[swift-build-dev] [Pitch] Swift run Command

David Hart david at hartbit.com
Mon May 15 02:47:09 CDT 2017

Hello evolution (and build-dev),

I’d like to pitch a QOL proposal to improve the development of command-line Swift Packages by introducing a `swift run` command. I’d value any feedback before moving forward.



Swift run Command

Proposal: SE-XXXX <https://github.com/hartbit/swift-evolution/blob/swift-run-command/proposals/XXXX-swift-run-command.md>
Authors: David Hart <http://github.com/hartbit/>
Review Manager: TBD
Status: TBD

The proposal introduces a new swift run command to build and run an executable defined in the current package.


It is common to want to build and run an executable during development. For now, one must first build it and then execute it from the build folder:

$ swift build
$ .build/debug/myexecutable
In Swift 4, the Swift Package Manager will build to a different path, containing a platform sub-folder (.build/macosx-x86_64/debug for mac and .build/linux-x86_64/debug for linux), making it more cumbersome to run the executable from the command line.

To improve the development workflow, the proposal suggest introducing a new first-level swift run command that will build if necessary and then run an executable defined in the Package.swift manifest, replacing the above steps into just one.

 <https://github.com/hartbit/swift-evolution/blob/swift-run-command/proposals/XXXX-swift-run-command.md#proposed-solution>Proposed solution

The swift run command would be defined as:

$ swift run --help
OVERVIEW: Build and run executable

USAGE: swift run [options] [executable] [-- arguments]

  --build-path            Specify build/cache directory [default: ./.build]
  --chdir, -C             Change working directory before any other operation
  --in-dir, -I            Change working directory before running the executable
  --color                 Specify color mode (auto|always|never) [default: auto]
  --configuration, -c     Build with configuration (debug|release) [default: debug]
  --enable-prefetching    Enable prefetching in resolver
  --skip-build            Skip building the executable product
  --verbose, -v           Increase verbosity of informational output
  -Xcc                    Pass flag through to all C compiler invocations
  -Xlinker                Pass flag through to all linker invocations
  -Xswiftc                Pass flag through to all Swift compiler invocations
  --help                  Display available options
If needed, the command will build the product before running it. As a result, it can be passed any options swift buildaccepts. As for swift test, it also accepts an extra --skip-build option to skip the build phase. A new --in-diroption is also introduced to run the executable from another directory.

After the options, the command optionally takes the name of an executable product defined in the Package.swiftmanifest and introduced in SE-0146 <https://github.com/hartbit/swift-evolution/blob/swift-run-command/proposals/0146-package-manager-product-definitions.md>. If called without an executable and the manifest defines one and only one executable product, it will default to running that one. In any other case, the command fails.

The executable can be called with arguments by prefixing them with a -- to separate them from the executable name.

 <https://github.com/hartbit/swift-evolution/blob/swift-run-command/proposals/XXXX-swift-run-command.md#alternatives-considered>Alternatives considered

One alternative to the Swift 4 change of build folder would be for the Swift Package Manager to create and update a symlink at .build/debug and .build/release that point to the latest build folder for that configuration. Although that should probably be done to retain backward-compatibility with tools that depended on the build location, it does not completely invalid the usefulness of the run command.
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