Implement compile time MergedDictionaties

[maxkatz6]

What does the pull request do?

Replaces:

<ResourceDictionary xmlns='https://github.com/avaloniaui'
                    xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'>
    <SolidColorBrush x:Key='brush1'>Red</SolidColorBrush>
</ResourceDictionary>

and

<ResourceDictionary xmlns='https://github.com/avaloniaui'
                    xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'>
    <SolidColorBrush x:Key='brush2'>Blue</SolidColorBrush>
    <ResourceDictionary.MergedDictionaries>
        <MergeResourceInclude Source='avares://Tests/Resources.xaml'/>
    </ResourceDictionary.MergedDictionaries>
</ResourceDictionary>

with equivalent of:

<ResourceDictionary xmlns='https://github.com/avaloniaui'
                    xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'>
    <SolidColorBrush x:Key='brush1'>Red</SolidColorBrush>
    <SolidColorBrush x:Key='brush2'>Blue</SolidColorBrush>
</ResourceDictionary>

(The first xaml file is still available for the ResourceInclude, at least with current implementation)

Important to mention, that this PR at current state is half efficient, because our theme-variant resources cannot be merged into a global theme. Because we have to attach/detach them in runtime to get working theme switch. This completely not forgotten PR aims to solve this by introducing ThemeDictionaries, which also can be merged into a parent ThemeDictionaries.

Also, no merging for StyleInclude was done in this PR. It might give us a slight improvement, but I doubt it will be any significant due to differences how they are resolved.

Breaking changes

If we remove original resources, then it won't be possible to ResourceInclude parts of the theme.
It wasn't done yet in this PR. Not sure if we need it. But it could save some kilobytes of app size.

Benchmarks

I run couple of different benchmarks that depend on our XAML themes + a new one.
Results are based on this branch and master branch (which already has #9413 included). I planned to do another run of benchmarks on a commit before #9413 was merged, but there are too many other PRs were merged in between (including the great interface removal (tm)) making it not very reliable.

FindFluentControlTheme

A new benchmark, which shows the most improvement.
Before this PR resource lookup had to iterate over each ResourceInclude looking for the control theme. The more controls (and ResourceIncludes), the slower it is.
After this PR it just looks up merged dictionary (partially merged due to limitations explained above). Shouldn't be much slower with no matter how many controls we have.

There also is the same benchmark for Simple theme, but it shows same relative improvement, so I removed it to avoid informational noise.

Master:

Method	type	Mean	Error	StdDev	Median	Gen 0	Gen 1	Allocated
FindFluentControlTheme	Button	599.51 ns	5.229 ns	4.891 ns	597.86 ns	-	-	-
FindFluentControlTheme	DatePicker	104.66 ns	0.515 ns	0.481 ns	104.70 ns	-	-	-
FindFluentControlTheme	TextBox	246.04 ns	0.802 ns	0.751 ns	245.77 ns	-	-	-

This PR with merged resource dictionaries:

Method	type	Mean	Error	StdDev	Gen 0	Gen 1	Allocated
FindFluentControlTheme	Button	36.93 ns	0.386 ns	0.342 ns	-	-	-
FindFluentControlTheme	DatePicker	35.85 ns	0.158 ns	0.132 ns	-	-	-
FindFluentControlTheme	TextBox	40.43 ns	0.111 ns	0.104 ns	-	-	-

InitFluentTheme/InitSimpleTheme

This benchmark creates a fluent/simple theme and resolves a single resource from there.
Not a huge difference, except Simple them. No idea what happened there, but I suppose it became even more simple (IL-wise).

Master:

Method	Mean	Error	StdDev	Median	Gen 0	Gen 1	Allocated
InitFluentTheme	475,002.16 ns	4,808.775 ns	4,498.132 ns	473,144.19 ns	52.2461	21.9727	991,560 B
InitSimpleTheme	88,004.18 ns	1,678.955 ns	1,488.350 ns	87,441.86 ns	11.9629	3.1738	227,264 B

This PR with merged resource dictionaries

Method	Mean	Error	StdDev	Gen 0	Gen 1	Allocated
InitFluentTheme	416,758.14 ns	1,167.943 ns	1,092.494 ns	48.3398	21.4844	910,240 B
InitSimpleTheme	57,204.09 ns	110.930 ns	92.631 ns	7.1411	1.7700	134,984 B

Create control benchmarks

SimpleTheme is used.
Marginal improvement, but still an improvement.

