3. Getting Started

This section outlines the ASIS application development and usage cycle. We first take a sample problem and present an ASIS application that offers a solution; then we show how to build the executable with ASIS-for-GNAT and how to prepare an ASIS ‘Context’ to be processed by the program; and finally we show the output produced by our program when it is applied to itself.

3.1. The Problem

We wish to process some set of Ada compilation units as follows: for every unit, print its full expanded Ada name, whether this unit is a spec, a body or a subunit, and whether this unit is a user-defined unit, an Ada predefined unit or an implementation-specific unit (such as a part of a Run-Time Library).

3.2. An ASIS Application that Solves the Problem

with Ada.Wide_Text_IO;        use Ada.Wide_Text_IO;
with Ada.Characters.Handling; use Ada.Characters.Handling;

--  ASIS-specific context clauses:
with Asis;
with Asis.Implementation;
with Asis.Ada_Environments;
with Asis.Compilation_Units;
with Asis.Exceptions;
with Asis.Errors;

procedure Example1 is
   My_Context : Asis.Context;
   --  ASIS Context is an abstraction of an Ada compilation environment,
   --  it defines a set of ASIS Compilation Units available through
   --  ASIS queries

begin
   --  first, by initializing an ASIS implementation, we make it
   --  ready for work
   Asis.Implementation.Initialize ("-ws");
   --  The "-ws" parameter of the Initialize procedure means
   --  "turn off all the ASIS warnings"

   --  then we define our Context by making an association with
   --  the "physical" environment:
   Asis.Ada_Environments.Associate
    (My_Context, "My Asis Context", "-CA");
   --  "-CA" as a Context parameter means "consider all the tree
   --  files in the current directory"
   --  See ASIS-for-GNAT Reference Manual for the description of the
   --  parameters of the Associate query, see also chapter
   --  "ASIS Context" for the description of different kinds of
   --  ASIS Context in case of ASIS-for-GNAT

   --  by opening a Context we make it ready for processing by ASIS
   --  queries
   Asis.Ada_Environments.Open (My_Context);
   Processing_Units: declare
      Next_Unit : Asis.Compilation_Unit;
      --  ASIS Compilation_Unit is the abstraction to represent Ada
      --  compilation units as described in RM 95

      All_Units : Asis.Compilation_Unit_List :=
      --  ASIS lists are one-dimensional unconstrained arrays.
      --  Therefore, when declaring an object of an ASIS list type,
      --  we have to provide either a constraint or explicit
      --  initialization expression:

         Asis.Compilation_Units.Compilation_Units (My_Context);
      --  The Compilation_Units query returns a list of all the units
      --  contained in an ASIS Context
   begin
      Put_Line
        ("A Context contains the following compilation units:");
      New_Line;
      for I in All_Units'Range loop
         Next_Unit := All_Units (I);
         Put ("   ");

         --  to get a unit name, we just need a Unit_Full_Name
         --  query. ASIS uses Wide_String as a string type,
         --  that is why we are using Ada.Wide_Text_IO

         Put (Asis.Compilation_Units.Unit_Full_Name (Next_Unit));
         --  to get more info about a unit, we ask about unit class
         --  and about unit origin

         case Asis.Compilation_Units.Unit_Kind (Next_Unit) is
            when Asis.A_Library_Unit_Body =>
               Put (" (body)");
            when Asis.A_Subunit =>
               Put (" (subunit)");
            when others =>
               Put (" (spec)");
         end case;

         case Asis.Compilation_Units.Unit_Origin (Next_Unit) is
            when Asis.An_Application_Unit =>
               Put_Line (" - user-defined unit");
            when Asis.An_Implementation_Unit =>
               Put_Line (" - implementation-specific unit");
            when Asis.A_Predefined_Unit =>
               Put_Line (" - Ada predefined unit");
            when Asis.Not_An_Origin =>
               Put_Line
                 (" - unit does not actually exist in a Context");
         end case;

      end loop;
   end Processing_Units;

