How to write files to current directory instead of bazel-out

Bazel doesn't allow you to modify the state of your workspace, by design.

The short answer is that you don't want the results of the past builds to modify the state of your workspace, hence potentially modifying the results of the future builds. It'll violate reproducibility if running Bazel multiple times on the same workspace results in different outputs.

Given your example: imagine calling bazel run //src:foo which inserts

#define true false
#define false true

at the top of the src/foo.cc. What happens if you call bazel run //src:foo again?

The long answer: https://docs.bazel.build/versions/master/rule-challenges.html#assumption-aim-for-correctness-throughput-ease-of-use-latency

Here's more information on the output directory: https://docs.bazel.build/versions/master/output_directories.html#documentation-of-the-current-bazel-output-directory-layout

There could be a workaround to use genrule. Below is an example that I use genrule to copy a file to the .git folder.

genrule(
    name = "precommit",
    srcs = glob(["git/**"]),
    outs = ["precommit.txt"],
    # folder contain this BUILD.bazel file is tool which will be symbol linked, we use cd -P to get to the physical path
    cmd = "echo 'setup pre-commit.sh' > $(OUTS) && cd -P tools && ./path/to/your-script.sh",
    local = 1,  # required
)