Move IO#readline to Ruby

This commit moves IO#readline to Ruby.  In order to call C functions,
keyword arguments must be converted to hashes.  Prior to this commit,
code like `io.readline(chomp: true)` would allocate a hash.  This
commits moves the keyword "denaturing" to Ruby, allowing us to send
positional arguments to the C API and avoiding the hash allocation.

Here is an allocation benchmark for the method:

```
x = GC.stat(:total_allocated_objects)
File.open("/usr/share/dict/words") do |f|
  f.readline(chomp: true) until f.eof?
end
p ALLOCATIONS: GC.stat(:total_allocated_objects) - x
```

Before this commit, the output was this:

```
$ make run
./miniruby -I./lib -I. -I.ext/common  -r./arm64-darwin22-fake  ./test.rb
{:ALLOCATIONS=>707939}
```

Now it is this:

```
$ make run
./miniruby -I./lib -I. -I.ext/common  -r./arm64-darwin22-fake  ./test.rb
{:ALLOCATIONS=>471962}
```

[Bug #19890] [ruby-core:114803]

internal/vm.h

@@ -58,6 +58,8 @@ VALUE rb_yield_refine_block(VALUE refinement, VALUE refinements);
 VALUE ruby_vm_special_exception_copy(VALUE);
 PUREFUNC(st_table *rb_vm_fstring_table(void));
 
+void rb_lastline_set_up(VALUE val, unsigned int up);
+
 /* vm_eval.c */
 VALUE rb_current_realfilepath(void);
 VALUE rb_check_block_call(VALUE, ID, int, const VALUE *, rb_block_call_func_t, VALUE);

io.c

@@ -4357,22 +4357,28 @@ rb_io_set_lineno(VALUE io, VALUE lineno)
     return lineno;
 }
 
-/*
- *  call-seq:
- *    readline(sep = $/, chomp: false)   -> string
- *    readline(limit, chomp: false)      -> string
- *    readline(sep, limit, chomp: false) -> string
- *
- *  Reads a line as with IO#gets, but raises EOFError if already at end-of-stream.
- *
- *  Optional keyword argument +chomp+ specifies whether line separators
- *  are to be omitted.
- */
-
+/* :nodoc: */
 static VALUE
-rb_io_readline(int argc, VALUE *argv, VALUE io)
+io_readline(rb_execution_context_t *ec, VALUE io, VALUE sep, VALUE lim, VALUE chomp)
 {
-    VALUE line = rb_io_gets_m(argc, argv, io);
+    if (NIL_P(lim)) {
+        // If sep is specified, but it's not a string and not nil, then assume
+        // it's the limit (it should be an integer)
+        if (!NIL_P(sep) && NIL_P(rb_check_string_type(sep))) {
+            // If the user has specified a non-nil / non-string value
+            // for the separator, we assume it's the limit and set the
+            // separator to default: rb_rs.
+            lim = sep;
+            sep = rb_rs;
+        }
+    }
+
+    if (!NIL_P(sep)) {
+        StringValue(sep);
+    }
+
+    VALUE line = rb_io_getline_1(sep, NIL_P(lim) ? -1L : NUM2LONG(lim), RTEST(chomp), io);
+    rb_lastline_set_up(line, 1);
 
     if (NIL_P(line)) {
         rb_eof_error();
@@ -15420,7 +15426,6 @@ Init_IO(void)
     rb_define_method(rb_cIO, "read", io_read, -1);
     rb_define_method(rb_cIO, "write", io_write_m, -1);
     rb_define_method(rb_cIO, "gets", rb_io_gets_m, -1);
-    rb_define_method(rb_cIO, "readline", rb_io_readline, -1);
     rb_define_method(rb_cIO, "getc", rb_io_getc, 0);
     rb_define_method(rb_cIO, "getbyte", rb_io_getbyte, 0);
     rb_define_method(rb_cIO, "readchar",  rb_io_readchar, 0);

