gh-80448: argparse: Fix IndexError on store_true action (#15656)

shihai1991 · Rémi Lapeyre · JelleZijlstra · web-flow · commit e02cc6d42aee · 2022-11-11T17:51:38.000-08:00
Co-authored-by: Rémi Lapeyre &lt;remi.lapeyre@henki.fr&gt;
Co-authored-by: Jelle Zijlstra &lt;jelle.zijlstra@gmail.com&gt;
Co-authored-by: Shantanu &lt;12621235+hauntsaninja@users.noreply.github.com&gt;
diff --git a/Lib/argparse.py b/Lib/argparse.py
@@ -1997,7 +1997,11 @@ def consume_optional(start_index):
                     # arguments, try to parse more single-dash options out
                     # of the tail of the option string
                     chars = self.prefix_chars
-                    if arg_count == 0 and option_string[1] not in chars:
+                    if (
+                        arg_count == 0
+                        and option_string[1] not in chars
+                        and explicit_arg != ''
+                    ):
                         action_tuples.append((action, [], option_string))
                         char = option_string[0]
                         option_string = char + explicit_arg[0]
diff --git a/Lib/test/test_argparse.py b/Lib/test/test_argparse.py
@@ -296,7 +296,7 @@ class TestOptionalsSingleDashCombined(ParserTestCase):
         Sig('-z'),
     ]
     failures = ['a', '--foo', '-xa', '-x --foo', '-x -z', '-z -x',
-                '-yx', '-yz a', '-yyyx', '-yyyza', '-xyza']
+                '-yx', '-yz a', '-yyyx', '-yyyza', '-xyza', '-x=']
     successes = [
         ('', NS(x=False, yyy=None, z=None)),
         ('-x', NS(x=True, yyy=None, z=None)),
diff --git a/Misc/NEWS.d/next/Library/2019-09-03-15-45-19.bpo-36267.z42Ex7.rst b/Misc/NEWS.d/next/Library/2019-09-03-15-45-19.bpo-36267.z42Ex7.rst
@@ -0,0 +1 @@
+Fix IndexError in :class:`argparse.ArgumentParser` when a ``store_true`` action is given an explicit argument.

Original file line number	Diff line number	Diff line change
`@@ -296,7 +296,7 @@ class TestOptionalsSingleDashCombined(ParserTestCase):`
`296`	`296`	`Sig('-z'),`
`297`	`297`	`]`
`298`	`298`	`failures = ['a', '--foo', '-xa', '-x --foo', '-x -z', '-z -x',`
`299`		`- '-yx', '-yz a', '-yyyx', '-yyyza', '-xyza']`
	`299`	`+ '-yx', '-yz a', '-yyyx', '-yyyza', '-xyza', '-x=']`
`300`	`300`	`successes = [`
`301`	`301`	`('', NS(x=False, yyy=None, z=None)),`
`302`	`302`	`('-x', NS(x=True, yyy=None, z=None)),`
Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	+Fix IndexError in :class:`argparse.ArgumentParser` when a ``store_true`` action is given an explicit argument.