Using build configurations

Control the build configuration for your app or package.

Overview

Package manager supports two general build configurations: Debug (default) and Release.

Debug

By default, running swift build builds the package using its debug configuration. Alternatively, you can use swift build -c debug. Package manager locates the build artifacts in a directory called debug under the .build folder. When building in the debug configuration, a Swift target uses the following Swift compiler flags:

• -Onone: Compile without any optimization.
• -g: Generate debug information.
• -enable-testing: Enable the Swift compiler's testability feature.

A C language target in the debug configuration uses the following flags:

• -O0: Compile without any optimization.
• -g: Generate debug information.

Release

To build in release mode, type swift build -c release. Package manager locates the build artifacts in a directory called release under the .build folder. When building in the release configuration, a Swift target uses the following Swift compiler flags:

• -O: Compile with optimizations.
• -whole-module-optimization: Optimize input files (per module) together instead of individually.

A C language target in the release configuration uses the following flags:

• -O2: Compile with optimizations.

Additional Flags

You can pass additional flags to the C, C++, or Swift compilers in three different ways:

• Command-line flags passed to these tools: flags like -Xcc (for the C compiler) or -Xswiftc (for the Swift compiler) pass relevant flags for all targets in the manifest.

• Target-specific flags in the manifest: use options like cSettings or swiftSettings for fine-grained control of compilation flags for particular targets.

• A destination JSON file: once you have a set of working command-line flags to apply to all targets, collect them in a JSON file and pass them in through extra-cc-flags and extra-swiftc-flags with --destination example.json.

One difference is that C flags passed on the -Xcc command-line or using a manifest's cSettings are supplied to the Swift compiler tool for convenience, but extra-cc-flags aren't.