[SR-3948] Support Build Settings

[rballard]

Previous ID	SR-3948
Radar	rdar://problem/23270646
Original Reporter	@rballard
Type	New Feature

Additional Detail from JIRA

Votes	6
Component/s	Package Manager
Labels	New Feature
Assignee	None
Priority	Medium

md5: acfa70332a18c4718006cf3e62144d2e

is duplicated by:

• SR-883 Support conditional dependencies
• SR-3233 Demands -Xlinker invocation even though modulemap already contains it
• SR-3488 C/C++ packages can't be built for Android
• SR-3838 Swift Package Manager can't specify C-language mode (-std option) per module
• SR-4194 Lookup pkg-config files in system packages
• SR-5851 swift build can't change -target
• SR-8497 Make cross-test-target dependencies possible
• SR-3484 Swift PM fails to build package with C++ and ObjC++ targets

relates to:

• SR-3660 Add support for custom build configuration

Issue Description:

The package manager has no way to provide specific settings, such as compiler flags, for building the targets in a package. Some settings are critical for production code, such as the "deployment target" (the minimum OS version that the built code will run on). We need to provide a way to set at least the most important settings which users will need control over.

[swift-ci]

Comment by Amr Aboelela (JIRA)

In UserToolchain.swift:

self.extraSwiftCFlags = [

        "-target", destination.target,

        "-sdk", destination.sdk.asString

    \] + destination.extraSwiftCFlags

And in build_ubuntu_cross_compilation_toolchain:

swift build --destination /tmp/cross-toolchain/ubuntu-xenial-destination.json

...

cat > "$cross_tc_basename/ubuntu-xenial-destination.json" <<EOF

{

"version": 1,

"sdk": "$(pwd)/$cross_tc_basename/$linux_sdk_name",

"toolchain-bin-dir": "$(pwd)/$cross_tc_basename/$xc_tc_name/usr/bin",

"target": "linux-unknown-x86_64",

...

}

So the answer of our question seems to create a destination.json file, fill it with the deployment target then run:

$ swift build --destination destination.json