Tk Source Code: View Ticket

Ticket UUID:	434c8dd8046ba3c0a7307fa8dc3a8e3a64e005bd
Title:	Crash in Tk_ConfigureWidget when a default value of a canvas item option is invalid
Type:	Bug	Version:	8.6.18, 9.0.5, 9.1b1
Submitter:	serhiy.storchaka	Created on:	2026-09-25 16:32:57
Subsystem:	05. Canvas Items	Assigned To:	jan.nijtmans
Priority:	5 Medium	Severity:	Critical
Status:	Closed	Last Modified:	2026-10-08 12:53:35
Resolution:	Fixed	Closed By:	jan.nijtmans
		Closed on:	2026-10-08 12:53:35
Description:	If the default value of a canvas item option cannot be applied, `Tk_ConfigureWidget()` crashes while formatting the error message (default value for "%.50s" in widget "%.50s") because it passes `specPtr->dbName`, which is NULL for all canvas item options. This happens, for example, if fontconfig finds no fonts: since [1440417fff] widgets report "failed to allocate font due to internal system font engine problem", but `.c create text 10 10 -text abc` segfaults instead. Reproduced on Linux with an empty fontconfig configuration (`FONTCONFIG_FILE` pointing to a file without font directories) in 8.6.18, 9.0.5 and 9.1.
User Comments:	jan.nijtmans added on 2026-10-08 12:53:35: Fixed in [a2791cb1444037f5\|trunk], backported to core-9-0-branch and core-8-6-branch Many thanks! serhiy.storchaka added on 2026-09-25 16:34:01: Proposed fix in [dc71571171] (branch canvas-default-error-crash): use the option name in the error message if the option has no database name. Now `.c create text` reports the error with `(default value for "-font" in widget ".c")` instead of crashing.