swift-module-digester: diagnose added associated types as ABI breakages even they have default type.

Author: nkcsgexi

test/api-digester/Outputs/Cake-abi.txt

@@ -69,6 +69,7 @@ cake1: Struct fixedLayoutStruct has removed conformance to P1
 
 /* Protocol Requirement Change */
 cake1: AssociatedType AssociatedTypePro.T1 has removed default type Int
+cake2: AssociatedType RequiementChanges.addedTypeWithDefault has been added as a protocol requirement
 cake2: AssociatedType RequiementChanges.addedTypeWithoutDefault has been added as a protocol requirement
 cake2: Func RequiementChanges.addedFunc() has been added as a protocol requirement
 cake2: Var RequiementChanges.addedVar has been added as a protocol requirement

test/api-digester/Outputs/Cake.txt

@@ -47,6 +47,7 @@ cake1: Struct fixedLayoutStruct has removed conformance to P1
 
 /* Protocol Requirement Change */
 cake1: AssociatedType AssociatedTypePro.T1 has removed default type Int
+cake2: AssociatedType RequiementChanges.addedTypeWithDefault has been added as a protocol requirement
 cake2: AssociatedType RequiementChanges.addedTypeWithoutDefault has been added as a protocol requirement
 cake2: Func RequiementChanges.addedFunc() has been added as a protocol requirement
 cake2: Var RequiementChanges.addedVar has been added as a protocol requirement

tools/swift-api-digester/swift-api-digester.cpp

@@ -942,14 +942,7 @@ class PrunePass : public MatchedNodeListener, public SDKTreeDiffPass {
       }
       // Complain about added protocol requirements
       if (auto *D = dyn_cast<SDKNodeDecl>(Right)) {
-        if (D->isProtocolRequirement()) {
-          bool ShouldComplain = !D->isOverriding();
-          // We should allow added associated types with default.
-          if (auto ATD = dyn_cast<SDKNodeDeclAssociatedType>(D)) {
-            if (ATD->getDefault())
-              ShouldComplain = false;
-          }
-          if (ShouldComplain)
+        if (D->isProtocolRequirement() && !D->isOverriding()) {
             Ctx.getDiags().diagnose(SourceLoc(), diag::protocol_req_added,
                                     D->getScreenInfo());
         }