Add script to debug fixed point numbers in lldb

.gitignore

@@ -10,3 +10,7 @@ imported_assets
 *_old.glb
 /replay.json
 *.replay.tmp
+
+# Python debugger formatter tests
+__pycache__/
+*.pyc

README.md

@@ -2,6 +2,15 @@
 
 Fancy heavily advanced platform fighting game
 
+## Debugging fixed-point values with lldb
+
+If using CodeLLDB:
+```json
+"preRunCommands": [
+    "command script import ${workspaceFolder}/tools/lldb_fixed.py"
+]
+```
+
 ## Direct P2P Debugging
 
 ```text
@@ -16,18 +25,9 @@ cargo run -- --debug-match --players 2 --local-port 7001 \
 
 ## Production Build
 
-Production builds use the `production` Cargo profile and do not dynamically
-link Bevy or Rust. Development builds retain Bevy dynamic linking for faster
-iteration. Cargo stores the production profile under `target/production`,
-separate from development artifacts under `target/debug`.
-
 ```sh
 cargo run --locked \
   --bin process-assets --no-default-features --features debug_features
 cargo build --locked \
   --profile production --no-default-features --features debug_features
-```
-
-The asset preprocessing command must be run from the repository root. It
-populates `imported_assets/Default`, which is then consumed by the production
-game without running the asset processor at startup.
+```

tools/lldb_fixed.py

@@ -0,0 +1,123 @@
+"""LLDB summaries for Rust's `fixed` crate.
+
+Load this file from LLDB with:
+
+    command script import /path/to/shinespark/tools/lldb_fixed.py
+
+The implementation does not use floating-point arithmetic, so displayed values
+are exact even for FixedI128/FixedU128 values.
+"""
+
+import re
+
+try:
+    import lldb
+except ImportError:
+    # Keep the pure parsing and formatting helpers testable without LLDB.
+    lldb = None
+
+
+_FIXED_TYPE_RE = re.compile(r"(?:^|::)Fixed([IU])(8|16|32|64|128)<(.+)>$")
+_DIRECT_TYPENUM_RE = re.compile(r"(?:^|::)U(\d+)$")
+_TYPENUM_BIT_RE = re.compile(r"(?:^|::)B([01])(?=\s*[,>])")
+
+
+def parse_fixed_type(type_name):
+    """Return (signed, storage_bits, fractional_bits), or None."""
+    if not type_name:
+        return None
+
+    match = _FIXED_TYPE_RE.search(type_name.replace(" ", ""))
+    if match is None:
+        return None
+
+    signed = match.group(1) == "I"
+    storage_bits = int(match.group(2))
+    fractional_type = match.group(3)
+
+    direct = _DIRECT_TYPENUM_RE.search(fractional_type)
+    if direct is not None:
+        fractional_bits = int(direct.group(1))
+    else:
+        # typenum represents UInt<N, B> as a binary tree. Its textual Rust
+        # type lists the bits from most significant to least significant.
+        digits = _TYPENUM_BIT_RE.findall(fractional_type)
+        if not digits:
+            return None
+        fractional_bits = int("".join(digits), 2)
+
+    if fractional_bits > storage_bits:
+        return None
+    return signed, storage_bits, fractional_bits
+
+
+def normalize_bits(raw_bits, signed, storage_bits):
+    """Interpret a possibly unsigned LLDB integer using the fixed type's width."""
+    mask = (1 << storage_bits) - 1
+    raw_bits &= mask
+    if signed and raw_bits >= 1 << (storage_bits - 1):
+        raw_bits -= 1 << storage_bits
+    return raw_bits
+
+
+def format_fixed(raw_bits, fractional_bits):
+    """Format a scaled integer exactly as a decimal string."""
+    if fractional_bits == 0:
+        return str(raw_bits)
+
+    negative = raw_bits < 0
+    magnitude = -raw_bits if negative else raw_bits
+    whole = magnitude >> fractional_bits
+    remainder = magnitude & ((1 << fractional_bits) - 1)
+
+    if remainder == 0:
+        result = str(whole)
+    else:
+        # remainder / 2^n == (remainder * 5^n) / 10^n, which gives a finite,
+        # exact decimal representation without converting through a float.
+        decimal = str(remainder * 5**fractional_bits).zfill(fractional_bits)
+        result = f"{whole}.{decimal.rstrip('0')}"
+
+    return f"-{result}" if negative else result
+
+
+def _parse_lldb_integer(value):
+    text = value.GetValue()
+    if text is not None:
+        try:
+            return int(text, 0)
+        except ValueError:
+            pass
+
+    # GetValueAsUnsigned is also useful on LLDB versions that do not render
+    # primitive values through GetValue. It is sufficient for all <= 64-bit
+    # fixed types; current LLDB versions render i128/u128 through GetValue.
+    return value.GetValueAsUnsigned()
+
+
+def fixed_summary(value, _internal_dict):
+    layout = parse_fixed_type(value.GetTypeName())
+    if layout is None:
+        return None
+
+    signed, storage_bits, fractional_bits = layout
+    bits = value.GetChildMemberWithName("bits")
+    if not bits.IsValid():
+        return None
+
+    raw_bits = _parse_lldb_integer(bits)
+    raw_bits = normalize_bits(raw_bits, signed, storage_bits)
+    return format_fixed(raw_bits, fractional_bits)
+
+
+def __lldb_init_module(debugger, _internal_dict):
+    # LLDB's type-name regex sees the concrete fixed type rather than project
+    # aliases such as FGi32 and FGWide.
+    debugger.HandleCommand(
+        "type summary add --python-function lldb_fixed.fixed_summary "
+        "--category Shinespark --regex "
+        "'^fixed::Fixed(I|U)(8|16|32|64|128)<.+>$'"
+    )
+    # A dedicated category makes the formatter work even when CodeLLDB has not
+    # enabled rustc's standard `Rust` formatter category yet.
+    debugger.HandleCommand("type category enable Shinespark")

