Output better XAML errors

grokys commented 4 years ago

Avalonia XAML error messages are sometimes less than ideal. This can be a big issue particularly for new users as the error messages tend to confuse more than help. Here's a few problems with them:

They duplicate the line/column numbers
They include the csproj which isn't (ever?) useful
The type information is noisy (always includes assembly and full namespace)
Types/members not quoted
They don't always give the correct column info (the open tag is marked as having the error when in reality the error occurs on e.g. a property)
The error message isn't always clear
They include irrelevant information
Setting value to a readonly property should show a better error https://github.com/AvaloniaUI/Avalonia/issues/12218

Some examples follow. This list isn't exhaustive but shows some of the more common errors:

Missing property

Invalid XAML

<Button Foo="Bar"/>

Avalonia

Unable to resolve suitable regular or attached property Foo on type Avalonia.Controls:Avalonia.Controls.Button (line 5 position 6) Line 5, position 6. [D:\projects\AvaloniaUI\Avalonia\samples\ControlCatalog\ControlCatalog.csproj]

WPF

The property 'Foo' does not exist in XML namespace 'http://schemas.microsoft.com/winfx/2006/xaml/presentation'. Line 4 Position 13.

Evaluation

Duplicate line/column numbers
csproj path is included
Types/members not quoted
This isn't attached property format so no need to mention "attached property"
Avalonia.Controls:Avalonia.Controls.Button is overkill: Button would suffice
The WPF error isn't much better to be honest

Better Error Message

Unable to resolve property 'Foo' on type 'Button'. Line 5, position 6.

Missing Event Handler

Invalid XAML:

<Button Click="Foo"/>

Avalonia:

Unable to find suitable setter or adder for property Click of type Avalonia.Controls:Avalonia.Controls.Button for argument netstandard:System.String, available setter parameter lists are: [D:\projects\AvaloniaUI\Avalonia\samples\ControlCatalog\ControlCatalog.csproj]
System.EventHandler`1<Avalonia.Interactivity.RoutedEventArgs> (line 5 position 13) Line 5, position 13. [D:\projects\AvaloniaUI\Avalonia\samples\ControlCatalog\ControlCatalog.csproj]

WPF:

'MainWindow' does not contain a definition for 'Foo' and no accessible extension method 'Foo' accepting a first argument of type 'MainWindow' could be found (are you missing a using directive or an assembly reference?)

Evaluation

netstandard:System.String is overkill
System.EventHandler``1<Avalonia.Interactivity.RoutedEventArgs> isn't particularly useful for new users
Appears as two error messages
Says "property Click" but Click is an event
Again, WPF isn't much better though at least it's less verbose

Better Error Message

Unable to find suitable handler for event 'Button.Click'. Valid handler signature is 'void Button_Click(object sender, RoutedEventArgs e)'.

Invalid value

Invalid XAML:

<Button HorizontalAlignment="Foo"/>

Avalonia:

Unable to find suitable setter or adder for property HorizontalAlignment of type Avalonia.Layout:Avalonia.Layout.Layoutable for argument netstandard:System.String, available setter parameter lists are: [D:\projects\AvaloniaUI\Avalonia\samples\ControlCatalog\ControlCatalog.csproj]
Avalonia.UnsetValueType [D:\projects\AvaloniaUI\Avalonia\samples\ControlCatalog\ControlCatalog.csproj]
Avalonia.Data.IBinding [D:\projects\AvaloniaUI\Avalonia\samples\ControlCatalog\ControlCatalog.csproj]
Avalonia.Layout.HorizontalAlignment (line 5 position 13) Line 5, position 13. [D:\projects\AvaloniaUI\Avalonia\samples\ControlCatalog\ControlCatalog.csproj]

WPF:

Requested value 'Foo' was not found.

Evaluation

Appears as three error messages
The info about UnsetValueType/IBinding isn't very useful as this obviously isn't a binding

Better Error Message

'Foo' is not a valid value for 'HorizontalAlignment'.

grokys commented 4 years ago

Another from gitter: https://gitter.im/AvaloniaUI/Avalonia?at=5f32b56eb103e45c830e2c2d

rstm-sf commented 3 years ago

Maybe add warning support as well? For example, Obsolete

maxkatz6 commented 4 months ago

"Unable to find the parent scope for AvaloniaProperty lookup" error can add a hint about where TemplateBinding can be used. And recommendation to use Bindings instead: https://github.com/AvaloniaUI/Avalonia/issues/15572

maxkatz6 commented 2 months ago

This too: https://github.com/AvaloniaUI/Avalonia/issues/16144

maxkatz6 commented 3 weeks ago

This too https://github.com/AvaloniaUI/Avalonia/discussions/16580#discussioncomment-10246589

AvaloniaUI / Avalonia