[clang-tools-extra] [clang-doc] Add a breadcrumb navigation bar (PR #173297)

[Paul Kirth via cfe-commits]

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@@ -697,10 +697,46 @@ static TemplateParamInfo convertTemplateArgToInfo(const clang::Decl *D,
   return TemplateParamInfo(Str);
 }
 
+// Check if the DeclKind is one for which we support contextual relationships.
+// There might be other ContextDecls, like blocks, that we currently don't
+// handle at all.
+static bool isSupportedContext(Decl::Kind DeclKind) {
+  switch (DeclKind) {
+  case Decl::Kind::Record:
+  case Decl::Kind::CXXRecord:
+  case Decl::Kind::ClassTemplateSpecialization:
+  case Decl::Kind::ClassTemplatePartialSpecialization:
+  case Decl::Kind::Namespace:
+    return true;
+  default:
+    return false;
+  }
+}
+
+template <typename T> static void findParent(Info &I, const T *D) {
+  assert(D && "Invalid Decl");
+
+  // Only walk up contexts if D is a record or namespace.
+  if (!isSupportedContext(D->getKind()))
+    return;
+
+  const DeclContext *ParentCtx = dyn_cast<DeclContext>(D)->getLexicalParent();
+  while (ParentCtx) {
+    if (isSupportedContext(ParentCtx->getDeclKind())) {
+      // Break when we reach the first record or namespace.
+      I.ParentUSR = getUSRForDecl(dyn_cast<Decl>(ParentCtx));
+      break;
+    }
+    ParentCtx = ParentCtx->getParent();
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ilovepi wrote:

I cant recall if getLexicalParent() can return a `nullptr` or if that's structurally impossible. We can either add a check, or assert that its non-null.

https://github.com/llvm/llvm-project/pull/173297