Exit if --no-execute is enabled don't interactively read from the ter…

…minal

Don't go into implicit interactive mode without ever executing
anything - not even `exit` or reacting to ctrl-d. That just renders
the shell useless and unquittable.

src/fish.cpp

@@ -503,6 +503,10 @@ int main(int argc, char **argv) {
         parser.libdata().exit_current_script = false;
     } else if (my_optind == argc) {
         // Implicitly interactive mode.
+        if (opts.no_exec && isatty(STDIN_FILENO)) {
+            FLOGF(error, L"no-execute mode enabled and no script given. Exiting");
+            return EXIT_FAILURE;  // above line should always exit
+        }
         res = reader_read(parser, STDIN_FILENO, {});
     } else {
         const char *file = *(argv + (my_optind++));

tests/checks/invocation.fish

@@ -53,3 +53,6 @@ $fish -c 'string escape y$argv' -c 'string escape x$argv' 1 2 3
 # CHECK: x1
 # CHECK: x2
 # CHECK: x3
+
+# Should just do nothing.
+$fish --no-execute

tests/pexpects/generic.py

@@ -51,5 +51,8 @@
 sendline("echo hoge >|  \n cat")
 expect_prompt("hoge")
 
+sendline("$fish --no-execute 2>&1")
+expect_prompt("error: no-execute mode enabled and no script given. Exiting")
+
 sendline("source; or echo failed")
 expect_prompt("failed")