From 1c89f3d1f8c1f4d40a31fd54bd2061403b02e59b Mon Sep 17 00:00:00 2001
From: Artem Chikin <achikin@apple.com>
Date: Thu, 15 Jul 2021 16:37:19 -0700
Subject: [PATCH] [Dependency Scanning] Restore passing external target map as
 inputs to the scanning action. I got overzealous when deleting code in
 https://github.com/apple/swift-driver/pull/749 and removed one piece of
 functionality that we still rely on. Although the external target map is no
 longer necessary when scanning dependencies using libSwiftScan, we still use
 it for resolution of `canImport` statements during the scan. We need to
 figure out a better way to deal with that in the scanner, but in the meantime
 this will restore functionality.

---
 .../ModuleDependencyScanning.swift            | 26 +++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/Sources/SwiftDriver/ExplicitModuleBuilds/ModuleDependencyScanning.swift b/Sources/SwiftDriver/ExplicitModuleBuilds/ModuleDependencyScanning.swift
index 3174155fb..121e63de5 100644
--- a/Sources/SwiftDriver/ExplicitModuleBuilds/ModuleDependencyScanning.swift
+++ b/Sources/SwiftDriver/ExplicitModuleBuilds/ModuleDependencyScanning.swift
@@ -52,11 +52,37 @@ public extension Driver {
                                  moduleDependencyGraphUse: .dependencyScan)
     // FIXME: MSVC runtime flags
 
+    // Pass in external target dependencies to be treated as placeholder dependencies by the scanner
+    if let externalTargetPaths = externalTargetModulePathMap {
+      let dependencyPlaceholderMapFile =
+      try serializeExternalDependencyArtifacts(externalTargetPaths: externalTargetPaths)
+      commandLine.appendFlag("-placeholder-dependency-module-map-file")
+      commandLine.appendPath(dependencyPlaceholderMapFile)
+    }
+
     // Pass on the input files
     commandLine.append(contentsOf: inputFiles.map { .path($0.file) })
     return (inputs, commandLine)
   }
 
+  /// Serialize a map of placeholder (external) dependencies for the dependency scanner.
+   private func serializeExternalDependencyArtifacts(externalTargetPaths: ExternalTargetModulePathMap)
+   throws -> VirtualPath {
+     var placeholderArtifacts: [SwiftModuleArtifactInfo] = []
+     // Explicit external targets
+     for (moduleId, binaryModulePath) in externalTargetPaths {
+       let modPath = TextualVirtualPath(path: VirtualPath.absolute(binaryModulePath).intern())
+       placeholderArtifacts.append(
+           SwiftModuleArtifactInfo(name: moduleId.moduleName,
+                                   modulePath: modPath))
+     }
+     let encoder = JSONEncoder()
+     encoder.outputFormatting = [.prettyPrinted]
+     let contents = try encoder.encode(placeholderArtifacts)
+     return VirtualPath.createUniqueTemporaryFileWithKnownContents(.init("\(moduleOutputInfo.name)-external-modules.json"),
+                                                                   contents)
+   }
+
   /// Returns false if the lib is available and ready to use
   private func initSwiftScanLib() throws -> Bool {
     // If `-nonlib-dependency-scanner` was specified or the libSwiftScan library cannot be found,