13.1. Proper handling of function attributes

13.1.1. Current problem

In Ada, a lot of attributes are defined as refering to built-in functions (every attribute that “takes arguments”, is actually a function).

Libadalang’s parser is wrong in that regard. Historically, it parses AttributeRef with arguments as part of the AttributeRef node, rather than as a CallExpr where the callee is the AttributeRef node.

Recently, we made it so that it will do that only for the cases that we already implemented using the old tree. Attributes will be parsed correctly in the general case:

%  parse -r expr "A'B(12, 15)"
CallExpr[1:1-1:12]
|name:
|  AttributeRef[1:1-1:4]
|  |prefix:
|  |  Id[1:1-1:2]: A
|  |attribute:
|  |  Id[1:3-1:4]: B
|  |args: <null>
|suffix:
|  AssocList[1:5-1:11]
|  |  ParamAssoc[1:5-1:7]
|  |  |designator: <null>
|  |  |r_expr:
|  |  |  Int[1:5-1:7]: 12
|  |  ParamAssoc[1:9-1:11]
|  |  |designator: <null>
|  |  |r_expr:
|  |  |  Int[1:9-1:11]: 15

But will be parsed incorrectly (legacy) for all attributes that should be functions but are not handled as such by LAL:

% parse -r expr "A'First(12)"
AttributeRef[1:1-1:12]
|prefix:
|  Id[1:1-1:2]: A
|attribute:
|  Id[1:3-1:8]: First
|args:
|  AssocList[1:9-1:11]
|  |  ParamAssoc[1:9-1:11]
|  |  |designator: <null>
|  |  |r_expr:
|  |  |  Int[1:9-1:11]: 12

Those legacy attributes are handled, but the way they’re handled is incorrect and will fail when the fact that the attribute denotes functions is inevitable, such as in the following example:

procedure Foo is
    function Image (A : Integer) return String renames Integer'Image;
begin
    null;
end Foo;

13.1.2. Proposed Solution

To solve this, we need to synthetize the subprogram nodes corresponding to each attribute. If we have a unified mechanism to easily synthetise subprograms with given profiles, we can potentially also dramatically simplify the name resolution of said attributes, because for the moment resolution of those is hard-coded.