Fix crash in meson format

There was a case where a trailing comma was missing a whitespaces attribute

Fixes #13242

mesonbuild/mformat.py

@@ -626,6 +626,7 @@ class ArgumentFormatter(FullAstVisitor):
             if need_comma and not has_trailing_comma:
                 comma = mparser.SymbolNode(mparser.Token('comma', node.filename, 0, 0, 0, (0, 0), ','))
                 comma.condition_level = node.condition_level
+                comma.whitespaces = mparser.WhitespaceNode(mparser.Token('whitespace', node.filename, 0, 0, 0, (0, 0), ''))
                 node.commas.append(comma)
             elif has_trailing_comma and not need_comma:
                 node.commas.pop(-1)

test cases/format/1 default/gh13242.meson

@@ -0,0 +1,18 @@
+# Minimized meson.build
+test(
+    args: [
+        shared_library(
+            f'tstlib-@name@',
+            build_by_default: false,
+            override_options: opt,
+        ),
+    ],
+)
+
+test(
+    should_fail: (settings.get('x', false) and not settings['y'] and dep.version(
+        
+    ).version_compare(
+        '>=1.2.3',
+    )),
+)

test cases/format/1 default/meson.build

@@ -7,6 +7,7 @@ meson_files = {
     'self': files('meson.build'),
     'comments': files('crazy_comments.meson'),
     'indentation': files('indentation.meson'),
+    'gh13242': files('gh13242.meson'),
 }
 
 foreach name, f : meson_files