[webkit-dev] LayoutTests results fallback graph

[Adam Barth]

Hi webkit-dev,

In trying to understand how our LayoutTest results system works, I've
created a digram of the fallback graph among the various
platform-specific directories:

https://docs.google.com/drawings/d/1z65SKkWrD4Slm6jobIphHwwRADyUtjOAxwGBVKBY8Kc/edit?hl=en_US

Unfortunately, the fallback graph is not a tree, as one might imagine
initially.  I'd like to propose two small changes, which will
hopefully make the system more sensible globally.  I'm happy to do all
the work required to make these changes:

1) The "win" port should fall back either to "all" (the platform
independent results) or to "mac," but not to "mac-snowleopard", as it
does currently.  (I slightly prefer "all", but "mac" would also be
fine with me.)

2) The "chromium" port should fall back directly to "all" rather than
taking a detour through various Apple-maintained ports, as it does
currently.

These changes have the following virtues:

A) The resulting fallback graph will be a tree, making the fallback
graph easier to understand for both humans and automated tools.
B) The Chromium port will behave more like the other ports (e.g., GTK
and Qt), rather than being a parasite on Apple-maintained ports.

These changes might increase the number of image baselines we store in
the tree for "chromium-mac"-derived ports (because there will be fewer
redundant fallback paths), but I expect that cost to be relatively
small because essentially every port has different image baselines
anyway.

Thoughts?
Adam