#12958: Properly detect if GHCi is running in MinTTY -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.2.1 Component: GHCi | Version: 8.0.1 Keywords: | Operating System: Windows Architecture: | Type of failure: Poor/confusing Unknown/Multiple | error message Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Since the user experience of GHCi is known to be rather poor when run in MinTTY (e.g., see #12720), GHCi emits a warning when it thinks it's being run in a terminal that uses MinTTY (such as Cygwin or MSYS2). [http://git.haskell.org/ghc.git/blob/17ac9b19438d5e8f6de33f99828e8c0e7c8c1129... Here] is the code that checks for this in `ghci.c`: {{{#!c if (getenv("_")) { printf("WARNING: GHCi invoked via 'ghci.exe' in *nix-like shells (cygwin-bash, in particular)\n"); printf(" doesn't handle Ctrl-C well; use the 'ghcii.sh' shell wrapper instead\n"); fflush(stdout); } }}} This is a rather shoddy way to detect MinTTY's presence, however. It's quite easy to define an environmental variable named `_` in terminals that don't use MinTTY (e.g., ConEmu). After seeing Phab:D2809, I learned of a much more reliable way to detect for MinTTY's presence: {{{#!hs queryCygwinTerminal :: Win32.HANDLE -> IO Bool queryCygwinTerminal h = do fileType <- Win32.getFileType h if fileType /= Win32.fILE_TYPE_PIPE then pure False else do fn <- getFileNameByHandle h pure (("\\cygwin-" `isPrefixOf` fn || "\\msys-" `isPrefixOf` fn) && "-pty" `isInfixOf` fn && "-master" `isSuffixOf` fn) `catch` \ (_ :: IOError) -> pure False getFileNameByHandle :: Win32.HANDLE -> IO String getFileNameByHandle h = do let sizeOfDWORD = sizeOf (undefined :: Win32.DWORD) let sizeOfWchar = sizeOf (undefined :: CWchar) -- note: implicitly assuming that DWORD has stronger alignment than wchar_t let bufSize = sizeOfDWORD + mAX_PATH * sizeOfWchar allocaBytes bufSize $ \ buf -> do getFileInformationByHandleEx h fileNameInfo buf (fromIntegral bufSize) len :: Win32.DWORD <- peek buf let len' = fromIntegral len `div` sizeOfWchar peekCWStringLen (buf `plusPtr` sizeOfDWORD, min len' mAX_PATH) getFileInformationByHandleEx :: Win32.HANDLE -> CInt -> Ptr a -> Win32.DWORD -> IO () getFileInformationByHandleEx h cls buf bufSize = do lib <- Win32.getModuleHandle (Just "kernel32.dll") ptr <- Win32.getProcAddress lib "GetFileInformationByHandleEx" let c_GetFileInformationByHandleEx = mk_GetFileInformationByHandleEx (castPtrToFunPtr ptr) Win32.failIfFalse_ "getFileInformationByHandleEx" (c_GetFileInformationByHandleEx h cls buf bufSize) type F_GetFileInformationByHandleEx a = Win32.HANDLE -> CInt -> Ptr a -> Win32.DWORD -> IO Win32.BOOL foreign import WINAPI "dynamic" mk_GetFileInformationByHandleEx :: FunPtr (F_GetFileInformationByHandleEx a) -> F_GetFileInformationByHandleEx a }}} We should port this to C and use this in `ghci.c` instead of what we have now. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12958 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler