncher/Generators/KegaFusion.Generator.cs:122-124"
+- emulator: kega-fusion
+  build: standalone
+  kind: fixed_name
+  names:
+  - 32X_S_BIOS.BIN
+  case_insensitive: true
+  search_dir: bios
+  passes_to: Fusion.ini 32XSSH2BIOS, only if the file exists
+  fails_when_missing: 32XSSH2BIOS not written
+  source_ref: "emulatorLauncher/Generators/KegaFusion.Generator.cs:126-128"
+- emulator: kega-fusion
+  build: standalone
+  kind: passes_path
+  names: []
+  search_dir: bios
+  passes_to: Fusion.ini GenesisBIOS = bios
+  fails_when_missing: false
+  source_ref: "emulatorLauncher/Generators/KegaFusion.Generator.cs:99, 103"
+- emulator: melonds
+  build: standalone
+  kind: fixed_name
+  names:
+  - firmware.bin
+  case_insensitive: true
+  search_dir: bios
+  passes_to: "melonDS.toml [DS] FirmwarePath, only if the file exists"
+  fails_when_missing: FirmwarePath not written
+  depends_on_option: melonds_externalBIOS on
+  source_ref: "emulatorLauncher/Generators/MelonDS.Generator.cs:167, 174-175"
+- emulator: melonds
+  build: standalone
+  kind: fixed_name
+  names:
+  - bios7.bin
+  case_insensitive: true
+  search_dir: bios
+  passes_to: "melonDS.toml [DS] BIOS7Path, only if the file exists"
+  fails_when_missing: BIOS7Path not written
+  depends_on_option: melonds_externalBIOS on
+  source_ref: "emulatorLauncher/Generators/MelonDS.Generator.cs:168, 177-178"
+- emulator: melonds
+  build: standalone
+  kind: fixed_name
+  names:
+  - bios9.bin
+  case_insensitive: true
+  search_dir: bios
+  passes_to: "melonDS.toml [DS] BIOS9Path, only if the file exists"
+  fails_when_missing: BIOS9Path not written
+  depends_on_option: melonds_externalBIOS on
+  source_ref: "emulatorLauncher/Generators/MelonDS.Generator.cs:169, 180-181"
+- emulator: mupen64
+  build: standalone
+  kind: fixed_name
+  names:
+  - IPL_JAP.n64
+  case_insensitive: true
+  search_dir: bios/Mupen64plus
+  passes_to: "Config/mupen64plus.cfg [Rosalie's Mupen GUI Core 64DD] 64DD_JapaneseIPL,\
+    \ only if the file exists"
+  fails_when_missing: 64DD_JapaneseIPL not written
+  source_ref: "emulatorLauncher/Generators/Mupen64.Generator.cs:228-230"
+- emulator: mupen64
+  build: standalone
+  kind: fixed_name
+  names:
+  - IPL_USA.n64
+  case_insensitive: true
+  search_dir: bios/Mupen64plus
+  passes_to: "Config/mupen64plus.cfg [Rosalie's Mupen GUI Core 64DD] 64DD_AmericanIPL,\
+    \ only if the file exists"
+  fails_when_missing: 64DD_AmericanIPL not written
+  source_ref: "emulatorLauncher/Generators/Mupen64.Generator.cs:232-234"
+- emulator: mupen64
+  build: standalone
+  kind: fixed_name
+  names:
+  - IPL_DEV.n64
+  case_insensitive: true
+  search_dir: bios/Mupen64plus
+  passes_to: "Config/mupen64plus.cfg [Rosalie's Mupen GUI Core 64DD] 64DD_DevelopmentIPL,\
+    \ only if the file exists"
+  fails_when_missing: 64DD_DevelopmentIPL not written
+  source_ref: "emulatorLauncher/Generators/Mupen64.Generator.cs:236-238"
+- emulator: project64
+  build: standalone
+  kind: fixed_name
+  names:
+  - IPL_JAP.n64
+  case_insensitive: true
+  search_dir: bios/Mupen64plus
+  passes_to: "Config/Project64.cfg [Settings] Disk IPL ROM Path, only if the file\
+    \ exists"
+  fails_when_missing: Disk IPL ROM Path not written
+  source_ref: "emulatorLauncher/Generators/Project64.Generator.cs:91-93"
+- emulator: project64
+  build: standalone
+  kind: fixed_name
+  names:
+  - IPL_USA.n64
+  case_insensitive: true
+  search_dir: bios/Mupen64plus
+  passes_to: "Config/Project64.cfg [Settings] Disk IPL USA ROM Path, only if the file\
+    \ exists"
+  fails_when_missing: Disk IPL USA ROM Path not written
+  source_ref: "emulatorLauncher/Generators/Project64.Generator.cs:95-97"
+- emulator: project64
+  build: standalone
+  kind: fixed_name
+  names:
+  - IPL_DEV.n64
+  case_insensitive: true
+  search_dir: bios/Mupen64plus
+  passes_to: "Config/Project64.cfg [Settings] Disk IPL TOOL ROM Path, only if the\
+    \ file exists"
+  fails_when_missing: Disk IPL TOOL ROM Path not written
+  source_ref: "emulatorLauncher/Generators/Project64.Generator.cs:99-101"
+- emulator: mgba
+  build: standalone
+  kind: fixed_name
+  names:
+  - gb_bios.bin
+  case_insensitive: true
+  search_dir: bios
+  passes_to: "config.ini [ports.qt] gb.bios, only if the file exists"
+  fails_when_missing: gb.bios not written
+  source_ref: "emulatorLauncher/Generators/mGBA.Generator.cs:112-114"
+- emulator: mgba
+  build: standalone
+  kind: fixed_name
+  names:
+  - sgb2_boot.bin
+  case_insensitive: true
+  search_dir: bios
+  passes_to: "config.ini [ports.qt] sgb.bios, only if the file exists"
+  fails_when_missing: sgb.bios not written
+  source_ref: "emulatorLauncher/Generators/mGBA.Generator.cs:116-118"
+- emulator: mgba
+  build: standalone
+  kind: fixed_name
+  names:
+  - gbc_bios.bin
+  case_insensitive: true
+  search_dir: bios
+  passes_to: "config.ini [ports.qt] gbc.bios, only if the file exists"
+  fails_when_missing: gbc.bios not written
+  source_ref: "emulatorLauncher/Generators/mGBA.Generator.cs:120-122"
+- emulator: mgba
+  build: standalone
+  kind: fixed_name
+  names:
+  - gba_bios.bin
+  case_insensitive: true
+  search_dir: bios
+  passes_to: "config.ini [ports.qt] gba.bios, only if the file exists"
+  fails_when_missing: gba.bios not written
+  source_ref: "emulatorLauncher/Generators/mGBA.Generator.cs:124-126"
 - emulator: hatari
  build: standalone
  kind: fixed_name
@@ -23,13 +23,19 @@ SOURCE_FILES = (
    f"{GENERATORS}/Bizhawk.Generator.cs",
    f"{GENERATORS}/Duckstation.Generator.cs",
    f"{GENERATORS}/Hatari.Generator.cs",
+    f"{GENERATORS}/Jgenesis.Generator.cs",
+    f"{GENERATORS}/KegaFusion.Generator.cs",
    f"{GENERATORS}/LibRetro.CoreOptions.cs",
    f"{GENERATORS}/Mednafen.Generator.cs",
+    f"{GENERATORS}/MelonDS.Generator.cs",
    f"{GENERATORS}/Mesen.Generator.cs",
+    f"{GENERATORS}/Mupen64.Generator.cs",
    f"{GENERATORS}/OpenMSX.Generator.cs",
    f"{GENERATORS}/Pcsx2.Generator.cs",
+    f"{GENERATORS}/Project64.Generator.cs",
    f"{GENERATORS}/Uae.Generator.cs",
    f"{GENERATORS}/Xemu.Generator.cs",
+    f"{GENERATORS}/mGBA.Generator.cs",
    FEATURES,
 )

@@ -54,6 +60,7 @@ class Source:
        self.text = text
        self._starts = [0] + [m.end() for m in re.finditer(r"\n", text)]
        self._blocks: list[tuple[int, int]] | None = None
+        self._ends: list[int] | None = None

    def line(self, offset: int) -> int:
        return bisect.bisect_right(self._starts, offset)
@@ -107,6 +114,15 @@ class Source:
            raise LauncherPatternMissing(self.path, f"block around line {self.line(offset)}")
        return max(holding)

+    def header(self, block: tuple[int, int]) -> str:
+        """The statement that owns a block's opening brace, comments removed."""
