CrashReproducer generation improvements

Add some improvements to crash reproducer:
* Allow environmental variable `SWIFT_CRASH_DIAGNOSTICS_DIR` to specify
  where the reproducer is written to.
* Add a testcase for generation reproducer since we can direct
  reproducer into a directory that can be cleared after testcase
* Do use parseable output when producing reproducer (to avoid polluting
  the stdout where build system might except build commands)

Author: cachemeifyoucan

Sources/SwiftDriver/Jobs/FrontendJobHelpers.swift

@@ -1082,6 +1082,12 @@ extension Driver {
     reproJob.commandLine.appendFlag(.genReproducer)
     reproJob.commandLine.appendFlag(.genReproducerDir)
     reproJob.commandLine.appendPath(output)
+    reproJob.commandLine.removeAll {
+      guard case let .flag(opt) = $0 else {
+        return false
+      }
+      return opt == Option.frontendParseableOutput.spelling
+    }
     reproJob.outputs.removeAll()
     reproJob.outputCacheKeys.removeAll()
     return reproJob

Sources/SwiftDriverExecution/MultiJobExecutor.swift

@@ -23,6 +23,7 @@ import class TSCBasic.DiagnosticsEngine
 import class TSCBasic.Process
 import protocol TSCBasic.DiagnosticData
 import protocol TSCBasic.FileSystem
+import struct TSCBasic.AbsolutePath
 import struct TSCBasic.Diagnostic
 import struct TSCBasic.ProcessResult
 import func TSCBasic.withTemporaryDirectory
@@ -678,7 +679,13 @@ class ExecuteJobRule: LLBuildRule {
   }
 
   private func handleSignalledJob(for job: Job) throws {
-    try withTemporaryDirectory(dir: fileSystem.tempDirectory, prefix: "swift-reproducer", removeTreeOnDeinit: false) { tempDir in
+    let reproDir: AbsolutePath
+    if let pathFromEnv = context.env["SWIFT_CRASH_DIAGNOSTICS_DIR"] {
+      reproDir = try AbsolutePath(validating: pathFromEnv)
+    } else {
+      reproDir = try fileSystem.tempDirectory
+    }
+    try withTemporaryDirectory(dir: reproDir, prefix: "swift-crash-reproducer", removeTreeOnDeinit: false) { tempDir in
       guard let reproJob = context.executorDelegate.getReproducerJob(job: job, output: VirtualPath.absolute(tempDir)) else {
         return
       }

Tests/SwiftDriverTests/CachingBuildTests.swift

@@ -1053,6 +1053,52 @@ final class CachingBuildTests: XCTestCase {
     }
   }
 
+  func testCrashReproducer() throws {
+    try withTemporaryDirectory { path in
+      try localFileSystem.changeCurrentWorkingDirectory(to: path)
+      let moduleCachePath = path.appending(component: "ModuleCache")
+      let casPath = path.appending(component: "cas")
+      try localFileSystem.createDirectory(moduleCachePath)
+      let main = path.appending(component: "testCachingBuild.swift")
+      let mainFileContent = "import C;"
+      try localFileSystem.writeFileContents(main) {
+        $0.send(mainFileContent)
+      }
+      let cHeadersPath: AbsolutePath =
+          try testInputsPath.appending(component: "ExplicitModuleBuilds")
+                            .appending(component: "CHeaders")
+      let swiftModuleInterfacesPath: AbsolutePath =
+          try testInputsPath.appending(component: "ExplicitModuleBuilds")
+                            .appending(component: "Swift")
+      let sdkArgumentsForTesting = (try? Driver.sdkArgumentsForTesting()) ?? []
+      var env = ProcessEnv.block
+      env["SWIFT_CRASH_DIAGNOSTICS_DIR"] = path.nativePathString(escaped: true)
+      var driver = try Driver(args: ["swiftc",
+                                     "-I", cHeadersPath.nativePathString(escaped: true),
+                                     "-I", swiftModuleInterfacesPath.nativePathString(escaped: true),
+                                     "-explicit-module-build", "-enable-deterministic-check",
+                                     "-module-cache-path", moduleCachePath.nativePathString(escaped: true),
+                                     "-cache-compile-job", "-cas-path", casPath.nativePathString(escaped: true),
+                                     "-working-directory", path.nativePathString(escaped: true),
+                                     "-Xfrontend", "-debug-crash-after-parse",
+                                     main.nativePathString(escaped: true)] + sdkArgumentsForTesting,
+                              env: env)
+      guard driver.isFrontendArgSupported(.genReproducer) else {
+        throw XCTSkip("crash reproducer not supported")
+      }
+      let jobs = try driver.planBuild()
+      do {
+        try driver.run(jobs: jobs)
+        XCTFail("Build should fail")
+      } catch {
+        XCTAssertTrue(driver.diagnosticEngine.hasErrors)
+        XCTAssertTrue(driver.diagnosticEngine.diagnostics.contains {
+          $0.message.behavior == .note && $0.message.data.description.starts(with: "crash reproducer")
+          })
+      }
+    }
+  }
+
   func testDeterministicCheck() throws {
     try withTemporaryDirectory { path in
       try localFileSystem.changeCurrentWorkingDirectory(to: path)