Detect permissions issues running flutter on Windows

[DanTup]

I think this is a reasonable fix for #17972 (/ #17967 / #17742). Currently Windows users just get stuck in an infinite loop if they put Flutter in a folder they don't have write access to (such as Program Files and then run as non-Admin).

[devoncarew]

@goderbauer, are you the best one to review this PR?

[devoncarew]

@DanTup, @mit-mit, what about updating the getting started page for windows to specifically call out not installing flutter into Program Files?

[mit-mit]

Sure, but there are many other folders with similar issues.

[DanTup]

I think there could be value calling it out given how common it seems to be (probably because people are used to install apps there). I think Program Files, Program Files (x86) and Windows are the main ones (I can't find a full list on the MS site though). It's better to avoid the issue altogether than have someone put it in the wrong place and have to move it?

[goderbauer]

This may encourage users to run flutter ad admin, which is something we shouldn't do IMHO. Actually, on Linux we explicitly disallow that. Can we rephrase this to something that doesn't push users towards running things as admin? E.g. "This may be because flutter doesn't have write permissions for %FLUTTER_ROOT%. Consider moving flutter to a writable path, e.g. your home directory."

[goderbauer]

+1 to warning people about extracting Flutter into directories that are known to be problematic.

It might be even better to give users an explicit example path in the instructions that they should use. The instructions currently say:

Extract the zip-file and place the contained flutter in the desired installation location for the Flutter SDK

This could be changed to: "Extract the zip-file and place the contained flutter directory in the desired installation location for the Flutter SDK (e.g. C:\src\flutter)"

[DanTup]

I've tweaked the text, let me know if this looks better. I can also tweak the website tomorrow if there are no objections to your suggestion.

[goderbauer]

LGTM

[goderbauer]

nit: maybe say "try moving the flutter directory..." since we don't want people to just move the flutter executable?

[DanTup]

Done. I've also changed the next instance of folder to location since it seemed weird to mix directory and folder and if I made them all the same there were three instances of directory in that line (move your flutter directory to a writeable directory such as your home directory).

Now reads:

This may be because flutter doesn't have write permissions for
this path. Try moving the flutter directory to a writable location,
such as within your home directory.

I'll land this, but feel free to request changes (or just change it) if you're not sold on it :)

[DanTup]

Extract the zip-file and place the contained flutter directory in the desired installation location for the Flutter SDK (e.g. C:\src\flutter)

I was going to add to this:

Do not extract Flutter to a folder that requires elevated permissions (like C:\Program Files\).

However this could be misinterpreted as that being a suggestion of somewhere good. Is the first change above enough, or should we include something like the second line (but maybe word it in a less ambiguous way)?