[XamlC] Fix error XDataTypeSyntax message format

[simonrozsival]

Description of Change

Invalid syntax in x:DataType reported a weird error message:

MainPage.xaml : XamlC error : Input string was not in a correct format. Failure to parse near offset 69. Unexpected closing brace without a corresponding opening brace. [MyMauiApp/MyMauiApp.csproj::TargetFramework=net9.0-maccatalyst]

With the fix in the error message, this is printed instead:

MainPage.xaml(11,33): XamlC error XFC0102: x:DataType expects a string literal, an {{x:Type}} markup or {{x:Null}}. [MyMauiApp/MyMauiApp.csproj::TargetFramework=net9.0-maccatalyst]

Questions

• Should this be fixed in main or just in net9.0?
• Are the double curly brackets what we actually want? Is it necessary to prevent string interpolation in some context?

[StephaneDelcroix]

thanks for this. could go to main, and yes, those messages are processed by String.Format to replace positional arguments

[simonrozsival]

@StephaneDelcroix I thought that could be the case. Should we then maybe drop the {{ }} altogether?

MainPage.xaml(11,33): XamlC error XFC0102: x:DataType expects a string literal, an {{x:Type}} markup or {{x:Null}}.

vs.

MainPage.xaml(11,33): XamlC error XFC0102: x:DataType expects a string literal, an x:Type markup or x:Null.

[StephaneDelcroix]

the processed error message should show single {}

[simonrozsival]

@StephaneDelcroix I'm getting the {{x:Type}} with double curly braces in the build output.