new-sdist: Use a Windows-safe file modification time. (#5611)

Using the Unix epoch is causing problems on Windows because it's
before MS-DOS's epoch of 1980-01-01. Picking a different, memorable
one ought to solve that.

Closes #5596.

cabal-install/Distribution/Client/CmdSdist.hs

@@ -271,7 +271,13 @@ packageToSdist verbosity projectRootDir format outputFile pkg = do
                     where
                         (first, rest) = BSL.splitAt 9 bs
                         rest' = BSL.tail rest
-            write . normalize . GZip.compress . Tar.write $ entries
+                -- The Unix epoch, which is the default value, is
+                -- unsuitable because it causes unpacking problems on
+                -- Windows; we need a post-1980 date. One gigasecond
+                -- after the epoch is during 2001-09-09, so that does
+                -- nicely. See #5596.
+                setModTime entry = entry { Tar.entryTime = 1000000000 }
+            write . normalize . GZip.compress . Tar.write $ fmap setModTime entries
             when (outputFile /= "-") $
                 notice verbosity $ "Wrote tarball sdist to " ++ outputFile ++ "\n"
         Archive ZipFormat -> do

cabal-install/changelog

@@ -3,6 +3,11 @@
 2.6.0.0 (current development version)
 	* New solver flag: '--reject-unconstrained-dependencies'. (#2568)
 
+2.4.0.1
+	* 'new-sdist' now generates tarballs with file modification
+	  times from a date in 2001. Using the Unix epoch caused
+	  problems on Windows. (#5596)
+
 2.4.0.0 Mikhail Glushenkov <mikhail.glushenkov@gmail.com> September 2018
         * Bugfix: "cabal new-build --ghc-option '--bogus' --ghc-option '-O1'"
 	  no longer ignores all arguments except the last one (#5512).