Building with Bazel - Z3 Theorem Prover

Bazel is a fast, scalable build system that works well for large projects and provides excellent support for reproducible builds and remote caching.

Bazel support in Z3 is primarily tested on Ubuntu with Clang but may work on other platforms and compilers.

Prerequisites

Bazel - Install from bazel.build
C++20 compiler - Clang recommended, GCC also supported
Python - For some build steps

Quick Start

Build all Z3 targets:

bazel build //...

That’s it! Bazel handles dependency resolution, configuration, and compilation automatically.

Installation

Linux (Ubuntu/Debian)

# Using Bazelisk (recommended)
npm install -g @bazel/bazelisk

# Or using apt (may be outdated)
sudo apt install bazel

# Or download from releases
wget https://github.com/bazelbuild/bazel/releases/download/6.0.0/bazel-6.0.0-linux-x86_64
chmod +x bazel-6.0.0-linux-x86_64
sudo mv bazel-6.0.0-linux-x86_64 /usr/local/bin/bazel

macOS

# Using Homebrew
brew install bazel

# Or using Bazelisk
brew install bazelisk

Windows

# Using Chocolatey
choco install bazel

# Or download from https://bazel.build/install/windows

Basic Usage

Build All Targets

Build everything in the repository:

bazel build //...

Build Specific Targets

Build only the Z3 library:

bazel build //src:libz3

Run Tests

Run all tests:

bazel test //...

Clean Build

Remove build artifacts:

bazel clean

Deep clean (removes all cached data):

bazel clean --expunge

Build Configuration

Optimization Levels

Bazel supports different compilation modes:

# Fast build (default, some optimizations)
bazel build //...

# Optimized build (-c opt)
bazel build -c opt //...

# Debug build (-c dbg)
bazel build -c dbg //...

Compiler Selection

Use a specific compiler:

# Use Clang
bazel build --repo_env=CC=clang --repo_env=CXX=clang++ //...

# Use GCC
bazel build --repo_env=CC=gcc --repo_env=CXX=g++ //...

Z3’s Bazel build is primarily tested with Clang on Ubuntu. Other configurations may require adjustments.

Platform-Specific Options

For cross-compilation or specific platforms:

# 32-bit build on 64-bit system
bazel build --cpu=k8 //...

# Specify platform
bazel build --platforms=@platforms//os:linux //...

Advanced Features

Parallel Builds

Bazel automatically parallelizes builds. Control job count:

# Use 8 parallel jobs
bazel build --jobs=8 //...

# Use all available cores (default)
bazel build //...

Remote Caching

Enable remote caching for faster builds across machines:

# Use HTTP cache
bazel build --remote_cache=http://cache.example.com //...

# Use gRPC cache
bazel build --remote_cache=grpc://cache.example.com:9090 //...

Build Event Protocol

Generate build event logs:

bazel build --build_event_json_file=build_events.json //...

Verbose Output

Show detailed build information:

# Show all commands
bazel build --subcommands //...

# Verbose output
bazel build --verbose_failures //...

Bazel Configuration File

Create a .bazelrc file in the repository root for persistent settings:

# .bazelrc

# Use Clang by default
build --repo_env=CC=clang
build --repo_env=CXX=clang++

# Optimize builds by default
build -c opt

# Use 8 parallel jobs
build --jobs=8

# Show command lines on failure
build --verbose_failures

# Color output
common --color=yes

Then simply run:

bazel build //...

Workspace Structure

Bazel uses BUILD files to define targets. Z3’s structure includes:

z3/
├── WORKSPACE          # Bazel workspace definition
├── BUILD              # Root build file
├── src/
│   ├── BUILD         # Source build definitions
│   └── ...
└── examples/
    └── BUILD         # Example build definitions

Common Targets

Library Targets

# Build the main Z3 library
bazel build //src:libz3

# Build static library
bazel build //src:libz3_static

Executable Targets

# Build Z3 executable
bazel build //src:z3

# Run Z3 directly
bazel run //src:z3 -- --help

Test Targets

# Run all tests
bazel test //...

# Run specific test suite
bazel test //tests:unit_tests

Querying Build Graph

Bazel provides powerful query capabilities:

# List all targets
bazel query //...

# Show dependencies of a target
bazel query 'deps(//src:libz3)'

# Show reverse dependencies
bazel query 'rdeps(//..., //src:libz3)'

# Find all C++ libraries
bazel query 'kind(cc_library, //...)'

Integration with IDEs

VS Code

Install the Bazel extension:

// .vscode/settings.json
{
  "bazel.executable": "/usr/local/bin/bazel",
  "bazel.buildifierExecutable": "/usr/local/bin/buildifier"
}

CLion

CLion has built-in Bazel support:

Open the Z3 repository
Select File → Project Structure
Choose Bazel as the project type

Compilation Database

Generate compile_commands.json for other IDEs:

# Install bazel-compilation-database
pip install bazel-compilation-database

# Generate compilation database
bazel-compdb //...

Troubleshooting

Build Failures

Clean and rebuild:

bazel clean
bazel build //...