+        if self._ends is None:
+            self._ends = [o for o, c in _code_chars(self.text) if c in ";{}"]
+        previous = bisect.bisect_left(self._ends, block[0]) - 1
+        start = self._ends[previous] + 1 if previous >= 0 else 0
+        text = re.sub(r"//[^\n]*|/\*.*?\*/", "", self.text[start : block[0]], flags=re.S)
+        return " ".join(text.split())
+
    def statement_span(self, block: tuple[int, int]) -> tuple[int, int]:
        """Lines of a block, from the statement that owns its opening brace."""
        first, last = self.lines(*block)
@@ -1169,10 +1185,223 @@ def duckstation(sources: dict[str, Source]) -> list[Record]:
    ]


+# Generators that write each BIOS path into the emulator's configuration
+# only when the file exists: string x = Path.Combine(bios, ..., "name");
+# if (File.Exists(x)) ini.WriteValue("section", "key", x).
+GUARDED_WRITES = {
+    f"{GENERATORS}/Jgenesis.Generator.cs": "jgenesis",
+    f"{GENERATORS}/KegaFusion.Generator.cs": "kega-fusion",
+    f"{GENERATORS}/MelonDS.Generator.cs": "melonds",
+    f"{GENERATORS}/Mupen64.Generator.cs": "mupen64",
+    f"{GENERATORS}/Project64.Generator.cs": "project64",
+    f"{GENERATORS}/mGBA.Generator.cs": "mgba",
+}
+
+_METHOD = re.compile(
+    r"(?:(?:public|private|protected|internal|static|override|virtual)\s+)+[\w<>\[\],. ]+\s\w+\s*\("
+)
+_TRANSPARENT = re.compile(r"(?:using\s*\(.*\)|try)")
+_IF = re.compile(r"(?:else\s+)?if\s*\((.*)\)")
+_GUARD = re.compile(
+    r'if \(File\.Exists\((\w+)\)\)\s*(\w+)\.WriteValue\("([^"]*)", "([^"]+)", ([^;\n]+)\);'
+)
+_BIOS_ROOT = r'(?:Program\.)?AppConfig\.GetFullPath\("bios"\)'
+
+
+def _negate(condition: str) -> str:
+    """The condition under which an early return is not taken.
+
+    A conjunction of inequalities becomes the disjunction of equalities,
+    anything else is wrapped in not (...).
+    """
+    tests = condition.split(" && ")
+    compared = [re.fullmatch(rf"(\w+) != ({STRING})", t) for t in tests]
+    if all(compared):
+        return " || ".join(f"{m.group(1)} == {m.group(2)}" for m in compared)
+    return f"not ({condition})"
+
+
+Reach = tuple[tuple[int, int], list[str], list[tuple[int, int]]]
+
+
+def _conditions(src: Source, offset: int) -> Reach | None:
+    """The method holding offset, the conditions under which it is reached,
+    and the lines of the early returns among them.
+
+    Each enclosing if adds its condition, and an early return at the top of
+    the method adds the condition that does not return. None when a block in
+    between is not an if, a using or a try: a loop or an else would need its
+    own reading.
+    """
+    enclosing: list[str] = []
+    for block in sorted((b for b in src.blocks() if b[0] < offset < b[1]), reverse=True):
+        header = src.header(block)
+        if _METHOD.match(header):
+            returns, spans = [], []
+            for found in re.finditer(r"\bif \(", src.text[block[0] : offset]):
+                paren = block[0] + found.end() - 1
+                if src.enclosing(paren) != block:
+                    continue
+                cond = _call_args(src, paren)
+                tail = re.compile(r"\s*return\b[^;]*;").match(src.text, paren + len(cond) + 2)
+                if tail:
+                    returns.append(_negate(" ".join(cond.split())))
+                    spans.append(src.lines(block[0] + found.start(), tail.end()))
+            return block, returns + enclosing[::-1], spans
+        condition = _IF.fullmatch(header)
+        if condition:
+            text = " ".join(condition.group(1).split())
+            switch = re.fullmatch(
+                r'SystemConfig\.isOptSet\("(\w+)"\) && SystemConfig\.getOptBoolean\("\1"\)', text
+            )
+            enclosing.append(f"{switch.group(1)} on" if switch else text)
+        elif not _TRANSPARENT.fullmatch(header):
+            return None
+    return None
+
+
+def _config_name(src: Source, method: tuple[int, int], writer: str) -> str:
+    """The file the writer variable opens, read in its method or else in the file."""
