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Merijn Verstraaten authored
Summary: As proposed by Richard on Trac. This patch adds a new flag -fdefer-typed-holes and changes the semantics of the -fno-warn-typed-holes flag. To summarise, by default GHC has typed holes enabled and produces a compile error when it encounters a typed hole. When -fdefer-type-errors OR -fdefer-typed-holes is enabled, hole errors are converted to warnings and result in runtime errors when evaluated. The warning flag -fwarn-typed-holes is on by default. Without -fdefer-type-errors or -fdefer-typed-holes this flag is a no-op, since typed holes are an error under these conditions. If either of the defer flags are enabled (converting typed hole errors into warnings) the -fno-warn-typed-holes flag disables the warnings. This means compilation silently succeeds and evaluating a hole will produce a runtime error. The rationale behind allowing typed holes warnings to be silenced is that tools like Syntastic for vim highlight warnings and hole warnings may be undesirable. Signed-off-by: Merijn Verstraaten <merijn@inconsistent.nl> Test Plan: validate Reviewers: austin, simonpj, thomie Reviewed By: simonpj, thomie Subscribers: Fuuzetsu, thomie, carter Differential Revision: https://phabricator.haskell.org/D442 GHC Trac Issues: #9497 Conflicts: compiler/main/DynFlags.hs
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