io.rb

@@ -120,4 +120,17 @@ class IO
   def write_nonblock(buf, exception: true)
     Primitive.io_write_nonblock(buf, exception)
   end
+
+  # call-seq:
+  #   readline(sep = $/, chomp: false)   -> string
+  #   readline(limit, chomp: false)      -> string
+  #   readline(sep, limit, chomp: false) -> string
+  #
+  # Reads a line as with IO#gets, but raises EOFError if already at end-of-stream.
+  #
+  # Optional keyword argument +chomp+ specifies whether line separators
+  # are to be omitted.
+  def readline(sep = $/, limit = nil, chomp: false)
+    Primitive.io_readline(sep, limit, chomp)
+  end
 end

test/ruby/test_io.rb

@@ -1898,6 +1898,110 @@ class TestIO < Test::Unit::TestCase
     end)
   end
 
+  def test_readline_bad_param_raises
+    File.open(__FILE__) do |f|
+      assert_raise(TypeError) do
+        f.readline Object.new
+      end
+    end
+
+    File.open(__FILE__) do |f|
+      assert_raise(TypeError) do
+        f.readline 1, 2
+      end
+    end
+  end
+
+  def test_readline_raises
+    File.open(__FILE__) do |f|
+      assert_equal File.read(__FILE__), f.readline(nil)
+      assert_raise(EOFError) do
+        f.readline
+      end
+    end
+  end
+
+  def test_readline_separators
+    File.open(__FILE__) do |f|
+      line = f.readline("def")
+      assert_equal File.read(__FILE__)[/\A.*?def/m], line
+    end
+
+    File.open(__FILE__) do |f|
+      line = f.readline("def", chomp: true)
+      assert_equal File.read(__FILE__)[/\A.*?(?=def)/m], line
+    end
+  end
+
+  def test_readline_separators_limits
+    t = Tempfile.open("readline_limit")
+    str = "#" * 50
+    sep = "def"
+
+    t.write str
+    t.write sep
+    t.write str
+    t.flush
+
+    # over limit
+    File.open(t.path) do |f|
+      line = f.readline sep, str.bytesize
+      assert_equal(str, line)
+    end
+
+    # under limit
+    File.open(t.path) do |f|
+      line = f.readline(sep, str.bytesize + 5)
+      assert_equal(str + sep, line)
+    end
+
+    # under limit + chomp
+    File.open(t.path) do |f|
+      line = f.readline(sep, str.bytesize + 5, chomp: true)
+      assert_equal(str, line)
+    end
+  ensure
+    t&.close!
+  end
+
+  def test_readline_limit_without_separator
+    t = Tempfile.open("readline_limit")
+    str = "#" * 50
+    sep = "\n"
+
+    t.write str
+    t.write sep
+    t.write str
+    t.flush
+
+    # over limit
+    File.open(t.path) do |f|
+      line = f.readline str.bytesize
+      assert_equal(str, line)
+    end
+
+    # under limit
+    File.open(t.path) do |f|
+      line = f.readline(str.bytesize + 5)
+      assert_equal(str + sep, line)
+    end
+
+    # under limit + chomp
+    File.open(t.path) do |f|
+      line = f.readline(str.bytesize + 5, chomp: true)
+      assert_equal(str, line)
+    end
+  ensure
+    t&.close!
+  end
+
+  def test_readline_chomp_true
+    File.open(__FILE__) do |f|
+      line = f.readline(chomp: true)
+      assert_equal File.readlines(__FILE__).first.chomp, line
+    end
+  end
+
   def test_set_lineno_readline
     pipe(proc do |w|
       w.puts "foo"

vm.c

@@ -1750,6 +1750,17 @@ rb_lastline_set(VALUE val)
     vm_svar_set(GET_EC(), VM_SVAR_LASTLINE, val);
 }
 
+void
+rb_lastline_set_up(VALUE val, unsigned int up)
+{
+    rb_control_frame_t * cfp = GET_EC()->cfp;
+
+    for(unsigned int i = 0; i < up; i++) {
+        cfp = RUBY_VM_PREVIOUS_CONTROL_FRAME(cfp);
+    }
+    vm_cfp_svar_set(GET_EC(), cfp, VM_SVAR_LASTLINE, val);
+}
+
 /* misc */
 
 const char *