json-parser: add location to JSON parsing errors

Now that all calls to parse_error have a token, add the line and column
to the message.  As far as I can see the two important TODOs (better
errors and better EOI handling) are done, and the others (token range
information and "parsed size"?) do not really matter or are handled
better by json-streamer.c.  So remove the list, which had sat unchanged
since 2009.

This needs some adjustments to provide a good x and y for error messages.
First of all, they switch from zero-based to one-based, which is safe
because they were both sitting unused.  Second, right now the x and y
are those of the *last* character in the token.  Modify json-lexer.c to
freeze tok->x and tok->y at the first character added to the GString.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20260626101727.1727389-7-pbonzini@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

3 files changed, 10 insertions, 14 deletions

diff --git a/include/qobject/json-parser.h b/include/qobject/json-parser.h
index 3479e63758..e078b36b2d 100644
--- a/include/qobject/json-parser.h
+++ b/include/qobject/json-parser.h
@@ -17,6 +17,7 @@
 typedef struct JSONLexer {
     int start_state, state;
     GString *token;
+    int cur_x, cur_y;
     int x, y;
 } JSONLexer;
 
diff --git a/qobject/json-lexer.c b/qobject/json-lexer.c
index 51341d96e4..7753ba6c09 100644
--- a/qobject/json-lexer.c
+++ b/qobject/json-lexer.c
@@ -277,7 +277,8 @@ void json_lexer_init(JSONLexer *lexer, bool enable_interpolation)
     lexer->start_state = lexer->state = enable_interpolation
         ? IN_START_INTERP : IN_START;
     lexer->token = g_string_sized_new(3);
-    lexer->x = lexer->y = 0;
+    lexer->cur_x = lexer->cur_y = 1;
+    lexer->x = lexer->y = 1;
 }
 
 static void json_lexer_feed_char(JSONLexer *lexer, char ch, bool flush)
@@ -285,10 +286,10 @@ static void json_lexer_feed_char(JSONLexer *lexer, char ch, bool flush)
     int new_state;
     bool char_consumed = false;
 
-    lexer->x++;
+    lexer->cur_x++;
     if (ch == '\n') {
-        lexer->x = 0;
-        lexer->y++;
+        lexer->cur_x = 1;
+        lexer->cur_y++;
     }
 
     while (flush ? lexer->state != lexer->start_state : !char_consumed) {
@@ -316,6 +317,8 @@ static void json_lexer_feed_char(JSONLexer *lexer, char ch, bool flush)
         case IN_START:
             g_string_truncate(lexer->token, 0);
             new_state = lexer->start_state;
+            lexer->x = lexer->cur_x;
+            lexer->y = lexer->cur_y;
             break;
         case JSON_ERROR:
             json_message_process_token(lexer, lexer->token, JSON_ERROR,
diff --git a/qobject/json-parser.c b/qobject/json-parser.c
index 0dcc94fefd..5935730c0c 100644
--- a/qobject/json-parser.c
+++ b/qobject/json-parser.c
@@ -133,15 +133,6 @@ typedef struct JSONParserStackEntry {
 
 #define BUG_ON(cond) assert(!(cond))
 
-/**
- * TODO
- *
- * 0) make errors meaningful again
- * 1) add geometry information to tokens
- * 3) should we return a parsed size?
- * 4) deal with premature EOI
- */
-
 static inline JSONParserStackEntry *current_entry(JSONParserContext *ctxt)
 {
     return g_queue_peek_tail(ctxt->stack);
@@ -180,7 +171,8 @@ static void G_GNUC_PRINTF(3, 4) parse_error(JSONParserContext *ctxt,
     va_start(ap, msg);
     vsnprintf(message, sizeof(message), msg, ap);
     va_end(ap);
-    error_setg(&ctxt->err, "JSON parse error, %s", message);
+    error_setg(&ctxt->err, "%d:%d: JSON parse error, %s",
+               token->y, token->x, message);
 }
 
 static int cvt4hex(const char *s)