Propagate response files correctly to the new driver.

If a response file is being passed to the legacy driver
because it is too large to fit on the system's command line,
then it should also be passed when spawning the new driver.
Currently, however, the legacy driver attempts to pass the
*expanded* arguments to the new driver, which can cause the
invocation to fail, requiring the new driver to be disabled
in order to compile.

This change passes the original arguments into `run_driver`
as well as the expanded ones, so that the branch that spawns
the new driver can use the original arguments instead.

Author: allevato

lib/DriverTool/driver.cpp

@@ -184,7 +184,8 @@ static bool appendSwiftDriverName(SmallString<256> &buffer) {
 }
 
 static int run_driver(StringRef ExecName,
-                       const ArrayRef<const char *> argv) {
+                       const ArrayRef<const char *> argv,
+                       const ArrayRef<const char *> originalArgv) {
   // This is done here and not done in FrontendTool.cpp, because
   // FrontendTool.cpp is linked to tools, which don't use swift modules.
   initializeSwiftModules();
@@ -244,7 +245,8 @@ static int run_driver(StringRef ExecName,
       subCommandArgs.push_back(NewDriverPath.c_str());
 
       // Push on the source program arguments
-      subCommandArgs.insert(subCommandArgs.end(), argv.begin() + 1, argv.end());
+      subCommandArgs.insert(subCommandArgs.end(),
+                            originalArgv.begin() + 1, originalArgv.end());
 
       // Execute the subcommand.
       subCommandArgs.push_back(nullptr);
@@ -393,12 +395,13 @@ int swift::mainEntry(int argc_, const char **argv_) {
     return 2;
   }
 
+  ArrayRef<const char *> originalArgv(argv_, &argv_[argc_]);
   if (isRepl) {
     // Preserve argv for the stack trace.
     SmallVector<const char *, 256> replArgs(argv.begin(), argv.end());
     replArgs.erase(&replArgs[1]);
-    return run_driver(ExecName, replArgs);
+    return run_driver(ExecName, replArgs, originalArgv);
   } else {
-    return run_driver(ExecName, argv);
+    return run_driver(ExecName, argv, originalArgv);
   }
 }

test/Driver/LegacyDriver/Inputs/print-args.sh

@@ -0,0 +1,5 @@
+#!/usr/bin/env sh
+
+for arg in "$@" ; do
+  echo "$arg"
+done

test/Driver/LegacyDriver/legacy-driver-propagates-response-file-to-new-driver.swift

@@ -0,0 +1,17 @@
+// Verify that when the legacy driver (swift-frontend executable invoked as
+// swiftc) spawns the new driver, it passes the original arguments (i.e.,
+// preserving response files) instead of trying to spawn the process with the
+// expansion, which may exceed `ARG_MAX`.
+
+// REQUIRES: shell
+// RUN: %{python} -c 'for i in range(500001): print("-DTEST5_" + str(i))' > %t.resp
+// RUN: cp %S/Inputs/print-args.sh %swift_obj_root/bin/legacy-driver-propagates-response-file.sh
+// RUN: env SWIFT_USE_NEW_DRIVER=legacy-driver-propagates-response-file.sh %swiftc_driver_plain %s @%t.resp | %FileCheck %s
+// RUN: rm %swift_obj_root/bin/legacy-driver-propagates-response-file.sh
+
+// CHECK:      -Xfrontend
+// CHECK-NEXT: -new-driver-path
+// CHECK-NEXT: -Xfrontend
+// CHECK-NEXT: legacy-driver-propagates-response-file.sh
+// CHECK:      @{{.*}}.resp
+// CHECK-NOT:  -DTEST5_{{.*}}

test/Driver/LegacyDriver/lit.local.cfg

@@ -0,0 +1,7 @@
+# Make a local copy of the environment.
+config.environment = dict(config.environment)
+
+# Remove the settings that force tests to use the old driver so that tests
+# in this directory can set `SWIFT_USE_NEW_DRIVER` to test those code paths.
+del config.environment['SWIFT_USE_OLD_DRIVER']
+del config.environment['SWIFT_AVOID_WARNING_USING_OLD_DRIVER']