For persistent issues:

bazel clean --expunge
bazel build //...

Compiler Not Found

Specify compiler explicitly:

bazel build --repo_env=CC=/usr/bin/clang --repo_env=CXX=/usr/bin/clang++ //...

Slow Builds

Enable remote caching or increase parallelism:

bazel build --jobs=auto //...

Dependency Issues

Show the dependency graph:

bazel query 'deps(//src:libz3)' --output graph

Cache Problems

Clear the Bazel cache:

bazel clean --expunge

Comparison with Other Build Systems

Feature	Bazel	CMake	Make
Speed	Fast (parallel, cached)	Moderate	Slow (recursive)
Scalability	Excellent	Good	Limited
Reproducibility	Excellent	Good	Poor
Cross-platform	Good	Excellent	Platform-specific
IDE Integration	Growing	Excellent	Limited
Learning Curve	Steep	Moderate	Easy
Remote Caching	Native	Via addons	Not available
OCaml Support	Limited	Limited	Yes

Best Practices

Use Bazelisk

Bazelisk automatically downloads the correct Bazel version:

npm install -g @bazel/bazelisk
# Now 'bazel' command uses bazelisk

Configure .bazelrc

Store common options in .bazelrc instead of typing them:

# .bazelrc
build -c opt
test --test_output=errors

Use Query for Understanding

Before modifying build files, understand dependencies:

bazel query 'deps(//src:libz3)' --output graph | dot -Tpng > deps.png

Remote Caching for CI

Set up remote caching for continuous integration to speed up builds:

# In CI configuration
bazel build --remote_cache=https://your-cache.example.com //...

Performance Tips

Use --jobs=auto - Let Bazel optimize parallelism
Enable remote caching - Share build artifacts across machines
Use bazel-compilation-database - For better IDE integration
Avoid bazel clean - Let Bazel manage incremental builds
Use .bazelrc - Configure once, build everywhere

When to Use Bazel

Bazel is ideal when:

Building large codebases with many dependencies
You need reproducible builds
Working in a team with shared build cache
Cross-compilation is required
Integration with other Bazel projects

Consider CMake instead if:

You need extensive IDE support
Building small to medium projects
You need OCaml bindings (use Make)
Team is more familiar with CMake

Next Steps

Learn about CMake builds for cross-platform flexibility
See Make builds for simple Unix builds
Explore Visual Studio builds for Windows development
Visit bazel.build for comprehensive Bazel documentation

Getting Started

Core Concepts

Building Z3

Guides

​Prerequisites

​Quick Start

​Installation

​Linux (Ubuntu/Debian)

​macOS

​Windows

​Basic Usage

​Build All Targets

​Build Specific Targets

​Run Tests

​Clean Build

​Build Configuration

​Optimization Levels

​Compiler Selection

​Platform-Specific Options

​Advanced Features

​Parallel Builds

​Remote Caching

​Build Event Protocol

​Verbose Output

​Bazel Configuration File

​Workspace Structure

​Common Targets

​Library Targets

​Executable Targets

​Test Targets

​Querying Build Graph

​Integration with IDEs

​VS Code

​CLion

​Compilation Database

​Troubleshooting

​Build Failures

​Compiler Not Found

​Slow Builds

​Dependency Issues

​Cache Problems

​Comparison with Other Build Systems

​Best Practices

​Use Bazelisk

​Configure .bazelrc

​Use Query for Understanding

​Remote Caching for CI

​Performance Tips

​When to Use Bazel

​Next Steps

Build docs developers (and LLMs) love

Prerequisites

Quick Start

Installation

Linux (Ubuntu/Debian)

macOS

Windows

Basic Usage

Build All Targets

Build Specific Targets

Run Tests

Clean Build

Build Configuration

Optimization Levels

Compiler Selection

Platform-Specific Options

Advanced Features

Parallel Builds

Remote Caching

Build Event Protocol

Verbose Output

Bazel Configuration File

Workspace Structure

Common Targets

Library Targets

Executable Targets

Test Targets

Querying Build Graph

Integration with IDEs

VS Code

CLion

Compilation Database

Troubleshooting

Build Failures

Compiler Not Found

Slow Builds

Dependency Issues

Cache Problems

Comparison with Other Build Systems

Best Practices

Use Bazelisk

Configure .bazelrc

Use Query for Understanding

Remote Caching for CI

Performance Tips

When to Use Bazel

Next Steps