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Posted on • Originally published at pikotutorial.com

Separating builds for different configs with Bazel

#cpp #bazel #pikotutorial

Welcome to the next pikoTutorial !

Let's consider a simple project with the following structure:

project/ ├── .bazelrc ├── BUILD ├── main.cpp ├── WORKSPACE
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The main function has 2 compile switches:

#include <iostream>  int main(int argc, char** argv) { #ifdef FEATURE_1_ENABLED  std::cout << "Hello from feature 1 code!" << std::endl; #endif #ifdef FEATURE_2_ENABLED  std::cout << "Hello from feature 2 code!" << std::endl; #endif }
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And we have 2 separate Bazel configurations including these switches:

build:feature_1 --compilation_mode=dbg build:feature_1 --copt=-DFEATURE_1_ENABLED build:feature_2 --compilation_mode=opt build:feature_2 --copt=-DFEATURE_2_ENABLED
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When we build the application with the following command:

bazel build --config=feature_1 //:my_app
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I can run the application by invoking:

./bazel-bin/my_app
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But as soon as I build the second configuration of the application with command:

bazel build --config=feature_2 //:my_app
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I lost my previous binary because the build artifacts have been overwritten. A solution for that is separation of build directories with --symlink_prefix option added in the .bazelrc file:

build:feature_1 --compilation_mode=dbg build:feature_1 --copt=-DFEATURE_1_ENABLED build:feature_1 --symlink_prefix=./build/feature_1/ build:feature_2 --compilation_mode=opt build:feature_2 --copt=-DFEATURE_2_ENABLED build:feature_2 --symlink_prefix=./build/feature_2/
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From now on, at every point of time, you can run the first version of the application with command:

./build/feature_1/bin/my_app
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And the second version with command:

./build/feature_2/bin/my_app
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They will no longer be overwritten.

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