From 7a66d56918d7f20c6517f5e9fa1b2904b08374d5 Mon Sep 17 00:00:00 2001
From: Michael Snoyman <michael@snoyman.com>
Date: Tue, 27 Jun 2017 19:43:06 +0300
Subject: [PATCH 1/2] Unpack by hash

---
 ChangeLog.md       |  3 +++
 src/Stack/Fetch.hs | 12 ++++++++----
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/ChangeLog.md b/ChangeLog.md
index bc1e52ad24..1673ea2ffd 100644
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -57,6 +57,9 @@ Other enhancements:
 * MinGW bin folder now is searched for dynamic libraries. See [#3126](https://github.com/commercialhaskell/stack/issues/3126)
 * When using Nix, nix-shell now depends always on git to prevent runtime errors
   while fetching metadata
+* The `stack unpack` command now accepts a form where an explicit
+  Hackage revision hash is specified, e.g. `stack unpack
+  foo-1.2.3@gitsha1:deadbeef`.
 
 Bug fixes:
 
diff --git a/src/Stack/Fetch.hs b/src/Stack/Fetch.hs
index 7db9c15daa..1439d114ff 100644
--- a/src/Stack/Fetch.hs
+++ b/src/Stack/Fetch.hs
@@ -59,7 +59,7 @@ import              Data.Monoid
 import              Data.Set (Set)
 import qualified    Data.Set as Set
 import qualified    Data.Text as T
-import              Data.Text.Encoding (decodeUtf8)
+import              Data.Text.Encoding (encodeUtf8, decodeUtf8)
 import              Data.Text.Metrics
 import              Data.Typeable (Typeable)
 import              Data.Word (Word64)
@@ -146,7 +146,7 @@ unpackPackages mMiniBuildPlan dest input = do
         ([], x) -> return $ partitionEithers x
         (errs, _) -> throwM $ CouldNotParsePackageSelectors errs
     resolved <- resolvePackages mMiniBuildPlan
-        (Map.fromList $ map (, Nothing) idents)
+        (Map.fromList idents)
         (Set.fromList names)
     ToFetchResult toFetch alreadyUnpacked <- getToFetch (Just dest') resolved
     unless (Map.null alreadyUnpacked) $
@@ -165,8 +165,12 @@ unpackPackages mMiniBuildPlan dest input = do
             Right x -> Right $ Left x
             Left _ ->
                 case parsePackageIdentifierFromString s of
-                    Left _ -> Left s
-                    Right x -> Right $ Right x
+                    Right x -> Right $ Right (x, Nothing)
+                    Left _ -> maybe (Left s) (Right . Right) $ do
+                      (identS, '@':revisionS) <- return $ break (== '@') s
+                      Right ident <- return $ parsePackageIdentifierFromString identS
+                      hash <- T.stripPrefix "gitsha1:" $ T.pack revisionS
+                      Just (ident, Just $ GitSHA1 $ encodeUtf8 hash)
 
 -- | Ensure that all of the given package idents are unpacked into the build
 -- unpack directory, and return the paths to all of the subdirectories.

From 8b0d0879e15cd0599ed9c3290252f41f52ce5885 Mon Sep 17 00:00:00 2001
From: Michael Snoyman <michael@snoyman.com>
Date: Tue, 27 Jun 2017 21:03:28 +0300
Subject: [PATCH 2/2] Mark as experimental

---
 ChangeLog.md | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/ChangeLog.md b/ChangeLog.md
index 1673ea2ffd..f5415505b9 100644
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -59,7 +59,9 @@ Other enhancements:
   while fetching metadata
 * The `stack unpack` command now accepts a form where an explicit
   Hackage revision hash is specified, e.g. `stack unpack
-  foo-1.2.3@gitsha1:deadbeef`.
+  foo-1.2.3@gitsha1:deadbeef`. Note that this should be considered
+  _experimental_, Stack will likely move towards a different hash
+  format in the future.
 
 Bug fixes: