ModulePrinting: Avoid merging synthesized extensions with comments, and print the comments. rdar://25157796

Author: nkcsgexi

lib/AST/ASTPrinter.cpp

@@ -329,7 +329,7 @@ struct SynthesizedExtensionAnalyzer::Implementation {
   isApplicable(ExtensionDecl *Ext) {
     SynthesizedExtensionInfo Result;
     std::unique_ptr<ExtensionMergeInfo> MergeInfo(new ExtensionMergeInfo());
-    MergeInfo->HasDocComment = false;
+    MergeInfo->HasDocComment = !Ext->getRawComment().isEmpty();
     if (!Ext->isConstrainedExtension()) {
       if (IncludeUnconditional)
         Result.Ext = Ext;

test/IDE/print_synthesized_extensions.swift

@@ -1,5 +1,5 @@
 // RUN: rm -rf %t && mkdir %t
-// RUN: %target-swift-frontend -emit-module-path %t/print_synthesized_extensions.swiftmodule %s
+// RUN: %target-swift-frontend -emit-module-path %t/print_synthesized_extensions.swiftmodule -emit-module-doc -emit-module-doc-path %t/print_synthesized_extensions.swiftdoc %s
 // RUN: %target-swift-ide-test -print-module -annotate-print -synthesize-extension -print-interface -module-to-print=print_synthesized_extensions -I %t -source-filename=%s > %t.syn.txt
 // RUN: FileCheck %s < %t.syn.txt
 
@@ -123,6 +123,20 @@ public struct S10 : P1 {
   }
 }
 
+public protocol P4 {}
+
+/// Extension on P4Func1
+public extension P4 {
+  func P4Func1() {}
+}
+
+/// Extension on P4Func2
+public extension P4 {
+  func P4Func2() {}
+}
+
+public struct S11 : P4 {}
+
 // CHECK: <synthesized>
 // CHECK: extension <ref:Struct>S1</ref> where T : P2 {
 // CHECK:     <decl:Func>public func <loc>p2member()</loc></decl></synthesized>
@@ -155,6 +169,16 @@ public struct S10 : P1 {
 // CHECK:     <decl:Func>public func <loc>S9IntFunc()</loc></decl>
 // CHECK: }</synthesized>
 
+// CHECK:  <synthesized>/// Extension on P4Func1
+// CHECK:  extension <ref:Struct>S11</ref> {
+// CHECK:      <decl:Func>public func <loc>P4Func1()</loc></decl>
+// CHECK:  }</synthesized>
+
+// CHECK:  <synthesized>/// Extension on P4Func2
+// CHECK:  extension <ref:Struct>S11</ref> {
+// CHECK:  <decl:Func>public func <loc>P4Func2()</loc></decl>
+// CHECK:  }</synthesized>
+
 // CHECK:  <synthesized>
 // CHECK: extension <ref:Struct>S4</ref> {
 // CHECK:     <decl:Func>public func <loc>p1IntFunc(<decl:Param>i: <ref:Struct>Int</ref></decl>)</loc> -> <ref:Struct>Int</ref></decl>