Add IO#ttyname that returns the tty name or nil

ext/io/console/console.c

@@ -84,6 +84,11 @@ getattr(int fd, conmode *t)
 static ID id_getc, id_close;
 static ID id_gets, id_flush, id_chomp_bang;
 
+#ifndef HAVE_RB_INTERNED_STR_CSTR
+# define rb_str_to_interned_str(str) rb_str_freeze(str)
+# define rb_interned_str_cstr(str) rb_str_freeze(rb_usascii_str_new_cstr(str))
+#endif
+
 #if defined HAVE_RUBY_FIBER_SCHEDULER_H
 # include "ruby/fiber/scheduler.h"
 #elif defined HAVE_RB_SCHEDULER_TIMEOUT
@@ -1814,6 +1819,61 @@ io_getpass(int argc, VALUE *argv, VALUE io)
     return str_chomp(str);
 }
 
+#if defined(_WIN32) || defined(HAVE_TTYNAME_R) || defined(HAVE_TTYNAME)
+/*
+ * call-seq:
+ *   io.ttyname       -> string or nil
+ *
+ * Returns name of associated terminal (tty) if +io+ is not a tty.
+ * Returns +nil+ otherwise.
+ */
+static VALUE
+console_ttyname(VALUE io)
+{
+    int fd = rb_io_descriptor(io);
+    if (!isatty(fd)) return Qnil;
+# if defined _WIN32
+    return rb_usascii_str_new_lit("con");
+# elif defined HAVE_TTYNAME_R
+    {
+	char termname[1024], *tn = termname;
+	size_t size = sizeof(termname);
+	int e;
+	if (ttyname_r(fd, tn, size) == 0)
+	    return rb_interned_str_cstr(tn);
+	if ((e = errno) == ERANGE) {
+	    VALUE s = rb_str_new(0, size);
+	    while (1) {
+		tn = RSTRING_PTR(s);
+		size = rb_str_capacity(s);
+		if (ttyname_r(fd, tn, size) == 0) {
+		    return rb_str_to_interned_str(rb_str_resize(s, strlen(tn)));
+		}
+		if ((e = errno) != ERANGE) break;
+		if ((size *= 2) >= INT_MAX/2) break;
+		rb_str_resize(s, size);
+	    }
+	}
+	rb_syserr_fail_str(e, rb_sprintf("ttyname_r(%d)", fd));
+	UNREACHABLE_RETURN(Qnil);
+    }
+# elif defined HAVE_TTYNAME
+    {
+	const char *tn = ttyname(fd);
+	if (!tn) {
+	    int e = errno;
+	    rb_syserr_fail_str(e, rb_sprintf("ttyname(%d)", fd));
+	}
+	return rb_interned_str_cstr(tn);
+    }
+# else
+#   error No ttyname function
+# endif
+}
+#else
+# define console_ttyname rb_f_notimplement
+#endif
+
 /*
  * IO console methods
  */
@@ -1881,6 +1941,7 @@ InitVM_console(void)
     rb_define_method(rb_cIO, "pressed?", console_key_pressed_p, 1);
     rb_define_method(rb_cIO, "check_winsize_changed", console_check_winsize_changed, 0);
     rb_define_method(rb_cIO, "getpass", console_getpass, -1);
+    rb_define_method(rb_cIO, "ttyname", console_ttyname, 0);
     rb_define_singleton_method(rb_cIO, "console", console_dev, -1);
     {
 	/* :stopdoc: */

ext/io/console/extconf.rb

@@ -5,6 +5,7 @@
 # See https://bugs.ruby-lang.org/issues/20345
 MakeMakefile::RbConfig ||= ::RbConfig
 
+have_func("rb_interned_str_cstr")
 have_func("rb_io_path")
 have_func("rb_io_descriptor")
 have_func("rb_io_get_write_io")
@@ -47,6 +48,7 @@
   elsif have_func("rb_scheduler_timeout") # 3.0
     have_func("rb_io_wait")
   end
+  have_func("ttyname_r") or have_func("ttyname")
   create_makefile("io/console") {|conf|
     conf << "\n""VK_HEADER = #{vk_header}\n"
   }

test/io/console/test_io_console.rb

@@ -441,6 +441,10 @@ def test_console_kw
     def test_sync
       assert_equal(["true"], run_pty("p IO.console.sync"))
     end
+
+    def test_ttyname
+      assert_equal(["true"], run_pty("p STDIN.ttyname == STDOUT.ttyname"))
+    end
   end
 
   private
@@ -531,6 +535,12 @@ def test_sync
     def test_getch_timeout
       assert_nil(IO.console.getch(intr: true, time: 0.1, min: 0))
     end
+
+    def test_ttyname
+      ttyname = IO.console.ttyname
+      assert_not_nil(ttyname)
+      File.open(ttyname) {|f| assert_predicate(f, :tty?)}
+    end
   end
 end
 
@@ -546,7 +556,7 @@ def test_getch_timeout
   if noctty
     require 'tempfile'
     NOCTTY = noctty
-    def test_noctty
+    def run_noctty(src)
       t = Tempfile.new("noctty_out")
       t.close
       t2 = Tempfile.new("noctty_run")
@@ -557,7 +567,7 @@ def test_noctty
         '-e',   'STDOUT.reopen(f)',
         '-e',   'STDERR.reopen(f)',
         '-e',   'require "io/console"',
-        '-e',   'f.puts IO.console.inspect',
+        '-e',   "f.puts (#{src}).inspect",
         '-e',   'f.flush',
         '-e',   'File.unlink(ARGV[1])',
         '-e', '}',
@@ -568,11 +578,18 @@ def test_noctty
         sleep 0.1
       end
       t.open
-      assert_equal("nil", t.gets(nil).chomp)
+      t.gets.lines(chomp: true)
     ensure
       t.close! if t and !t.closed?
       t2.close!
     end
+
+    def test_noctty
+      assert_equal(["nil"], run_noctty("IO.console"))
+      if IO.method_defined?(:ttyname)
+        assert_equal(["nil"], run_noctty("STDIN.ttyname rescue $!"))
+      end
+    end
   end
 end