Side-by-side support of different bazel versions

[RNabel]

ATTENTION! Please read and follow:

• if this is a question about how to build / test / query / deploy using Bazel, ask it on StackOverflow instead: https://stackoverflow.com/questions/tagged/bazel
• if this is a discussion starter, send it to bazel-discuss@googlegroups.com
• if this is a bug or feature request, fill the form below as best as you can.

Description of the problem / feature request:

Support for multiple versions installed side-by-side by default. Maybe a built in way to switch between them. My apologies if this belongs in the discussion starter category.

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

Concurrent work on multiple projects using different versions of bazel. See this PR against homebrew for further context.

Bugs: what's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

N/A

What operating system are you running Bazel on?

macOS.

What's the output of bazel info release?

N/A

If bazel info release returns "development version" or "(@non-git)", tell us how you built Bazel.

N/A

What's the output of git remote get-url origin ; git rev-parse master ; git rev-parse HEAD ?

N/A

Have you found anything relevant by searching the web?

Yep, a general discussion can be found in this email thread.

Any other information, logs, or outputs that you want to share?

N/A

[RNabel]

There's a workaround for this: place a shell script called bazel within the tools folder of your workspace which invokes the correct bazel binary. When you run bazel from within your workspace, it checks whether there is a file called tools/bazel and, if so, executes it with all the arguments itself was called with.

Thus, you can have different versions installed under, say, ~/.bazel_installations/<version>/, which the script checks and delegates to it:

if [ -f "${BAZEL_TARGET_PATH}" ]; then
  exec -a "$0" "${BAZEL_TARGET_PATH}" "$@"
fi

or downloads it if it is not present and invokes it once it's placed at the right location.

Note:

• Doesn't work on Windows (because bazel on linux / macos is a bash script checking tools/bazel but on Windows bazel is the straight-up binary)
• From version 0.14.0 onwards the bazel team publishes binary-only versions for all platforms, meaning that your script under tools/bazel only needs to download the binary and mv it to the correct location.