Are you tired of tedious and time-consuming builds with Bazel? Do you struggle to manage complex dependencies and variables in your build process? Look no further! In this article, we will delve into the world of Bazel make variables substitution, a powerful feature that can revolutionize your build workflow.
What are Bazel Make Variables?
Bazel make variables are a way to define and manage variables in your build process. These variables can be used to store values, such as compiler flags, library paths, or other build settings, and can be substituted into your build rules and scripts.
Make variables are defined in the `WORKSPACE` file or in individual `BUILD` files, and can be accessed and used throughout your build process.
Why Use Bazel Make Variables Substitution?
So, why should you use Bazel make variables substitution? Here are just a few reasons:
- Faster Builds**: By defining variables once and reusing them throughout your build process, you can speed up your builds and reduce the risk of errors.
- Easier Maintenance**: Make variables make it easy to manage complex dependencies and settings, making it easier to maintain and update your build process.
- Improved Consistency**: By using variables to define build settings, you can ensure consistency across your build process, reducing the risk of errors and inconsistencies.
Defining Bazel Make Variables
To define a Bazel make variable, you use the `make_variable` function in your `WORKSPACE` file or `BUILD` file.
make_variable(
name = "CC_FLAGS",
value = "-Wall -Werror",
)
In this example, we define a make variable named `CC_FLAGS` with a value of `-Wall -Werror`. This variable can then be used throughout our build process.
Using Bazel Make Variables Substitution
To use a Bazel make variable in your build rule, you simply reference the variable in your rule definition.
cc_library(
name = "my_library",
srcs = ["my_source.cc"],
copts = ["$(CC_FLAGS)"],
)
In this example, we reference the `CC_FLAGS` make variable in the `copts` attribute of our `cc_library` rule.
Bazel Make Variables Substitution Syntax
Bazel make variables substitution uses a simple syntax to reference and substitute variables.
The basic syntax is:
$(VARIABLE_NAME)
Where `VARIABLE_NAME` is the name of the make variable.
You can also use concatenation to combine multiple variables or values.
$(VARIABLE1)$(VARIABLE2)
This will substitute the values of `VARIABLE1` and `VARIABLE2` and concatenate them together.
Advanced Bazel Make Variables Substitution
Bazel make variables substitution provides several advanced features to help you manage complex build settings.
Conditional Substitution
You can use conditional statements to substitute different values based on certain conditions.
select({
"(CC_FLAGS): -Wall -Werror",
"default": "-Wno-error",
})
In this example, we use the `select` function to substitute different values for `CC_FLAGS` based on the condition.
Variable Expansion
You can use variable expansion to create new variables from existing ones.
make_variable(
name = "DEBUG_FLAGS",
value = "$(CC_FLAGS) -g",
)
In this example, we create a new variable `DEBUG_FLAGS` by expanding the `CC_FLAGS` variable and adding the `-g` flag.
Bazel Make Variables Substitution Best Practices
Here are some best practices to keep in mind when using Bazel make variables substitution:
- Use meaningful variable names**: Use descriptive names for your make variables to make it easy to understand their purpose.
- Keep it simple**: Avoid using complex logic or concatenation in your variable definitions.
- Use conditional substitution**: Use conditional statements to handle different build settings and scenarios.
- Document your variables**: Document your make variables and their purpose to make it easy for others to understand your build process.
Conclusion
Bazel make variables substitution is a powerful feature that can simplify and speed up your build process. By defining and managing variables, you can reduce errors, improve consistency, and make it easier to maintain and update your build process.
By following the examples and best practices outlined in this article, you can take your build workflow to the next level and maximize the benefits of Bazel make variables substitution.
| Variable Name | Description |
|---|---|
| CC_FLAGS | Compiler flags for C/C++ compilation |
| LDFLAGS | Linker flags for linking libraries |
| DEBUG_FLAGS | Flags for debugging and testing |
This table provides a sample list of make variables commonly used in Bazel builds.
By following the instructions and guidelines outlined in this article, you can master the art of Bazel make variables substitution and take your build workflow to the next level. Happy building!
Frequently Asked Question
Get ready to unleash the power of Bazel make variables substitution! Here are the top 5 questions and answers to get you started:
What is Bazel make variables substitution, and how does it work?
Bazel make variables substitution is a way to customize your build process by replacing placeholders in your BUILD files with actual values. It’s like having a superpower to dynamically generate code based on your build configuration! You can define variables in your .bazelrc file or on the command line, and then use them in your BUILD files using the $(variable_name) syntax.
How do I define a make variable in Bazel?
Easy peasy! You can define a make variable in your .bazelrc file using the `build –define` flag. For example, `build –define MY_VAR=my_value` sets the `MY_VAR` variable to `my_value`. You can also define variables on the command line using the `-D` flag, like this: `bazel build -D MY_VAR=my_value //path/to/target`.
Can I use make variables in my BUILD file?
Absolutely! You can use make variables in your BUILD file to customize your build rules and dependencies. Just use the $(variable_name) syntax to reference the variable, like this: `cc_library(name = “my_lib”, srcs = [“$(MY_VAR)/my_file.cc”])`. Bazel will replace the placeholder with the actual value of the variable during the build process.
What happens if I don’t define a make variable?
If you don’t define a make variable, Bazel will raise an error when it encounters the $(variable_name) syntax in your BUILD file. To avoid this, you can provide a default value for the variable using the `build –default` flag. For example, `build –default MY_VAR=my_default_value` sets the `MY_VAR` variable to `my_default_value` if it’s not defined elsewhere.
Can I use make variables in my macros?
Yes, you can! Make variables are especially useful in macros, where you can use them to generate custom code and configurations. Just define the variable in your .bazelrc file or on the command line, and then use it in your macro definition using the $(variable_name) syntax. Bazel will substitute the variable with its actual value when expanding the macro.
