perf: fix O(n²) descendant traversal + close #33 (disallow Luau keywords)

[R-unic]

Summary

Continued hot-path cleanup, plus GitHub issue #33.

Perf

• Node.GetDescendants() rebuilt/copied at every level of recursion (O(n²) for deep or chain-like subtrees) — rewritten as a single-pass BFS traversal.
• TypeChecker.GetReturnType walked the entire subtree of a function body (including nested function bodies) via GetDescendants<Return>(), then filtered back down via an ancestor check — replaced with a bounded traversal that stops at nested FunctionDeclaration boundaries.

Bugs found and fixed along the way

• FlowAnalyzer.Analyze() had stopped invoking the actual analysis pass entirely (a dropped BindState(...) call), so every flow-dependent diagnostic — unreachable code, use of uninitialized/maybe-uninitialized variables, assignment to immutable bindings — had silently stopped firing.
• FlowAnalyzer had no case for EnumDeclaration (unlike InterfaceDeclaration/EventDeclaration, which both mark their own symbol as initialized), so referencing an enum after declaring it incorrectly tripped "use of uninitialized variable". No existing test exercised an enum through the full pipeline, so this went unnoticed until flow analysis was actually running again.

Issue #33 — disallow Luau keywords as declaration names

• New LuauFactory.Keywords set (the 21 standard Lua/Luau keywords + Luau's continue).
• Resolver.DeclareSymbol now rejects declaring a variable, function, parameter, interface, or trait whose name collides — including inside ambient declare ... signatures, since their emitted forms (e.g. an interface's type X = {...} alias) are still real Luau text.
• Enum member names are exempt: they're always constant-folded to literal values at compile time and never appear in emitted Luau as an identifier (verified via actual codegen output).
• self is intentionally excluded (not a real collision case).
• Found and fixed one existing collision in the shipped intrinsics: a function-named parameter used across several Roblox API bindings (e.g. BindToRenderStep) — renamed to callback in the TypeGenerator's rename map and regenerated None.loom/PluginSecurity.loom to match, otherwise every compile would have immediately failed against the compiler's own bundled bindings.
• Bonus fix in the same area: PropertyAccess.Render always emitted dot-access with no bracket-access fallback for a keyword-colliding property name — fixed per-segment.

Test plan

• dotnet build — succeeds, no warnings
• dotnet test — 1798/1798 pass (1783 existing + 15 new, covering the new diagnostic, the ambient/enum exemptions, the two flow-analysis fixes, and the bracket-access rendering)
• Compiled a real project through Loom.CLI before/after the perf changes — output byte-identical
• Verified end-to-end: a trivial project now compiles cleanly against the regenerated intrinsics; declaring a keyword-named let/fn/parameter/interface (including inside declare) now errors with the new diagnostic; an enum with a keyword-named member still compiles and constant-folds correctly

Closes #33

🤖 Generated with Claude Code

[github-actions]

Qodana for .NET

245 new problems were found

Inspection name	Severity	Problems
Auto-property accessor is never used (private accessibility)	🔶 Warning	6
Auto-property accessor is never used (non-private accessibility)	🔶 Warning	5
Non-accessed positional property (non-private accessibility)	🔶 Warning	2
Redundant argument with default value	🔶 Warning	2
Type member is never used (private accessibility)	🔶 Warning	1
Unused parameter (private accessibility)	🔶 Warning	1
Type member is never used (non-private accessibility)	◽️ Notice	94
Use preferred style of 'new' expression when created type is not evident	◽️ Notice	83
Member can be made private (non-private accessibility)	◽️ Notice	18
Class is never instantiated (non-private accessibility)	◽️ Notice	4
Some values of the enum are not processed inside 'switch' statement	◽️ Notice	4
Auto-property can be made get-only (non-private accessibility)	◽️ Notice	3
Invert 'if' statement to reduce nesting	◽️ Notice	3
RoslynAnalyzers The member referenced by the MemberData attribute returns untyped data rows	◽️ Notice	3
Use preferred style for trailing comma before new line in multiline lists	◽️ Notice	2
RoslynAnalyzers Do not use Enumerable methods on indexable collections	◽️ Notice	2
RoslynAnalyzers Use concrete types when possible for improved performance	◽️ Notice	2
Auto-property can be made get-only (private accessibility)	◽️ Notice	1
Foreach loop can be converted into LINQ-expression but another 'GetEnumerator' method will be used	◽️ Notice	1
Merge null/pattern checks into complex pattern	◽️ Notice	1
Redundant string interpolation	◽️ Notice	1
Replace with 'field' keyword	◽️ Notice	1
Some values of the enum are not processed inside 'switch' statement and are handled via default section	◽️ Notice	1
Tail recursive call can be replaced with loop	◽️ Notice	1
Type member is never accessed via base type (non-private accessibility)	◽️ Notice	1
Method return value is never used (non-private accessibility)	◽️ Notice	1
Literal length can be reduced by using verbatim string	◽️ Notice	1

☁️ View the detailed Qodana report

Detected 1 dependency

Third-party software list

This page lists the third-party software dependencies used in Loom

Dependency	Version	Licenses
Tomlyn	2.6.0	BSD-2-Clause

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