Recognize file-header pragmas in GHCi (#21507)

5 files changed, 40 insertions, 0 deletions

diff --git a/docs/users_guide/9.6.1-notes.rst b/docs/users_guide/9.6.1-notes.rst
index 17637ee0f7..6730ad2b0c 100644
--- a/docs/users_guide/9.6.1-notes.rst
+++ b/docs/users_guide/9.6.1-notes.rst
@@ -66,6 +66,21 @@ Compiler
 - The :extension:`TypeInType` is now marked as deprecated. Its meaning has been included 
   in :extension:`PolyKinds` and :extension:`DataKinds`.
 
+
+GHCi
+~~~~
+
+- GHCi will now accept any file-header pragmas it finds, such as 
+  ``{-# OPTIONS_GHC ... #-}`` and ``{-# LANGUAGE ... #-}`` (see :ref:`pragmas`).  For example,
+  instead of using :ghci-cmd:`:set` to enable :ghc-flag:`-Wmissing-signatures`,
+  you could instead write:
+
+  .. code-block:: none
+
+      ghci> {-# OPTIONS_GHC -Wmissing-signatures #-}
+
+This can be convenient when pasting large multi-line blocks of code into GHCi.
+
 ``base`` library
 ~~~~~~~~~~~~~~~~
 
diff --git a/docs/users_guide/ghci.rst b/docs/users_guide/ghci.rst
index cb09eab3ff..4a9f75e9bf 100644
--- a/docs/users_guide/ghci.rst
+++ b/docs/users_guide/ghci.rst
@@ -3173,6 +3173,15 @@ example, to turn on :ghc-flag:`-Wmissing-signatures`, you would say:
 
     ghci> :set -Wmissing-signatures
 
+GHCi will also accept any file-header pragmas it finds, such as 
+``{-# OPTIONS_GHC ... #-}`` and ``{-# LANGUAGE ... #-}`` (see :ref:`pragmas`).  For example,
+instead of using :ghci-cmd:`:set` to enable :ghc-flag:`-Wmissing-signatures`,
+you could instead write:
+
+.. code-block:: none
+
+    ghci> {-# OPTIONS_GHC -Wmissing-signatures #-}
+
 Any GHC command-line option that is designated as dynamic (see the table
 in :ref:`flag-reference`), may be set using :ghci-cmd:`:set`. To unset an
 option, you can set the reverse option:
diff --git a/ghc/GHCi/UI.hs b/ghc/GHCi/UI.hs
index b19939e9ac..4eb9cd9324 100644
--- a/ghc/GHCi/UI.hs
+++ b/ghc/GHCi/UI.hs
@@ -78,6 +78,7 @@ import GHC.Types.Name.Reader as RdrName ( getGRE_NameQualifier_maybes, getRdrNam
 import GHC.Types.SrcLoc as SrcLoc
 import qualified GHC.Parser.Lexer as Lexer
 import GHC.Parser.Header ( toArgs )
+import qualified GHC.Parser.Header as Header
 import GHC.Types.PkgQual
 
 import GHC.Unit
@@ -1249,6 +1250,9 @@ runStmt input step = do
   let source = progname st
   let line = line_number st
 
+  -- Add any LANGUAGE/OPTIONS_GHC pragmas we find find.
+  set_pragmas pflags
+
   if | GHC.isStmt pflags input -> do
          hsc_env <- GHC.getSession
          mb_stmt <- liftIO (runInteractiveHsc hsc_env (hscParseStmtWithLocation source line input))
@@ -1282,6 +1286,12 @@ runStmt input step = do
 
     run_imports imports = mapM_ (addImportToContext . unLoc) imports
 
+    set_pragmas pflags =
+      let stringbuf = stringToStringBuffer input
+          (_msgs, loc_opts) = Header.getOptions pflags stringbuf "<interactive>"
+          opts = unLoc <$> loc_opts
+      in setOptions opts
+
     run_stmt :: GhciMonad m => GhciLStmt GhcPs -> m (Maybe GHC.ExecResult)
     run_stmt stmt = do
            m_result <- GhciMonad.runStmt stmt input step
diff --git a/testsuite/tests/ghci/scripts/T21507.script b/testsuite/tests/ghci/scripts/T21507.script
new file mode 100644
index 0000000000..7c5d3df4cf
--- /dev/null
+++ b/testsuite/tests/ghci/scripts/T21507.script
@@ -0,0 +1,5 @@
+:{
+{-# LANGUAGE TypeFamilies #-}
+type family T21507 a where
+  T21507 a = a
+:}
diff --git a/testsuite/tests/ghci/scripts/all.T b/testsuite/tests/ghci/scripts/all.T
index 9e7ca144a6..0ad107c4e4 100755
--- a/testsuite/tests/ghci/scripts/all.T
+++ b/testsuite/tests/ghci/scripts/all.T
@@ -368,3 +368,4 @@ test('T21110', [extra_files(['T21110A.hs'])], ghci_script,
                 ['T21110.script'])
 test('T17830', [filter_stdout_lines(r'======.*')], ghci_script, ['T17830.script'])
 test('T21294a', normal, ghci_script, ['T21294a.script'])
+test('T21507', normal, ghci_script, ['T21507.script'])