From b6ec758fbaa54b0393811d65c61647669af6c84c Mon Sep 17 00:00:00 2001
From: Axel Heider <axel.heider@hensoldt.net>
Date: Mon, 13 Mar 2023 19:25:00 +0100
Subject: [PATCH] parser: support empty list as DTB qeury

This is for convenience reasons, as it allows using `vm0.dtb = dtb([])`
instead of `dtb([{}]);` with a dummy element.

Signed-off-by: Axel Heider <axel.heider@hensoldt.net>
---
 camkes/parser/fdtQueryEngine.py          | 25 ++++++++++++------------
 camkes/parser/tests/testdtbmatchquery.py |  8 +++++++-
 2 files changed, 20 insertions(+), 13 deletions(-)

diff --git a/camkes/parser/fdtQueryEngine.py b/camkes/parser/fdtQueryEngine.py
index 8bae8343..41f9377c 100644
--- a/camkes/parser/fdtQueryEngine.py
+++ b/camkes/parser/fdtQueryEngine.py
@@ -590,20 +590,21 @@ def resolve_fdt_node(cls, node):
         resolved['this-node-path'] = node_path
         return resolved
 
+    # An empty query is supported for convenience reasons, it produces an empty
+    # result. Any real query must find a match, otherwise an error is raised.
     def resolve(self, args):
-        result = self.engine.query(args)
-        if not len(result):
-            raise ParseError(f'DTB query failed: {args}')
-
         query_results = []
-        for entry in result:
-            if not len(entry):
-                query_results.append({})
-            else:
-                node = entry[0]
-                node_resolved = self.resolve_fdt_node(node)
-                query_results.append(node_resolved)
-
+        if (len(args) > 0):
+            result = self.engine.query(args)
+            if not len(result):
+                raise ParseError(f'DTB query failed: {args}')
+            for entry in result:
+                if not len(entry):
+                    query_results.append({})
+                else:
+                    node = entry[0]
+                    node_resolved = self.resolve_fdt_node(node)
+                    query_results.append(node_resolved)
         return {
             'query': query_results,
             'dtb-size': [self.dtb_file_size]
diff --git a/camkes/parser/tests/testdtbmatchquery.py b/camkes/parser/tests/testdtbmatchquery.py
index c05fc4c7..4302a9ab 100755
--- a/camkes/parser/tests/testdtbmatchquery.py
+++ b/camkes/parser/tests/testdtbmatchquery.py
@@ -209,7 +209,13 @@ def test_multiple_queries(self):
         self.assertEquals(node['dtb-size'], [self.dtbSize])
 
     def test_blank(self):
-        self.assertRaises(ParseError, self.dtbQuery.resolve, [])
+        # For convenience reasons an empty query list is allowed and does not
+        # raise a ParseError. It returns an empty result list instead.
+        node = self.dtbQuery.resolve([])
+        self.assertIn('query', node)
+        self.assertEquals(len(node['query']), 0)
+        self.assertIn('dtb-size', node)
+        self.assertEquals(node['dtb-size'], [self.dtbSize])
 
     def test_blank_query(self):
         node = self.dtbQuery.resolve([{}])