+    opener = r"(\w+)\s*=\s*(?:\w+\.FromFile|new \w+)\((\w+)"
+    declared = {
+        m.group(1): "/".join(_strings(m.group(2)))
+        for m in re.finditer(
+            r'string (\w+) = Path\.Combine\(path, ((?:"[^"]+"(?:, )?)+)\);', src.text
+        )
+    }
+    local = [
+        m.group(2)
+        for m in re.finditer(opener, src.text[method[0] : method[1]])
+        if m.group(1) == writer and m.group(2) in declared
+    ]
+    if local:
+        return declared[local[0]]
+    files = {declared[m.group(2)] for m in re.finditer(opener, src.text) if m.group(2) in declared}
+    if len(files) != 1:
+        raise LauncherPatternMissing(src.path, f"configuration file opened as {writer}")
+    return files.pop()
+
+
+def _root_writes(src: Source, emulator: str) -> list[Record]:
+    """Configuration keys that receive the bios folder itself."""
+    records = []
+    for root in re.finditer(rf"string (\w+) = {_BIOS_ROOT};", src.text):
+        root_reach = _conditions(src, root.start())
+        if root_reach is None:
+            continue
+        method = root_reach[0]
+        for write in re.compile(
+            rf'(\w+)\.WriteValue\("([^"]*)", "([^"]+)", {root.group(1)}\);'
+        ).finditer(src.text, root.end(), method[1]):
+            reached = _conditions(src, write.start())
+            if reached is None:
+                continue
+            writer, section, key = write.groups()
+            target = f"[{section}] {key}" if section else key
+            records.append(
+                _record(
+                    emulator,
+                    "standalone",
+                    "passes_path",
+                    [],
+                    source_ref(
+                        (
+                            src.path,
+                            [
+                                *reached[2],
+                                src.lines(root.start(), root.end()),
+                                src.lines(write.start(), write.end()),
+                            ],
+                        )
+                    ),
+                    search_dir="bios",
+                    passes_to=f"{_config_name(src, method, writer)} {target} = bios",
+                    fails_when_missing=False,
+                    depends_on_option=", ".join(reached[1]) or None,
+                )
+            )
+    return records
+
+
+def _guarded_write(src: Source, emulator: str, guard: re.Match[str]) -> Record | None:
+    """The record of one guarded write, None when its shape is another one.
+
+    The written value must be the checked path itself (quoted or with its
+    separators replaced), the path a literal under the bios folder that
+    nothing reassigns before the check, and every block around the write an
+    if, a using or a try.
+    """
+    var, writer, section, key, value = guard.groups()
+    if not re.fullmatch(
+        rf"(?:{STRING} \+ )?{var}(?:\.Replace\({STRING}, {STRING}\))?(?: \+ {STRING})?",
+        value.strip(),
+    ):
+        return None
+    reached = _conditions(src, guard.start())
+    if reached is None:
+        return None
+    method, conditions, returns = reached
+    decls = list(
+        re.compile(
+            rf"string {var} = Path\.Combine\((\w+|{_BIOS_ROOT}), ((?:{STRING}, )*{STRING})\);"
+        ).finditer(src.text, method[0], guard.start())
+    )
+    if not decls or re.search(rf"\b{var}\s*=[^=]", src.text[decls[-1].end() : guard.start()]):
+        return None
+    decl = decls[-1]
+    root = decl.group(1)
+    if not re.fullmatch(_BIOS_ROOT, root) and not re.search(
+        rf"string {root} = {_BIOS_ROOT};", src.text[method[0] : decl.start()]
+    ):
+        return None
+    *folders, name = _strings(decl.group(2))
+    target = f"[{section}] {key}" if section else key
+    return _record(
+        emulator,
+        "standalone",
+        "fixed_name",
+        [name],
+        source_ref(
+            (
+                src.path,
+                [
+                    *returns,
+                    src.lines(decl.start(), decl.end()),
+                    src.lines(guard.start(), guard.end()),
+                ],
+            )
+        ),
+        case_insensitive=True,
+        search_dir="/".join(["bios", *folders]),
+        passes_to=f"{_config_name(src, method, writer)} {target}, only if the file exists",
+        fails_when_missing=f"{key} not written",
+        depends_on_option=", ".join(conditions) or None,
+    )
+
+
+def guarded_writes_in(src: Source, emulator: str) -> list[Record]:
+    """Every guarded write of one generator, then the keys given the bios folder."""
