Preserve as-parsed arrow type for HsUnrestrictedArrow

When linear types are disabled, HsUnrestrictedArrow is treated as
HslinearArrow.

Move this adjustment into the type checking phase, so that the parsed
source accurately represents the source as parsed.

Closes #18791

5 files changed, 71 insertions, 2 deletions

diff --git a/testsuite/tests/haddock/should_compile_flag_haddock/T17544_kw.stderr b/testsuite/tests/haddock/should_compile_flag_haddock/T17544_kw.stderr
index 146b686357..2681ca9fb9 100644
--- a/testsuite/tests/haddock/should_compile_flag_haddock/T17544_kw.stderr
+++ b/testsuite/tests/haddock/should_compile_flag_haddock/T17544_kw.stderr
@@ -85,7 +85,7 @@
           (Nothing)
           (PrefixCon
            [(HsScaled
-             (HsLinearArrow)
+             (HsUnrestrictedArrow)
              ({ T17544_kw.hs:19:18-19 }
               (HsTupleTy
                (NoExtField)
diff --git a/testsuite/tests/parser/should_compile/DumpRenamedAst.stderr b/testsuite/tests/parser/should_compile/DumpRenamedAst.stderr
index 220a2ecd0b..4b5c58d43b 100644
--- a/testsuite/tests/parser/should_compile/DumpRenamedAst.stderr
+++ b/testsuite/tests/parser/should_compile/DumpRenamedAst.stderr
@@ -370,7 +370,7 @@
                (Nothing)
                (PrefixCon
                 [(HsScaled
-                  (HsLinearArrow)
+                  (HsUnrestrictedArrow)
                   ({ DumpRenamedAst.hs:19:10-34 }
                    (HsParTy
                     (NoExtField)
diff --git a/testsuite/tests/printer/T18791.hs b/testsuite/tests/printer/T18791.hs
new file mode 100644
index 0000000000..c79204aa55
--- /dev/null
+++ b/testsuite/tests/printer/T18791.hs
@@ -0,0 +1,5 @@
+{-# LANGUAGE GADTs #-}
+module T18791 where
+
+data T where
+  MkT :: Int -> T
diff --git a/testsuite/tests/printer/T18791.stderr b/testsuite/tests/printer/T18791.stderr
new file mode 100644
index 0000000000..00f8efc801
--- /dev/null
+++ b/testsuite/tests/printer/T18791.stderr
@@ -0,0 +1,63 @@
+
+==================== Parser AST ====================
+
+({ T18791.hs:1:1 }
+ (HsModule
+  (VirtualBraces
+   (1))
+  (Just
+   ({ T18791.hs:2:8-13 }
+    {ModuleName: T18791}))
+  (Nothing)
+  []
+  [({ T18791.hs:(4,1)-(5,17) }
+    (TyClD
+     (NoExtField)
+     (DataDecl
+      (NoExtField)
+      ({ T18791.hs:4:6 }
+       (Unqual
+        {OccName: T}))
+      (HsQTvs
+       (NoExtField)
+       [])
+      (Prefix)
+      (HsDataDefn
+       (NoExtField)
+       (DataType)
+       ({ <no location info> }
+        [])
+       (Nothing)
+       (Nothing)
+       [({ T18791.hs:5:3-17 }
+         (ConDeclGADT
+          (NoExtField)
+          [({ T18791.hs:5:3-5 }
+            (Unqual
+             {OccName: MkT}))]
+          ({ T18791.hs:5:10-17 }
+           (False))
+          []
+          (Nothing)
+          (PrefixCon
+           [(HsScaled
+             (HsUnrestrictedArrow)
+             ({ T18791.hs:5:10-12 }
+              (HsTyVar
+               (NoExtField)
+               (NotPromoted)
+               ({ T18791.hs:5:10-12 }
+                (Unqual
+                 {OccName: Int})))))])
+          ({ T18791.hs:5:17 }
+           (HsTyVar
+            (NoExtField)
+            (NotPromoted)
+            ({ T18791.hs:5:17 }
+             (Unqual
+              {OccName: T}))))
+          (Nothing)))]
+       ({ <no location info> }
+        [])))))]
+  (Nothing)
+  (Nothing)))
\ No newline at end of file
diff --git a/testsuite/tests/printer/all.T b/testsuite/tests/printer/all.T
index 9e62577855..2c605be5b8 100644
--- a/testsuite/tests/printer/all.T
+++ b/testsuite/tests/printer/all.T
@@ -58,3 +58,4 @@ test('T14343b', normal, compile_fail, [''])
 test('T15761', normal, compile_fail, [''])
 test('T18052a', normal, compile,
      ['-ddump-simpl -ddump-types -dno-typeable-binds -dsuppress-uniques'])
+test('T18791', normal, compile, ['-ddump-parsed-ast'])