Fix for YAML 1.1 multi-document directive inheritance

src/parser.c

@@ -491,12 +491,6 @@ yaml_parser_parse_document_end(yaml_parser_t *parser, yaml_event_t *event)
         implicit = 0;
     }
 
-    while (!STACK_EMPTY(parser, parser->tag_directives)) {
-        yaml_tag_directive_t tag_directive = POP(parser, parser->tag_directives);
-        yaml_free(tag_directive.handle);
-        yaml_free(tag_directive.prefix);
-    }
-
     parser->state = YAML_PARSE_DOCUMENT_START_STATE;
     DOCUMENT_END_EVENT_INIT(*event, implicit, start_mark, end_mark);
 
@@ -1250,6 +1244,7 @@ yaml_parser_process_directives(yaml_parser_t *parser,
     };
     yaml_tag_directive_t *default_tag_directive;
     yaml_version_directive_t *version_directive = NULL;
+    int first_directive = 1;
     struct {
         yaml_tag_directive_t *start;
         yaml_tag_directive_t *end;
@@ -1266,6 +1261,17 @@ yaml_parser_process_directives(yaml_parser_t *parser,
     while (token->type == YAML_VERSION_DIRECTIVE_TOKEN ||
             token->type == YAML_TAG_DIRECTIVE_TOKEN)
     {
+        if (first_directive) {
+            /* First directive seen: this document has its own directives,
+             * so discard any inherited from the previous document. */
+            while (!STACK_EMPTY(parser, parser->tag_directives)) {
+                yaml_tag_directive_t tag_directive = POP(parser, parser->tag_directives);
+                yaml_free(tag_directive.handle);
+                yaml_free(tag_directive.prefix);
+            }
+            first_directive = 0;
+        }
+
         if (token->type == YAML_VERSION_DIRECTIVE_TOKEN) {
             if (version_directive) {
                 yaml_parser_set_parser_error(parser,

tests/CMakeLists.txt

@@ -19,10 +19,12 @@ foreach(name IN ITEMS
   test-nesting
   test-reader
   test-version
+  test-directive-inheritance
   )
   add_yaml_executable(${name})
 endforeach()
 
+add_test(NAME directive-inheritance COMMAND test-directive-inheritance)
 add_test(NAME version COMMAND test-version)
 add_test(NAME reader COMMAND test-reader)
 add_test(NAME nesting COMMAND test-nesting)

tests/test-directive-inheritance.c

@@ -0,0 +1,59 @@
+#include <yaml.h>
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+
+#ifdef NDEBUG
+#undef NDEBUG
+#endif
+#include <assert.h>
+
+/*
+ * Test: %TAG directive inheritance across documents in a multi-document stream.
+ *
+ * YAML 1.1 spec section 7.4:
+ *   "If the document specifies no directives, it is parsed using the same
+ *    settings as the previous document. If the document does specify any
+ *    directives, all directives of previous documents, if any, are ignored."
+ *
+ * libyaml bug: yaml_parser_parse_document_end() unconditionally clears
+ * parser->tag_directives, so document 2 (which has no directives) cannot
+ * inherit the %TAG mapping from document 1.  When the parser then encounters
+ * !x!bar in document 2 it cannot resolve the handle and throws a parse
+ * error. The assert inside the loop will FAIL until the bug is fixed.
+ */
+
+static const unsigned char yaml_input[] =
+    "%YAML 1.1\n"
+    "%TAG !x! tag:example.com,2026:\n"
+    "--- !x!food\n"
+    "x: 0\n"
+    "--- !x!bar\n"
+    "x: 1\n";
+
+int main(void)
+{
+    yaml_parser_t parser;
+    yaml_event_t event;
+    int done = 0;
+
+    assert(yaml_parser_initialize(&parser));
+    yaml_parser_set_input_string(&parser, yaml_input, sizeof(yaml_input) - 1);
+
+    printf("Testing Directive Inheritance ... ");
+    fflush(stdout);
+
+    while (!done) {
+        /* With the bug, this assert fires when the parser hits !x!bar
+         * in doc 2 and cannot resolve the handle.  A spec-compliant
+         * parser must succeed for the entire stream. */
+        assert(yaml_parser_parse(&parser, &event));
+        done = (event.type == YAML_STREAM_END_EVENT);
+        yaml_event_delete(&event);
+    }
+
+    yaml_parser_delete(&parser);
+    printf("PASSED\n");
+    return 0;
+}