xC: improve backlog helper capabilities

Snippets now receive positional parameters in the form of the buffer's
name in the locale encoding, and a filename if applicable
(we keep passing stdin along with the filename, which happens to
work out well for less(1)).

The default value of the configuration option also no longer uses
the "long prompt", which used to unhelpfully tell position in terms
of lines, but rather sets its own prompt that counts pages,
and makes sure to indicate the source buffer.

The main motivation behind this change is to make the 'v' command
work in less(1).  LESSSECURE must be omitted from the snippet
for this to work.

Bump liberty to receive a config parser that allows for less
convoluted escaping.

3 files changed, 21 insertions, 12 deletions

diff --git a/NEWS b/NEWS
index 0d126ec..859fa93 100644
--- a/NEWS
+++ b/NEWS
@@ -1,5 +1,7 @@
 Unreleased
 
+ * xC: improved backlog helper integration capabilities
+
  * xC: made it show WALLOPS messages, as PRIVMSG for the server buffer
 
  * xD: implemented WALLOPS, choosing to make it target even non-operators
diff --git a/liberty b/liberty
-Subproject 1b9d89cab3bb1df73c58ccd8528eafd21a8c6e4
+Subproject f545be725df9195a5b5897ad95a0220acf10f14
diff --git a/xC.c b/xC.c
index 909675d..2b81e79 100644
--- a/xC.c
+++ b/xC.c
@@ -2480,9 +2480,11 @@ static struct config_schema g_config_behaviour[] =
 	  .default_  = "1000",
 	  .on_change = on_config_backlog_limit_change },
 	{ .name      = "backlog_helper",
-	  .comment   = "Shell command to display a buffer's history",
+	  .comment   = "Shell command to page buffer history (args: name [path])",
 	  .type      = CONFIG_ITEM_STRING,
-	  .default_  = "\"LESSSECURE=1 less -M -R +Gb\"" },
+	  .default_  = "`name=$(echo \"$1\" | sed 's/[%?:.]/\\\\&/g'); "
+		"prompt='?f%F:'$name'. ?db- page %db?L of %D. .(?eEND:?PB%PB\\%..)'; "
+		"LESSSECURE=1 less +Gb -Ps\"$prompt\" \"${2:--R}\"`" },
 	{ .name      = "backlog_helper_strip_formatting",
 	  .comment   = "Strip formatting from backlog helper input",
 	  .type      = CONFIG_ITEM_BOOLEAN,
@@ -13366,15 +13368,19 @@ input_editor_cleanup (struct app_context *ctx)
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 
 static void
-launch_backlog_helper (struct app_context *ctx, int backlog_fd)
+launch_backlog_helper (struct app_context *ctx, int backlog_fd,
+	const char *name, const char *path)
 {
 	hard_assert (!ctx->running_backlog_helper);
 	switch (spawn_helper_child (ctx))
 	{
 	case 0:
 		dup2 (backlog_fd, STDIN_FILENO);
-		execl ("/bin/sh", "/bin/sh", "-c", get_config_string
-			(ctx->config.root, "behaviour.backlog_helper"), NULL);
+		char *localized_name =
+			iconv_xstrdup (ctx->term_from_utf8, (char *) name, -1, NULL);
+		execl ("/bin/sh", "/bin/sh", "-c",
+			get_config_string (ctx->config.root, "behaviour.backlog_helper"),
+			PROGRAM_NAME, localized_name, path, NULL);
 		print_error ("%s: %s",
 			"Failed to launch backlog helper", strerror (errno));
 		_exit (EXIT_FAILURE);
@@ -13419,7 +13425,7 @@ display_backlog (struct app_context *ctx, int flush_opts)
 
 	rewind (backlog);
 	set_cloexec (fileno (backlog));
-	launch_backlog_helper (ctx, fileno (backlog));
+	launch_backlog_helper (ctx, fileno (backlog), buffer->name, NULL);
 	fclose (backlog);
 	return true;
 }
@@ -13447,24 +13453,25 @@ on_display_full_log (int count, int key, void *user_data)
 	(void) key;
 	struct app_context *ctx = user_data;
 
-	char *path = buffer_get_log_path (ctx->current_buffer);
+	struct buffer *buffer = ctx->current_buffer;
+	char *path = buffer_get_log_path (buffer);
 	FILE *full_log = fopen (path, "rb");
-	free (path);
-
 	if (!full_log)
 	{
 		log_global_error (ctx, "Failed to open log file for #s: #l",
 			ctx->current_buffer->name, strerror (errno));
+		free (path);
 		return false;
 	}
 
-	if (ctx->current_buffer->log_file)
+	if (buffer->log_file)
 		// The regular flush will log any error eventually
-		(void) fflush (ctx->current_buffer->log_file);
+		(void) fflush (buffer->log_file);
 
 	set_cloexec (fileno (full_log));
-	launch_backlog_helper (ctx, fileno (full_log));
+	launch_backlog_helper (ctx, fileno (full_log), buffer->name, path);
 	fclose (full_log);
+	free (path);
 	return true;
 }