Master:

Method	Mean	Error	StdDev	Gen 0	Gen 1	Allocated
CreateCalendar	4,654.810 μs	52.3468 μs	43.7119 μs	195.3125	93.7500	3,633 KB
CreateCalendarWithLoaded	4,437.421 μs	25.1641 μs	23.5385 μs	195.3125	93.7500	3,658 KB
CreateControl	3.575 μs	0.0186 μs	0.0165 μs	0.1450	-	3 KB
CreateDecorator	3.679 μs	0.0152 μs	0.0127 μs	0.1450	-	3 KB
CreateScrollViewer	53.876 μs	0.0771 μs	0.0644 μs	3.6621	0.5493	68 KB
CreateButton	21.217 μs	0.0864 μs	0.0808 μs	1.3428	0.0610	25 KB
CreateTextBox	240.633 μs	1.1244 μs	0.9968 μs	10.7422	2.9297	203 KB

This PR with merged resource dictionaries:

Method	Mean	Error	StdDev	Gen 0	Gen 1	Allocated
CreateCalendar	4,141.446 μs	22.8560 μs	21.3795 μs	195.3125	93.7500	3,633 KB
CreateCalendarWithLoaded	4,094.625 μs	13.3628 μs	11.1585 μs	195.3125	93.7500	3,658 KB
CreateControl	2.921 μs	0.0162 μs	0.0143 μs	0.1450	-	3 KB
CreateDecorator	2.969 μs	0.0081 μs	0.0076 μs	0.1450	-	3 KB
CreateScrollViewer	49.632 μs	0.2777 μs	0.2462 μs	3.6621	-	68 KB
CreateButton	19.855 μs	0.1860 μs	0.1649 μs	1.3428	0.0610	25 KB
CreateTextBox	231.171 μs	1.1218 μs	0.9944 μs	10.9863	2.9297	203 KB

Other metrics affected by this PR:

• Avalonia.Themes.Fluent binary size: increased from 3.3mb to 3.6mb. Because we basically duplicate resource definitions now by saving original files in the assembly. If we remove original ones, it will be improved, but users won't be able to include parts of the theme.

[avaloniaui-team]

You can test this PR using the following package version. 11.0.999-cibuild0026789-beta. (feed url: https://pkgs.dev.azure.com/AvaloniaUI/AvaloniaUI/_packaging/avalonia-nightly/nuget/v3/index.json) [PRBUILDID]

[timunie]

Can I still swap out a resource dictionary during runtime? I use it for example for translations

[kekekeks]

As long as you use regular ResourceInclude and not MergeResourceInclude

[avaloniaui-team]

You can test this PR using the following package version. 11.0.999-cibuild0027010-beta. (feed url: https://pkgs.dev.azure.com/AvaloniaUI/AvaloniaUI/_packaging/avalonia-nightly/nuget/v3/index.json) [PRBUILDID]

[grokys]

I can't speak for the implementation (this is @kekekeks' area, and yours I guess ;) ) but I've been wanting this feature for ages!

There's been some internal discussion about whether this should be a separate element or a compiler directive, i.e. <MergeResourceInclude> or something like <ResourceInclude x:Merge="True">.

I think the main reason that <MergeResourceInclude> was chosen was that it won't cause errors in designers that aren't aware of this directive, but someone may want to give more details here.

[avaloniaui-team]

You can test this PR using the following package version. 11.0.999-cibuild0027448-beta. (feed url: https://pkgs.dev.azure.com/AvaloniaUI/AvaloniaUI/_packaging/avalonia-nightly/nuget/v3/index.json) [PRBUILDID]