Add builtins.hashFile

For text files it is possible to do it like so:
`builtins.hashString "sha256" (builtins.readFile /tmp/a)`
but that doesn't work for binary files.

With builtins.hashFile any kind of file can be conveniently hashed.

1 files changed, 4 insertions, 0 deletions

diff --git a/tests/lang/eval-okay-hashstring.nix b/tests/lang/eval-okay-hashstring.nix
new file mode 100644
index 000000000000..b0f62b245ca8
--- /dev/null
+++ b/tests/lang/eval-okay-hashstring.nix
@@ -0,0 +1,4 @@
+let
+  strings = [ "" "text 1" "text 2" ];
+in
+  builtins.concatLists (map (hash: map (builtins.hashString hash) strings) ["md5" "sha1" "sha256" "sha512"])