SwiftPM should support swift install

[dduan]

Description

tl;dr swift install is a command that builds the default execuatble target in release mode, and copy the result somewhere.

The somewhere should default to a fixed location that the user can access (for example, ~/swift/bin). The user can access it directly, or add it to their PATH. This location can be overriden by a envvar, for example, $SWIFTBIN.

Why is this a great idea? Sometimes you don't want to distribute your CLI applications via a public channel such as Homebrew. Maybe it's not meant for others to use, maybe you want to control what version to use by building from source.

Imagine a in-house tool whose source is part of a repository. The tool is meant to be version locked with whatever the repo's git revision is.

monorepo
├── ...
├── tools
│   └── great-swift-tool
│       └── Package.swift
└── tmp # git ignored
    └── bin

How does one build great-swift-tool and put it under ./tmp/bin today? Easy:

swift build --package-path tools/great-swift-tool -c release
cp tools/great-swift-tool/.build/release/great-swift-tool-executable tmp/bin

... put that in a shell script or make target and forget it, right?

IMO this is unnecessarily complicated in 2 ways:

1. the user has to know that the build result is in .build/release
2. the user has to write out the executable's name

With the proposed solution, this could be simplified as 1 command:

SWIFTBIN=tmp/bin swift install --package-path tools/great-swift-tool

I think that'd be pretty cool.

(In the future the command can take a git repository with for a SwiftPM project as input: swift install https://github.com/swiftlang/swift-format)

Expected behavior

No response

Actual behavior

No response

Steps to reproduce

No response

Swift Package Manager version/commit hash

No response

Swift & OS version (output of swift --version && uname -a)

No response

[kkebo]

There is already experimental--prefixed swift package install.

#6768

[unnamedd]

A good inspiration can be Cargo (from Rust).
There, we have the same possibilities that were brought here.

Here is the help from cargo install:

➜ cargo install --help
Install a Rust binary

Usage: cargo install [OPTIONS] [CRATE[@<VER>]]...

Arguments:
  [CRATE[@<VER>]]...  Select the package from the given source

Options:
      --version <VERSION>     Specify a version to install
      --index <INDEX>         Registry index to install from
      --registry <REGISTRY>   Registry to use
      --git <URL>             Git URL to install the specified crate from
      --branch <BRANCH>       Branch to use when installing from git
      --tag <TAG>             Tag to use when installing from git
      --rev <SHA>             Specific commit to use when installing from git
      --path <PATH>           Filesystem path to local crate to install from
      --root <DIR>            Directory to install packages into
  -f, --force                 Force overwriting existing crates or binaries
      --no-track              Do not save tracking information
      --list                  List all installed packages and their versions
      --message-format <FMT>  Error format
      --debug                 Build in debug mode (with the 'dev' profile) instead of release mode
  -v, --verbose...            Use verbose output (-vv very verbose/build.rs output)
  -q, --quiet                 Do not print cargo log messages
      --color <WHEN>          Coloring: auto, always, never
      --config <KEY=VALUE>    Override a configuration value
  -Z <FLAG>                   Unstable (nightly-only) flags to Cargo, see 'cargo -Z help' for details
  -h, --help                  Print help