[Git][ghc/ghc][wip/jeltsch/querying-newline-modes] Add an operation `System.IO.hGetNewlineMode`

22 Dec 2025

Wolfgang Jeltsch pushed to branch wip/jeltsch/querying-newline-modes at Glasgow Haskell Compiler / GHC


Commits:
9c8a9fda by Wolfgang Jeltsch at 2025-12-22T15:05:53+02:00
Add an operation `System.IO.hGetNewlineMode`

This commit also contains some small code and documentation changes for
related operations, for the sake of consistency.

- - - - -


8 changed files:

- libraries/base/changelog.md
- libraries/base/src/System/IO.hs
- libraries/ghc-internal/src/GHC/Internal/IO/Handle.hs
- libraries/ghc-internal/src/GHC/Internal/System/IO.hs
- testsuite/tests/interface-stability/base-exports.stdout
- testsuite/tests/interface-stability/base-exports.stdout-javascript-unknown-ghcjs
- testsuite/tests/interface-stability/base-exports.stdout-mingw32
- testsuite/tests/interface-stability/base-exports.stdout-ws-32


Changes:

=====================================
libraries/base/changelog.md
=====================================
@@ -1,6 +1,7 @@
 # Changelog for [`base` package](http://hackage.haskell.org/package/base)
 
 ## 4.23.0.0 *TBA*
+  * Add `System.IO.hGetNewlineMode`. ([CLC proposal #370](https://github.com/haskell/core-libraries-committee/issues/370))
   * Add `{-# WARNING in "x-partial" #-}` to `Data.List.{init,last}`.
     Use `{-# OPTIONS_GHC -Wno-x-partial #-}` to disable it.
     ([CLC proposal #87](https://github.com/haskell/core-libraries-committee/issues/292))


=====================================
libraries/base/src/System/IO.hs
=====================================
@@ -175,6 +175,7 @@ module System.IO
      -- Binary-mode 'Handle's do no newline translation at all.
 
      hSetNewlineMode,
+     hGetNewlineMode,
      Newline(..),
      nativeNewline,
      NewlineMode(..),


=====================================
libraries/ghc-internal/src/GHC/Internal/IO/Handle.hs
=====================================
@@ -40,7 +40,7 @@ module GHC.Internal.IO.Handle (
    hIsOpen, hIsClosed, hIsReadable, hIsWritable, hGetBuffering, hIsSeekable,
    hSetEcho, hGetEcho, hIsTerminalDevice,
 
-   hSetNewlineMode, Newline(..), NewlineMode(..), nativeNewline,
+   hSetNewlineMode, hGetNewlineMode, Newline(..), NewlineMode(..), nativeNewline,
    noNewlineTranslation, universalNewlineMode, nativeNewlineMode,
 
    hShow,
@@ -238,7 +238,7 @@ hSetBuffering handle mode =
           return Handle__{ haBufferMode = mode,.. }
 
 -- -----------------------------------------------------------------------------

--- hSetEncoding
+-- Setting and getting the text encoding
 
 -- | The action 'hSetEncoding' @hdl@ @encoding@ changes the text encoding
 -- for the handle @hdl@ to @encoding@.  The default encoding when a 'Handle' is
@@ -624,16 +624,24 @@ hSetBinaryMode handle bin =
                           haOutputNL = outputNL nl, .. }
 
 -- -----------------------------------------------------------------------------
--- hSetNewlineMode
+-- Setting and getting the newline mode
 
--- | Set the 'NewlineMode' on the specified 'Handle'.  All buffered
+-- | Set the 'NewlineMode' for the specified 'Handle'.  All buffered
 -- data is flushed first.
 hSetNewlineMode :: Handle -> NewlineMode -> IO ()
-hSetNewlineMode handle NewlineMode{ inputNL=i, outputNL=o } =
+hSetNewlineMode handle NewlineMode{..} =
   withAllHandles__ "hSetNewlineMode" handle $ \h_@Handle__{} ->
     do
          flushBuffer h_
-         return h_{ haInputNL=i, haOutputNL=o }
+         return h_{ haInputNL = inputNL, haOutputNL = outputNL }
+
+-- | Return the current 'NewlineMode' for the specified 'Handle'.
+--
+-- @since 4.23.0.0
+hGetNewlineMode :: Handle -> IO NewlineMode
+hGetNewlineMode hdl =
+  withHandle_ "hGetNewlineMode" hdl $ \h_@Handle__{..} ->
+    return NewlineMode{ inputNL = haInputNL, outputNL = haOutputNL }
 
