Fix docs cron again (#8208)

Unfortunately, I missed the fact that we had our own logic for
handling process failures which resulted in uncatchable
exceptions. I’ve changed one place to use the upstream handling and
the other to call `fail` which throws an IOException like I would have
expected.

changelog_begin
changelog_end

ci/cron/src/Main.hs

@@ -43,9 +43,9 @@ shell_exit_code :: String -> IO (Exit.ExitCode, String, String)
 shell_exit_code cmd = do
     System.readCreateProcessWithExitCode (System.shell cmd) ""
 
-die :: String -> Exit.ExitCode -> String -> String -> IO a
-die cmd (Exit.ExitFailure exit) out err =
-    Exit.die $ unlines ["Subprocess:",
+die :: String -> Int -> String -> String -> IO a
+die cmd exit out err =
+    fail $ unlines ["Subprocess:",
                          cmd,
                         "failed with exit code " <> show exit <> "; output:",
                         "---",
@@ -55,15 +55,9 @@ die cmd (Exit.ExitFailure exit) out err =
                         "---",
                         err,
                         "---"]
-die _ _ _ _ = Exit.die "Type system too weak."
-
 
 shell :: String -> IO String
-shell cmd = do
-    (exit, out, err) <- shell_exit_code cmd
-    if exit == Exit.ExitSuccess
-    then return out
-    else die cmd exit out err
+shell cmd = System.readCreateProcess (System.shell cmd) ""
 
 shell_ :: String -> IO ()
 shell_ cmd = do
@@ -78,9 +72,9 @@ robustly_download_nix_packages = do
             (exit, out, err) <- shell_exit_code cmd
             case (exit, n) of
               (Exit.ExitSuccess, _) -> return ()
-              (_, 0) -> die cmd exit out err
+              (Exit.ExitFailure exit, 0) -> die cmd exit out err
               _ | "unexpected end-of-file" `Data.List.isInfixOf` err -> h (n - 1)
-              _ -> die cmd exit out err
+              (Exit.ExitFailure exit, _) -> die cmd exit out err
 
 add_github_contact_header :: HTTP.Request -> HTTP.Request
 add_github_contact_header req =