Add line-graphics = auto

Closes #834

NEWS.adoc

@@ -7,6 +7,7 @@ master
 Improvements:
 
  - Jump from blame to commit. (#355)
+ - Add line-graphics = auto. (#834)
 
 Bug fixes:
 

doc/tigrc.5.adoc

@@ -191,9 +191,10 @@ The following variables can be set:
 	 - replace		: A replaced reference.
 	 - branch		: Any other reference.
 
-'line-graphics' (mixed) [ascii|default|utf-8|<bool>]::
+'line-graphics' (mixed) [ascii|default|utf-8|auto|<bool>]::
 
-	What type of character graphics for line drawing.
+	What type of character graphics for line drawing. "auto" means "utf-8"
+	if the locale is UTF-8, "default" otherwise.
 
 'truncation-delimiter' (mixed) [utf-8|<string>]::
 

src/options.c

@@ -594,10 +594,24 @@ parse_option(struct option_info *option, const char *prefix, const char *arg)
 		return parse_step(option->value, arg);
 
 	if (!strncmp(option->type, "enum", 4)) {
-		const char *type = option->type + STRING_SIZE("enum ");
-		const struct enum_map *map = find_enum_map(type);
+		if (!strcmp(name, "line-graphics") && !strcasecmp(arg, "auto")) {
+			const char *locale;
+			int *value = option->value;
 
-		return parse_enum(name, option->value, arg, map);
+			if ((((locale = getenv("LC_ALL")) && *locale) ||
+			     ((locale = getenv("LC_CTYPE")) && *locale) ||
+			     ((locale = getenv("LANG")) && *locale)) &&
+			    (strstr(locale, "UTF") || strstr(locale, "utf")))
+				*value = GRAPHIC_UTF_8;
+			else
+				*value = GRAPHIC_DEFAULT;
+			return SUCCESS;
+		} else {
+			const char *type = option->type + STRING_SIZE("enum ");
+			const struct enum_map *map = find_enum_map(type);
+
+			return parse_enum(name, option->value, arg, map);
+		}
 	}
 
 	if (!strcmp(option->type, "int")) {

tigrc

@@ -88,7 +88,7 @@ set show-changes		= yes		# Show changes commits in the main view?
 set show-untracked		= yes		# Show also untracked changes?
 set wrap-lines			= no		# Wrap long lines in pager views?
 set tab-size			= 8		# Number of spaces to use when expanding tabs
-set line-graphics		= default	# Enum: ascii, default, utf-8
+set line-graphics		= default	# Enum: ascii, default, utf-8, auto
 set truncation-delimiter	= ~		# Character drawn for truncations, or "utf-8"
 
 # Format reference names based on type.