[commands] Separate view parsing errors from BadArgument.

This causes them to be raised from a new exception named
ArgumentParsingError with 3 children for ease with i18n. This is
technically a breaking change since it no longer derives from
BadArgument, though catching UserInputError will prevent this change
from affecting the user.

discord/ext/commands/errors.py

@@ -32,7 +32,9 @@ __all__ = ['CommandError', 'MissingRequiredArgument', 'BadArgument',
            'DisabledCommand', 'CommandInvokeError', 'TooManyArguments',
            'UserInputError', 'CommandOnCooldown', 'NotOwner',
            'MissingPermissions', 'BotMissingPermissions', 'ConversionError',
-           'BadUnionArgument']
+           'BadUnionArgument', 'ArgumentParsingError',
+           'UnexpectedQuoteError', 'InvalidEndOfQuotedStringError',
+           'ExpectedClosingQuoteError', ]
 
 class CommandError(DiscordException):
     r"""The base exception type for all command related errors.
@@ -229,3 +231,55 @@ class BadUnionArgument(UserInputError):
             fmt = ' or '.join(to_string)
 
         super().__init__('Could not convert "{0.name}" into {1}.'.format(param, fmt))
+
+class ArgumentParsingError(UserInputError):
+    """An exception raised when the parser fails to parse a user's input.
+
+    This derives from :exc:`UserInputError`. There are child classes
+    that implement more granular parsing errors for i18n purposes.
+    """
+    pass
+
+class UnexpectedQuoteError(ArgumentParsingError):
+    """An exception raised when the parser encounters a quote mark inside a non-quoted string.
+
+    This derives from :exc:`ArgumentParsingError`.
+
+    Attributes
+    ------------
+    quote: :class:`str`
+        The quote mark that was found inside the non-quoted string.
+    """
+    def __init__(self, quote):
+        self.quote = quote
+        super().__init__('Unexpected quote mark, {0!r}, in non-quoted string'.format(quote))
+
+class InvalidEndOfQuotedStringError(ArgumentParsingError):
+    """An exception raised when a space is expected after the closing quote in a string
+    but a different character is found.
+
+    This derives from :exc:`ArgumentParsingError`.
+
+    Attributes
+    -----------
+    char: :class:`str`
+        The character found instead of the expected string.
+    """
+    def __init__(self, char):
+        self.char = char
+        super().__init__('Expected space after closing quotation but received {0!r}'.format(char))
+
+class ExpectedClosingQuoteError(ArgumentParsingError):
+    """An exception raised when a quote character is expected but not found.
+
+    This derives from :exc:`ArgumentParsingError`.
+
+    Attributes
+    -----------
+    close_quote: :class:`str`
+        The quote character expected.
+    """
+
+    def __init__(self, close_quote):
+        self.close_quote = close_quote
+        super().__init__('Expected closing {}.'.format(close_quote))

discord/ext/commands/view.py

@@ -24,7 +24,7 @@ FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 DEALINGS IN THE SOFTWARE.
 """
 
-from .errors import BadArgument
+from .errors import UnexpectedQuoteError, InvalidEndOfQuotedStringError, ExpectedClosingQuoteError
 
 class StringView:
     def __init__(self, buffer):
@@ -151,7 +151,7 @@ def quoted_word(view):
         if not current:
             if is_quoted:
                 # unexpected EOF
-                raise BadArgument('Expected closing {}.'.format(close_quote))
+                raise ExpectedClosingQuoteError(close_quote)
             return ''.join(result)
 
         # currently we accept strings in the format of "hello world"
@@ -162,7 +162,7 @@ def quoted_word(view):
                 # string ends with \ and no character after it
                 if is_quoted:
                     # if we're quoted then we're expecting a closing quote
-                    raise BadArgument('Expected closing {}.'.format(close_quote))
+                    raise ExpectedClosingQuoteError(close_quote)
                 # if we aren't then we just let it through
                 return ''.join(result)
 
@@ -177,14 +177,14 @@ def quoted_word(view):
 
         if not is_quoted and current in _all_quotes:
             # we aren't quoted
-            raise BadArgument('Unexpected quote mark in non-quoted string')
+            raise UnexpectedQuoteError(current)
 
         # closing quote
         if is_quoted and current == close_quote:
             next_char = view.get()
             valid_eof = not next_char or next_char.isspace()
             if not valid_eof:
-                raise BadArgument('Expected space after closing quotation')
+                raise InvalidEndOfQuotedStringError(next_char)
 
             # we're quoted so it's okay
             return ''.join(result)

docs/ext/commands/api.rst

@@ -226,6 +226,18 @@ Exceptions
 .. autoexception:: discord.ext.commands.MissingRequiredArgument
     :members:
 
+.. autoexception:: discord.ext.commands.ArgumentParsingError
+    :members:
+
+.. autoexception:: discord.ext.commands.UnexpectedQuoteError
+    :members:
+
+.. autoexception:: discord.ext.commands.InvalidEndOfQuotedStringError
+    :members:
+
+.. autoexception:: discord.ext.commands.ExpectedClosingQuoteError
+    :members:
+
 .. autoexception:: discord.ext.commands.BadArgument
     :members:
 
@@ -278,6 +290,10 @@ Exception Hierarchy
                 - :exc:`~.commands.TooManyArguments`
                 - :exc:`~.commands.BadArgument`
                 - :exc:`~.commands.BadUnionArgument`
+                - :exc:`~.commands.ArgumentParsingError`
+                    - :exc:`~.commands.UnexpectedQuoteError`
+                    - :exc:`~.commands.InvalidEndOfQuotedStringError`
+                    - :exc:`~.commands.ExpectedClosingQuoteError`
             - :exc:`~.commands.CommandNotFound`
             - :exc:`~.commands.CheckFailure`
                 - :exc:`~.commands.NoPrivateMessage`