Refactor --init mode for library package support, Adds test stubs to libs

[aciidgh]

Adds two modes to --init: --init library and --init exec with executable as default if not specified.

--init exec or --init behaves same as before

--init library mode:

• Creates this folder structure :

Creating Library package: MyAwesomePackage
Creating Package.swift
Creating Sources/
Creating Sources/MyAwesomePackage.swift
Creating Tests/
Creating Tests/LinuxMain.swift
Creating Tests/MyAwesomePackage/
Creating Tests/MyAwesomePackage/MyAwesomePackage.swift

• Sources/MyAwesomePackage.swift contains empty struct of the same name :

struct MyAwesomePackage {

}

• Tests/MyAwesomePackage/MyAwesomePackage.swift :

import XCTest
@testable import MyAwesomePackage

class MyAwesomePackage: XCTestCase {

    func testExample() {
        // This is an example of a functional test case.
        // Use XCTAssert and related functions to verify your tests produce the correct results.
    }

}

#if os(Linux)
extension MyAwesomePackage: XCTestCaseProvider {
    var allTests : [(String, () throws -> Void)] {
        return [
            ("testExample", testExample),
        ]
    }
}
#endif

• Tests/LinuxMain.swift :

import XCTest
@testable import MyAwesomePackagetest

XCTMain([
    MyAwesomePackage(),
])

Executable currently don't support proper testing so no test stubs are generated for executables :
swift-test works properly on OSX but fails with the below error on Linux for packages containing main.swift, however works correctly for libs :

Compiling Swift Module 'MyAwesomePackagetest' (1 sources)
Linking test-Package.xctest
/home/aciid/temo/MyAwesomePackage/.build/debug/MyAwesomePackage.build/main.swift.o: In function `main':
/home/aciid/temo/MyAwesomePackage/Sources/main.swift:(.text+0x0): multiple definition of `main'
/tmp/LinuxMain-c1efa2.o:/tmp/LinuxMain-c1efa2.o:(.text+0x0): first defined here
clang: error: linker command failed with exit code 1 (use -v to see invocation)
<unknown>:0: error: link command failed with exit code 1 (use -v to see invocation)
<unknown>:0: error: build had 1 command failures
error: exit(1): swift-build-tool -f /home/aciid/temo/MyAwesomePackage/.build/debug.yaml test

[mxcl]

Only libraries are testable at this time, it works on Darwin because we build an xctest bundle, however it would stop working if we built there were two executable modules being compiled into the bundle.

It doesn't work on Linux because we build a main into the test runner.

So at this time, I'm not sure we can merge this unless we change --init to make a library or we ask the user if they want a library or we encourage modular development by creating a library and an executable module.

---

I considered compiling executable modules in two parts, a module with everything except the main.swift and then the executable product with the main.swift, however this simply won't work if any non-private state exists in main.swift.

---

Possibly there is a solution if on Linux we compile each module as a dylib, but I'm not 100% sure how this would affect the _main symbols

[aciidgh]

how about having two modes for --init for library and executable, something like:
--init library and --init exec and defaulting to executable if not specified?

[mxcl]

Sounds reasonable, would enjoy input from @ddunbar and @mattt.

[aciidgh]

waiting for inputs from @ddunbar and @mattt in the meanwhile @mxcl updated PR and description to add library and exec modes to --init

[aciidgh]

rebased

[mxcl]

K, looks good. Lets make it executable though since we don’t abbreviate generally here at the Fruit Company.

[aciidgh]

@mxcl done

[mxcl]

@swift-ci Please test

[aciidgh]

@mxcl is there any changes required in this PR?

[mxcl]

We can squash and merge. I'll update the swift-3 branch if needed tomorrow.

[aciidgh]

Rebased and squashed

[mxcl]

@swift-ci Please test