[IDE] Avoid printing some Swift extensions twice in mixed source frameworks

`printModuleInterfaceDecl` printes extensions right after the type
they are associated with is printed. Extensions associated with a
type that appears in the "target" module shouldn't be added to
`SwiftDecls` because that would lead to double printing them.

Author: xedin

lib/IDE/ModuleInterfacePrinting.cpp

@@ -145,17 +145,6 @@ static bool printModuleInterfaceDecl(Decl *D,
     Printer.callAvoidPrintDeclPost(D);
     return false;
   }
-  if (auto Ext = dyn_cast<ExtensionDecl>(D)) {
-    // Clang extensions (categories) are always printed in source order.
-    // Swift extensions are printed with their associated type unless it's
-    // a cross-module extension.
-    if (!extensionHasClangNode(Ext)) {
-      auto ExtendedNominal = Ext->getExtendedNominal();
-      if (!ExtendedNominal ||
-          Ext->getModuleContext() == ExtendedNominal->getModuleContext())
-        return false;
-    }
-  }
 
   // It'd be nice to avoid cloning the options here, but that would require
   // SynthesizedExtensionAnalyzer to promise to stay within the lifetime of
@@ -677,6 +666,14 @@ void swift::ide::printModuleInterface(
         addToClangDecls(Ext, extensionGetClangNode(Ext));
         continue;
       }
+
+      // Swift extensions are printed with their associated type unless it's
+      // a cross-module extension.
+      if (auto extendedTy = Ext->getExtendedNominal()) {
+        if (TargetMod->isSameModuleLookingThroughOverlays(
+                extendedTy->getModuleContext()))
+          continue;
+      }
     }
 
     if (!IsSubmodule) {

test/SynthesizeInterfaceTool/Inputs/Frameworks/TestExt.framework/Headers/MyType.h

@@ -0,0 +1,2 @@
+@interface MyType
+@end

test/SynthesizeInterfaceTool/Inputs/Frameworks/TestExt.framework/Modules/TestExt.swiftmodule/arm64-apple-macos.swiftinterface

@@ -0,0 +1,16 @@
+// swift-interface-format-version: 1.0
+// swift-compiler-version: Apple Swift version 6.2
+// swift-module-flags: -target arm64-apple-macos10.13 -enable-library-evolution -swift-version 5 -module-name TestExt
+
+@_exported import TestExt
+
+extension MyType {
+  public struct MyInnerType {
+    public func test() {}
+  }
+}
+
+extension Int {
+    public struct OtherInnerType {
+    }
+}

test/SynthesizeInterfaceTool/Inputs/Frameworks/TestExt.framework/Modules/module.modulemap

@@ -0,0 +1,4 @@
+framework module TestExt {
+  header "MyType.h"
+  export *
+}

test/SynthesizeInterfaceTool/test-swift-extension-printing.swift

@@ -0,0 +1,20 @@
+// RUN: %target-swift-synthesize-interface -module-name TestExt -F %S/Inputs/Frameworks -o - | %FileCheck %s
+
+// REQUIRES: OS=macosx && CPU=arm64
+
+// CHECK: open class MyType
+
+// CHECK: extension MyType {
+// CHECK:     public struct MyInnerType {
+// CHECK:         public func test()
+// CHECK:     }
+// CHECK: }
+
+// CHECK-NOT: public struct MyInnerType
+
+// CHECK: extension Int {
+// CHECK:     public struct OtherInnerType {
+// CHECK:     }
+// CHECK: }
+
+// CHECK-NOT: public struct MyInnerType