Add support for Deref attribute

ada/nodes.lkt

@@ -12676,6 +12676,7 @@ class AttributeRef: Name {
         elif rel_name == s"Index" then self.index_equation()
         elif rel_name == s"Abort_Signal" then %eq(node.ref_var(), node.std_entity(s"abort_signal_")) and %eq(node.type_var(), null[Entity[BaseTypeDecl]])
         elif rel_name in s"Has_Same_Storage" | s"Overlaps_Storage" then self.storage_equation()
+        elif rel_name == s"Deref" then self.deref_equation()
         else raise[Equation] PropertyError("Unhandled attribute")
     }
 
@@ -12942,6 +12943,18 @@ class AttributeRef: Name {
         self.prefix.sub_equation() and %eq(node.type_var(), typ)
     }
 
+    |" Return the xref equation for the ``Deref`` attribute.
+    @with_dynvars(env, origin, entry_point)
+    fun deref_equation(): Equation =
+        self.prefix.xref_type_equation
+        and %eq(node.type_var, node.prefix.ref_var)
+        and self.args?[0].do(
+            (arg) => arg.expr.sub_equation
+            and %eq(arg.expr.expected_type_var, node.system_address_type)
+            and arg.expr.matches_expected_type,
+            default_val=%false
+        )
+
     |" Return the xref equation for the ``Has_Same_Storage`` and
     |" ``Overlaps_Storage`` attributes.
     @with_dynvars(env, origin, entry_point)
@@ -14862,7 +14875,8 @@ class Identifier: BaseId implements TokenNode {
     # For other args, we deactivate this parsing, so that they're correctly
     # parsed as ``CallExpr (AttrRef (pfx, attr), args)``.
     fun is_attr_with_args(): Bool =
-        node.symbol in s"First" | s"Last" | s"Range" | s"Length" | s"Has_Same_Storage" | s"Overlaps_Storage"
+        node.symbol in s"First" | s"Last" | s"Range" | s"Length"
+        | s"Has_Same_Storage" | s"Overlaps_Storage" | s"Deref"
 
     @with_dynvars(origin)
     fun complete_items(): Array[CompletionItem] = self.parent.complete_items()

testsuite/tests/name_resolution/deref_attribute/test.adb

@@ -0,0 +1,11 @@
+with System;
+
+procedure Test (A : System.Address) is
+   I : Integer := Integer'Deref(A);
+   pragma Test_Statement;
+
+   B : Boolean := Integer'Deref(A) = 2;
+   pragma Test_Statement;
+begin
+   null;
+end;

testsuite/tests/name_resolution/deref_attribute/test.out

@@ -0,0 +1,64 @@
+Analyzing test.adb
+##################
+
+Resolving xrefs for node <ObjectDecl ["I"] test.adb:4:4-4:36>
+*************************************************************
+
+Expr: <Id "Integer" test.adb:4:8-4:15>
+  references:    <DefiningName "Integer" __standard:4:8-4:15>
+  type:          None
+  expected type: None
+Expr: <AttributeRef test.adb:4:19-4:35>
+  references:    None
+  type:          <ConcreteTypeDecl ["Integer"] __standard:4:3-4:54>
+  expected type: <ConcreteTypeDecl ["Integer"] __standard:4:3-4:54>
+Expr: <Id "Integer" test.adb:4:19-4:26>
+  references:    <DefiningName "Integer" __standard:4:8-4:15>
+  type:          None
+  expected type: None
+Expr: <Id "Deref" test.adb:4:27-4:32>
+  references:    None
+  type:          None
+  expected type: None
+Expr: <Id "A" test.adb:4:33-4:34>
+  references:    <DefiningName "A" test.adb:3:17-3:18>
+  type:          <ConcreteTypeDecl ["Address"] system.ads:67:4-67:28>
+  expected type: <ConcreteTypeDecl ["Address"] system.ads:67:4-67:28>
+
+Resolving xrefs for node <ObjectDecl ["B"] test.adb:7:4-7:40>
+*************************************************************
+
+Expr: <Id "Boolean" test.adb:7:8-7:15>
+  references:    <DefiningName "Boolean" __standard:3:8-3:15>
+  type:          None
+  expected type: None
+Expr: <RelationOp test.adb:7:19-7:39>
+  type:          <ConcreteTypeDecl ["Boolean"] __standard:3:3-3:33>
+  expected type: <ConcreteTypeDecl ["Boolean"] __standard:3:3-3:33>
+Expr: <AttributeRef test.adb:7:19-7:35>
+  references:    None
+  type:          <ConcreteTypeDecl ["Integer"] __standard:4:3-4:54>
+  expected type: <ConcreteTypeDecl ["Integer"] __standard:4:3-4:54>
+Expr: <Id "Integer" test.adb:7:19-7:26>
+  references:    <DefiningName "Integer" __standard:4:8-4:15>
+  type:          None
+  expected type: None
+Expr: <Id "Deref" test.adb:7:27-7:32>
+  references:    None
+  type:          None
+  expected type: None
+Expr: <Id "A" test.adb:7:33-7:34>
+  references:    <DefiningName "A" test.adb:3:17-3:18>
+  type:          <ConcreteTypeDecl ["Address"] system.ads:67:4-67:28>
+  expected type: <ConcreteTypeDecl ["Address"] system.ads:67:4-67:28>
+Expr: <OpEq "=" test.adb:7:36-7:37>
+  references:    None
+  type:          None
+  expected type: None
+Expr: <Int test.adb:7:38-7:39>
+  references:    None
+  type:          <ConcreteTypeDecl ["Universal_Int_Type_"] __standard:116:3-116:45>
+  expected type: <ConcreteTypeDecl ["Integer"] __standard:4:3-4:54>
+
+
+Done.

testsuite/tests/name_resolution/deref_attribute/test.yaml

@@ -0,0 +1,2 @@
+driver: name-resolution
+input_sources: [test.adb]