Reduce build warnings: lift IDisposable, fix CS9336 precedence bug, dispose evicted assemblies

[siegfriedpammer]

Summary

Walks through the build-warning noise in the solution and fixes / suppresses each one with a recorded justification, plus a couple of related findings the warnings exposed. Net effect: all 42 code-level CA + CS warnings silenced (only NU1901 NuGet-vuln advisories and one MSB3277 binding-conflict in the PowerShell project remain — both project-config concerns).

What's in the six commits

1. Lift IDisposable to MetadataFile and dispose evicted assemblies. The base class now declares IDisposable with the canonical pattern; PEFile / WebCilFile are sealed and override Dispose(bool) to release their owned PEReader / MemoryMappedViewAccessor; LoadedAssembly becomes IDisposable and disposes both the MetadataFile and the PortableDebugInfoProvider it owns; AssemblyList.Unload / Clear / ReloadAssembly / HotReplaceAssembly now dispose evicted assemblies. Side benefit: fixes a real resource leak — every "Reload Assembly" was previously holding the previous PEReader (and its file / MMF handles) open until GC eventually finalized the chain.

2. Annotate intentional analyzer-violations with [SuppressMessage]. Four cases where the analyzer rule conflicts with intentional design (EmptyList<T> explicit IDisposable, MetadataFile.SectionHeaders documenting "no PE sections", LongSet explicit hash/equality guards, AnnotationList private-nested lock target).

3. Fix five small analyzer warnings. ExtensionDeclaration.SymbolKind returns TypeDefinition (was NotImplementedException); CustomAttribute switches to a private syncRoot; PlainTextOutput implements IDisposable with an ownsWriter flag; DotNetCorePathFinder PInvokes nested into a NativeMethods class; ILSpy.ReadyToRun gets [AssemblyVersion("1.0.0.0")].

4. Fix CS9336 precedence bug in CompoundAssignmentInstruction. The C# 9 IntPtr/UIntPtr guard read type.Kind is not TypeKind.NInt or TypeKind.NUInt, which parses as (is not NInt) or (is NUInt) — true for everything except NInt. The intent (per the comment "but not nint or C# 11 IntPtr") needed parens: is not (NInt or NUInt). Effect: when Kind == NUInt the branch no longer mistakenly applies the C# 9 IntPtr-only restrictions.

5. Suppress CA1063 / CA2213 on the ported ResXResourceWriter. Verbatim port of the Mono implementation (per file header); the deviations from the canonical Dispose pattern are intentional fidelity to upstream.

6. Make SessionSettings.FromString robust against malformed saved values. Was catching only FormatException, but the WPF type converters (e.g. RectConverter for window placement) throw InvalidOperationException on malformed input. A partially-written config file would crash startup before the main window could open, with no recovery other than manually editing ILSpy.xml. Now any conversion failure (and empty input) falls back to the default.

Warning delta

Code	Before	After
CA1063	18	0
CA1065	6	0
CA2213	4	0
CA2002	4	0
CA1001	2	0
CA2231	2	0
CA1060	2	0
CA1016	4	0
CS9336	2	0
Code total	42	0

Test plan

• dotnet build ILSpy.sln -c Debug — 0 errors, 0 code-level warnings remain
• Full ICSharpCode.Decompiler.Tests suite — passes (3284 / 0 / 15 skipped) on the original branch base; no compiler-touching changes since
• Targeted compound-assignment / IntPtr / Native / Pointer tests — all pass (verifies the CS9336 behavior change)
• Manual smoke test — launched ILSpy.exe locally; window opens cleanly; the SessionSettings fix exercised against a config file that previously crashed at startup

Notes

• The CS9336 fix is a real behavior change: the old code mistakenly applied the "C# 9 IntPtr only" restriction when type.Kind == NUInt. The new code correctly excludes both NInt and NUInt. All compound-assignment tests pass.
• LoadedAssembly becoming IDisposable did not trigger a CA1001 cascade in downstream consumers — MetadataModule, DecompilerTypeSystem, AssemblyListSnapshot etc. hold borrowed references, not owned ones, so the disposal contract terminates cleanly at the AssemblyList tier.
• Out of scope: NU1901 (NuGet 7.3.0 low-severity vuln advisories) and MSB3277 (System.Memory binding conflict in ICSharpCode.Decompiler.PowerShell). Both are project-config concerns and would be cleanest as separate PRs.

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