[Frontend] Lock the swiftmodule when rebuilding from the swiftinterface

When rebuilding a module interface from the textual interface, lock the
destination path of the created swiftmodule instead of the source
swiftinterface. The swiftinterface files are likely to be in the SDK and
may be on a read-only filesystem.

rdar://60247977

Author: xymus

lib/Frontend/ModuleInterfaceBuilder.cpp

@@ -290,7 +290,7 @@ bool ModuleInterfaceBuilder::buildSwiftModule(StringRef OutPath,
   // processes are doing the same.
   // FIXME: We should surface the module building step to the build system so
   // we don't need to synchronize here.
-  llvm::LockFileManager Locked(interfacePath);
+  llvm::LockFileManager Locked(OutPath);
   switch (Locked) {
   case llvm::LockFileManager::LFS_Error:{
     // ModuleInterfaceBuilder takes care of correctness and locks are only

test/Driver/lock_interface.swift

@@ -1,23 +1,29 @@
-// REQUIRES: rdar59977439
 // RUN: %empty-directory(%t)
+// RUN: %empty-directory(%t/sdk)
 // RUN: %empty-directory(%t/module-cache-lock)
 // RUN: %empty-directory(%t/module-cache-no-lock)
-// RUN: echo 'public func foo() {}' > %t/Foo.swift
-// RUN: %target-swift-frontend-typecheck -emit-module-interface-path %t/Foo.swiftinterface %t/Foo.swift -enable-library-evolution
+// RUN: echo 'public func foo() {}' > %t/sdk/Foo.swift
+// RUN: %target-swift-frontend-typecheck -emit-module-interface-path %t/sdk/Foo.swiftinterface %t/sdk/Foo.swift -enable-library-evolution
+// RUN: chmod a-w %t/sdk
+
 // RUN: touch %t/main.swift %t/file-01.swift %t/file-02.swift %t/file-03.swift
 // RUN: echo 'import Foo' > %t/file-01.swift
 // RUN: echo 'import Foo' > %t/file-02.swift
 // RUN: echo 'import Foo' > %t/file-03.swift
-// RUN: %target-swiftc_driver -j20 %t/main.swift %t/file-01.swift %t/file-02.swift %t/file-03.swift -I %t -Xfrontend -Rmodule-interface-rebuild -module-cache-path %t/module-cache &> %t/result.txt
+// RUN: %target-swiftc_driver -j20 %t/main.swift %t/file-01.swift %t/file-02.swift %t/file-03.swift -I %t/sdk -Xfrontend -Rmodule-interface-rebuild -module-cache-path %t/module-cache &> %t/result.txt
 // RUN: %FileCheck %s  -check-prefix=CHECK-REBUILD < %t/result.txt
 
-// RUN: %target-swiftc_driver -j20 %t/main.swift %t/file-01.swift %t/file-02.swift %t/file-03.swift -I %t -Xfrontend -Rmodule-interface-rebuild -Xfrontend -disable-interface-lock -module-cache-path %t/module-cache-no-lock &> %t/result.txt
+// RUN: %target-swiftc_driver -j20 %t/main.swift %t/file-01.swift %t/file-02.swift %t/file-03.swift -I %t/sdk -Xfrontend -Rmodule-interface-rebuild -Xfrontend -disable-interface-lock -module-cache-path %t/module-cache-no-lock &> %t/result.txt
 
 // RUN: %FileCheck %s  -check-prefix=CHECK-REBUILD-NO-LOCK < %t/result.txt
 
+// Reset the permissions
+// RUN: chmod a+w %t/sdk
+
 // Ensure we only build Foo module once from the interface
 // CHECK-REBUILD: rebuilding module 'Foo' from interface
 // CHECK-REBUILD-NOT: rebuilding module 'Foo' from interface
+// CHECK-REBUILD-NOT: building module interface without lock file
 
 // CHECK-REBUILD-NO-LOCK: rebuilding module 'Foo' from interface
 // CHECK-REBUILD-NO-LOCK: rebuilding module 'Foo' from interface