Make Ctrl-C to kill only the command running in the foreground

Ignore `INT` signal while executing a command in the foreground and
always reset all signal handlers to default in the child process.

Fixes #1331

NEWS.adoc

@@ -12,6 +12,7 @@ Bug fixes:
  - Fix reopening the blame view from the main view.
  - Fix editing when stdin is redirected. (#1330)
  - Fix compilation warnings with ncurses 6.5.
+ - Make `Ctrl-C` to kill only the command running in the foreground. (#1331)
 
 tig-2.5.9
 ---------

src/display.c

@@ -84,6 +84,7 @@ open_external_viewer(const char *argv[], const char *dir, bool silent, bool conf
 		ok = io_run_bg(argv, dir);
 
 	} else {
+		signal(SIGINT, SIG_IGN);
 		clear();
 		refresh();
 		endwin();                  /* restore original tty modes */
@@ -101,6 +102,7 @@ open_external_viewer(const char *argv[], const char *dir, bool silent, bool conf
 		fseek(opt_tty.file, 0, SEEK_END);
 		tcsetattr(opt_tty.fd, TCSAFLUSH, opt_tty.attr);
 		set_terminal_modes();
+		signal(SIGINT, SIG_DFL);
 	}
 
 	if (watch_update(WATCH_EVENT_AFTER_COMMAND) && do_refresh) {

src/io.c

@@ -436,6 +436,13 @@ io_exec(struct io *io, enum io_type type, const char *dir, char * const env[], c
 					putenv(env[i]);
 		}
 
+		signal(SIGHUP, SIG_DFL);
+		signal(SIGINT, SIG_DFL);
+		signal(SIGPIPE, SIG_DFL);
+#ifdef DEBUG
+		signal(SIGSEGV, SIG_DFL);
+#endif
+
 		execvp(argv[0], (char *const*) argv);
 
 		close(STDOUT_FILENO);