Better error message for bad parameter default (pallets#1805)

raise TypeError when multiple parameter has single default

Author: Saif807380

CHANGES.rst

@@ -182,6 +182,8 @@ Unreleased
     previous item. :issue:`1353`
 -   The ``Path`` param type can be passed ``path_type=pathlib.Path`` to
     return a path object instead of a string. :issue:`405`
+-   ``TypeError`` is raised when parameter with ``multiple=True`` or
+    ``nargs > 1`` has non-iterable default. :issue:`1749`
 
 
 Version 7.1.2

src/click/core.py

@@ -2011,7 +2011,15 @@ def _convert(value, level):
             if level == 0:
                 return self.type(value, self, ctx)
 
-            return tuple(_convert(x, level - 1) for x in value)
+            try:
+                iter_value = iter(value)
+            except TypeError:
+                raise TypeError(
+                    "Value for parameter with multiple = True or nargs > 1"
+                    " should be an iterable."
+                )
+
+            return tuple(_convert(x, level - 1) for x in iter_value)
 
         return _convert(value, (self.nargs != 1) + bool(self.multiple))
 

tests/test_options.py

@@ -117,6 +117,20 @@ def cli(message):
     assert "Error: Missing option '-m' / '--message'." in result.output
 
 
+def test_multiple_bad_default(runner):
+    @click.command()
+    @click.option("--flags", multiple=True, default=False)
+    def cli(flags):
+        pass
+
+    result = runner.invoke(cli, [])
+    assert result.exception
+    assert (
+        "Value for parameter with multiple = True or nargs > 1 should be an iterable."
+        in result.exception.args
+    )
+
+
 def test_empty_envvar(runner):
     @click.command()
     @click.option("--mypath", type=click.Path(exists=True), envvar="MYPATH")