;dev:cli: to help run's command line parsing, double the first -- [#2328]

So that when cmdargs eats it, another remains.

hledger/Hledger/Cli.hs

@@ -235,15 +235,24 @@ main = withGhcDebug' $ do
   -- cmdname = the full unabbreviated command name, or ""
   -- confcmdargs = arguments for the subcommand, from config file
 
+  let
+    -- | cmdargs eats the first double-dash (--) argument, causing problems for
+    -- the run command. To work around it, we'll insert another.
+    -- This doesn't break anything that we know of.
+    doubleDoubleDash args
+      | "--" `elem` args = let (as,bs) = break (=="--") args in as <> ["--"] <> bs
+      | otherwise = args
+
   -- Do some argument preprocessing to help cmdargs
   cliargs <- getArgs
     >>= expandArgsAt         -- interpolate @ARGFILEs
     <&> replaceNumericFlags  -- convert -NUM to --depth=NUM
+    <&> doubleDoubleDash     -- repeat the -- arg as a cmdargs workaround
   let
     (clicmdarg, cliargswithoutcmd, cliargswithcmdfirst) = moveFlagsAfterCommand cliargs
     cliargswithcmdfirstwithoutclispecific = dropCliSpecificOpts cliargswithcmdfirst
     (cliargsbeforecmd, cliargsaftercmd) = second (drop 1) $ break (==clicmdarg) cliargs
-  dbgIO "cli args" cliargs
+  dbgIO "cli args, with some preprocessing like doubling --" cliargs
   dbg1IO "cli args with options moved after command, if any" cliargswithcmdfirst
   dbgIO "cli command argument found" clicmdarg
   dbgIO "cli args before command"    cliargsbeforecmd