[Downloader] Catch OSErrors from invalid repo names (#3029)

* [Downloader] Ensure repo names only contain the characters stated

* Create 2827.bugfix.rst

* [Downloader] Catch OSErrors from invalid filenames

* Update 2827.bugfix.rst

* Style

* do the thing again

* Update 2827.bugfix.rst

changelog.d/downloader/2827.bugfix.rst

@@ -0,0 +1 @@
+Repo names can now only contain the characters listed in the help text (A-Z, 0-9, underscores, and hyphens).

redbot/cogs/downloader/downloader.py

@@ -1,6 +1,7 @@
 import asyncio
 import contextlib
 import os
+import re
 import shutil
 import sys
 from pathlib import Path
@@ -222,12 +223,17 @@ class Downloader(commands.Cog):
     async def _repo_add(self, ctx, name: str, repo_url: str, branch: str = None):
         """Add a new repo.
 
-        The name can only contain characters A-z, numbers and underscores.
+        Repo names can only contain characters A-z, numbers, underscores, and hyphens.
         The branch will be the default branch if not specified.
         """
         agreed = await do_install_agreement(ctx)
         if not agreed:
             return
+        if re.match("^[a-zA-Z0-9_\-]*$", name) is None:
+            await ctx.send(
+                _("Repo names can only contain characters A-z, numbers, underscores, and hyphens.")
+            )
+            return
         try:
             # noinspection PyTypeChecker
             repo = await self._repo_manager.add_repo(name=name, url=repo_url, branch=branch)
@@ -241,6 +247,12 @@ class Downloader(commands.Cog):
                 branch,
                 exc_info=err,
             )
+        except OSError:
+            await ctx.send(
+                _(
+                    "Something went wrong trying to add that repo. Your repo name might have an invalid character."
+                )
+            )
         else:
             await ctx.send(_("Repo `{name}` successfully added.").format(name=name))
             if repo.install_msg is not None: