[PATCH] launch_editor(): indicate that Git waits for user input

[Junio C Hamano <gitster@pobox.com>]

When a graphical GIT_EDITOR is spawned by a Git command that opens
and waits for it for the user input (e.g. "git rebase -i") pops its
window elsewhere that is obscure, the user may be left staring the
original terminal window s/he invoked the Git command from, without
even realizing that now s/he needs to interact with another window
the editor is waiting in, before Git can proceed.

Show a message to the original terminal, and get rid of it when the
editor returns.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---

 * I tried this with "emacsclient" but it turns out that Emacs folks
   have already thought about this issue, and the program says
   "Waiting for Emacs..." while it does its thing, so from that
   point of view, perhaps as Stefan said originally, the editor Lars
   had trouble with is what is at fault and needs fixing?  I dunno.

   Also, emacsclient seems to conclude its message, once the editing
   is done, by emitting LF _before_ we have a chance to do the "go
   back to the beginning and clear" dance, so it probably is not a
   very good example to emulate the situation Lars had trouble with.
   You cannot observe the nuking of the "launched, waiting..." with
   it.

 editor.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/editor.c b/editor.c
index 7519edecdc..1321944716 100644
--- a/editor.c
+++ b/editor.c
@@ -40,6 +40,28 @@ int launch_editor(const char *path, struct strbuf *buffer, const char *const *en
 		const char *args[] = { editor, real_path(path), NULL };
 		struct child_process p = CHILD_PROCESS_INIT;
 		int ret, sig;
+		static const char *close_notice = NULL;
+
+		if (isatty(2) && !close_notice) {
+			char *term = getenv("TERM");
+
+			if (term && strcmp(term, "dumb"))
+				/*
+				 * go back to the beginning and erase the
+				 * entire line if the terminal is capable
+				 * to do so, to avoid wasting the vertical
+				 * space.
+				 */
+				close_notice = "\r\033[K";
+			else
+				/* otherwise, complete and waste the line */
+				close_notice = "done.\n";
+		}
+
+		if (close_notice) {
+			fprintf(stderr, "Launched your editor, waiting...");
+			fflush(stderr);
+		}
 
 		p.argv = args;
 		p.env = env;
@@ -53,11 +75,14 @@ int launch_editor(const char *path, struct strbuf *buffer, const char *const *en
 		sig = ret - 128;
 		sigchain_pop(SIGINT);
 		sigchain_pop(SIGQUIT);
+
 		if (sig == SIGINT || sig == SIGQUIT)
 			raise(sig);
 		if (ret)
 			return error("There was a problem with the editor '%s'.",
 					editor);
+		if (close_notice)
+			fputs(close_notice, stderr);
 	}
 
 	if (!buffer)
-- 
2.15.0-360-gf2497ca0e5