+    found = [_guarded_write(src, emulator, guard) for guard in _GUARD.finditer(src.text)]
+    records = [record for record in found if record is not None]
+    if not records:
+        raise LauncherPatternMissing(src.path, "File.Exists guarded WriteValue")
+    return records + _root_writes(src, emulator)
+
+
+def guarded_writes(sources: dict[str, Source]) -> list[Record]:
+    """One fixed name per configuration key, written only when the file exists."""
+    return [
+        record
+        for path, emulator in GUARDED_WRITES.items()
+        for record in guarded_writes_in(sources[path], emulator)
+    ]
+
+
 EXTRACTORS: tuple[Callable[[dict[str, Source]], list[Record]], ...] = (
    amiberry,
    ares,
    duckstation,
+    guarded_writes,
    hatari,
    hatari_libretro,
    mesen,
@@ -201,6 +201,94 @@ HATARI_FEATURES = """
 """


+KEGA = """
+    private void SetupConfiguration(string path, string system)
+    {
+        string iniFile = Path.Combine(path, "Fusion.ini");
+
+        using (var ini = IniFile.FromFile(iniFile))
+        {
+            string biosPath = AppConfig.GetFullPath("bios");
+            if (!Directory.Exists(biosPath)) try { Directory.CreateDirectory(biosPath); }
+                catch { }
+
+            ini.WriteValue("", "GenesisBIOS", biosPath);
+
+            // BIOS
+            string euBios = Path.Combine(biosPath, "bios_CD_E.bin");
+            if (File.Exists(euBios))
+                ini.WriteValue("", "SCDEURBIOS", euBios);
+
+            string bios32Xg = Path.Combine(biosPath, "32X_G_BIOS.BIN");
+            if (File.Exists(bios32Xg))
+                ini.WriteValue("", "32XM68KBIOS", bios32Xg);
+        }
+    }
+"""
+
+JGENESIS = """
+    private void SetupTomlConfiguration(string path)
+    {
+        string settingsFile = Path.Combine(path, "jgenesis-config.toml");
+        using (IniFileJGenesis ini = new IniFileJGenesis(settingsFile, IniOptionsJGenesis.UseSpaces))
+        {
+            ConfigureGenesis(ini, system);
+        }
+    }
+
+    private void ConfigureGenesis(IniFileJGenesis ini, string system)
+    {
+        if (system != "genesis" && system != "sega_cd")
+            return;
+
+        if (system == "sega_cd")
+        {
+            string segaCdBios = Path.Combine(AppConfig.GetFullPath("bios"), "bios_CD_U.bin");
+
+            ini.WriteValue("sega_cd", "per_region_bios", "true");
+
+            if (File.Exists(segaCdBios))
+                ini.WriteValue("sega_cd", "bios_path", "'" + segaCdBios + "'");
+        }
+    }
+"""
+
+MELONDS = """
+    private void SetupConfiguration(string path, string rom)
+    {
+        string settingsFile = Path.Combine(path, "melonDS.toml");
+
+        using (IniTomlFile ini = IniTomlFile.FromFile(settingsFile, IniTomlOptions.UseSpaces))
+        {
+            if (SystemConfig.isOptSet("melonds_externalBIOS") && SystemConfig.getOptBoolean("melonds_externalBIOS"))
+            {
+                string bios7 = Path.Combine(AppConfig.GetFullPath("bios"), "bios7.bin");
+
+                if (File.Exists(bios7))
+                    ini.WriteValue("DS", "BIOS7Path", "\\"" + bios7.Replace("\\\\", "/") + "\\"");
+            }
+        }
+    }
+"""
+
+# Kronos: the path is replaced by an option before the check, so the name
+# checked is not the literal.
