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

[Paul Kirth via cfe-commits]

================
@@ -697,10 +697,39 @@ 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) {
+  if (DeclKind == Decl::Kind::Record || DeclKind == Decl::Kind::CXXRecord ||
+      DeclKind == Decl::Kind::Namespace ||
+      DeclKind == Decl::Kind::ClassTemplateSpecialization ||
+      DeclKind == Decl::Kind::ClassTemplatePartialSpecialization)
+    return true;
+  return false;
+}
+
+template <typename T> static void findParent(Info &I, const T *D) {
+  // Only walk up contexts if D is a record or namespace.
+  if (isSupportedContext(D->getKind())) {
+    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();
+    }
+  }
----------------
ilovepi wrote:

```suggestion
  assert(D && "invalid Decl");
  if (!isSupportedContext(D->getKind()))
    return;
    
  // Only walk up contexts if D is a record or namespace.
  const DeclContext *ParentCtx = dyn_cast<DeclContext>(D)->getLexicalParent();
  while (ParentCtx) {
    if (isSupportedContext(ParentCtx->getDeclKind())) {
      // Break when we reach the first valid parent (record or namespace).
      I.ParentUSR = getUSRForDecl(dyn_cast<Decl>(ParentCtx));
      break;
    }
    ParentCtx = ParentCtx->getParent();
  }
```

You can use an early return to simplify. We can also just assert D isn't `nullptr` as a sanity check.

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