track SDK dependencies rdar://115777026

Author: pusukuri

Sources/Build/BuildDescription/SwiftTargetBuildDescription.swift

@@ -645,6 +645,12 @@ public final class SwiftTargetBuildDescription {
             }
         }
 
+        // rdar://115777026
+        // Compiler commands need to track SDK dependencies to trigger rebuilds when the SDK changes
+        if let sdkPath = self.buildParameters.sdkPath, self.buildParameters.targetTriple.isDarwin() {
+            args += ["-sdk", sdkPath.pathString]
+        }
+
         return args
     }
 

Sources/CoreCommands/SwiftTool.swift

@@ -695,6 +695,7 @@ public final class SwiftTool {
 
         return try BuildParameters(
             dataPath: dataPath,
+            sdkPath: toolchain.sdkRootPath,
             configuration: options.build.configuration,
             toolchain: toolchain,
             triple: triple,

Sources/PackageModel/SwiftSDKs/SwiftSDK.swift

@@ -478,8 +478,8 @@ public struct SwiftSDK: Equatable {
         let sdkPath: AbsolutePath?
         #if os(macOS)
         // Get the SDK.
-        if let value = lookupExecutablePath(filename: ProcessEnv.vars["SDKROOT"]) {
-            sdkPath = value
+        if let value = ProcessEnv.vars["SDKROOT"] {
+            sdkPath = try AbsolutePath(validating: value)
         } else {
             // No value in env, so search for it.
             let sdkPathStr = try TSCBasic.Process.checkNonZeroExit(

Sources/SPMBuildCore/BuildParameters/BuildParameters.swift

@@ -29,6 +29,9 @@ public struct BuildParameters: Encodable {
     /// The path to the data directory.
     public var dataPath: AbsolutePath
 
+    /// The path to the SDKROOT directory.
+    public var sdkPath: AbsolutePath?
+
     /// The build configuration.
     public var configuration: BuildConfiguration
 
@@ -119,6 +122,7 @@ public struct BuildParameters: Encodable {
 
     public init(
         dataPath: AbsolutePath,
+        sdkPath: AbsolutePath?,
         configuration: BuildConfiguration,
         toolchain: Toolchain,
         triple: Triple? = nil,
@@ -145,6 +149,7 @@ public struct BuildParameters: Encodable {
         )
 
         self.dataPath = dataPath
+        self.sdkPath = toolchain.sdkRootPath
         self.configuration = configuration
         self._toolchain = _Toolchain(toolchain: toolchain)
         self.triple = triple

Sources/SPMTestSupport/MockBuildTestHelper.swift

@@ -85,6 +85,7 @@ public func mockBuildParameters(
 ) -> BuildParameters {
     try! BuildParameters(
         dataPath: buildPath,
+        sdkPath: toolchain.sdkRootPath,
         configuration: config,
         toolchain: toolchain,
         triple: targetTriple,

Sources/swift-bootstrap/main.swift

@@ -279,6 +279,7 @@ struct SwiftBootstrapBuildTool: ParsableCommand {
 
             let buildParameters = try BuildParameters(
                 dataPath: dataPath,
+                sdkPath: self.targetToolchain.sdkRootPath,
                 configuration: configuration,
                 toolchain: self.targetToolchain,
                 triple: self.hostToolchain.targetTriple,

Tests/BuildTests/IncrementalBuildTests.swift

@@ -14,6 +14,7 @@ import Basics
 import PackageModel
 import SPMTestSupport
 import XCTest
+import class TSCBasic.Process
 
 /// Functional tests of incremental builds.  These are fairly ad hoc at this
 /// point, and because of the time they take, they need to be kept minimal.
@@ -145,4 +146,28 @@ final class IncrementalBuildTests: XCTestCase {
             XCTAssertNoMatch(log2, .contains("Planning build"))
         }
     }
+    // testing the fix for tracking SDK dependencies to avoid triggering rebuilds when the SDK changes (rdar://115777026)
+    func testSDKTracking() throws {
+#if os(macOS)
+        try XCTSkipIf(!UserToolchain.default.supportsSDKDependentTests(), "skipping because test environment doesn't support this test")
+
+        try fixture(name: "ValidLayouts/SingleModule/Library") { fixturePath in
+            let dummySwiftcPath = SwiftPM.xctestBinaryPath(for: "dummy-swiftc")
+            let swiftCompilerPath = try UserToolchain.default.swiftCompilerPath
+            let environment = [
+                "SWIFT_EXEC": dummySwiftcPath.pathString,
+                "SWIFT_ORIGINAL_PATH": swiftCompilerPath.pathString
+            ]
+            let sdkPathStr = try TSCBasic.Process.checkNonZeroExit(
+                arguments: ["/usr/bin/xcrun", "--sdk", "macosx", "--show-sdk-path"],
+                environment: environment
+            ).spm_chomp()
+
+            let newSdkPathStr = "/tmp/../\(sdkPathStr)"
+            // Perform a full build again because SDK changed.
+            let log1 = try executeSwiftBuild(fixturePath, env: ["SDKROOT": newSdkPathStr]).stdout
+            XCTAssertMatch(log1, .contains("Compiling Library"))
+        }
+#endif
+    }
 }