"does not have mandatory providers: 'TemplateVariableInfo'" error

[jjmaestro]

I was playing with this toolchain and I was trying to use the toolchain as part of genrule toolchains:

genrule(
    name = "test",
    outs = ["out.txt"],
    cmd = "echo foo > $@",
    toolchains = [
        "@zig_sdk//toolchain:linux_amd64_gnu.2.38",
    ],
)

When I try to build the target, I get:

ERROR: /src/workspace/BUILD:1:8: in toolchains attribute of genrule rule //:test: \
  '@@hermetic_cc_toolchain~~toolchains~zig_sdk//toolchain:linux_amd64_gnu.2.38' \
  does not have mandatory providers: 'TemplateVariableInfo'

I was expecting the toolchain to also declare TemplateVariableInfo so that the tools in the toolchain could be used via Makefile variables as well, like e.g. rules_bison does.

[jjmaestro]

Also, is there a convenient way to select whatever the current toolchain is, similar to @rules_bison//bison:current_bison_toolchain?