Merge pull request #33223 from artemcm/ImplicitActions

Do not attempt to parse the PlaceholderSwiftModule map when not present

Author: artemcm

lib/Serialization/ModuleDependencyScanner.cpp

@@ -131,7 +131,9 @@ class PlaceholderSwiftModuleScanner : public ModuleDependencyScanner {
 
     // FIXME: Find a better place for this map to live, to avoid
     // doing the parsing on every module.
-    parsePlaceholderModuleMap(PlaceholderDependencyModuleMap);
+    if (!PlaceholderDependencyModuleMap.empty()) {
+      parsePlaceholderModuleMap(PlaceholderDependencyModuleMap);
+    }
   }
 
   std::error_code findModuleFilesInDirectory(

test/ScanDependencies/module_deps.swift

@@ -67,7 +67,7 @@ import SubE
 // CHECK-NEXT:    "-target",
 // CHECK-NEXT:    "-Xcc",
 // CHECK:         "-fapinotes-swift-version=4"
-
+// CHECK-NOT: "error: cannot open Swift placeholder dependency module map from"
 // CHECK: "bridgingHeader":
 // CHECK-NEXT: "path":
 // CHECK-SAME: Bridging.h