--- a/com/mojang/brigadier/CommandDispatcher.java
+++ b/com/mojang/brigadier/CommandDispatcher.java
@@ -297,15 +_,21 @@
         List<ParseResults<S>> potentials = null;
         final int cursor = originalReader.getCursor();
 
-        for (final CommandNode<S> child : node.getRelevantNodes(originalReader)) {
+        for (final CommandNode<S> child : node.getRelevantNodes(originalReader, source)) { // Paper - prioritize mc commands in function parsing
             if (!child.canUse(source)) {
                 continue;
             }
             final CommandContextBuilder<S> context = contextSoFar.copy();
             final StringReader reader = new StringReader(originalReader);
+            boolean stop = false; // Paper - Handle non-recoverable exceptions
             try {
                 try {
                     child.parse(reader, context);
+                    // Paper start - Handle non-recoverable exceptions
+                } catch (final io.papermc.paper.brigadier.TagParseCommandSyntaxException e) {
+                    stop = true;
+                    throw e;
+                    // Paper end - Handle non-recoverable exceptions
                 } catch (final RuntimeException ex) {
                     throw CommandSyntaxException.BUILT_IN_EXCEPTIONS.dispatcherParseException().createWithContext(reader, ex.getMessage());
                 }
@@ -320,6 +_,7 @@
                 }
                 errors.put(child, ex);
                 reader.setCursor(cursor);
+                if (stop) return new ParseResults<>(contextSoFar, originalReader, errors); // Paper - Handle non-recoverable exceptions
                 continue;
             }
 
@@ -451,7 +_,7 @@
     }
 
     private String getSmartUsage(final CommandNode<S> node, final S source, final boolean optional, final boolean deep) {
-        if (!node.canUse(source)) {
+        if (source != null && !node.canUse(source)) { // Paper
             return null;
         }
 
@@ -465,7 +_,7 @@
                 final String redirect = node.getRedirect() == root ? "..." : "-> " + node.getRedirect().getUsageText();
                 return self + ARGUMENT_SEPARATOR + redirect;
             } else {
-                final Collection<CommandNode<S>> children = node.getChildren().stream().filter(c -> c.canUse(source)).collect(Collectors.toList());
+                final Collection<CommandNode<S>> children = node.getChildren().stream().filter(c -> source == null || c.canUse(source)).collect(Collectors.toList()); // Paper
                 if (children.size() == 1) {
                     final String usage = getSmartUsage(children.iterator().next(), source, childOptional, childOptional);
                     if (usage != null) {
@@ -537,10 +_,14 @@
         int i = 0;
         for (final CommandNode<S> node : parent.getChildren()) {
             CompletableFuture<Suggestions> future = Suggestions.empty();
+            // Paper start - Don't suggest if the requirement isn't met
+            if (parent != this.root || node.canUse(context.getSource())) {
             try {
-                future = node.listSuggestions(context.build(truncatedInput), new SuggestionsBuilder(truncatedInput, truncatedInputLowerCase, start));
+                future = node.listSuggestions(context.build(truncatedInput), new SuggestionsBuilder(truncatedInput, truncatedInputLowerCase, start)); // CraftBukkit
             } catch (final CommandSyntaxException ignored) {
             }
+            }
+            // Paper end - Don't suggest if the requirement isn't met
             futures[i++] = future;
         }