[test] Add batch mode to hb-subset and use it

time meson test --suite=subset down from:
real	0m22.822s
user	0m44.561s
sys	0m9.255s

to:
real	0m19.418s
user	0m38.171s
sys	0m3.587s

Does not seem to help much, but it is something.

Part of https://github.com/harfbuzz/harfbuzz/issues/3089

test/subset/run-repack-tests.py

@@ -22,6 +22,12 @@ except ImportError:
 
 ots_sanitize = shutil.which ("ots-sanitize")
 
+def subset_cmd (command):
+	global process
+	process.stdin.write ((';'.join (command) + '\n').encode ("utf-8"))
+	process.stdin.flush ()
+	return process.stdout.readline().decode ("utf-8").strip ()
+
 def cmd (command):
 	p = subprocess.Popen (
 		command, stdout=subprocess.PIPE, stderr=subprocess.PIPE,
@@ -45,10 +51,10 @@ def run_test (test, should_check_ots):
 		    "--unicodes=%s" % test.codepoints_string (),
 		    "--drop-tables-=GPOS,GSUB,GDEF",]
 	print (' '.join (cli_args))
-	_, return_code = cmd (cli_args)
+	ret = subset_cmd (cli_args)
 
-	if return_code:
-		return fail_test (test, cli_args, "%s returned %d" % (' '.join (cli_args), return_code))
+	if ret != "success":
+		return fail_test (test, cli_args, "%s failed" % ' '.join (cli_args))
 
 	try:
 		with TTFont (out_file) as font:
@@ -87,6 +93,11 @@ if len (args) != 1:
 
 has_ots = has_ots()
 
+process = subprocess.Popen ([hb_subset, '--batch'],
+                            stdin=subprocess.PIPE,
+                            stdout=subprocess.PIPE,
+                            stderr=sys.stdout)
+
 fails = 0
 
 path = args[0]

test/subset/run-tests.py

@@ -22,6 +22,12 @@ except ImportError:
 
 ots_sanitize = shutil.which ("ots-sanitize")
 
+def subset_cmd (command):
+	global process
+	process.stdin.write ((';'.join (command) + '\n').encode ("utf-8"))
+	process.stdin.flush ()
+	return process.stdout.readline().decode ("utf-8").strip ()
+
 def cmd (command):
 	p = subprocess.Popen (
 		command, stdout=subprocess.PIPE, stderr=subprocess.PIPE,
@@ -51,10 +57,10 @@ def run_test (test, should_check_ots):
 		    "--drop-tables-=sbix"]
 	cli_args.extend (test.get_profile_flags ())
 	print (' '.join (cli_args))
-	_, return_code = cmd (cli_args)
+	ret = subset_cmd (cli_args)
 
-	if return_code:
-		return fail_test (test, cli_args, "%s returned %d" % (' '.join (cli_args), return_code))
+	if ret != "success":
+		return fail_test (test, cli_args, "%s failed" % ' '.join (cli_args))
 
 	expected_file = os.path.join (test_suite.get_output_directory (), test.get_font_ttx_name ())
 	with open(expected_file, encoding="utf-8") as expected_ttx:
@@ -115,6 +121,11 @@ if not len (args):
 
 has_ots = has_ots()
 
+process = subprocess.Popen ([hb_subset, '--batch'],
+                            stdin=subprocess.PIPE,
+                            stdout=subprocess.PIPE,
+                            stderr=sys.stdout)
+
 fails = 0
 for path in args:
 	with open (path, mode="r", encoding="utf-8") as f:

util/hb-subset.cc

@@ -130,6 +130,40 @@ struct subset_consumer_t
 int
 main (int argc, char **argv)
 {
+  if (argc == 2 && !strcmp (argv[1], "--batch"))
+  {
+    unsigned int ret = 0;
+    char buf[4092];
+    while (fgets (buf, sizeof (buf), stdin))
+    {
+      size_t l = strlen (buf);
+      if (l && buf[l - 1] == '\n') buf[l - 1] = '\0';
+      main_font_text_t<subset_consumer_t, 10, 0, EOF> driver;
+      char *args[32];
+      argc = 0;
+      char *p = buf, *e;
+      args[argc++] = p;
+      unsigned start_offset = 0;
+      while ((e = strchr (p + start_offset, ';')) && argc < (int) ARRAY_LENGTH (args))
+      {
+	*e++ = '\0';
+	while (*e == ':')
+	  e++;
+	args[argc++] = p = e;
+      }
+      int result = driver.main (argc, args);
+      if (result == 0)
+        fprintf (stdout, "success\n");
+      else
+        fprintf (stdout, "failure\n");
+      ret |= result;
+      fflush (stdout);
+
+      if (ret)
+	break;
+    }
+    return ret;
+  }
   main_font_text_t<subset_consumer_t, 10, 0> driver;
   return driver.main (argc, argv);
 }