Confusing error when no Shakefile exists

[ncfavier]

Running shake inside a directory without a Shakefile results in the confusing error

shake: Could not find `build.ninja'
CallStack (from HasCallStack):
  errorIO, called at src/Run.hs:43:48 in shake-0.19.8-5dTtoKBl3Mu6WvgsSKPzeR-shake:Run
HasCallStack backtrace:
  collectBacktraces, called at libraries/ghc-internal/src/GHC/Internal/Exception.hs:169:13 in ghc-internal:GHC.Internal.Exception
  toExceptionWithBacktrace, called at libraries/ghc-internal/src/GHC/Internal/IO.hs:260:11 in ghc-internal:GHC.Internal.IO
  throwIO, called at libraries/ghc-internal/src/GHC/Internal/Control/Exception/Base.hs:195:43 in ghc-internal:GHC.Internal.Control.Exception.Base

This should instead report that there is no Shakefile.