tools/test_lldb_fixed.py

@@ -0,0 +1,58 @@
+import unittest
+
+import lldb_fixed
+
+
+class ParseFixedTypeTests(unittest.TestCase):
+    def test_direct_typenum_alias(self):
+        self.assertEqual(
+            lldb_fixed.parse_fixed_type("fixed::FixedI32<typenum::uint::U16>"),
+            (True, 32, 16),
+        )
+
+    def test_expanded_typenum(self):
+        type_name = (
+            "fixed::FixedI32<"
+            "typenum::uint::UInt<"
+            "typenum::uint::UInt<"
+            "typenum::uint::UInt<"
+            "typenum::uint::UInt<"
+            "typenum::uint::UInt<typenum::uint::UTerm, typenum::bit::B1>, "
+            "typenum::bit::B0>, typenum::bit::B0>, typenum::bit::B0>, "
+            "typenum::bit::B0>>"
+        )
+        self.assertEqual(lldb_fixed.parse_fixed_type(type_name), (True, 32, 16))
+
+    def test_unsigned_type(self):
+        self.assertEqual(
+            lldb_fixed.parse_fixed_type("fixed::FixedU64<typenum::uint::U24>"),
+            (False, 64, 24),
+        )
+
+    def test_unrelated_type(self):
+        self.assertIsNone(lldb_fixed.parse_fixed_type("core::primitive::i32"))
+
+
+class FormatFixedTests(unittest.TestCase):
+    def test_q16_16(self):
+        self.assertEqual(lldb_fixed.format_fixed(3 << 15, 16), "1.5")
+        self.assertEqual(lldb_fixed.format_fixed(-(3 << 15), 16), "-1.5")
+        self.assertEqual(lldb_fixed.format_fixed(1, 16), "0.0000152587890625")
+
+    def test_integer_value_has_no_decimal_suffix(self):
+        self.assertEqual(lldb_fixed.format_fixed(12 << 16, 16), "12")
+
+    def test_q96_32(self):
+        raw = (1 << 100) + (1 << 31)
+        self.assertEqual(
+            lldb_fixed.format_fixed(raw, 32),
+            "295147905179352825856.5",
+        )
+
+    def test_twos_complement_normalization(self):
+        self.assertEqual(lldb_fixed.normalize_bits(0xFFFF8000, True, 32), -32768)
+        self.assertEqual(lldb_fixed.normalize_bits(0xFFFF8000, False, 32), 0xFFFF8000)
+
+
+if __name__ == "__main__":
+    unittest.main()