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ModernUO/CLAUDE.md
Kamron Batman ca338f023c fix(opl): refuse property list invalidation raised from inside GetProperties 
Any property getter reached from GetProperties that calls InvalidateProperties
takes the tooltip build down with it:

  System.ArgumentNullException: Value cannot be null. (Parameter 'array')
    at Server.ObjectPropertyList.AppendStringDirect(String value)
    at Server.Mobiles.PlayerMobile.GetProperties(IPropertyList list)

InvalidateProperties rebuilds in place -- Reset() then GetProperties() again on
the same instance -- and Reset() does two destructive things to a build already
in flight. It returns the pooled interpolation scratch buffer, which the compiler
rents in the interpolated-string handler ctor and returns in the closing Add, so
every hole is evaluated while that buffer is live; the next Append* then spans a
null array. It also rewinds the packet cursor, so properties already written are
overwritten by the nested pass.

There is no correct recovery, and retrying the build would only hide the defect,
so the engine refuses: the nested call logs an error with a stack trace, throws
in DEBUG so it gets found and fixed, and in RELEASE returns without touching the
list -- a possibly stale tooltip, but no crash, no corrupted packet, and nothing
leaked back to the pool. Getters that genuinely must invalidate should defer with
Timer.DelayCall(InvalidateProperties).

The guard flag lives on the ObjectPropertyList rather than on the entity: it is
that list's own lifecycle, it costs nothing (both Item and ObjectPropertyList
absorb it in existing padding, and the list is allocated lazily), and it stays
correct when builds for different entities nest.

Factions PlayerState was the getter that surfaced this, and it is now maintained
rather than lazily computed:

- Rank is a plain field read. The lazy `if (m_InvalidateRank)` recompute is gone
  along with the flag itself; UpdateRank() recomputes at each point an input
  actually changes (the RankIndex setter, the end of the KillPoints setter once
  the swap bookkeeping and ZeroRankOffset have settled, Faction.AddMember after
  the member is inserted, and FactionState after a load once the ordering is
  final). All six readers of Rank were checked; none relied on the old side
  effect.
- Both constructors seed the lowest rank. Nothing recomputes on read any more, so
  Rank must be usable immediately -- including for members that never get a
  RankIndex assigned, which is every member with no kill points.
- Rank always resolves. Ranks are ordered by Required descending ending at 0, so
  a negative percent (RankIndex out of sync with ZeroRankOffset) matched nothing
  and left m_Rank null -- an NRE on Rank.Title. It no longer divides by a zero
  ZeroRankOffset either.
- Fixes a pre-existing staleness bug: the KillPoints setter writes m_RankIndex
  directly in two places, bypassing the property setter, so the cached rank was
  never refreshed when a player crossed zero kill points.

PropertyList also publishes the list into m_PropertyList before building it
rather than assigning through `??=` afterwards, so a nested InvalidateProperties
sees the build in progress instead of recursing into a second throwaway list.

ObjectPropertyList re-rents its scratch buffer instead of spanning a null array,
so a stray Reset() from any other caller degrades rather than aborting
GetProperties.

Documents the rule as audit rule 19 in CLAUDE.md, a new section in
dev-docs/property-lists.md, and the property-lists and code-audit skills.
2026-07-28 21:20:35 -07:00

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ModernUO

.NET 10 Ultima Online server emulator. Single-threaded game loop. All game logic runs on one thread.

  • Server engine: Projects/Server/ — do NOT modify without explicit request
  • Game content: Projects/UOContent/ — primary editing target
  • Build: dotnet build from repo root

Code Audit Rules

Apply these when writing or reviewing .cs files under Projects/.

