Fix case insensitive short args parsing.

Author: kschwab

pydantic_settings/sources.py

@@ -1512,7 +1512,7 @@ def parse_args_insensitive_method(
             ) -> Any:
                 insensitive_args = []
                 for arg in shlex.split(shlex.join(args)) if args else []:
-                    flag_prefix = rf'\{self.cli_flag_prefix_char}' * 2
+                    flag_prefix = rf'\{self.cli_flag_prefix_char}{{1,2}}'
                     matched = re.match(rf'^({flag_prefix}[^\s=]+)(.*)', arg)
                     if matched:
                         arg = matched.group(1).lower() + matched.group(2)

tests/test_settings.py

@@ -2694,18 +2694,27 @@ class BadCliPositionalArg(BaseSettings):
 
 def test_cli_case_insensitive_arg():
     class Cfg(BaseSettings, cli_exit_on_error=False):
-        Foo: str
-        Bar: str
+        foo: str = Field(validation_alias=AliasChoices('F', 'Foo'))
+        bar: str = Field(validation_alias=AliasChoices('B', 'Bar'))
 
-    cfg = Cfg(_cli_parse_args=['--FOO=--VAL', '--BAR', '"--VAL"'])
-    assert cfg.model_dump() == {'Foo': '--VAL', 'Bar': '"--VAL"'}
+    cfg = Cfg(_cli_parse_args=['--FOO=--VAL', '--BAR', '"--VAL"', ])
+    assert cfg.model_dump() == {'foo': '--VAL', 'bar': '"--VAL"'}
+
+    cfg = Cfg(_cli_parse_args=['-f=-V', '-b', '"-V"', ])
+    assert cfg.model_dump() == {'foo': '-V', 'bar': '"-V"'}
 
     cfg = Cfg(_cli_parse_args=['--Foo=--VAL', '--Bar', '"--VAL"'], _case_sensitive=True)
-    assert cfg.model_dump() == {'Foo': '--VAL', 'Bar': '"--VAL"'}
+    assert cfg.model_dump() == {'foo': '--VAL', 'bar': '"--VAL"'}
+
+    cfg = Cfg(_cli_parse_args=['-F=-V', '-B', '"-V"'], _case_sensitive=True)
+    assert cfg.model_dump() == {'foo': '-V', 'bar': '"-V"'}
 
     with pytest.raises(SettingsError, match='error parsing CLI: unrecognized arguments: --FOO=--VAL --BAR "--VAL"'):
         Cfg(_cli_parse_args=['--FOO=--VAL', '--BAR', '"--VAL"'], _case_sensitive=True)
 
+    with pytest.raises(SettingsError, match='error parsing CLI: unrecognized arguments: -f=-V -b "-V"'):
+        Cfg(_cli_parse_args=['-f=-V', '-b', '"-V"'], _case_sensitive=True)
+
     with pytest.raises(SettingsError, match='Case-insensitive matching is only supported on the internal root parser'):
         CliSettingsSource(Cfg, root_parser=CliDummyParser(), case_sensitive=False)