incompatible_no_implicit_file_export: implicitly exported files have private visibility

[aehlig]

If the flag --incompatible_no_implicit_file_export is enabled, files that are implicitly exported because they are mentioned in the BUILD have private visibility regardless of the default visibility of the package.

Migration: add an explicit exports_files for all files that should be used outside the package they belong to.

Design document: https://github.com/bazelbuild/proposals/blob/master/designs/2019-10-24-file-visibility.md

[drigz]

This flag causes a build error in an empty workspace with Bazel 2.0:

$ echo > WORKSPACE
$ bazel build @bazel_tools//tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator:all_lcov_merger_lib --incompatible_no_implicit_file_export
ERROR: /path/to/bazel/cache/10d1bb0ae85cffec5f45c68b4660ed75/external/bazel_tools/tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator/BUILD:4:1: in java_import rule @bazel_tools//tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator:all_lcov_merger_lib: target '@remote_coverage_tools//:all_lcov_merger_tools_deploy.jar' is not visible from target '@bazel_tools//tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator:all_lcov_merger_lib'. Check the visibility declaration of the former target if you think the dependency is legitimate
ERROR: Analysis of target '@bazel_tools//tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator:all_lcov_merger_lib' failed; build aborted: Analysis of target '@bazel_tools//tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator:all_lcov_merger_lib' failed; build aborted

I've also seen this error referring to @remote_coverage_tools//:all_lcov_merger_tools_deploy.jar.

This causes our build to fail for reasons I don't fully understand. Do @remote_coverage_tools and @bazel_tools need to be fixed before we can try applying this flag to our repositories, or should we remove the dependency on the broken targets?

See also: bazelbuild/continuous-integration#887