build cache and bazel build --config=foo

[Ming Zhao]

Current the build output is stored inside
bazel-out/${toolchain_identifier}-${build-mode}, like bazel-out/clang-fastbuild

which causes an issue that if I switch build config like bazel build
--config=asan, the existing build cache inside fastbuild will be
overwritten, once I want to switch back to normal fastbuild, the whole
build cache needs to be invalidated and pretty much everything needs
to be recompiled. I guess there might not be a problem for Google
internally because you have another remote cache, but given that there
is no cache support in bazel yet, is there any recommended way to work
around this problem? Thanks!

- Ming

[Han-Wen Nienhuys]

You can switch --output_base to have a different action cache for the
asan build.

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--
Han-Wen Nienhuys
Google Munich
han...@google.com

[Ming Zhao]

I would expect I can do something like
build:asan --output_base bazel-asan
in my bazel.rc, but it turned out --output_base has to be specified in
the command line explicitly.

But thanks any way.

[Kristina Chodorow]

output_base is not a build option (it's called a startup option because it's parsed before the server starts up and goes before the command, e.g., bazel --output_base=bazel-asan build //foo) so you'd have to say

startup --output_base bazel-asan

Unfortunately, this doesn't really work for you because you can't say startup:asan (the startup flags are used before the bazel server launches but the asan config is parsed by the bazel server).

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[cns...@gmail.com]

Instead of --output_base, is --platform_suffix a good option? 

build:asan --platform_suffix asan