embedded: enable serialization of debug info in embedded mode

This is important to get diagnostics for errors which are located in imported modules.
Such errors can sometimes only be detected when building the client module, because the error can be in a generic function which is specialized in the client module.

rdar://151162353

Author: eeckstein

lib/Frontend/Frontend.cpp

@@ -207,7 +207,6 @@ SerializationOptions CompilerInvocation::computeSerializationOptions(
   serializationOpts.ModuleLinkName = opts.ModuleLinkName;
   serializationOpts.UserModuleVersion = opts.UserModuleVersion;
   serializationOpts.AllowableClients = opts.AllowableClients;
-  serializationOpts.SerializeDebugInfoSIL = opts.SerializeDebugInfoSIL;
 
   serializationOpts.PublicDependentLibraries =
       getIRGenOptions().PublicLinkLibraries;
@@ -268,6 +267,18 @@ SerializationOptions CompilerInvocation::computeSerializationOptions(
   serializationOpts.EmbeddedSwiftModule =
       LangOpts.hasFeature(Feature::Embedded);
 
+  serializationOpts.SerializeDebugInfoSIL = opts.SerializeDebugInfoSIL;
+
+  // Enable serialization of debug info in embedded mode.
+  // This is important to get diagnostics for errors which are located in imported modules.
+  // Such errors can sometimes only be detected when building the client module, because
+  // the error can be in a generic function which is specialized in the client module.
+  if (serializationOpts.EmbeddedSwiftModule &&
+      // Except for the stdlib core. We don't want to get error locations inside stdlib internals.
+      !getParseStdlib()) {
+    serializationOpts.SerializeDebugInfoSIL = true;
+  }
+
   serializationOpts.IsOSSA = getSILOptions().EnableOSSAModules;
 
   serializationOpts.SkipNonExportableDecls =

test/embedded/multi-module-debug-info.swift

@@ -0,0 +1,35 @@
+// RUN: %empty-directory(%t)
+// RUN: %{python} %utils/split_file.py -o %t %s
+
+// RUN: %target-swift-frontend -emit-module -o %t/MyModule.swiftmodule %t/MyModule.swift -enable-experimental-feature Embedded -parse-as-library
+// RUN: %target-swift-frontend -c -I %t %t/Main.swift -enable-experimental-feature Embedded -verify -o /dev/null
+
+// REQUIRES: OS=macosx || OS=linux-gnu
+// REQUIRES: swift_feature_Embedded
+
+// BEGIN MyModule.swift
+
+public struct MyError: Error {
+}
+
+@inline(never)
+public func foo<T>(_ t: T) throws {
+  throw MyError() // expected-error {{cannot use a value of protocol type 'any Error' in embedded Swift}}
+}
+
+@inline(never)
+public func callit<T>(_ t: T) {
+  do {
+    try foo(t)
+  } catch {
+  }
+}
+
+// BEGIN Main.swift
+
+import MyModule
+
+public func testit() {
+  callit(27) // expected-note {{generic specialization called here}}
+}
+