xcdo automatically adds necessary or helpful compiler flags to swiftc and clang. Inspired by xcrun, which sets essential environment variables. xcdo is intended for exploratory use, not from a build system.

Use xcdo instead of xcrun when running swiftc or clang. It's possible to alias xcrun to xcdo.

Use the -### flag to show, but not execute, the underlying xcrun command. For example:

xcdo -### -sdk iphoneos clang++ -c source.cpp

will print:

xcrun -sdk iphoneos clang++ -target arm64-apple-ios13.0 -std=c++17 -Wall -c source.cpp

xcrun sets the correct sysroot/sdk, but not the correct target triple. Both swiftc and clang assume compilation for the current host, which for macOS is x86_64. When building for other SDKs, the correct target is needed as well.

xcdo determines which target -triple to use based on the -sdk flag. The mapping is:

Using clang -v or swiftc -v prints the underlying commands being run. These command lines often contain temp files, but they are deleted by at the end of the command. xcdo adds -save-temps whenever -v is given, to allow the temp files to be inspected.

Unless -whole-module-optimization is used, xcdo adds -enable-batch-mode.

If -emit-module-interface is specified, then -enable-library-evolution is added if not present, since it is required to produce .swiftinterface files.

Swift incremental compilation requires a JSON output-file-map. When using -incremental, xcdo will generate an output-file-map if none is given. Also, -driver-show-incremental is added.

See Swift's documentation Driver: Incremental Builds for details on swift incremental builds.

clang defaults to -std=c++98, which is quite old. xcdo defaults to -std=c++17 when no -std flag is used.

xcdo adds -Wall when no other -W flag is used.

clang does not enable ARC by default. xcdo enables ARC when compiling objc/objc++ sources by adding -fobjc-arc.

Generated assembly can be noisy. Running clang -S with xcdo will add -fomit-frame-pointer and -fno-unwind-tables. Thanks to Greg Parker for sharing this tip https://twitter.com/gparker/status/1147723601656729600.