Can't build for esp32 board

[Grumskiz]

I have been using the Eclipse Plugin successfully for the disco_l475_iot1 board.
Now I would like to use the esp32.

I followed the documentation for this board to set up the espressif toolchain.
I have verified that I am able to build and flash samples using west.
Zephyr, the SDK, the espressif toolchain, west, and Eclipse are all up-to-date versions and I'm running Linux.

Unfortunately, it seems that the Eclipse Plugin does not support this toolchain variant.
Naive use of the standard Zephyr SDK will fail like this:
/opt/zephyr-sdk/xtensa//xtensa-zephyr-elf/bin/xtensa-zephyr-elf-gcc not found - Please check your toolchain installation

It appears that:

• the build process looks for the ESP32 toolchain in the main SDK folder, which is not the correct place
• it incorrectly concatenates strings, or tries to select a subfolder that is an empty string

I tried setting up a Custom Toolchain in the project preferences, with ZEPHYR_TOOLCHAIN_VARIANT set to espressif and the toolchain path pointing to the correct location.
This build setting is silently ignored and erased by the plugin and it will default back to the standard Zephyr SDK option, yielding the same error as above.

The failed builds also break the build system somewhat. It's required to clean the project before rebuilding, otherwise the build system will crash with a NullPointerException.

I'd be happy to try out more, but I'm not sure where to go from here.