reinject: Fix crash when reinjecting a file from outside the repository

Commit 4bf7940d6b introduced this
problem, but was otherwise doing a good thing. Problem being
that fileRef "/foo" used to return ":./foo", which was actually wrong,
but as long as there was no foo in the local repository, catKey
could operate on it without crashing. After that fix though, fileRef
would return eg "../../foo", resulting in fileRef returning
":./../../foo", which will make git cat-file crash since that's
not a valid path in the repo.

Fix is simply to make fileRef detect paths outside the repo and return
Nothing. Then catKey can be skipped. This needed several bugfixes to
dirContains as well, in previous commits.

In Command.Smudge, this led to needing to check for Nothing. That case
should actually never happen, because the fileoutsiderepo check will
detect it earlier.

Sponsored-by: Brock Spratlen on Patreon

Git/Ref.hs

@@ -64,17 +64,22 @@ branchRef = underBase "refs/heads"
 
 {- A Ref that can be used to refer to a file in the repository, as staged
  - in the index.
+ - 
+ - If the input file is located outside the repository, returns Nothing.
  -}
-fileRef :: RawFilePath -> IO Ref
-fileRef f = do
+fileRef :: RawFilePath -> Repo -> IO (Maybe Ref)
+fileRef f repo = do
 	-- The filename could be absolute, or contain eg "../repo/file",
 	-- neither of which work in a ref, so convert it to a minimal
 	-- relative path.
 	f' <- relPathCwdToFile f
- 	-- Prefixing the file with ./ makes this work even when in a
-	-- subdirectory of a repo. Eg, ./foo in directory bar refers
-	-- to bar/foo, not to foo in the top of the repository.
-	return $ Ref $ ":./" <> toInternalGitPath f'
+	print ("f'", f', repoPath repo, repoPath repo `dirContains` f')
+	return $ if repoPath repo `dirContains` f'
+ 		-- Prefixing the file with ./ makes this work even when in a
+		-- subdirectory of a repo. Eg, ./foo in directory bar refers
+		-- to bar/foo, not to foo in the top of the repository.
+		then Just $ Ref $ ":./" <> toInternalGitPath f'
+		else Nothing
 
 {- A Ref that can be used to refer to a file in a particular branch. -}
 branchFileRef :: Branch -> RawFilePath -> Ref
@@ -85,11 +90,14 @@ dateRef :: Ref -> RefDate -> Ref
 dateRef r (RefDate d) = Ref $ fromRef' r <> "@" <> encodeBS d
 
 {- A Ref that can be used to refer to a file in the repository as it
- - appears in a given Ref. -}
-fileFromRef :: Ref -> RawFilePath -> IO Ref
-fileFromRef r f = do
-	(Ref fr) <- fileRef f
-	return (Ref (fromRef' r <> fr))
+ - appears in a given Ref. 
+ -
+ - If the file path is located outside the repository, returns Nothing.
+ -}
+fileFromRef :: Ref -> RawFilePath -> Repo -> IO (Maybe Ref)
+fileFromRef r f repo = fileRef f repo >>= return . \case
+	Just (Ref fr) -> Just (Ref (fromRef' r <> fr))
+	Nothing -> Nothing
 
 {- Checks if a ref exists. Note that it must be fully qualified,
  - eg refs/heads/master rather than master. -}