Fix DefaultItemExcludes handling in XSharp.SDK.Props

[hpetriffer]

Two independent defects in XSharp.SDK.Props

Both were found while tracking down sporadic XS9014 / XS9019 errors in a solution where a classic and an SDK-style project share one directory. Each commit stands on its own.

1. DefaultItemExcludes is assigned, not appended

<DefaultItemExcludes>$(VOBinaryFiles);$(AppXamlFiles);$(HeaderFiles);...</DefaultItemExcludes>

Microsoft.NET.Sdk.DefaultItems.props always writes $(DefaultItemExcludes);…. Here the inherited value is dropped, so anything a user sets in Directory.Build.props is silently ignored for .xsproj while it works as documented for .csproj. That is a surprising difference to debug — nothing fails, the setting just has no effect.

Evaluation order confirms the fix is narrow: with -v:diag on a real project, the final value contains the X# list followed by $(BaseOutputPath)/**, $(BaseIntermediateOutputPath)/**, publish/**, **/*.user. Those come from the .NET SDK, which is imported after this file, so the prefix picks up user values only.

2. The X# item globs have no Exclude

<EmbeddedResource Include="**/*.resx" KeepDuplicates="false">
<Compile Include="**/*.designer.prg" KeepDuplicates="false">
<NativeResource Include="**/*.rc">

These reach into obj\ and bin\. Any generated file left there from an earlier configuration becomes a project item, which shows up as XS0579 / CS0579 Duplicate attribute. It is easy to hit whenever IntermediateOutputPath changes and the old directory stays on disk.

Exclude="$(XSharpDefaultItemExcludes)" is added to all seven globs. Two details worth reviewing:

• The property is computed before the item types owned by X# are appended to DefaultItemExcludes. Using the appended value would exclude exactly the files these globs are meant to collect.
• The output directories are listed explicitly, because the .NET SDK appends them to DefaultItemExcludes only after this file is imported — too late for these globs. Condition="'$(BaseOutputPath)' != ''" guards keep a bare /** from being formed.

$(DefaultExcludesInProjectFolder) is referenced although it is still empty at this point, so the value is picked up should the import order ever change.

Verification

The file was evaluated standalone against a directory tree with decoys in obj\Debug\ and bin\Debug\:

EXCL=[;;bin\/**;obj\/**]
EmbeddedResource=[a.resx]        obj\Debug\stale.resx, bin\Debug\old.resx not collected
Compile=[foo.designer.prg]       obj\Debug\gen.designer.prg not collected
NativeResource=[r.rc]            bin\Debug\old.rc not collected
VOBinary=[x.xsfrm]  None=[a.vh]  ApplicationDefinition=[App.xaml]

-p:DefaultItemExcludes=meins\**  ->  EXCL=[meins\**;;bin\/**;obj\/**]

Not verified inside a full SDK build — that needs the file deployed to C:\Program Files (x86)\XSharp\MSBuild\. The import-order assumptions above are taken from a -v:diag evaluation of a real .xsproj.

Not included

The same ItemGroup also ignores $(EnableDefaultItems) and the per-type switches (EnableDefaultCompileItems, EnableDefaultEmbeddedResourceItems, …); the .NET SDK guards every default item group with them. Fixing that removes items from projects that set EnableDefaultItems=false and rely on the current behaviour, so it is left out here and is worth its own discussion.