+REASSIGNED = """
+    private void SetupConfiguration(string path)
+    {
+        string conf = Path.Combine(path, "kronos.ini");
+        using (var ini = IniFile.FromFile(conf))
+        {
+            string bios = Path.Combine(AppConfig.GetFullPath("bios"), "saturn_bios.bin");
+            if (SystemConfig.isOptSet("kronos_force_bios"))
+                bios = Path.Combine(AppConfig.GetFullPath("bios"), SystemConfig["kronos_force_bios"]);
+            if (File.Exists(bios))
+                ini.WriteValue("1.0", "General\\\\Bios", bios.Replace("\\\\", "/"));
+        }
+    }
+"""
+
+
 def _psx_sources() -> dict[str, rl.Source]:
    return _sources(
        **{
@@ -314,6 +402,68 @@ class NamesInLauncherOrder(unittest.TestCase):
        self.assertEqual(option["search_dir"], "bios/hatari/tos")


+def _one(text: str, emulator: str, path: str = f"{G}/X.Generator.cs") -> list[dict]:
+    return rl.guarded_writes_in(_sources(**{path: text})[path], emulator)
+
+
+class GuardedConfigWrites(unittest.TestCase):
+    def test_kega_fusion_one_record_per_key(self):
+        records = _one(KEGA, "kega-fusion")
+        fixed = [r for r in records if r["kind"] == "fixed_name"]
+        self.assertEqual(
+            [(r["names"], r["passes_to"], r["fails_when_missing"]) for r in fixed],
+            [
+                (["bios_CD_E.bin"], "Fusion.ini SCDEURBIOS, only if the file exists",
+                 "SCDEURBIOS not written"),
+                (["32X_G_BIOS.BIN"], "Fusion.ini 32XM68KBIOS, only if the file exists",
+                 "32XM68KBIOS not written"),
+            ],
+        )
+        self.assertEqual(fixed[0]["source_ref"], f"{G}/X.Generator.cs:14-16")
+        self.assertTrue(all(r["search_dir"] == "bios" and r["case_insensitive"] for r in fixed))
+        self.assertNotIn("depends_on_option", fixed[0])
+
+    def test_kega_fusion_genesis_key_receives_the_folder(self):
+        (folder,) = [r for r in _one(KEGA, "kega-fusion") if r["kind"] == "passes_path"]
+        self.assertEqual(folder["names"], [])
+        self.assertEqual(folder["passes_to"], "Fusion.ini GenesisBIOS = bios")
+        self.assertEqual(folder["source_ref"], f"{G}/X.Generator.cs:7, 11")
+
+    def test_early_return_and_enclosing_if_are_conditions(self):
+        (record,) = _one(JGENESIS, "jgenesis")
+        self.assertEqual(
+            record["depends_on_option"],
+            'system == "genesis" || system == "sega_cd", system == "sega_cd"',
+        )
+        self.assertEqual(
+            record["passes_to"], "jgenesis-config.toml [sega_cd] bios_path, only if the file exists"
+        )
+        self.assertEqual(record["source_ref"], f"{G}/X.Generator.cs:12-13, 17, 21-22")
+
+    def test_option_switch_is_named(self):
+        (record,) = _one(MELONDS, "melonds")
+        self.assertEqual(record["names"], ["bios7.bin"])
+        self.assertEqual(record["depends_on_option"], "melonds_externalBIOS on")
+        self.assertEqual(
+            record["passes_to"], "melonDS.toml [DS] BIOS7Path, only if the file exists"
+        )
+
+    def test_reassigned_path_is_not_a_fixed_name(self):
+        with self.assertRaises(rl.LauncherPatternMissing):
+            _one(REASSIGNED, "kronos")
+
+    def test_write_inside_a_loop_is_not_read(self):
+        looped = KEGA.replace("// BIOS", "foreach (var x in xs)\n            {").replace(
+            '"32XM68KBIOS", bios32Xg);', '"32XM68KBIOS", bios32Xg);\n            }'
+        )
+        with self.assertRaises(rl.LauncherPatternMissing):
+            _one(looped, "kega-fusion")
+
+    def test_pinned_kega_fusion_generator_is_read(self):
+        self.assertIn(f"{G}/KegaFusion.Generator.cs", rl.SOURCE_FILES)
+        self.assertEqual(rl.GUARDED_WRITES[f"{G}/KegaFusion.Generator.cs"], "kega-fusion")
+
+
 class AbsentConstructStopsTheScrape(unittest.TestCase):
    def test_each_extractor_raises_on_an_empty_source(self):
        empty = {path: rl.Source(path, "") for path in rl.SOURCE_FILES}