  1. LINQ — Tier 1 (zero-cost patterns) free on hot paths; Tier 2 (low overhead) OK on warm paths; Tier 3 (allocating) forbidden on hot paths → dev-docs/code-standards.md
  2. No Console.WriteLine — use LogFactory.GetLogger(typeof(MyClass)) → logger.Information(...) (requires using Server.Logging;)
  3. Threading policy — game logic runs only on the main loop; never touch game state (World, mobiles, items, maps, timers) from a background thread. Heavy work that needs game state must be chunked across ticks, not threaded. Heavy work that does not need game state (large-file parse, external I/O) must run on a background thread and must yield to world saves (defer while World.Saving/WorldState.PendingSave). Publish results back to the loop as an immutable snapshot swapped via a single volatile reference — the only sanctioned volatile. No lock/Mutex/ConcurrentDictionary in game logic. Rule #10 covers how background work hands results back to the loop → dev-docs/threading-model.md
  4. No World.Mobiles/World.Items iteration — use spatial queries: map.GetMobilesInRange<T>(), map.GetItemsInRange<T>()
  5. Clean up refs in OnDelete()/OnAfterDelete() — null out Item/Mobile references
  6. Cancel timers in OnDelete()/OnAfterDelete() — call _token.Cancel() or _timer?.Stop()
  7. STArrayPool<T>.Shared not ArrayPool<T>.Shared — single-threaded optimized, no locks
  8. PooledRefList<T> not new List<T>() on hot paths — zero GC pressure, stack-allocated ref struct
  9. Serialization — class must be partial, constructor needs [Constructible], TimerExecutionToken must NOT have [SerializableField]. New classes: use [SerializationGenerator(version)] (omit encoded). When bumping versions, add MigrateFrom(VXContent) (X = previous version). Never modify Deserialize(reader, version) for version bumps — that method is only for pre-codegen legacy saves. When migrating from pre-codegen Serialize/Deserialize: pass false if old code used reader.ReadInt(), bump version +1, and keep old logic as private void Deserialize(IGenericReader reader, int version) → dev-docs/runuo-migration-docs/02-serialization.md
  10. No Task.Run/new Thread() for game logic (tandem with rule #3) — game logic is the single-threaded event loop. Backgrounding is allowed only for work that does not itself touch game state (external service calls, large-file parse). When such work must feed game logic: run the heavy/I/O part off-loop and ConfigureAwait(false) its awaits so a continuation never resumes on the loop and silently foregrounds heavy work; then hand the result back explicitly — publish an immutable snapshot swapped via a volatile reference (the loop reads it lock-free), or marshal the apply step with Core.LoopContext.Post(() => …). Never touch game state off-thread; never let the scheduler decide where the heavy work runs → dev-docs/threading-model.md
  11. Never assume era — if code uses Core.AOS/Core.SE/etc., ask which expansion to target
  12. Naming — _camelCase private fields, PascalCase properties/methods/classes; don't flag legacy m_ but use _ for new code
  13. No empty gumps — every gump must produce visual elements. An empty gump leaks on client+server (no way to close it). Use static DisplayTo() to validate before constructing → dev-docs/gump-system.md
  14. PropertyList string literals must be holes — $"{"Map"}\t{value}" not $"Map\t{value}". The handler treats bare text as delimiters, {} holes as arguments. Only \t should be a bare literal → dev-docs/property-lists.md
  15. Braces required on all control flow — if, else, for, foreach, while, do, switch must always have braces, even for single-line bodies → dev-docs/code-standards.md
  16. Prefer switch expressions and switch-when — use switch expressions for value mapping and switch-when for pattern matching where they improve readability. Exception: skip if unreadable or cold path → dev-docs/code-standards.md
  17. No System.Text.StringBuilder — use ValueStringBuilder with stackalloc (bounded output) or ValueStringBuilder.Create() (unbounded). Supports $"..." interpolation directly. Always use using var for disposal. Use Reset() instead of reassigning → dev-docs/string-handling.md
  18. Interpolation anti-patterns on handler-aware APIs — Send*/Say/Emote/PublicOverhead*/IPropertyList.Add/gump AddLabel/AddHtml/Html.Center/SpanWriter.Write* all have ref RawInterpolatedStringHandler overloads that allocate zero strings, but only when the call-site argument is a $"..." literal directly. Avoid: ternaries with interpolated branches (Send(c ? $"a" : $"b")), switch expressions with interpolated arms, pre-built var s = $"..." locals (single-use), .ToString() / .String() / string.Format inside holes, string concat ({a + b}), LINQ string ops in holes. Use :L format spec for lowercase ({rank:L} not rank.ToString().ToLowerInvariant()) → dev-docs/string-handling.md § Interpolation Anti-Patterns
  19. No InvalidateProperties() from inside GetProperties — every property a GetProperties override reads must be a pure read. InvalidateProperties() rebuilds the list in place (Reset() + rebuild), and Reset() returns the pooled interpolation buffer — which the compiler rents for the whole $"..." expression, so every hole is evaluated while it is live — and rewinds the packet cursor. A getter that invalidates therefore throws ArgumentNullException (parameter "array") out of GetProperties from an unrelated-looking line, or silently corrupts the tooltip. The engine refuses and logs an error; DEBUG throws. Lazy recomputation in a getter is fine — the notification is not. Invalidate in the setter that changes the value, or defer with Timer.DelayCall(InvalidateProperties) → dev-docs/property-lists.md § Never Invalidate From Inside GetProperties

