Stop passing -resource-dir to the swift-frontend if the flag wasn't passed in on the command-line

The original C++ Driver works this way and this flag is being repurposed in the
future. Make an exception for `-scan-dependencies` jobs because of a remaining
issue with in-process scanning that needs to be tracked down.

Author: finagolfin

Sources/SwiftDriver/Jobs/FrontendJobHelpers.swift

@@ -392,11 +392,15 @@ extension Driver {
       try addPathArgument(.absolute(workingDirectory), to: &commandLine, remap: jobNeedPathRemap)
     }
 
-    // Resource directory.
-    try addPathOption(option: .resourceDir,
-                      path: VirtualPath.lookup(frontendTargetInfo.runtimeResourcePath.path),
-                      to: &commandLine,
-                      remap: jobNeedPathRemap)
+    // Only pass in a resource directory to the frontend if one was passed to
+    // swift-driver. Make an exception for scan-dependencies jobs for now till
+    // we figure out a remaining problem with in-process scanning.
+    if parsedOptions.hasArgument(.resourceDir) || kind == .scanDependencies {
+      try addPathOption(option: .resourceDir,
+                        path: VirtualPath.lookup(frontendTargetInfo.runtimeResourcePath.path),
+                        to: &commandLine,
+                        remap: jobNeedPathRemap)
+    }
 
     if self.useStaticResourceDir {
       commandLine.appendFlag("-use-static-resource-dir")

Tests/SwiftDriverTests/SwiftDriverTests.swift

@@ -860,8 +860,10 @@ final class SwiftDriverTests: XCTestCase {
     let plannedJobs = try driver1.planBuild().removingAutolinkExtractJobs()
     XCTAssertEqual(plannedJobs.count, 3)
     XCTAssertEqual(plannedJobs[0].outputs.count, 1)
+    XCTAssert(!plannedJobs[0].commandLine.contains(.flag("-resource-dir")))
     XCTAssertTrue(matchTemporary(plannedJobs[0].outputs.first!.file, "foo.o"))
     XCTAssertEqual(plannedJobs[1].outputs.count, 1)
+    XCTAssert(!plannedJobs[1].commandLine.contains(.flag("-resource-dir")))
     XCTAssertTrue(matchTemporary(plannedJobs[1].outputs.first!.file, "bar.o"))
     XCTAssertTrue(plannedJobs[2].tool.name.contains(executableName("clang")))
     XCTAssertEqual(plannedJobs[2].outputs.count, 1)