fixup! Clean up and document syntax tree child access API

src/hooks.jl

@@ -45,11 +45,8 @@ function _incomplete_tag(n::SyntaxNode, codelen)
             return :none
         end
     end
-    if kind(c) == K"error" && begin
-                cs = children(c)
-                length(cs) > 0
-            end
-        for cc in cs
+    if kind(c) == K"error" && numchildren(c) > 0
+        for cc in children(c)
             if kind(cc) == K"error"
                 return :other
             end

src/syntax_tree.jl

@@ -223,10 +223,12 @@ function Base.copy(node::TreeNode)
     # copy the container but not the data (ie, deep copy the tree, shallow copy the data). copy(::Expr) is similar
     # copy "un-parents" the top-level `node` that you're copying
     newnode = typeof(node)(nothing, is_leaf(node) ? nothing : typeof(node)[], copy(node.data))
-    for child in children(node)
-        newchild = copy(child)
-        newchild.parent = newnode
-        push!(newnode, newchild)
+    if !is_leaf(node)
+        for child in children(node)
+            newchild = copy(child)
+            newchild.parent = newnode
+            push!(newnode, newchild)
+        end
     end
     return newnode
 end