Document best practices for consuming autoconf/make C++ external dependencies

[htuch]

Currently, at https://bazel.build/versions/master/docs/external.html, there's a variety of guidance for consuming external deps, but none that is suitable for handling existing C++ deps. It's certainly not scalable and even valid advice in many cases to suggest that the consuming projects of a dependency just write a BUILD file that they keep up to date on a best effort basis that parallels the existing autoconf/make based build system.

As I discovered in #2792, envoyproxy/envoy#716 and envoyproxy/envoy#747, there are a variety of approaches to encapsulating the autoconf/make process, with a repository_rule the cleanest way to do this. This should be a recommendation on https://bazel.build/versions/master/docs/external.html. In addition, we should have a simpler example, similar to envoyproxy/envoy#747 of how this is used. Currently, the only example in this vain is

bazel/tools/cpp/cc_configure.bzl

Line 288 in ac29b78

# has false positives

, linked to from https://bazel.build/versions/master/docs/skylark/repository_rules.html, which is crazy complicated.

[steven-johnson]

I eagerly await progress on this front :-)

[buchgr]

@htuch thanks for the bug report and we love contributions :-).

[htuch]

@buchgr I've added to #2792 the limitation of the repository_rule approach. I'll take an action item to do a PR to link to envoyproxy/envoy#747, but it's not exactly a clean example as a result of the issues described in #2792.

[buchgr]

cc: @mhlopko @lberki

[dslomov]

We need to work on a better autoconf approaches in the near future.

[prestonvanloon]

+1

I am having a hard time understanding this rule and how it is used. I'm trying to import gmplib which generates some headers as part of running ./configure. Does cc_configure() achieve this? I was unable to get it to work after a brief attempt.

[hlopko]

Preston: nope, cc_configure is a workspace rule that configures C++ toolchain (compiler, linker, flags...).

Try https://github.com/bazelbuild/rules_foreign_cc, they sound like what you need.

[dslomov]

See https://github.com/bazelbuild/rules_foreign_cc