editor: allow for saving/restoring terminal state

When EDITOR is invoked to modify a commit message, it will likely
change the terminal settings, and if it misbehaves will leave the
terminal output damaged as shown in recent reports from Windows
Terminal[1]

Instead use the functions provided by compat/terminal to save the
settings of the terminal and recover safely, but only do so if
instructed by the user through a new configuration "editor.rogue"
and the terminal is fully interactive.

[1] microsoft/terminal#9359

Helped-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com>

Documentation/config.txt

@@ -361,6 +361,8 @@ include::config/diff.txt[]
 
 include::config/difftool.txt[]
 
+include::config/editor.txt[]
+
 include::config/extensions.txt[]
 
 include::config/fastimport.txt[]

Documentation/config/editor.txt

@@ -0,0 +1,4 @@
+editor.rogue::
+	A boolean to indicate you might be using an editor
+	that can't be trusted to clean its terminal state
+	reliably.   Defaults to false.

editor.c

@@ -3,6 +3,7 @@
 #include "strbuf.h"
 #include "run-command.h"
 #include "sigchain.h"
+#include "compat/terminal.h"
 
 #ifndef DEFAULT_EDITOR
 #define DEFAULT_EDITOR "vi"
@@ -54,6 +55,7 @@ static int launch_specified_editor(const char *editor, const char *path,
 		return error("Terminal is dumb, but EDITOR unset");
 
 	if (strcmp(editor, ":")) {
+		int save_and_restore_term = 0;
 		struct strbuf realpath = STRBUF_INIT;
 		const char *args[] = { editor, NULL, NULL };
 		struct child_process p = CHILD_PROCESS_INIT;
@@ -76,21 +78,35 @@ static int launch_specified_editor(const char *editor, const char *path,
 			fflush(stderr);
 		}
 
+		if (git_config_get_bool("editor.rogue", &save_and_restore_term) == 0)
+		{
+			/* disable unless we are fully interactive */
+			if (save_and_restore_term && !isatty(2))
+				save_and_restore_term = 0;
+		}
+
 		strbuf_realpath(&realpath, path, 1);
 		args[1] = realpath.buf;
 
 		p.argv = args;
 		p.env = env;
 		p.use_shell = 1;
 		p.trace2_child_class = "editor";
+		if (save_and_restore_term)
+			save_and_restore_term = !save_term(1);
+
 		if (start_command(&p) < 0) {
+			if (save_and_restore_term)
+				restore_term();
 			strbuf_release(&realpath);
 			return error("unable to start editor '%s'", editor);
 		}
 
 		sigchain_push(SIGINT, SIG_IGN);
 		sigchain_push(SIGQUIT, SIG_IGN);
 		ret = finish_command(&p);
+		if (save_and_restore_term)
+			restore_term();
 		strbuf_release(&realpath);
 		sig = ret - 128;
 		sigchain_pop(SIGINT);