DRI_PRIME=1 is set unconditionally on linux when hardware adapter is used

[mukilan]

Originally reported in servo/servo#34814

The DRI_PRIME environment variable is being set by surfman unconditionally. This is the commit that introduced this feature.

According to the mesa documentation DRI_PRIME=1 will be interpreted as the number of the (non-default) GPU to use and not just as an 'enable low power mode' flag, but I don't know enough about this to say if surfman's usage of DRI_PRIME is a bug. It is also not clear to me if DRI_PRIME=1 is a bug if the system has only one gpu.

As seen in servo/servo#34814, this seems to break other applications (like some tinyfiledialog backends) in some cases. I

[mukilan]

surfman/src/platform/unix/generic/device.rs

Lines 29 to 36 in 300789d

	pub(crate) fn hardware() -> Adapter {
	Adapter::HardwarePrime
	}
	#[inline]
	pub(crate) fn low_power() -> Adapter {
	Adapter::Hardware
	}

It is also suspicious that it is hardware() that creates HardwarePrime adapter and not low_power() , which uses Hardware adapter.