feedback: upon first switch to a buffer, show its error message (if any)

When opening multiple files and some of them had an error, only the
first message was shown and the others were lost -- indicated only
by three dots.  Improve upon this by storing the first error message
for each buffer and showing this message when the buffer is first
switched to.

Requested-by: Mike Frysinger <vapier@gentoo.org>

src/definitions.h

@@ -567,6 +567,8 @@ typedef struct openfilestruct {
 		/* The syntax that applies to this file, if any. */
 #endif
 #ifdef ENABLE_MULTIBUFFER
+	char *errormessage;
+		/* The ALERT message (if any) that occurred when opening the file. */
 	struct openfilestruct *next;
 		/* The next open file, if any. */
 	struct openfilestruct *prev;

src/files.c

@@ -92,6 +92,8 @@ void make_new_buffer(void)
 
 	openfile->statinfo = NULL;
 	openfile->lock_filename = NULL;
+
+	openfile->errormessage = NULL;
 #endif
 #ifdef ENABLE_COLOR
 	openfile->syntax = NULL;
@@ -558,6 +560,11 @@ void redecorate_after_switch(void)
 	/* Prevent a possible Shift selection from getting cancelled. */
 	shift_held = TRUE;
 
+	if (openfile->errormessage) {
+		statusline(ALERT, openfile->errormessage);
+		free(openfile->errormessage);
+		openfile->errormessage = NULL;
+	} else
 	/* Indicate on the status bar where we switched to. */
 	mention_name_and_linecount();
 }
@@ -595,6 +602,7 @@ void close_buffer(void)
 	/* Free the undo stack. */
 	discard_until(NULL);
 #endif
+	free(orphan->errormessage);
 
 	openfile = orphan->prev;
 	free(orphan);

src/winio.c

@@ -2229,6 +2229,12 @@ void statusline(message_type importance, const char *msg, ...)
 	vsnprintf(compound, MAXCHARLEN * COLS + 1, msg, ap);
 	va_end(ap);
 
+#ifdef ENABLE_MULTIBUFFER
+	if (!we_are_running && importance == ALERT &&
+						!openfile->errormessage && openfile->next != openfile)
+		openfile->errormessage = copy_of(compound);
+#endif
+
 	/* If there are multiple alert messages, add trailing dots to the first. */
 	if (lastmessage == ALERT) {
 		if (start_col > 4) {