PrebuiltModuleGen: check if an interface is for macabi by reading interface contents

Previously, we were using the file name to infer whether an interface is for macabi.
However, this seems to be inaccurate because some macabi interfaces don't have "-macabi" in
the file names. This patch teaches the driver to open interface files and check
module target specifically.

Author: nkcsgexi

Sources/SwiftDriver/Jobs/PrebuiltModulesJob.swift

@@ -12,6 +12,15 @@
 import TSCBasic
 import SwiftOptions
 
+@_spi(Testing) public func isIosMacInterface(_ path: VirtualPath) throws -> Bool {
+  let data = try localFileSystem.readFileContents(path).cString
+  let myStrings = data.components(separatedBy: .newlines)
+  let prefix = "// swift-module-flags: "
+  let argLine = myStrings.first { $0.hasPrefix(prefix) }!
+  let args = argLine.dropFirst(prefix.count).components(separatedBy: " ")
+  return args[args.firstIndex(of: "-target")! + 1].contains("macabi")
+}
+
 func isIosMac(_ path: VirtualPath) -> Bool {
   // Infer macabi interfaces by the file name.
   // FIXME: more robust way to do this.
@@ -432,7 +441,7 @@ extension Driver {
       commandLine.appendFlag(.parseStdlib)
     }
     // Add macabi-specific search path.
-    if isIosMac(inputPath.path.file) {
+    if try isIosMacInterface(inputPath.path.file) {
       commandLine.appendFlag(.Fsystem)
       commandLine.append(.path(iosMacFrameworksSearchPath))
     }

Tests/SwiftDriverTests/SwiftDriverTests.swift

@@ -5030,6 +5030,17 @@ final class SwiftDriverTests: XCTestCase {
     }
   }
 
+  func testIsIosMacInterface() throws {
+    try withTemporaryFile { file in
+      try localFileSystem.writeFileContents(file.path) { $0 <<< "// swift-module-flags: -target x86_64-apple-ios15.0-macabi" }
+      XCTAssertTrue(try isIosMacInterface(VirtualPath.absolute(file.path)))
+    }
+    try withTemporaryFile { file in
+      try localFileSystem.writeFileContents(file.path) { $0 <<< "// swift-module-flags: -target arm64e-apple-macos12.0" }
+      XCTAssertFalse(try isIosMacInterface(VirtualPath.absolute(file.path)))
+    }
+  }
+
   func testSupportedFeatureJson() throws {
     let driver = try Driver(args: ["swiftc", "-emit-module", "foo.swift"])
     XCTAssertFalse(driver.supportedFrontendFeatures.isEmpty)