swift-api-digester: keep track of type declarations with fixed layout. (swiftlang#14991)

We need special logic to check abi-stability for decls with fixed
layout.

Author: nkcsgexi

include/swift/IDE/DigesterEnums.def

@@ -72,6 +72,7 @@ NODE_ANNOTATION(StaticChange)
 NODE_ANNOTATION(OwnershipChange)
 
 DECL_ATTR(deprecated)
+DECL_ATTR(fixedLayout)
 
 KEY(kind)
 KEY(name)

test/api-digester/Inputs/cake.swift

@@ -1,5 +1,7 @@
 public protocol P1 {}
 public protocol P2 {}
+
+@_fixed_layout
 public struct S1: P1 {
   public static func foo1() {}
   mutating public func foo2() {}
@@ -32,4 +34,4 @@ public func foo2(_ a: Int = #line, b: S1) {}
 
 public enum Number: Int {
   case one
-}
+}

test/api-digester/Outputs/cake.json

@@ -115,6 +115,9 @@
         "P1",
         "P2"
       ],
+      "declAttributes": [
+        "fixedLayout"
+      ],
       "children": [
         {
           "kind": "Function",

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

@@ -433,6 +433,7 @@ class SDKNodeDecl : public SDKNode {
   StringRef getFullyQualifiedName() const;
   bool isSDKPrivate() const;
   bool isDeprecated() const;
+  bool hasFixedLayout() const;
   bool isStatic() const { return IsStatic; };
   bool isFromExtension() const { return ExtInfo; }
   const ParentExtensionInfo& getExtensionInfo() const {
@@ -714,6 +715,10 @@ bool SDKNodeDecl::isDeprecated() const {
   return hasDeclAttribute(SDKDeclAttrKind::DAK_deprecated);
 }
 
+bool SDKNodeDecl::hasFixedLayout() const {
+  return hasDeclAttribute(SDKDeclAttrKind::DAK_fixedLayout);
+}
+
 bool SDKNodeDecl::isSDKPrivate() const {
   if (getName().startswith("__"))
     return true;
@@ -1295,6 +1300,11 @@ SDKNodeInitInfo::SDKNodeInitInfo(SDKContext &Ctx, ValueDecl *VD)
   if (VD->getAttrs().getDeprecated(VD->getASTContext()))
     DeclAttrs.push_back(SDKDeclAttrKind::DAK_deprecated);
 
+  // If this is fixed_layout struct.
+  if (VD->getAttrs().hasAttribute<FixedLayoutAttr>()) {
+    DeclAttrs.push_back(SDKDeclAttrKind::DAK_fixedLayout);
+  }
+
   // If the decl is declared in an extension, calculate the extension info.
   if (auto *Ext = dyn_cast_or_null<ExtensionDecl>(VD->getDeclContext())) {
     ExtInfo = new (Ctx) ParentExtensionInfo();