tree a9e577cda3a015b4d292c7f5ec04e9ec1779698f
parent 970739e4e35a9e54bc872d9a487b17aa735751f4
author Austin Eng <enga@chromium.org> 1637105835 +0000
committer Dawn LUCI CQ <dawn-scoped@luci-project-accounts.iam.gserviceaccount.com> 1637105835 +0000

Improve ScopedEnvironmentVar to distinguish between null and empty

Found while investigating Swiftshader support. Some Vulkan loaders
fail to create an instance if VK_ICD_FILENAMES is empty string
rather than entirely absent. It was set to empty string because
Dawn did not distinguish between nonexistent environment variables
and the empty string. This CL adds distinguishing between the two,
including tests for the behavior.

Bug: chromium:1266550
Change-Id: I1680a281f62e6b340009e01da65db9d485e2975e
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/69520
Auto-Submit: Austin Eng <enga@chromium.org>
Reviewed-by: Loko Kung <lokokung@google.com>
Commit-Queue: Austin Eng <enga@chromium.org>