 -- -----------------------------------------------------------------------------
 -- Duplicating a Handle


=====================================
libraries/ghc-internal/src/GHC/Internal/System/IO.hs
=====================================
@@ -214,6 +214,7 @@ module GHC.Internal.System.IO (
     -- Binary-mode 'Handle's do no newline translation at all.
     --
     hSetNewlineMode,
+    hGetNewlineMode,
     Newline(..), nativeNewline,
     NewlineMode(..),
     noNewlineTranslation, universalNewlineMode, nativeNewlineMode,


=====================================
testsuite/tests/interface-stability/base-exports.stdout
=====================================
@@ -10263,6 +10263,7 @@ module System.IO where
   hGetEcho :: Handle -> IO GHC.Internal.Types.Bool
   hGetEncoding :: Handle -> IO (GHC.Internal.Maybe.Maybe TextEncoding)
   hGetLine :: Handle -> IO GHC.Internal.Base.String
+  hGetNewlineMode :: Handle -> IO NewlineMode
   hGetPosn :: Handle -> IO HandlePosn
   hIsClosed :: Handle -> IO GHC.Internal.Types.Bool
   hIsEOF :: Handle -> IO GHC.Internal.Types.Bool


=====================================
testsuite/tests/interface-stability/base-exports.stdout-javascript-unknown-ghcjs
=====================================
@@ -13309,6 +13309,7 @@ module System.IO where
   hGetEcho :: Handle -> IO GHC.Internal.Types.Bool
   hGetEncoding :: Handle -> IO (GHC.Internal.Maybe.Maybe TextEncoding)
   hGetLine :: Handle -> IO GHC.Internal.Base.String
+  hGetNewlineMode :: Handle -> IO NewlineMode
   hGetPosn :: Handle -> IO HandlePosn
   hIsClosed :: Handle -> IO GHC.Internal.Types.Bool
   hIsEOF :: Handle -> IO GHC.Internal.Types.Bool


=====================================
testsuite/tests/interface-stability/base-exports.stdout-mingw32
=====================================
@@ -10543,6 +10543,7 @@ module System.IO where
   hGetEcho :: Handle -> IO GHC.Internal.Types.Bool
   hGetEncoding :: Handle -> IO (GHC.Internal.Maybe.Maybe TextEncoding)
   hGetLine :: Handle -> IO GHC.Internal.Base.String
+  hGetNewlineMode :: Handle -> IO NewlineMode
   hGetPosn :: Handle -> IO HandlePosn
   hIsClosed :: Handle -> IO GHC.Internal.Types.Bool
   hIsEOF :: Handle -> IO GHC.Internal.Types.Bool


=====================================
testsuite/tests/interface-stability/base-exports.stdout-ws-32
=====================================
@@ -10263,6 +10263,7 @@ module System.IO where
   hGetEcho :: Handle -> IO GHC.Internal.Types.Bool
   hGetEncoding :: Handle -> IO (GHC.Internal.Maybe.Maybe TextEncoding)
   hGetLine :: Handle -> IO GHC.Internal.Base.String
+  hGetNewlineMode :: Handle -> IO NewlineMode
   hGetPosn :: Handle -> IO HandlePosn
   hIsClosed :: Handle -> IO GHC.Internal.Types.Bool
   hIsEOF :: Handle -> IO GHC.Internal.Types.Bool



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/9c8a9fda71b3ca2acf730da4446de939...

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View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/9c8a9fda71b3ca2acf730da4446de939...
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Wolfgang Jeltsch (＠jeltsch)

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