[SwiftCaching] Don't leak output path in the explicit module map JSON

Using an abstract name for the module path for swift caching build
because caching build loads modules directly from CAS and the path is
insignificant. The abstract module path allows cache hits across
different output locations.

rdar://149960868

Author: cachemeifyoucan

Sources/SwiftDriver/ExplicitModuleBuilds/ExplicitDependencyBuildPlanner.swift

@@ -296,9 +296,9 @@ public typealias ExternalTargetModuleDetailsMap = [ModuleDependencyId: ExternalT
     // SwiftModuleArtifactInfo
     guard moduleId == .swift(dependencyGraph.mainModuleName) else { return }
     let dependencyFileContent =
-      try serializeModuleDependencies(for: moduleId,
-                                      swiftDependencyArtifacts: swiftDependencyArtifacts,
-                                      clangDependencyArtifacts: clangDependencyArtifacts)
+      try serializeModuleDependencies(swiftDependencyArtifacts: swiftDependencyArtifacts,
+                                      clangDependencyArtifacts: clangDependencyArtifacts,
+                                      cachingEnabled: cas != nil)
     if let cas = self.cas {
       // When using a CAS, write JSON into CAS and pass the ID on command-line.
       let casID = try cas.store(data: dependencyFileContent)
@@ -534,9 +534,9 @@ public typealias ExternalTargetModuleDetailsMap = [ModuleDependencyId: ExternalT
                             "-Xcc", "-fno-implicit-module-maps")
 
     let dependencyFileContent =
-      try serializeModuleDependencies(for: mainModuleId,
-                                      swiftDependencyArtifacts: swiftDependencyArtifacts,
-                                      clangDependencyArtifacts: clangDependencyArtifacts)
+      try serializeModuleDependencies(swiftDependencyArtifacts: swiftDependencyArtifacts,
+                                      clangDependencyArtifacts: clangDependencyArtifacts,
+                                      cachingEnabled: false)
 
     let dependencyFile =
       try VirtualPath.createUniqueTemporaryFileWithKnownContents(.init(validating: "\(mainModuleId.moduleName)-dependencies.json"),
@@ -548,15 +548,43 @@ public typealias ExternalTargetModuleDetailsMap = [ModuleDependencyId: ExternalT
   }
 
   /// Serialize the output file artifacts for a given module in JSON format.
-  private func serializeModuleDependencies(for moduleId: ModuleDependencyId,
-                                           swiftDependencyArtifacts: Set<SwiftModuleArtifactInfo>,
-                                           clangDependencyArtifacts: Set<ClangModuleArtifactInfo>
+  private func serializeModuleDependencies(swiftDependencyArtifacts: Set<SwiftModuleArtifactInfo>,
+                                           clangDependencyArtifacts: Set<ClangModuleArtifactInfo>,
+                                           cachingEnabled: Bool
   ) throws -> Data {
+    // Helper function to abstract the path.
+    func abstractPath(_ module: String, suffix: String) throws -> TextualVirtualPath {
+      let path = try VirtualPath(path: module + suffix)
+      return TextualVirtualPath(path: path.intern())
+    }
     // The module dependency map in CAS needs to be stable.
-    // Sort the dependencies by name.
+    // For caching build, updated the dependency info to exclude paths that are compiler outputs from the mapping.
+    // Use abstract names and paths because caching build loads modules directly from CAS.
     let allDependencyArtifacts: [ModuleDependencyArtifactInfo] =
-      swiftDependencyArtifacts.sorted().map {ModuleDependencyArtifactInfo.swift($0)} +
-      clangDependencyArtifacts.sorted().map {ModuleDependencyArtifactInfo.clang($0)}
+      try swiftDependencyArtifacts.sorted().map { info in
+        if !cachingEnabled {
+          return ModuleDependencyArtifactInfo.swift(info)
+        }
+        let updatedInfo = try SwiftModuleArtifactInfo(name: info.moduleName,
+                                                      modulePath: abstractPath(info.moduleName, suffix: ".swiftmodule"),
+                                                      docPath: nil,
+                                                      sourceInfoPath: nil,
+                                                      headerDependencies: info.prebuiltHeaderDependencyPaths,
+                                                      isFramework: info.isFramework,
+                                                      moduleCacheKey: info.moduleCacheKey)
+        return ModuleDependencyArtifactInfo.swift(updatedInfo)
+      } +
+      clangDependencyArtifacts.sorted().map { info in
+        if !cachingEnabled {
+          return ModuleDependencyArtifactInfo.clang(info)
+        }
+        let updatedInfo = try ClangModuleArtifactInfo(name: info.moduleName,
+                                                      modulePath: abstractPath(info.moduleName, suffix: ".pcm"),
+                                                      moduleMapPath: info.clangModuleMapPath,
+                                                      moduleCacheKey: info.clangModuleCacheKey,
+                                                      isBridgingHeaderDependency: info.isBridgingHeaderDependency)
+        return ModuleDependencyArtifactInfo.clang(updatedInfo)
+      }
     let encoder = JSONEncoder()
     // Use sorted key to ensure the order of the keys is stable.
     encoder.outputFormatting = [.prettyPrinted, .sortedKeys]