patch 8.0.1676: no compiler warning for wrong printf format

Problem:    No compiler warning for wrong printf format.
Solution:   Add a printf attribute for gcc. Fix reported problems. (Dominique
            Pelle, closes #2789)

src/channel.c

@@ -158,6 +158,7 @@ ch_log_lead(const char *what, channel_T *ch)
 
 static int did_log_msg = TRUE;
 
+#ifndef PROTO  /* prototype is in vim.h */
     void
 ch_log(channel_T *ch, const char *fmt, ...)
 {
@@ -174,6 +175,14 @@ ch_log(channel_T *ch, const char *fmt, ...)
 	did_log_msg = TRUE;
     }
 }
+#endif
+
+    static void
+ch_error(channel_T *ch, const char *fmt, ...)
+#ifdef __GNUC__
+__attribute__((format(printf, 2, 3)))
+#endif
+    ;
 
     static void
 ch_error(channel_T *ch, const char *fmt, ...)
@@ -1442,8 +1451,8 @@ channel_write_in(channel_T *channel)
 	ch_close_part(channel, PART_IN);
     }
     else
-	ch_log(channel, "Still %d more lines to write",
-					  buf->b_ml.ml_line_count - lnum + 1);
+	ch_log(channel, "Still %ld more lines to write",
+				   (long)(buf->b_ml.ml_line_count - lnum + 1));
 }
 
 /*
@@ -1536,8 +1545,8 @@ channel_write_new_lines(buf_T *buf)
 	    else if (written > 1)
 		ch_log(channel, "written %d lines to channel", written);
 	    if (lnum < buf->b_ml.ml_line_count)
-		ch_log(channel, "Still %d more lines to write",
-					      buf->b_ml.ml_line_count - lnum);
+		ch_log(channel, "Still %ld more lines to write",
+				       (long)(buf->b_ml.ml_line_count - lnum));
 
 	    in_part->ch_buf_bot = lnum;
 	}
@@ -2081,7 +2090,8 @@ channel_get_json(
 	{
 	    *rettv = item->jq_value;
 	    if (tv->v_type == VAR_NUMBER)
-		ch_log(channel, "Getting JSON message %d", tv->vval.v_number);
+		ch_log(channel, "Getting JSON message %ld",
+						      (long)tv->vval.v_number);
 	    remove_json_node(head, item);
 	    return OK;
 	}

src/proto/channel.pro

@@ -1,7 +1,6 @@
 /* channel.c */
 void ch_logfile(char_u *fname, char_u *opt);
 int ch_log_active(void);
-void ch_log(channel_T *ch, const char *fmt, ...);
 channel_T *add_channel(void);
 int has_any_channel(void);
 int channel_unref(channel_T *channel);

src/version.c

@@ -762,6 +762,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1676,
 /**/
     1675,
 /**/

src/vim.h

@@ -2549,4 +2549,11 @@ typedef enum {
 #define TERM_START_FORCEIT	2
 #define TERM_START_SYSTEM	4
 
+/* Not generated automatically, to add extra attribute. */
+void ch_log(channel_T *ch, const char *fmt, ...)
+#ifdef __GNUC__
+__attribute__((format(printf, 2, 3)))
+#endif
+;
+
 #endif /* VIM__H */