V713-005: Improve get_aspect for pragma Convention & co.

ada/ast.py

@@ -9645,6 +9645,26 @@ def xref_equation():
             )
         )
 
+    @langkit_property(return_type=T.Expr.entity)
+    def value_expr():
+        """
+        Return the expression representing the "value" of this pragma, which
+        will be used to fill the ``value`` field of the ``Aspect`` struct
+        returned by calls to ``get_aspect``. This property doesn't make sense
+        for all pragmas but tries to give the most reasonable answer, and in
+        particular tries to match what ``get_aspect`` would return if the
+        pragma was replaced by its equivalent aspect.
+        For example, on ``pragma Convention (C, X)``, the returned value is
+        ``C`` because one would write ``X : Integer with Convention => C``.
+        """
+        return If(
+            Entity.id.name_symbol.any_of(
+                'Import', 'Export', 'Interface', 'Convention'
+            ),
+            Entity.args.at(0).assoc_expr,
+            Entity.args._.at(1)._.assoc_expr
+        )
+
     @langkit_property(return_type=T.Name.entity.array)
     def associated_entity_names():
         return Cond(
@@ -15967,7 +15987,7 @@ def get_aspect_impl(name=Symbol):
         """
         return Entity.get_pragma(name).then(
             lambda p: Aspect.new(
-                exists=True, node=p, value=p.args._.at(1)._.assoc_expr
+                exists=True, node=p, value=p.value_expr
             )
         )._or(Entity.basic_decl.get_aspect_assoc(name).then(
             lambda aa: Aspect.new(exists=True, node=aa, value=aa.expr)

testsuite/tests/properties/get_aspect_pragma_convention/test.adb

@@ -0,0 +1,12 @@
+procedure Test is
+   X : Integer := 0
+      with Convention => C;
+   --% node.p_get_aspect("Convention").value
+
+   Y : Integer := 0;
+   --% node.p_get_aspect("Convention").value
+   pragma Convention (C, Y);
+begin
+   null;
+end Test;
+

testsuite/tests/properties/get_aspect_pragma_convention/test.out

@@ -0,0 +1,11 @@
+Working on node <ObjectDecl ["X"] test.adb:2:4-3:28>
+====================================================
+
+Eval 'node.p_get_aspect("Convention").value'
+Result: <Id "C" test.adb:3:26-3:27>
+
+Working on node <ObjectDecl ["Y"] test.adb:6:4-6:21>
+====================================================
+
+Eval 'node.p_get_aspect("Convention").value'
+Result: <Id "C" test.adb:8:23-8:24>

testsuite/tests/properties/get_aspect_pragma_convention/test.yaml

@@ -0,0 +1,2 @@
+driver: inline-playground
+input_sources: [test.adb]

user_manual/changes/V713-005.yaml

@@ -0,0 +1,21 @@
+type: bugfix
+title: Improve ``get_aspect`` for ``pragma Convention``
+description: |
+    Previously, calling ``get_aspect("Convention")`` on the declaration of
+    ``X`` in the snippet below would return an ``Aspect`` struct whose
+    ``value`` field would contain the identifier ``X``:
+
+    ..code:: ada
+
+        X : Integer;
+        pragma Convention (C, X);
+
+    It will now return ``C``, because that's what would have been returned if
+    one had used the Ada 2012 aspect notation instead:
+
+    ..code:: ada
+
+        X : Integer
+            with Convention => C;
+
+date: 2022-09-12