[XSG] Passing parameters to the inflators

[StephaneDelcroix]

There are multiple ways right now to give extra instructions, per file, to the XAML inflator

• XamlCompilationAttribute
• XamlProcessingAttribute (bright new)
• xaml-comp XML processing instruction

attributes have the advantage of being available at post-compile time for XamlC to process, and we use xaml-comp XML-PI for xaml files without code-behind

Initial thought was, for XSG, to deprecate XamlCompilaiton in favour of XamlProcessing. We think it would add flexibility feasibility of change, filtering and wildcards, if we were instead using properties on in .csproj files.

XamlC could be modified to only process the list of files with the right properties, AND MOSTLY not run at all if that list is empty

[StephaneDelcroix]

/cc @simonrozsival @jonathanpeppers please discuss

[simonrozsival]

attributes have the advantage of being available at post-compile time for XamlC to process, and we use xaml-comp XML-PI for xaml files without code-behind

What sort of information do we need post-build? My understanding is that we have 3 inflators now - XamlC (runs at compile time), SourceGen (runs at compile time), and XamlLoader (runs at build time). Once the project is built, the only way to inflate XAML documents which haven't been compiled at build-time is via XamlLoader.

We think it would add flexibility feasibility of change, filtering and wildcards, if we were instead using properties on in .csproj files.

I'm leaning more and more towards MSBuild properties/items, something like:

<PropertyGroup>
    <MauiDefaultXamlInflator>SourceGen</MauiDefaultXamlInflator>
</PropertyGroup>
<ItemGroup>
    <MauiXaml Include="some/page/which/cannot/be/built/with/sg/because/of/a/bug.xaml">
        <Inflator>XamlC</Inflator>
    </MauiXaml>
    <MauiXaml Include="**/*.rt.xaml">
        <Inflator>Runtime</Inflator>
    </MauiXaml>
</ItemGroup>

XamlC ... MOSTLY not run at all if that list is empty

What does it mean mostly not run? Do we still need to run it because of validation?

[jonathanpeppers]

I like the MSBuild example above, as it's what is mostly done for other .NET file types.

Does XamlC run on the .dll file after the C# compiler? It may not have the original .xaml source files and would not have access to the MSBuild metadata.

Could the MSBuild metadata above, generate C# attributes? Then you could actually have both options.

[StephaneDelcroix]

I did some experiment to see what was possible...

For every property/metadata we want to expose, we could have a

• MauiXamlPropertyName CompilerVisibleProperty
• and a PropertyName CompilerVisibleMetadata

so for setting the Inflator, we'd have

<PropertyGroup>
    <MauiXamlInflator>SourceGen</MauiXamlInflator>
</PropertyGroup>

for global option, and

<ItemGroup>
    <MauiXaml Update="some\file.xaml" Inflator="SourceGen" />
</ItemGroup>

for individual, or wildcard, files.

And here's the list of properties I'm thinking about:

• Inflator: Runtime | XamlC | SourceGen (multiple value, on test project only, will generate the constructor switch to test multiple inflators)
• NoWarn, to disable warnings in generated code
• Nullable to change project nullable defaults
• EnableDiagnostics (default to EnableDiagnostics), default would be different for Debug/Release
• LineInfo to disable the verbose (very verbose) #line info

All of this (but specifying multiple values to Inflator) is public API, but not meant to be used in "normal" situations

[StephaneDelcroix]

Does XamlC run on the .dll file after the C# compiler? It may not have the original .xaml source files and would not have access to the MSBuild metadata.

y, that's the case

Could the MSBuild metadata above, generate C# attributes? Then you could actually have both options.

that means the XamlC task would have to run to detect those attributes. we should instead modify XamlC so it accepts a list of files to process