Swift Build: pass some additional settings needed for cross-compilation

This patch ensures that the Swift Build SDK and platform name are set correctly for embedded Apple platforms (iOS, tvOS, watchOS) and Android, that the SDK variant is set correctly for Mac Catalyst, and that the deployment target version is correctly propagated from the `--triple` argument specified on the command line.

Author: jakepetroules

Sources/SwiftBuildSupport/SwiftBuildSystem.swift

@@ -418,16 +418,35 @@ public final class SwiftBuildSystem: SPMBuildCore.BuildSystem {
         }
     }
 
-    func makeBuildParameters() throws -> SwiftBuild.SWBBuildParameters {
-        // Generate the run destination parameters.
-        let runDestination = SwiftBuild.SWBRunDestinationInfo(
-            platform: self.buildParameters.triple.osNameUnversioned,
-            sdk: self.buildParameters.triple.osNameUnversioned,
-            sdkVariant: nil,
+    func makeRunDestination() -> SwiftBuild.SWBRunDestinationInfo {
+        let platformName: String
+        if self.buildParameters.triple.isAndroid() {
+            // Android triples are identified by the environment part of the triple
+            platformName = "android"
+        } else {
+            platformName = self.buildParameters.triple.darwinPlatform?.platformName ?? self.buildParameters.triple.osNameUnversioned
+        }
+
+        let sdkVariant: String?
+        if self.buildParameters.triple.environment == .macabi {
+            sdkVariant = "iosmac"
+        } else {
+            sdkVariant = nil
+        }
+
+        return SwiftBuild.SWBRunDestinationInfo(
+            platform: platformName,
+            sdk: platformName,
+            sdkVariant: sdkVariant,
             targetArchitecture: buildParameters.triple.archName,
             supportedArchitectures: [],
             disableOnlyActiveArch: false
         )
+    }
+
+    func makeBuildParameters() throws -> SwiftBuild.SWBBuildParameters {
+        // Generate the run destination parameters.
+        let runDestination = makeRunDestination()
 
         var verboseFlag: [String] = []
         if self.logLevel == .debug {
@@ -444,6 +463,18 @@ public final class SwiftBuildSystem: SPMBuildCore.BuildSystem {
         // FIXME: workaround for old Xcode installations such as what is in CI
         settings["LM_SKIP_METADATA_EXTRACTION"] = "YES"
 
+        let normalizedTriple = Triple(buildParameters.triple.triple, normalizing: true)
+        if let deploymentTargetSettingName = normalizedTriple.deploymentTargetSettingName {
+            let value = normalizedTriple.deploymentTargetVersion
+
+            // Only override the deployment target if a version is explicitly specified;
+            // for Apple platforms this normally comes from the package manifest and may
+            // not be set to the same value for all packages in the package graph.
+            if value != .zero {
+                settings[deploymentTargetSettingName] = value.description
+            }
+        }
+
         settings["LIBRARY_SEARCH_PATHS"] = try "$(inherited) \(buildParameters.toolchain.toolchainLibDir.pathString)"
         settings["OTHER_CFLAGS"] = (
             ["$(inherited)"]
@@ -562,3 +593,41 @@ fileprivate extension SwiftBuild.SwiftBuildMessage.DiagnosticInfo.Location {
         }
     }
 }
+
+fileprivate extension Triple {
+    var deploymentTargetSettingName: String? {
+        switch (self.os, self.environment) {
+        case (.macosx, _):
+            return "MACOSX_DEPLOYMENT_TARGET"
+        case (.ios, _):
+            return "IPHONEOS_DEPLOYMENT_TARGET"
+        case (.tvos, _):
+            return "TVOS_DEPLOYMENT_TARGET"
+        case (.watchos, _):
+            return "WATCHOS_DEPLOYMENT_TARGET"
+        case (_, .android):
+            return "ANDROID_DEPLOYMENT_TARGET"
+        default:
+            return nil
+        }
+    }
+
+    var deploymentTargetVersion: Version {
+        if isAndroid() {
+            // Android triples store the version in the environment
+            var environmentName = self.environmentName[...]
+            if environment != nil {
+                let prefixes = ["androideabi", "android"]
+                for prefix in prefixes {
+                    if environmentName.hasPrefix(prefix) {
+                        environmentName = environmentName.dropFirst(prefix.count)
+                        break
+                    }
+                }
+            }
+
+            return Version(parse: environmentName)
+        }
+        return osVersion
+    }
+}