swift-module-digester: removing setter from a subscript decl is API breaking.

Author: nkcsgexi

test/api-digester/Inputs/cake1.swift

@@ -78,4 +78,8 @@ public protocol AssociatedTypePro {
 
 public class RemoveSetters {
   public var Value = 4
+  public subscript(_ idx: Int) -> Int {
+    get { return 1 }
+    set(newValue) {}
+  }
 }

test/api-digester/Inputs/cake2.swift

@@ -85,5 +85,8 @@ public protocol AssociatedTypePro {
 
 public class RemoveSetters {
   public private(set) var Value = 4
+  public subscript(_ idx: Int) -> Int {
+    get { return 1 }
+  }
 }
 

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

@@ -9,6 +9,7 @@ cake1: Protocol P3 has generic signature change from <τ_0_0 : P1, τ_0_0 : P2>
 cake1: Constructor Somestruct2.init(_:) has been removed
 cake1: Constructor fixedLayoutStruct.init(b:a:) has been removed
 cake1: Func C4.foo() has been removed
+cake1: Subscript RemoveSetters.subscript(_:) has removed its setter
 cake1: Var RemoveSetters.Value has removed its setter
 
 /* Moved Decls */

test/api-digester/Outputs/Cake.txt

@@ -9,6 +9,7 @@ cake1: Protocol P3 has generic signature change from <Self : P1, Self : P2> to <
 cake1: Constructor Somestruct2.init(_:) has been removed
 cake1: Constructor fixedLayoutStruct.init(b:a:) has been removed
 cake1: Func C4.foo() has been removed
+cake1: Subscript RemoveSetters.subscript(_:) has removed its setter
 cake1: Var RemoveSetters.Value has removed its setter
 
 /* Moved Decls */

tools/swift-api-digester/ModuleAnalyzerNodes.cpp

@@ -762,7 +762,13 @@ bool SDKNode::operator==(const SDKNode &Other) const {
       LLVM_FALLTHROUGH;
     }
     case SDKNodeKind::DeclAssociatedType:
-    case SDKNodeKind::DeclSubscript:
+    case SDKNodeKind::DeclSubscript: {
+      auto *Left = dyn_cast<SDKNodeDeclSubscript>(this);
+      auto *Right = dyn_cast<SDKNodeDeclSubscript>(&Other);
+      if (Left && Right && Left->hasSetter() != Right->hasSetter())
+        return false;
+      LLVM_FALLTHROUGH;
+    }
     case SDKNodeKind::DeclTypeAlias: {
       auto Left = this->getAs<SDKNodeDecl>();
       auto Right = (&Other)->getAs<SDKNodeDecl>();

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

@@ -867,7 +867,16 @@ class PrunePass : public MatchedNodeListener, public SDKTreeDiffPass {
       break;
     }
 
-    case SDKNodeKind::DeclSubscript:
+    case SDKNodeKind::DeclSubscript: {
+      if (auto *LS = dyn_cast<SDKNodeDeclSubscript>(Left)) {
+        auto *RS = cast<SDKNodeDeclSubscript>(Right);
+        if (LS->hasSetter() && !RS->hasSetter()) {
+          Ctx.getDiags().diagnose(SourceLoc(), diag::removed_setter,
+                                  LS->getScreenInfo());
+        }
+      }
+      LLVM_FALLTHROUGH;
+    }
     case SDKNodeKind::DeclAssociatedType:
     case SDKNodeKind::DeclFunction:
     case SDKNodeKind::DeclSetter: