swift-module-digester: include unavailable variables with fixed layout order when checking ABI stability.

Author: nkcsgexi

test/api-digester/Inputs/cake.swift

@@ -49,6 +49,8 @@ public struct fixedLayoutStruct {
   public var a = 1
   private var b = 2
   var c = 3
+  @available(*, unavailable)
+  public let unavailableProperty = 1
 }
 
 extension Int: P1 { public func bar() {} }

test/api-digester/Outputs/cake-abi.json

@@ -839,6 +839,49 @@
           "fixedbinaryorder": 2,
           "hasStorage": true
         },
+        {
+          "kind": "Var",
+          "name": "unavailableProperty",
+          "printedName": "unavailableProperty",
+          "children": [
+            {
+              "kind": "TypeNominal",
+              "name": "Int",
+              "printedName": "Int",
+              "usr": "s:Si"
+            },
+            {
+              "kind": "Getter",
+              "name": "_",
+              "printedName": "_()",
+              "children": [
+                {
+                  "kind": "TypeNominal",
+                  "name": "Int",
+                  "printedName": "Int",
+                  "usr": "s:Si"
+                }
+              ],
+              "declKind": "Accessor",
+              "usr": "s:4cake17fixedLayoutStructV19unavailablePropertySivg",
+              "moduleName": "cake",
+              "implicit": true,
+              "declAttributes": [
+                "Transparent"
+              ]
+            }
+          ],
+          "declKind": "Var",
+          "usr": "s:4cake17fixedLayoutStructV19unavailablePropertySivp",
+          "moduleName": "cake",
+          "declAttributes": [
+            "HasInitialValue",
+            "Available"
+          ],
+          "fixedbinaryorder": 3,
+          "isLet": true,
+          "hasStorage": true
+        },
         {
           "kind": "Constructor",
           "name": "init",

tools/swift-api-digester/ModuleAnalyzerNodes.cpp

@@ -1200,6 +1200,17 @@ SwiftDeclCollector::constructInitNode(ConstructorDecl *CD) {
 
 bool swift::ide::api::
 SwiftDeclCollector::shouldIgnore(Decl *D, const Decl* Parent) {
+  if (Ctx.checkingABI()) {
+    if (auto *VD = dyn_cast<ValueDecl>(D)) {
+      // Private vars with fixed binary orders can have ABI-impact, so we should
+      // whitelist them if we're checking ABI.
+      if (getFixedBinaryOrder(VD).hasValue())
+        return false;
+      // Typealias should have no impact on ABI.
+      if (isa<TypeAliasDecl>(VD))
+        return true;
+    }
+  }
   if (D->isPrivateStdlibDecl(false))
     return true;
   if (AvailableAttr::isUnavailable(D))
@@ -1209,18 +1220,10 @@ SwiftDeclCollector::shouldIgnore(Decl *D, const Decl* Parent) {
   if (auto VD = dyn_cast<ValueDecl>(D)) {
     if (VD->getBaseName().empty())
       return true;
-
-    // Exclude type alias decls because they should have no impact on ABI.
-    if (isa<TypeAliasDecl>(VD) && Ctx.checkingABI())
-      return true;
     switch (VD->getFormalAccess()) {
     case AccessLevel::Internal:
     case AccessLevel::Private:
     case AccessLevel::FilePrivate:
-      // Private vars with fixed binary orders can have ABI-impact, so we should
-      // whitelist them if we're checking ABI.
-      if (Ctx.checkingABI() && getFixedBinaryOrder(VD).hasValue())
-        break;
       return true;
     case AccessLevel::Public:
     case AccessLevel::Open: