Split HsConDecl{H98,GADT}Details

Haskell98 and GADT constructors both use `HsConDeclDetails`, which includes
`InfixCon`. But `InfixCon` is never used for GADT constructors, which results
in an awkward unrepresentable state. This removes the unrepresentable state by:

* Renaming the existing `HsConDeclDetails` synonym to `HsConDeclH98Details`,
  which emphasizes the fact that it is now only used for Haskell98-style data
  constructors, and
* Creating a new `HsConDeclGADTDetails` data type with `PrefixConGADT` and
  `RecConGADT` constructors that closely resemble `PrefixCon` and `InfixCon`
  in `HsConDeclH98Details`. The key difference is that `HsConDeclGADTDetails`
  lacks any way to represent infix constructors.

The rest of the patch is refactoring to accommodate the new structure of
`HsConDecl{H98,GADT}Details`. Some highlights:

* The `getConArgs` and `hsConDeclArgTys` functions have been removed, as
  there is no way to implement these functions uniformly for all
  `ConDecl`s. For the most part, their previous call sites now
  pattern match on the `ConDecl`s directly and do different things for
  `ConDeclH98`s and `ConDeclGADT`s.

  I did introduce one new function to make the transition easier:
  `getRecConArgs_maybe`, which extracts the arguments from a `RecCon(GADT)`.
  This is still possible since `RecCon(GADT)`s still use the same representation
  in both `HsConDeclH98Details` and `HsConDeclGADTDetails`, and since the
  pattern that `getRecConArgs_maybe` implements is used in several places,
  I thought it worthwhile to factor it out into its own function.
* Previously, the `con_args` fields in `ConDeclH98` and `ConDeclGADT` were
  both of type `HsConDeclDetails`. Now, the former is of type
  `HsConDeclH98Details`, and the latter is of type `HsConDeclGADTDetails`,
  which are distinct types. As a result, I had to rename the `con_args` field
  in `ConDeclGADT` to `con_g_args` to make it typecheck.

  A consequence of all this is that the `con_args` field is now partial, so
  using `con_args` as a top-level field selector is dangerous. (Indeed, Haddock
  was using `con_args` at the top-level, which caused it to crash at runtime
  before I noticed what was wrong!) I decided to add a disclaimer in the 9.2.1
  release notes to advertise this pitfall.

Fixes #18844. Bumps the `haddock` submodule.

5 files changed, 14 insertions, 12 deletions

diff --git a/testsuite/tests/haddock/should_compile_flag_haddock/T17544.stderr b/testsuite/tests/haddock/should_compile_flag_haddock/T17544.stderr
index 9af02d8c66..2e5452129b 100644
--- a/testsuite/tests/haddock/should_compile_flag_haddock/T17544.stderr
+++ b/testsuite/tests/haddock/should_compile_flag_haddock/T17544.stderr
@@ -386,7 +386,7 @@
                  (False))
                 []
                 (Nothing)
-                (PrefixCon
+                (PrefixConGADT
                  [])
                 ({ T17544.hs:25:13-18 }
                  (HsAppTy
@@ -522,7 +522,7 @@
                  (False))
                 []
                 (Nothing)
-                (PrefixCon
+                (PrefixConGADT
                  [])
                 ({ T17544.hs:31:13-18 }
                  (HsAppTy
@@ -658,7 +658,7 @@
                  (False))
                 []
                 (Nothing)
-                (PrefixCon
+                (PrefixConGADT
                  [])
                 ({ T17544.hs:37:13-18 }
                  (HsAppTy
@@ -794,7 +794,7 @@
                  (False))
                 []
                 (Nothing)
-                (PrefixCon
+                (PrefixConGADT
                  [])
                 ({ T17544.hs:43:13-18 }
                  (HsAppTy
@@ -930,7 +930,7 @@
                  (False))
                 []
                 (Nothing)
-                (PrefixCon
+                (PrefixConGADT
                  [])
                 ({ T17544.hs:49:13-18 }
                  (HsAppTy
@@ -1066,7 +1066,7 @@
                  (False))
                 []
                 (Nothing)
-                (PrefixCon
+                (PrefixConGADT
                  [])
                 ({ T17544.hs:55:14-20 }
                  (HsAppTy
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 ccba2caf27..d1ff09f56c 100644
--- a/testsuite/tests/haddock/should_compile_flag_haddock/T17544_kw.stderr
+++ b/testsuite/tests/haddock/should_compile_flag_haddock/T17544_kw.stderr
@@ -39,7 +39,7 @@
            (False))
           []
           (Nothing)
-          (PrefixCon
+          (PrefixConGADT
            [])
           ({ T17544_kw.hs:16:18-20 }
            (HsTyVar
@@ -83,7 +83,7 @@
            (False))
           []
           (Nothing)
-          (PrefixCon
+          (PrefixConGADT
            [(HsScaled
              (HsUnrestrictedArrow
               (NormalSyntax))
diff --git a/testsuite/tests/parser/should_compile/DumpRenamedAst.stderr b/testsuite/tests/parser/should_compile/DumpRenamedAst.stderr
index 599d369ff5..e869299a76 100644
--- a/testsuite/tests/parser/should_compile/DumpRenamedAst.stderr
+++ b/testsuite/tests/parser/should_compile/DumpRenamedAst.stderr
@@ -374,7 +374,7 @@
                 (False))
                []
                (Nothing)
-               (PrefixCon
+               (PrefixConGADT
                 [(HsScaled
                   (HsUnrestrictedArrow
                    (NormalSyntax))
diff --git a/testsuite/tests/parser/should_compile/T15323.stderr b/testsuite/tests/parser/should_compile/T15323.stderr
index 0e2734dd48..8539599660 100644
--- a/testsuite/tests/parser/should_compile/T15323.stderr
+++ b/testsuite/tests/parser/should_compile/T15323.stderr
@@ -72,7 +72,7 @@
                    ({ T15323.hs:6:35 }
                     (Unqual
                      {OccName: v}))))))))]))
-          (PrefixCon
+          (PrefixConGADT
            [])
           ({ T15323.hs:6:41-54 }
            (HsAppTy
diff --git a/testsuite/tests/printer/T18791.stderr b/testsuite/tests/printer/T18791.stderr
index 09aee04678..e245ef0fbe 100644
--- a/testsuite/tests/printer/T18791.stderr
+++ b/testsuite/tests/printer/T18791.stderr
@@ -39,7 +39,7 @@
            (False))
           []
           (Nothing)
-          (PrefixCon
+          (PrefixConGADT
            [(HsScaled
              (HsUnrestrictedArrow
               (NormalSyntax))
@@ -61,4 +61,6 @@
        ({ <no location info> }
         [])))))]
   (Nothing)
-  (Nothing)))
\ No newline at end of file
+  (Nothing)))
+
+