Ada Source code modifications using ASIS(Ada Semantics interface specifications)

Question

i am developing a tool for finding sub type range overflow problems in Ada source code.for this purpose i am using ASIS for finding assignment statements in Ada source code and finding type of the variables on the right side of the assignment expression.now i want to replace the variables(not of record type) of the assignment expression with 'first, 'last values of the variable type in the assignment statement so that i will get compilation error if any range overflow happens.below is an example what i am trying to convey.

procedure Example is
   subtype A_Type is integer 1 .. 10;
   subtype B_Type is integer -5 .. 5;
   subtype C_Type is integer 1 .. 12;

   A : A_Type;
   B : B_Type;
   C : C_Type;
begin
   C := A + B;
end Example;

I want modify C := A + B; with C := A_Type'Last + B_Type'Last in the source code. C := A_Type'Last + B_Type'Last assignment statement will get warning at compile time or Constraint error during run time.

Is it possible do above modifications with ASIS?

Answer 1

For your purpose, you shouldn't rewrite the source text you are processing. You should rather write a new program, which only contains exactly the required declarations and assignments.

So the output should be something like:

with Type_Declarations;

procedure Test_Driver is
begin
   declare
      C : Type_Declarations.C_Type;
   begin
      C := Type_Declarations."+" (Type_Declarations.A_Type'First, Type_Declarations.B_Type'First);
      C := Type_Declarations."+" (Type_Declarations.A_Type'First, Type_Declarations.B_Type'Last);
      C := Type_Declarations."+" (Type_Declarations.A_Type'Last, Type_Declarations.B_Type'First);
      C := Type_Declarations."+" (Type_Declarations.A_Type'Last, Type_Declarations.B_Type'Last);
   end;
end Test_Driver;

Answer 2

ASIS was not designed to make modifications like that. You can, however take a look at libadalang from AdaCore, which supports this (and works on partial sources, so you won't have to precompile your sources)

Answer 3

GNAT includes utilities gnat2xml and xml2gnat; gnat2xml generates a representation of the source based on ASIS, and xml2gnat converts it back to Ada. You could maybe modify the XML output of the first and feed it back to the second.

Not that I’m recommending this; the XML schema isn’t documented, and is complicated.

Answer 4

If you want a tool that can apply modifications to Ada source code, you might be interested in our DMS Software Reengineering Toolkit with its Ada front end.

DMS parses source code to ASTs, and makes those ASTs available for modification using DMS's Abstract Syntax Tree procedural interface (direct hacking at the tree nodes) and/or DMS's rewrite rules (source-to-source transformations "if you see this replace it by that" written in [Ada] language surface syntax, that directly manipulates the trees. After your changes are made, DMS can prettyprint the source to regenerate valid Ada source code, even preserving comments and formatting in those places that have not been modified.