feat: add foreignBuild case to TargetDependency

Add support for foreign build system dependencies (KMP, Rust, CMake, etc.)
by introducing a new `foreignBuild` case on `TargetDependency` and a
`ForeignBuildCacheInput` model for content hashing.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: fortmarek

Sources/XcodeGraph/Models/ForeignBuildCacheInput.swift

@@ -0,0 +1,8 @@
+import Path
+
+public enum ForeignBuildCacheInput: Equatable, Hashable, Codable, Sendable {
+    case file(AbsolutePath)
+    case folder(AbsolutePath)
+    case glob(String)
+    case script(String)
+}

Sources/XcodeGraph/Models/TargetDependency.swift

@@ -50,6 +50,13 @@ public enum TargetDependency: Equatable, Hashable, Codable, Sendable {
     case package(product: String, type: PackageType, condition: PlatformCondition? = nil)
     case sdk(name: String, status: LinkingStatus, condition: PlatformCondition? = nil)
     case xctest
+    indirect case foreignBuild(
+        name: String,
+        script: String,
+        output: TargetDependency,
+        cacheInputs: [ForeignBuildCacheInput],
+        condition: PlatformCondition? = nil
+    )
 
     public var condition: PlatformCondition? {
         switch self {
@@ -68,6 +75,8 @@ public enum TargetDependency: Equatable, Hashable, Codable, Sendable {
         case .sdk(name: _, status: _, condition: let condition):
             condition
         case .xctest: nil
+        case .foreignBuild(name: _, script: _, output: _, cacheInputs: _, condition: let condition):
+            condition
         }
     }
 
@@ -88,6 +97,8 @@ public enum TargetDependency: Equatable, Hashable, Codable, Sendable {
         case .sdk(name: let name, status: let status, condition: _):
             return .sdk(name: name, status: status, condition: condition)
         case .xctest: return .xctest
+        case .foreignBuild(name: let name, script: let script, output: let output, cacheInputs: let cacheInputs, condition: _):
+            return .foreignBuild(name: name, script: script, output: output, cacheInputs: cacheInputs, condition: condition)
         }
     }
 }

Sources/XcodeGraphMapper/Extensions/TargetDependency+Extensions.swift

@@ -20,6 +20,8 @@ extension TargetDependency {
             return path.basenameWithoutExt
         case .xctest:
             return "xctest"
+        case let .foreignBuild(name, _, _, _, _):
+            return name
         }
     }
 }

Sources/XcodeGraphMapper/Mappers/Targets/TargetDependency+GraphMapping.swift

@@ -101,6 +101,17 @@ extension TargetDependency {
                 source: .developer
             )
 
+        case let .foreignBuild(_, _, output, _, _):
+            return try await output.graphDependency(
+                sourceDirectory: sourceDirectory,
+                target: target,
+                xcframeworkMetadataProvider: xcframeworkMetadataProvider,
+                libraryMetadataProvider: libraryMetadataProvider,
+                frameworkMetadataProvider: frameworkMetadataProvider,
+                systemFrameworkMetadataProvider: systemFrameworkMetadataProvider,
+                developerDirectoryProvider: developerDirectoryProvider
+            )
+
         // MARK: - XCTest (System Provided)
 
         case .xctest:

Tests/XcodeGraphTests/Models/TargetDependencyTests.swift

@@ -36,6 +36,28 @@ final class TargetDependencyTests: XCTestCase {
         XCTAssertCodable(subject)
     }
 
+    func test_codable_foreignBuild() {
+        // Given
+        let subject = TargetDependency.foreignBuild(
+            name: "SharedKMP",
+            script: "./gradlew build",
+            output: .xcframework(
+                path: try! AbsolutePath(validating: "/path/to/output.xcframework"),
+                expectedSignature: nil,
+                status: .required
+            ),
+            cacheInputs: [
+                .file(try! AbsolutePath(validating: "/path/to/input.kt")),
+                .folder(try! AbsolutePath(validating: "/path/to/src")),
+                .glob("**/*.kt"),
+                .script("git rev-parse HEAD"),
+            ]
+        )
+
+        // Then
+        XCTAssertCodable(subject)
+    }
+
     func test_filtering() {
         let expected: PlatformCondition? = .when([.macos])
 
@@ -57,6 +79,17 @@ final class TargetDependencyTests: XCTestCase {
                 condition: expected
             ),
             .project(target: "", path: try! AbsolutePath(validating: "/"), condition: expected),
+            .foreignBuild(
+                name: "KMP",
+                script: "./build.sh",
+                output: .xcframework(
+                    path: try! AbsolutePath(validating: "/output.xcframework"),
+                    expectedSignature: nil,
+                    status: .required
+                ),
+                cacheInputs: [.file(try! AbsolutePath(validating: "/input.kt"))],
+                condition: expected
+            ),
         ]
 
         for subject in subjects {