Fix printing of default option value to handle empty strings

CHANGES.rst

@@ -8,6 +8,8 @@ Unreleased
 -   Fix an issue with type hints for ``click.open_file()``. :issue:`2717`
 -   Fix issue where error message for invalid ``click.Path`` displays on
     multiple lines. :issue:`2697`
+-   Fixed issue that prevented a default value of ``""`` from being displayed in
+    the help for an option. :issue:`2500`
 
 
 Version 8.1.7

src/click/core.py

@@ -2804,6 +2804,8 @@ def _write_opts(opts: t.Sequence[str]) -> str:
                 )[1]
             elif self.is_bool_flag and not self.secondary_opts and not default_value:
                 default_string = ""
+            elif default_value == "":
+                default_string = '""'
             else:
                 default_string = str(default_value)
 

tests/test_options.py

@@ -786,6 +786,14 @@ def test_show_default_string(runner):
     assert "[default: (unlimited)]" in message
 
 
+def test_show_default_with_empty_string(runner):
+    """When show_default is True and default is set to an empty string."""
+    opt = click.Option(["--limit"], default="", show_default=True)
+    ctx = click.Context(click.Command("cli"))
+    message = opt.get_help_record(ctx)[1]
+    assert '[default: ""]' in message
+
+
 def test_do_not_show_no_default(runner):
     """When show_default is True and no default is set do not show None."""
     opt = click.Option(["--limit"], show_default=True)