[Xamarin.Android.Build.Tasks] Try a case insensitive lookup as a backup for Legacy Designer fixup

[dellis1972]

We have a very odd situation regarding the NuGet Xamarin.CommunityToolkit.MauiCompat.

The NuGet package ships with a file .net/__res_name_case_map.txt in the
Xamarin.CommunityToolkit.MauiCompat.aar which contains the
case map changes for the AndroidResource items. The purpose of this file is to allow
the user to use Camel case (or any case) names in C# code, while the android resource
compilation is left as all lowercase. This is because android requires lowercase resource
items.

The contents of this file are as follows

Resources/Layout/CameraFragment.axml;layout/camerafragment.xml

As you can see from this camerafragment is remaped to CameraFragment. With this
change we would expect to see code in C# which uses CameraFragment. This is true
as per https://github.com/xamarin/XamarinCommunityToolkit/blob/5a6062f3c3543acda3c36ca4683cd8fc7fe86ba7/src/CommunityToolkit/Xamarin.CommunityToolkit/Views/CameraView/Android/CameraFragment.android.cs#L129.

We can see that the code in the NuGet is using the CameraFragment casing.
However when we look at the IL that comes from the NuGet package we see the following

ikdasm ~/.nuget/packages/xamarin.communitytoolkit.mauicompat/2.0.2-preview1013/lib/net6.0-android31.0/Xamarin.CommunityToolkit.MauiCompat.dll| grep Layout::camerafragment
      IL_0131:  stsfld     int32 Xamarin.CommunityToolkit.MauiCompat.Resource/Layout::camerafragment
    IL_0001:  ldsfld     int32 Xamarin.CommunityToolkit.MauiCompat.Resource/Layout::camerafragment

For some reason as part of the maui release the following script was run on the code
https://github.com/xamarin/XamarinCommunityToolkit/blob/5a6062f3c3543acda3c36ca4683cd8fc7fe86ba7/MauiCompat.sh#L561.

This force changes the case of the CameraFragment to camerafragment across the whole project.
But the NuGet still includes the .aar with the case map changes (which are no longer needed).
I'm not sure why this happens but it results in the following build error when trying to consume this package
under .net8.0-android with the new Resource Designer.

XA8000
Could not find Android Resource ‘@layout/camerafragment’. Please update @(AndroidResource) to add the missing resource.

This is because we are looking for the lowercase version of the resource in the Designer assembly property list, but because
of the remap file. We only have the Camel case version.

The current workaround is to fallback to a case insensitive lookup... My first thought was to always use a case insensitive
lookup. But there are cases where users have two files with different cases. This is possible on systems like Linux and MacOS.

[jonpryor]

@dellis1972 wrote:

My first thought was to always use a case insensitive lookup. But there are cases where users have two files with different cases. This is possible on systems like Linux and MacOS.

(macOS is case-insensitive by default, like Windows, so you can't have two files with different cases unless you create a new filesystem, e.g. APFS Case Sensitive.)

I think we may be overthinking this? For file-backed resources, we always lowercase the filename before passing on to aapt2/etc., because those tools require lowercase filenames. (This doesn't apply to resources declared within files, such as colors or strings.)

It thus should not be possible to have two file-based Android resources which differ only in case.

@dellis1972: does __res_name_case_map.txt only contain file-based resources, not all resources?

If __res_name_case_map.txt only deals with file-based resources, then I think your original thought was correct: always use case-insensitive (for file-based resources). If it applies to all resources…ugh.

Though I suspect that FixBody() is used for all resource types (colors, strings, ids, etc.), not just file-based resources, in which case we do need the "check for case-sensitive first, then fallback" approach.

[dellis1972]

__res_name_case_map.txt only contains the files which have case changes.
But I think the fallback approach will be the safest option in this case.

[jonpryor]

This could be a problem, as .Add() will throw if a "duplicate key" already exists:

var d = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
d.Add ("A", "a");
d.Add ("a", "a");
// throws System.ArgumentException: An item with the same key has already been added. Key: a

Either we should use caseInsensitiveLookup.TryAdd(key, property.GetMethod) (.NET Standard 2.1), or we should use the indexer caseInsensitiveLookup[key] = property.GetMethod, though using the indexer means that caseInsensitiveLookup will always contain the last case-insensitive value encountered rather than the first (which might be fine?).

[dellis1972]

well we only use .netstandard 2.0 so I guess that makes the decision for us.

[jonpryor]

[Xamarin.Android.Build.Tasks] case-insensitive Legacy Designer fixup (#8376)

Context: 628d6cb869c872c34d17b014724a43e8d451fb93
Context: dc3ccf28cdbe9f8c0a705400b83c11a85c81a980

We have a very odd situation with the
[`Xamarin.CommunityToolkit.MauiCompat` NuGet package][0]:

The NuGet package ships with a file `.net/__res_name_case_map.txt`
(628d6cb8) in `Xamarin.CommunityToolkit.MauiCompat.aar` which contains
the case mapchanges for the `@(AndroidResource)` items.  The purpose
of this file is to allow the user to use PascalCase (or any case) names
in C# code, while the Android Resource compilation is left as all
lowercase.  This is because Android requires that file-backed resource
names consist of only lowercase letters.

The contents of this file includes:

	Resources/Layout/CameraFragment.axml;layout/camerafragment.xml

which tells us that the Android `R.layout.camerafragment` resource id
should be "bound" as `Resouce.Layout.CameraFragment`, which allows
[`CameraFragment.android.cs` to build][1]:

	public override AView? OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) =>
	    inflater.Inflate(Resource.Layout.CameraFragment, null);

However, when we look at the IL that comes from the NuGet package we
see the following

	ikdasm ~/.nuget/packages/xamarin.communitytoolkit.mauicompat/2.0.2-preview1013/lib/net6.0-android31.0/Xamarin.CommunityToolkit.MauiCompat.dll| grep Layout::camerafragment
	…
	    IL_0131:  stsfld     int32 Xamarin.CommunityToolkit.MauiCompat.Resource/Layout::camerafragment
	    IL_0001:  ldsfld     int32 Xamarin.CommunityToolkit.MauiCompat.Resource/Layout::camerafragment

For some reason as part of the maui release [the following script][2]
was run on the code:

	sed -i '' 's/MauiCompat.Resource.Layout.CameraFragment/MauiCompat.Resource.Layout.camerafragment/g' ./src/CommunityToolkit/Xamarin.CommunityToolkit.MauiCompat/**/CameraFragment.android.cs

This force changes the case of `CameraFragment` to `camerafragment`.
However, the NuGet still includes the `.aar` with the case map
changes, which are now inconsistent. 

I'm not sure why this happens but it results in the following build
error when trying to consume this package under net8.0-android with
the new Resource Designer Assembly (dc3ccf28):

	error XA8000: Could not find Android Resource ‘@layout/camerafragment’. Please update @(AndroidResource) to add the missing resource.

This is because we are looking for the lowercase version of the
resource in the Designer assembly property list, but because of the
remap file we only know about the PascalCase version. 

As a workaround, fallback to a *case-insensitive* lookup.

[0]: https://www.nuget.org/packages/Xamarin.CommunityToolkit.MauiCompat/
[1]: https://github.com/xamarin/XamarinCommunityToolkit/blob/5a6062f3c3543acda3c36ca4683cd8fc7fe86ba7/src/CommunityToolkit/Xamarin.CommunityToolkit/Views/CameraView/Android/CameraFragment.android.cs#L129
[2]: https://github.com/xamarin/XamarinCommunityToolkit/blob/5a6062f3c3543acda3c36ca4683cd8fc7fe86ba7/MauiCompat.sh#L561