Allow if-expression for discriminant constraints

The rule (not visible in the RM grammar) is that
if we have a single positional discriminant, we
can omit the extra pair of parenthesis.

grammar.js

@@ -107,6 +107,7 @@ module.exports = grammar({
       [$.attribute_definition_clause, $._attribute_reference],
       [$.component_choice_list, $.discrete_choice],
       [$.component_choice_list, $.positional_array_aggregate],
+      [$.discriminant_association, $._parenthesized_expression],
    ],
    inline: $ => [
       $._name_not_function_call,
@@ -413,11 +414,17 @@ module.exports = grammar({
          field('subtype_mark', $._name_not_function_call),
          optional($._constraint),
       ),
-      discriminant_constraint: $ => seq(    // RM 3.7.1
+      discriminant_constraint: $ => choice(    // RM 3.7.1
+         //  If we have a single positional discriminant, it can be an
+         //  if-expression without additional parenthesis  "A : R (if cond then
+         //  1 else 0)" but otherwise extra parenthesis are needed.
+         $._parenthesized_expression,   // not in ARM
+         seq(
             '(',
             comma_separated_list_of($.discriminant_association),
             ')',
          ),
+      ),
       discriminant_association: $ => seq(  // RM 3.7.1
          optional(seq(
             list_of('|', $._name_for_component_choice),

src/grammar.json

@@ -1868,6 +1868,13 @@
       ]
     },
     "discriminant_constraint": {
+      "type": "CHOICE",
+      "members": [
+        {
+          "type": "SYMBOL",
+          "name": "_parenthesized_expression"
+        },
+        {
           "type": "SEQ",
           "members": [
             {
@@ -1904,6 +1911,8 @@
               "value": ")"
             }
           ]
+        }
+      ]
     },
     "discriminant_association": {
       "type": "SEQ",
@@ -15331,6 +15340,10 @@
     [
       "component_choice_list",
       "positional_array_aggregate"
+    ],
+    [
+      "discriminant_association",
+      "_parenthesized_expression"
     ]
   ],
   "precedences": [],

src/node-types.json

@@ -2588,9 +2588,29 @@
       "multiple": true,
       "required": true,
       "types": [
+        {
+          "type": "case_expression",
+          "named": true
+        },
+        {
+          "type": "declare_expression",
+          "named": true
+        },
         {
           "type": "discriminant_association",
           "named": true
+        },
+        {
+          "type": "expression",
+          "named": true
+        },
+        {
+          "type": "if_expression",
+          "named": true
+        },
+        {
+          "type": "quantified_expression",
+          "named": true
         }
       ]
     }

test/corpus/records.txt

@@ -508,18 +508,19 @@ end;
       (handled_sequence_of_statements
         (null_statement)))))
 
-========================
+================================================================================
 Record with discr
-========================
+================================================================================
 
 procedure Proc is
    type Rec (Len : Natural) is null record;
    R : Rec (0);
+   R2 : Rec (if N > 0 then 1 else 0);
 begin
    null;
 end;
 
---------
+--------------------------------------------------------------------------------
 
 (compilation
   (compilation_unit
@@ -540,7 +541,23 @@ end;
           (identifier)
           (identifier)
           (discriminant_constraint
-            (discriminant_association
+            (expression
+              (term
+                (numeric_literal)))))
+        (object_declaration
+          (identifier)
+          (identifier)
+          (discriminant_constraint
+            (if_expression
+              (expression
+                (term
+                  (identifier))
+                (relational_operator)
+                (term
+                  (numeric_literal)))
+              (expression
+                (term
+                  (numeric_literal)))
               (expression
                 (term
                   (numeric_literal)))))))