add abstract closed families

grammar/type.js

@@ -235,11 +235,19 @@ module.exports = {
 
   _tyfam_equations: $ => layout($, alias($._type_instance, $.equation)),
 
+  /**
+   * This syntax is valid in `.hs-boot` files.
+   */
+  abstract_family: $ => layout_single($, '..'),
+
   decl_tyfam: $ => seq(
     'type',
     'family',
     $._tyfam,
-    optional_where_as($, $._tyfam_equations, $.equations),
+    optional_where($, choice(
+      alias($._tyfam_equations, $.equations),
+      $.abstract_family,
+    )),
   ),
 
   // ------------------------------------------------------------------------

grammar/util.js

@@ -31,6 +31,15 @@ semis = ($, rule) => sep1(semi($), rule),
 // layout
 // ------------------------------------------------------------------------
 
+/**
+ * More general variant of `layout_sort`.
+ */
+layout_sort_single = ($, start, rule) => seq(
+  choice(start, alias($._cmd_layout_start_explicit, '{')),
+  rule,
+  $._layout_end,
+)
+
 /**
  * Wrap a repeated rule in a layout.
  * This is used for `where`, `let`, `of`, `if` and `do`, and the toplevel module.
@@ -47,7 +56,16 @@ layout_sort = ($, start, rule) => seq(
     semi_opt($),
   )),
   $._layout_end,
-),
+)
+
+/**
+ * Same as `layout`, but using `layout_sort_single`.
+ * This is necessary for braces without repeating layout elements.
+ * Usually it is enough to just use `braces` for this (e.g. records), but if the rule is in a choice with a full
+ * layout, we need to allow the layout start token since the scanner emits that unconditionally based on preceding
+ * tokens.
+ */
+layout_single = ($, rule) => layout_sort_single($, $._cmd_layout_start, rule)
 
 /**
  * Alias for `layout_sort` using the common layout type for the start token, which corresponds to declarations and GADT
@@ -90,7 +108,10 @@ module.exports = {
   sep1,
   sep2,
   semis,
+  layout_sort,
+  layout_sort_single,
   layout,
+  layout_single,
   unboxed,
   unboxed_tuple,
   unboxed_sum,

test/corpus/family.txt

@@ -802,3 +802,20 @@ type instance ∀ a . A a = a
             (type_variable))))
       (type_name
         (type_variable)))))
+
+================================================================================
+family: abstract closed family, hs-boot
+================================================================================
+
+type family A where
+  ..
+
+--------------------------------------------------------------------------------
+
+(haskell
+  (declarations
+    (type_family
+      (head
+        (type_name
+          (type)))
+      (abstract_family))))