Dev-Docs Reference

Topic File
Code standards & LINQ tiers dev-docs/code-standards.md
Serialization system dev-docs/serialization.md
Content patterns (Items, Mobiles, Creatures) dev-docs/content-patterns.md
Era & expansion handling dev-docs/era-expansion.md
Timer system dev-docs/timers.md
Event scheduler (wall-clock/calendar) dev-docs/event-scheduler.md
Object property lists (tooltips) dev-docs/property-lists.md
Gump (UI dialog) system dev-docs/gump-system.md
Commands & targeting dev-docs/commands-targeting.md
Event system dev-docs/events.md
Threading model dev-docs/threading-model.md
Server lifecycle & bootstrap phases (Configure/ConfigurePrompts/Initialize) dev-docs/server-lifecycle.md
Configuration system dev-docs/configuration.md
Networking & packets dev-docs/networking-packets.md
Region system dev-docs/regions.md
String handling & ValueStringBuilder dev-docs/string-handling.md
RunUO migration (overview) dev-docs/runuo-migration-docs/00-overview.md
RunUO migration (all docs) dev-docs/runuo-migration-docs/

Claude Skills (Opt-In)

Detailed Claude Code skills live in dev-docs/claude-skills/. They are not auto-loaded — they must be copied to .claude/skills/ to activate.

When to offer: If the user is building complex content (new items, creatures, spells, gumps, quests, packets, serialization work, etc.), ask:

I have detailed Claude Code skills for this kind of work. Want me to enable them? I'll copy the relevant files from dev-docs/claude-skills/ to .claude/skills/.

Then copy only the relevant skill files based on the task:

Task Skills to enable
New Item or Mobile modernuo-content-patterns, modernuo-serialization, modernuo-property-lists
Creature / spawn modernuo-content-patterns, modernuo-serialization, modernuo-timers
Spell or ability modernuo-content-patterns, modernuo-serialization, modernuo-timers, modernuo-era-expansion
Gump / UI dialog modernuo-gump-system, modernuo-commands-targeting
Quest or event system modernuo-events, modernuo-content-patterns, modernuo-configuration
Scheduled / seasonal / holiday events modernuo-event-scheduler, modernuo-timers
Custom regions / dynamic areas modernuo-regions, modernuo-content-patterns
Packet / networking modernuo-networking, modernuo-threading
Commands modernuo-commands-targeting
Timer work modernuo-timers, modernuo-serialization
Config system modernuo-configuration
Era-conditional code modernuo-era-expansion
String building / formatting modernuo-string-handling
Code review / audit modernuo-code-audit
Any .cs file edit modernuo-code-audit (always offer for code changes)
RunUO Migration
Migrate any RunUO script migrate-from-runuo/migrate-foundation (always), plus system-specific skills below
Migrate Item/Mobile/Creature migrate-from-runuo/migrate-foundation, migrate-from-runuo/migrate-serialization, migrate-from-runuo/migrate-items-mobiles
Migrate serialization migrate-from-runuo/migrate-serialization
Migrate timers migrate-from-runuo/migrate-timers
Migrate gumps migrate-from-runuo/migrate-gumps
Migrate packets migrate-from-runuo/migrate-packets
Migrate property lists migrate-from-runuo/migrate-property-lists
Migrate events/commands migrate-from-runuo/migrate-commands-events
Migrate persistence (WorldSave) migrate-from-runuo/migrate-persistence
Migrate multi-file system migrate-from-runuo/migrate-systems

To enable a skill: cp dev-docs/claude-skills/<name>.md .claude/skills/

Migration skills reference the deep docs in dev-docs/runuo-migration-docs/ and point to existing ModernUO skills for best practices.

The modernuo-code-audit skill auto-triggers on .cs file edits and flags convention violations (warnings only, asks before fixing).