C++: Support attribute arguments that are expressions

cpp/ql/lib/semmle/code/cpp/Specifier.qll

@@ -281,6 +281,11 @@ class AttributeArgument extends Element, @attribute_arg {
     attribute_arg_constant(underlyingElement(this), unresolveElement(result))
   }
 
+  /**
+   * Gets the value of this argument, if its value is a expression.
+   */
+  Expr getValueExpr() { attribute_arg_expr(underlyingElement(this), unresolveElement(result)) }
+
   /**
    * Gets the attribute to which this is an argument.
    */
@@ -308,7 +313,10 @@ class AttributeArgument extends Element, @attribute_arg {
           else
             if underlyingElement(this) instanceof @attribute_arg_constant_expr
             then tail = this.getValueConstant().toString()
-            else tail = this.getValueText()
+            else
+              if underlyingElement(this) instanceof @attribute_arg_expr
+              then tail = this.getValueExpr().toString()
+              else tail = this.getValueText()
         ) and
         result = prefix + tail
       )

cpp/ql/lib/semmlecode.cpp.dbscheme

@@ -937,6 +937,7 @@ case @attribute_arg.kind of
 | 2 = @attribute_arg_constant
 | 3 = @attribute_arg_type
 | 4 = @attribute_arg_constant_expr
+| 5 = @attribute_arg_expr
 ;
 
 attribute_arg_value(
@@ -951,6 +952,10 @@ attribute_arg_constant(
     unique int arg: @attribute_arg ref,
     int constant: @expr ref
 )
+attribute_arg_expr(
+    unique int arg: @attribute_arg ref,
+    int expr: @expr ref
+)
 attribute_arg_name(
     unique int arg: @attribute_arg ref,
     string name: string ref

cpp/ql/lib/upgrades/fc81eb5a3a7cdde8d9ad813da1e8f1e90dadbb91/upgrade.properties

@@ -0,0 +1,2 @@
+description: Support expression attribute arguments
+compatibility: backwards