lean: substitute release commit sha1

pkgs/applications/science/logic/lean/default.nix

@@ -7,7 +7,11 @@ stdenv.mkDerivation rec {
   src = fetchFromGitHub {
     owner  = "leanprover-community";
     repo   = "lean";
-    rev    = "v${version}";
+    # lean's version string contains the commit sha1 it was built
+    # from. this is then used to check whether an olean file should be
+    # rebuilt. don't use a tag as rev because this will get replaced into
+    # src/githash.h.in in preConfigure.
+    rev    = "a5822ea47ebc52eec6323d8f1b60f6ec025daf99";
     sha256 = "sha256-gJhbkl19iilNyfCt2TfPmghYA3yCjg6kS+yk/x/k14Y=";
   };
 
@@ -20,6 +24,13 @@ stdenv.mkDerivation rec {
   # library.
   doCheck = true;
 
+  preConfigure = assert builtins.stringLength src.rev == 40; ''
+     substituteInPlace src/githash.h.in \
+       --subst-var-by GIT_SHA1 "${src.rev}"
+     substituteInPlace library/init/version.lean.in \
+       --subst-var-by GIT_SHA1 "${src.rev}"
+  '';
+
   postPatch = "patchShebangs .";
 
   postInstall = lib.optionalString stdenv.isDarwin ''