Check if resource directory exists in -sdk and fall back to default if not

Author: finagolfin

include/swift/AST/DiagnosticsFrontend.def

@@ -24,6 +24,13 @@
 WARNING(warning_no_such_sdk,none,
         "no such SDK: '%0'", (StringRef))
 
+WARNING(warning_no_resource_dir_in_sdk, none,
+        "You passed in an external -sdk without a Swift runtime.\n"
+        "Either specify a directory containing the runtime libraries with\n"
+        "the -resource-dir flag, or use -sysroot instead to point at a C/C++\n"
+        "sysroot alone. Falling back to this path for the Swift runtime modules\n"
+        "and libraries:\n"
+        "%0", (StringRef))
 ERROR(error_no_frontend_args, none,
       "no arguments provided to '-frontend'", ())
 

lib/Frontend/CompilerInvocation.cpp

@@ -2421,7 +2421,12 @@ static bool ParseSearchPathArgs(SearchPathOptions &Opts, ArgList &Args,
     llvm::sys::path::append(
         SDKResourcePath, "usr", "lib",
         FrontendOpts.UseSharedResourceFolder ? "swift" : "swift_static");
-    Opts.RuntimeResourcePath = SDKResourcePath.str();
+    // Check for eg <sdkRoot>/usr/lib/swift/
+    if (llvm::sys::fs::exists(SDKResourcePath))
+      Opts.RuntimeResourcePath = SDKResourcePath.str();
+    else
+      Diags.diagnose(SourceLoc(), diag::warning_no_resource_dir_in_sdk,
+                     Opts.RuntimeResourcePath);
   }
 
   Opts.SkipAllImplicitImportPaths |= Args.hasArg(OPT_nostdimport);