[REPL] When using the default resource directory, prefer loading Swift dylibs from /usr/lib/swift.

rdar://problem/46355503

Author: mikeash

include/swift/AST/SearchPathOptions.h

@@ -72,6 +72,9 @@ class SearchPathOptions {
 
   /// Don't look in for compiler-provided modules.
   bool SkipRuntimeLibraryImportPath = false;
+  
+  /// Whether the runtime library path is set to the compiler-relative default.
+  bool RuntimeLibraryPathIsDefault = true;
 
   /// Return a hash code of any components from these options that should
   /// contribute to a Swift Bridging PCH hash.

include/swift/Frontend/Frontend.h

@@ -182,7 +182,7 @@ class CompilerInvocation {
 
   void setMainExecutablePath(StringRef Path);
 
-  void setRuntimeResourcePath(StringRef Path);
+  void setRuntimeResourcePath(StringRef Path, bool IsDefault = false);
 
   void setSDKPath(const std::string &Path) {
     SearchPathOpts.SDKPath = Path;

lib/Frontend/CompilerInvocation.cpp

@@ -39,7 +39,7 @@ void CompilerInvocation::setMainExecutablePath(StringRef Path) {
   llvm::sys::path::remove_filename(LibPath); // Remove /swift
   llvm::sys::path::remove_filename(LibPath); // Remove /bin
   llvm::sys::path::append(LibPath, "lib", "swift");
-  setRuntimeResourcePath(LibPath.str());
+  setRuntimeResourcePath(LibPath.str(), /*IsDefault=*/true);
 }
 
 static void updateRuntimeLibraryPath(SearchPathOptions &SearchPathOpts,
@@ -53,9 +53,11 @@ static void updateRuntimeLibraryPath(SearchPathOptions &SearchPathOpts,
   SearchPathOpts.RuntimeLibraryImportPath = LibPath.str();
 }
 
-void CompilerInvocation::setRuntimeResourcePath(StringRef Path) {
+void CompilerInvocation::setRuntimeResourcePath(StringRef Path,
+                                                bool IsDefault) {
   SearchPathOpts.RuntimeResourcePath = Path;
   updateRuntimeLibraryPath(SearchPathOpts, LangOpts.Target);
+  SearchPathOpts.RuntimeLibraryPathIsDefault = IsDefault;
 }
 
 void CompilerInvocation::setTargetTriple(StringRef Triple) {

lib/Immediate/Immediate.cpp

@@ -51,10 +51,22 @@
 using namespace swift;
 using namespace swift::immediate;
 
+/// The path for Swift libraries in the OS.
+#define OS_LIBRARY_PATH "/usr/lib/swift"
+
 static void *loadRuntimeLib(StringRef runtimeLibPathWithName) {
 #if defined(_WIN32)
   return LoadLibraryA(runtimeLibPathWithName.str().c_str());
 #else
+#if defined(__APPLE__) && defined(__MACH__)
+  if (!llvm::sys::path::is_absolute(runtimeLibPathWithName)) {
+    // Try an absolute path search for Swift in the OS first.
+    llvm::SmallString<128> absolutePath(OS_LIBRARY_PATH);
+    llvm::sys::path::append(absolutePath, runtimeLibPathWithName);
+    auto result = dlopen(absolutePath.c_str(), RTLD_LAZY | RTLD_GLOBAL);
+    if (result) return result;
+  }
+#endif
   return dlopen(runtimeLibPathWithName.str().c_str(), RTLD_LAZY | RTLD_GLOBAL);
 #endif
 }
@@ -66,8 +78,16 @@ static void *loadRuntimeLib(StringRef sharedLibName, StringRef runtimeLibPath) {
   return loadRuntimeLib(Path);
 }
 
-void *swift::immediate::loadSwiftRuntime(StringRef runtimeLibPath) {
-  return loadRuntimeLib("libswiftCore" LTDL_SHLIB_EXT, runtimeLibPath);
+void *swift::immediate::loadSwiftRuntime(StringRef runtimeLibPath,
+                                         bool IsDefault) {
+  StringRef LibName = "libswiftCore" LTDL_SHLIB_EXT;
+#if defined(__APPLE__) && defined(__MACH__)
+  if (IsDefault) {
+    auto result = loadRuntimeLib(LibName);
+    if (result) return result;
+  }
+#endif
+  return loadRuntimeLib(LibName, runtimeLibPath);
 }
 
 static bool tryLoadLibrary(LinkLibrary linkLib,
@@ -240,7 +260,9 @@ int swift::RunImmediately(CompilerInstance &CI, const ProcessCmdLine &CmdLine,
   //
   // This must be done here, before any library loading has been done, to avoid
   // racing with the static initializers in user code.
-  auto stdlib = loadSwiftRuntime(Context.SearchPathOpts.RuntimeLibraryPath);
+  auto stdlib = loadSwiftRuntime(
+    Context.SearchPathOpts.RuntimeLibraryPath,
+    Context.SearchPathOpts.RuntimeLibraryPathIsDefault);
   if (!stdlib) {
     CI.getDiags().diagnose(SourceLoc(),
                            diag::error_immediate_mode_missing_stdlib);

lib/Immediate/ImmediateImpl.h

@@ -38,7 +38,8 @@ namespace immediate {
 /// calls or \c null if an error occurred.
 ///
 /// \param runtimeLibPath Path to search for compiler-relative stdlib dylibs.
-void *loadSwiftRuntime(StringRef runtimeLibPath);
+/// \param IsDefault If true, the path is the default compiler-relative path.
+void *loadSwiftRuntime(StringRef runtimeLibPath, bool IsDefault);
 bool tryLoadLibraries(ArrayRef<LinkLibrary> LinkLibraries,
                       SearchPathOptions SearchPathOpts,
                       DiagnosticEngine &Diags);

lib/Immediate/REPL.cpp

@@ -968,7 +968,8 @@ class REPLEnvironment {
     ASTContext &Ctx = CI.getASTContext();
     Ctx.LangOpts.EnableAccessControl = false;
     if (!ParseStdlib) {
-      if (!loadSwiftRuntime(Ctx.SearchPathOpts.RuntimeLibraryPath)) {
+      if (!loadSwiftRuntime(Ctx.SearchPathOpts.RuntimeLibraryPath,
+                            Ctx.SearchPathOpts.RuntimeLibraryPathIsDefault)) {
         CI.getDiags().diagnose(SourceLoc(),
                                diag::error_immediate_mode_missing_stdlib);
         return;