Add frontend option -no-serialize-debugging-options (#20555)

By default, the frontend tries to figure out if the built module is
likely to be distributed in some way, and uses that to decide whether
to include options that help with debugging (such as local search
paths). There's long been a -serialize-debugging-options that forces
those options to be included even when it looks like a framework is
being built, but the opposite has been absent until now.

Note that both of these options are still /frontend/ options, not
driver options, which means they could still change in the future.
(I'd really like to get to a point where debugging doesn't need to
sniff these options out from the module this way, but there are some
complications we'd need to work out. Swift 1 expediency coming back to
cause trouble again.)

rdar://problem/37954803

Author: jrose-apple

include/swift/Frontend/FrontendOptions.h

@@ -146,9 +146,10 @@ class FrontendOptions {
   /// Indicates that the input(s) should be parsed as the Swift stdlib.
   bool ParseStdlib = false;
 
-  /// If set, emitted module files will always contain options for the
-  /// debugger to use.
-  bool AlwaysSerializeDebuggingOptions = false;
+  /// When true, emitted module files will always contain options for the
+  /// debugger to use. When unset, the options will only be present if the
+  /// module appears to not be a public module.
+  Optional<bool> SerializeOptionsForDebugging;
 
   /// If set, inserts instrumentation useful for testing the debugger.
   bool DebuggerTestingTransform = false;

include/swift/Option/FrontendOptions.td

@@ -133,6 +133,9 @@ def print_clang_stats : Flag<["-"], "print-clang-stats">,
 
 def serialize_debugging_options : Flag<["-"], "serialize-debugging-options">,
   HelpText<"Always serialize options for debugging (default: only for apps)">;
+def no_serialize_debugging_options :
+  Flag<["-"], "no-serialize-debugging-options">,
+  HelpText<"Never serialize options for debugging (default: only for apps)">;
 
 def autolink_library : Separate<["-"], "autolink-library">,
   HelpText<"Add dependent library">, Flags<[FrontendOption]>;

lib/Frontend/ArgsToFrontendOptionsConverter.cpp

@@ -148,8 +148,12 @@ bool ArgsToFrontendOptionsConverter::convert(
   if (const Arg *A = Args.getLastArg(OPT_module_link_name))
     Opts.ModuleLinkName = A->getValue();
 
-  Opts.AlwaysSerializeDebuggingOptions |=
-      Args.hasArg(OPT_serialize_debugging_options);
+  if (const Arg *A = Args.getLastArg(OPT_serialize_debugging_options,
+                                     OPT_no_serialize_debugging_options)) {
+    Opts.SerializeOptionsForDebugging =
+        A->getOption().matches(OPT_serialize_debugging_options);
+  }
+
   Opts.EnableSourceImport |= Args.hasArg(OPT_enable_source_import);
   Opts.ImportUnderlyingModule |= Args.hasArg(OPT_import_underlying_module);
   Opts.EnableParseableModuleInterface |=

lib/Frontend/Frontend.cpp

@@ -141,7 +141,7 @@ CompilerInvocation::computeSerializationOptions(const SupplementaryOutputPaths &
   // so only serialize them if the module isn't going to be shipped to
   // the public.
   serializationOpts.SerializeOptionsForDebugging =
-      !moduleIsPublic || opts.AlwaysSerializeDebuggingOptions;
+      opts.SerializeOptionsForDebugging.getValueOr(!moduleIsPublic);
 
   return serializationOpts;
 }

test/Serialization/search-paths.swift

@@ -17,6 +17,10 @@
 // RUN: %target-swift-frontend -emit-module -o %t -I %t/secret -F %t/Frameworks -Fsystem %t/SystemFrameworks -parse-as-library %S/Inputs/has_xref.swift -application-extension
 // RUN: %target-swift-frontend %s -typecheck -I %t
 
+// Make sure -no-serialize-debugging-options has the desired effect.
+// RUN: %target-swift-frontend -emit-module -o %t -I %t/secret -F %t/Frameworks -Fsystem %t/SystemFrameworks -parse-as-library %S/Inputs/has_xref.swift -application-extension -no-serialize-debugging-options
+// RUN: %target-swift-frontend %s -typecheck -I %t -verify -show-diagnostics-after-fatal
+
 // Make sure we don't end up with duplicate search paths.
 // RUN: %target-swiftc_driver -emit-module -o %t/has_xref.swiftmodule -I %t/secret -F %t/Frameworks -Fsystem %t/SystemFrameworks -parse-as-library %S/Inputs/has_xref.swift %S/../Inputs/empty.swift -Xfrontend -serialize-debugging-options
 // RUN: %target-swift-frontend %s -typecheck -I %t