[AST] Handle accessors specially in isInMacroExpansionInContext

Rather than looking at their DeclContext, look at the location of
their storage. This allows us to differentiate accessors added by
macro expansions vs accessors that are attached to storage that's
in a macro expansion.

Author: hamishknight

lib/AST/Decl.cpp

@@ -1007,11 +1007,21 @@ SourceRange Decl::getSourceRangeIncludingAttrs() const {
 }
 
 bool Decl::isInMacroExpansionInContext() const {
-  auto *dc = getDeclContext();
-  auto parentFile = dc->getParentSourceFile();
   auto *mod = getModuleContext();
   auto *file = mod->getSourceFileContainingLocation(getStartLoc());
 
+  auto parentFile = [&]() {
+    // For accessors, the storage decl is the more accurate thing to check
+    // since the entire property/subscript could be macro-generated, in which
+    // case the accessor shouldn't be considered "added by macro expansion".
+    if (auto *accessor = dyn_cast<AccessorDecl>(this)) {
+      auto storageLoc = accessor->getStorage()->getLoc();
+      if (storageLoc.isValid())
+        return mod->getSourceFileContainingLocation(storageLoc);
+    }
+    return getDeclContext()->getParentSourceFile();
+  }();
+
   // Decls in macro expansions always have a source file. The source
   // file can be null if the decl is implicit or has an invalid
   // source location.