Fix opam installing packages without checking their checksum when the…

… local cache is corrupted in some cases

src/repository/opamRepository.ml

@@ -93,15 +93,14 @@ let fetch_from_cache =
       failwith "Version control not allowed as cache URL"
   in
   try
-    let hit_checksum, hit_file =
+    let hit_file =
       OpamStd.List.find_map (fun ck ->
           let f = cache_file cache_dir ck in
-          if OpamFilename.exists f then Some (ck, f) else None)
+          if OpamFilename.exists f then Some f else None)
         checksums
     in
     if List.for_all
-        (fun ck -> ck = hit_checksum ||
-                   OpamHash.check_file (OpamFilename.to_string hit_file) ck)
+        (fun ck -> OpamHash.check_file (OpamFilename.to_string hit_file) ck)
         checksums
     then Done (Up_to_date (hit_file, OpamUrl.empty))
     else mismatch hit_file

tests/reftests/local-cache.test

@@ -363,18 +363,12 @@ The following actions will be performed:
   - install good-sha256 1
 
 <><> Processing actions <><><><><><><><><><><><><><><><><><><><><><><><><><><><>
--> retrieved good-sha256.1  (cached)
-[ERROR] The compilation of good-sha256.1 failed at "test -f hello".
-
-
-
+[ERROR] Conflicting file hashes, or broken or compromised cache!
+          - sha256=hash (MISMATCH)
 
-<><> Error report <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>
-+- The following actions failed
-| - build good-sha256 1
-+- 
-- No changes have been performed
-# Return code 31 #
+-> retrieved good-sha256.1  (file://${BASEDIR}/archive.tgz)
+-> installed good-sha256.1
+Done.
 ### sh check-cache.sh
 MD5: link, to sha256 archive
-SHA256: archive, with mismatching checksum
+SHA256: archive, with matching checksum