cc_tool builds src for wrong platform

[anguslees]

rules_cc/cc/toolchains/tool.bzl

Line 68 in 8c94e11

cfg = "exec",

I think cc_tool(src) should be cfg=target, not cfg=exec.

Explanation: The cc_tool rule does not (itself) execute the tool as a build action (no ctx.actions.run). Presumably there will eventually be some other rule that uses the output from cc_tool as an attribute, and (importantly) also invokes the tool. That rule should consume the tool via an attribute with cfg=exec, so the tool transition can evaluate all the constraints correctly for that rule.

[pzembrod]

I don't think I quite understand the reasoning in the explanation. Why should a cc_tool() not run on the exec platform?

@matts1 fyi

[armandomontanez]

There were some aspects of the initial design that warranted putting cfg=exec there, but kind of agree with you. We should probably put cfg=exec at the cc_toolchain.tool_map attribute, and remove it from the cc_tool rule.

[matts1]

tool_map already has a transition to cfg=exec (source).

I think it should be safe to just replace exec with target.