[Explicit Module Builds] Restore prior behavior of consuming .h dependencies of binary module dependencies directly, instead of attempting to load their PCH

include/swift/Serialization/SerializationOptions.h

@@ -158,6 +158,7 @@ namespace swift {
     bool EmbeddedSwiftModule = false;
     bool IsOSSA = false;
     bool SkipNonExportableDecls = false;
+    bool ExplicitModuleBuild = false;
   };
 
 } // end namespace swift

lib/Frontend/Frontend.cpp

@@ -240,6 +240,8 @@ SerializationOptions CompilerInvocation::computeSerializationOptions(
 
   serializationOpts.SkipNonExportableDecls = opts.SkipNonExportableDecls;
 
+  serializationOpts.ExplicitModuleBuild = FrontendOpts.DisableImplicitModules;
+
   return serializationOpts;
 }
 

lib/Serialization/Serialization.cpp

@@ -53,6 +53,8 @@
 #include "swift/Serialization/SerializationOptions.h"
 #include "swift/Strings.h"
 #include "clang/AST/DeclTemplate.h"
+#include "clang/Frontend/CompilerInstance.h"
+#include "clang/Serialization/ASTReader.h"
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringExtras.h"
@@ -1297,15 +1299,28 @@ void Serializer::writeInputBlock() {
     off_t importedHeaderSize = 0;
     time_t importedHeaderModTime = 0;
     std::string contents;
-    if (!Options.ImportedHeader.empty()) {
+    auto importedHeaderPath = Options.ImportedHeader;
+    // We do not want to serialize the explicitly-specified .pch path if one was
+    // provided. Instead we write out the path to the original header source so
+    // that clients can consume it.
+    if (Options.ExplicitModuleBuild &&
+        llvm::sys::path::extension(importedHeaderPath)
+            .endswith(file_types::getExtension(file_types::TY_PCH)))
+      importedHeaderPath = clangImporter->getClangInstance()
+                               .getASTReader()
+                               ->getModuleManager()
+                               .lookupByFileName(importedHeaderPath)
+                               ->OriginalSourceFileName;
+
+    if (!importedHeaderPath.empty()) {
       contents = clangImporter->getBridgingHeaderContents(
-          Options.ImportedHeader, importedHeaderSize, importedHeaderModTime);
+          importedHeaderPath, importedHeaderSize, importedHeaderModTime);
     }
     assert(publicImportSet.count(bridgingHeaderImport));
     ImportedHeader.emit(ScratchRecord,
                         publicImportSet.count(bridgingHeaderImport),
                         importedHeaderSize, importedHeaderModTime,
-                        Options.ImportedHeader);
+                        importedHeaderPath);
     if (!contents.empty()) {
       contents.push_back('\0');
       ImportedHeaderContents.emit(ScratchRecord, contents);

lib/Serialization/SerializedModuleLoader.cpp

@@ -477,12 +477,19 @@ SerializedModuleLoaderBase::scanModuleFile(Twine modulePath, bool isFramework) {
 
   auto importedHeaderSet = binaryModuleImports.get().headerImports;
   std::vector<std::string> importedHeaders;
-  importedHeaders.reserve(importedHeaderSet.size());
-  llvm::transform(importedHeaderSet.keys(),
-                  std::back_inserter(importedHeaders),
-                  [](llvm::StringRef N) {
-                     return N.str();
-                  });
+  // FIXME: We only record these dependencies in CAS mode, because
+  // we require explicit PCH tasks to be produced for imported header
+  // of binary module dependencies. In the meantime, in non-CAS mode
+  // loading clients will consume the `.h` files encoded in the `.swiftmodules`
+  // directly.
+  if (Ctx.ClangImporterOpts.CASOpts) {
+    importedHeaders.reserve(importedHeaderSet.size());
+    llvm::transform(importedHeaderSet.keys(),
+                    std::back_inserter(importedHeaders),
+                    [](llvm::StringRef N) {
+      return N.str();
+    });
+  }
 
   auto &importedOptionalModuleSet = binaryModuleOptionalImports.get().moduleImports;
   std::vector<std::string> importedOptionalModuleNames;

test/ScanDependencies/header_deps_of_binary.swift

@@ -2,18 +2,20 @@
 // RUN: %empty-directory(%t)
 // RUN: %empty-directory(%t/clang-module-cache)
 // RUN: %empty-directory(%t/PCH)
+// RUN: %empty-directory(%t/HEADER)
 // RUN: %empty-directory(%t/SwiftModules)
+// RUN: %empty-directory(%t/CAS)
 
 // - Set up Foo Swift dependency
 // RUN: echo "extension Profiler {" >> %t/foo.swift
 // RUN: echo "    public static let count: Int = 42" >> %t/foo.swift
 // RUN: echo "}" >> %t/foo.swift
 
 // - Set up Foo bridging header
-// RUN: echo "struct Profiler { void* ptr; };" >> %t/foo.h
+// RUN: echo "struct Profiler { void* ptr; };" >> %t/HEADER/foo.h
 
 // - Compile bridging header
-// RUN: %target-swift-frontend -enable-objc-interop -emit-pch %t/foo.h -o %t/PCH/foo.pch -disable-implicit-swift-modules
+// RUN: %target-swift-frontend -enable-objc-interop -emit-pch %t/HEADER/foo.h -o %t/PCH/foo.pch -disable-implicit-swift-modules
 
 // - Set up explicit dependencies for Foo
 // RUN: %target-swift-emit-pcm -module-name SwiftShims %swift-lib-dir/swift/shims/module.modulemap -o %t/inputs/SwiftShims.pcm
@@ -50,21 +52,27 @@
 // RUN: %target-swift-frontend -emit-module -emit-module-path %t/SwiftModules/Foo.swiftmodule %t/foo.swift -module-name Foo -import-objc-header %t/PCH/foo.pch -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -disable-implicit-swift-modules -explicit-swift-module-map-file %t/foo_inputs_map.json 
 
 // - Scan main module
-// RUN: %target-swift-frontend -scan-dependencies %s -I %t/SwiftModules -I %S/Inputs/Swift -o %t/deps.json
+// RUN: %target-swift-frontend -scan-dependencies %s -I %t/SwiftModules -I %S/Inputs/Swift -o %t/deps.json -cache-compile-job -cas-path %t/cas
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
+// - Scan main module without a CAS and ensure no headerDependencies are emitted
+// RUN: %target-swift-frontend -scan-dependencies %s -I %t/SwiftModules -I %S/Inputs/Swift -o %t/deps_nocas.json
+// RUN: %validate-json %t/deps_nocas.json | %FileCheck %s --check-prefix=CHECK-NO-HEADERS
+
 // CHECK: "swift": "FooClient"
 // CHECK: "swift": "FooClient"
 // CHECK: "swiftPrebuiltExternal": "Foo"
 // CHECK:     "commandLine": [
 // CHECK:            "-include-pch",
 // CHECK-NEXT:       "-Xcc",
-// CHECK-NEXT:       "{{.*}}{{/|\\}}PCH{{/|\\}}foo.pch"
+// CHECK-NEXT:       "{{.*}}{{/|\\}}HEADER{{/|\\}}foo.h"
 
 
 // CHECK: "swiftPrebuiltExternal": "Foo"
 // CHECK:   "headerDependencies": [
-// CHECK:      "{{.*}}{{/|\\}}PCH{{/|\\}}foo.pch"
+// CHECK:      "{{.*}}{{/|\\}}HEADER{{/|\\}}foo.h"
 // CHECK:   ],
 
+// CHECK-NO-HEADERS-NOT: "headerDependencies"
+
 import FooClient