Cross compilation: explicitly exclude package / rule from a toolchain

[guibou]

Description of the problem / feature request:

The rules in my repository can be built by a few of the --compiler / --cpu combinations available. For example:

• Most of my "desktop" programs can accept all the --compiler (e.g. clang, gcc), but only the --cpu default.
• Some rules are only compatibles with some --cpu / --compiler tuples. For example, I have rules which only works for arm32bit / gcc.

I cannot use bazel build //... because it will try to use the default --compiler / --cpu to build all my targets. I must explicitly list all target I want to build.

The only workaround I'm aware of is to, for each rule, add a tags = ["manual"] conditionally using a select query. That's painful.

Could you add a way to, per package, tags rules by the list of toolchain (i.e. the --cpu / --compiler) for which these rules can be built.

Feature requests: what underlying problem are you trying to solve with this feature?

I'm trying to simplify my workflow which involves a lot of boilerplate external scripts which call bazel and a lot of boilerplate inside. Mostly, I have a continuous integration process which fails to test a few rules each time I forget to list these new rules explicitly in the build process.

What operating system are you running Bazel on?

Linux.

What's the output of bazel info release?

I'm using a patched bazel 0.15, but I have seen nothing on the release note of 0.16 or 0.17rc related to this issue.

[gregestren]

This should be addressed pretty effectively by the configurability roadmap in the sections on flagless multiplatform builds.

We also have precedent for skipping targets under //... that don't match the current platform.

[guibou]

@gregestren I saw the configurability roadmap and I'm looking forward for this plateforms attribute. Thank you.

[aiuto]

This is essentially a duplicate of #3780