Don't try to import .git directories from special remotes

Because git does not support storing git repositories inside a git
repository.

Annex/Import.hs

@@ -16,6 +16,7 @@ module Annex.Import (
 	downloadImport,
 	filterImportableContents,
 	makeImportMatcher,
+	listImportableContents,
 ) where
 
 import Annex.Common
@@ -54,6 +55,7 @@ import qualified Logs.ContentIdentifier as CIDLog
 import Control.Concurrent.STM
 import qualified Data.Map.Strict as M
 import qualified Data.Set as S
+import qualified System.FilePath.Posix as Posix
 
 {- Configures how to build an import tree. -}
 data ImportTreeConfig
@@ -480,3 +482,22 @@ filterImportableContents r matcher importable
 		<*> mapM (go dbhandle) (importableHistory ic)
 	
 	match dbhandle (loc, (_cid, sz)) = shouldImport dbhandle matcher loc sz
+	
+{- Gets the ImportableContents from the remote.
+ -
+ - Filters out any paths that include a ".git" component, because git does
+ - not allow storing ".git" in a git repository. While it is possible to
+ - write a git tree that contains that, git will complain and refuse to
+ - check it out.
+ -}
+listImportableContents :: Remote -> Annex (Maybe (ImportableContents (ContentIdentifier, ByteSize)))
+listImportableContents r = fmap removegitspecial
+	<$> Remote.listImportableContents (Remote.importActions r)
+  where
+	removegitspecial ic = ImportableContents
+		{ importableContents = 
+			filter (not . gitspecial . fst) (importableContents ic)
+		, importableHistory =
+			map removegitspecial (importableHistory ic)
+		}
+	gitspecial l = ".git" `elem` Posix.splitDirectories (fromImportLocation l)

CHANGELOG

@@ -11,6 +11,8 @@ git-annex (7.20190508) UNRELEASED; urgency=medium
     unwanted files are not imported. But, some preferred content
     expressions can't be checked before files are imported, and trying to
     import with such an expression will fail.
+  * Don't try to import .git directories from special remotes, because
+    git does not support storing git repositories inside a git repository.
   * Improve shape of commit tree when importing from unversioned special
     remotes.
   * init: When the repository already has a description, don't change it.

Command/Import.hs

@@ -291,7 +291,7 @@ seekRemote remote branch msubdir = do
 listContents :: Remote -> TVar (Maybe (ImportableContents (ContentIdentifier, Remote.ByteSize))) -> CommandStart
 listContents remote tvar = do
 	showStart' "list" (Just (Remote.name remote))
-	next $ Remote.listImportableContents (Remote.importActions remote) >>= \case
+	next $ listImportableContents remote >>= \case
 		Nothing -> giveup $ "Unable to list contents of " ++ Remote.name remote
 		Just importable -> do
 			importable' <- makeImportMatcher remote >>= \case

doc/bugs/import_tree_should_skip_.git.mdwn

@@ -19,6 +19,14 @@ The solution is certianly to
 1. filter out .git when importing
 2. avoid deleting .git when exporting
 
+   As long as the export tracking branch did not contain .git,
+   an export will harm no .git directories, because an exporttree
+   remote uses removeExportDirectoryWhenEmpty, not removeExportDirectory,
+   so will not delete non-empty directories. And other than deleting
+   directories, exporting only deletes files that are removed in the git
+   diff between two trees; if neither tree contained .git, the diff won't
+   contain it either, and so if importing skips .git, this will be ok.
+
 --[[Joey]]
 
 > [[fixed|done]] --[[Joey]]