   --  Cleaning up: we have to close out the Context, break its
   --  association with the external environment and finalize
   --  our ASIS implementation to release all the resources used:
   Asis.Ada_Environments.Close (My_Context);
   Asis.Ada_Environments.Dissociate (My_Context);
   Asis.Implementation.Finalize;
exception
   when Asis.Exceptions.ASIS_Inappropriate_Context |
        Asis.Exceptions.ASIS_Inappropriate_Compilation_Unit |
        Asis.Exceptions.ASIS_Failed =>
      --  we check not for all the ASIS-defined exceptions, but only
      --  those of them which can actually be raised in our ASIS
      --  application.
      --
      --  If an ASIS exception is raised, we output the ASIS error
      --  status and the ASIS diagnosis string:

      Put_Line ("ASIS exception is raised:");
      Put_Line ("ASIS diagnosis is:");
      Put_Line (Asis.Implementation.Diagnosis);
      Put      ("ASIS error status is: ");
      Put_Line
        (Asis.Errors.Error_Kinds'Wide_Image
           (Asis.Implementation.Status));
end Example1;

3.3. Required Sequence of Calls

An ASIS application must use the following sequence of calls:

• Asis.Implementation.Initialize (...);

  This initializes the ASIS implementation’s internal data structures. In general, calling an ASIS query is erroneous unless the Initialize procedure has been invoked.

• Asis.Ada_Environments.Associate (...);

  This call is the only means to define a value of a variable of the ASIS limited private type Context. The value represents some specific association of the ASIS Context with the ‘external world’. The way of making this association and the meaning of the corresponding parameters of the Associate query are implementation-specific, but as soon as this association has been made and a Context variable is opened, the ASIS Context designated by this variable may be considered to be a set of ASIS Compilation_Units available through the ASIS queries.

• Asis.Ada_Environments.Open (...);

  Opening an ASIS Context variable makes the corresponding Context accessible to all ASIS queries.

  After opening the Context, an ASIS application can start obtaining ASIS Compilation_Units from it, can further analyze Compilation_Units by decomposing them into ASIS Elements, etc. ASIS relies on the fact that the content of a Context remains ‘frozen’ as long as the Context remains open. It is erroneous to change through some non-ASIS program any data structures used by an ASIS implementation to define and implement this Context while the Context is open.

• Now all the ASIS queries can be used. It is possible to access Compilation_Units from the Context, to decompose units into syntactic Elements, to query syntactic and semantic properties of these Elements and so on.

• Asis.Ada_Environments.Close (...);

  After closing the Context it is impossible to retrieve any information from it. All the values of the ASIS objects of Compilation_Unit, Element and Line types obtained when this Context was open become obsolete, and it is erroneous to use them after the Context was closed. The content of this Context need not be frozen while the Context remains closed. Note that a closed Context keeps its association with the ‘external world’ and it may be opened again with the same association. Note also that the content (that is, the corresponding set of ASIS Compilation_Units) of the Context may be different from what was in the Context before, because the external world may have changed while the Context remained closed.

• Asis.Ada_Environments.Dissociate (...);

  This query breaks the association between the corresponding ASIS Context and the ‘external world’, and the corresponding Context variable becomes undefined.

• Asis.Implementation.Finalize (...);

  This releases all the resources used by an ASIS implementation.

An application can perform these steps in a loop. It may initialize and finalize an ASIS implementation several times, it may associate and dissociate the same Context several times while an ASIS implementation remains initialized, and it may open and close the same Context several times while the Context keeps its association with the ‘external world’. An application can have several ASIS Contexts opened at a time (the upper limit is implementation-specific), and for each open Context, an application can process several Compilation_Units obtained from this Context at a time (the upper limit is also implementation-specific). ASIS-for-GNAT does not impose any special limitations on the number of ASIS Contexts and on the number of the ASIS Compilation_Units processed at a time, as long as an ASIS application is within the general resource limitations of the underlying system.

3.4. Building the Executable for an ASIS application

The rest of this section assumes that you have ASIS-for-GNAT properly installed as an Ada library. As for other components of the GNAT technology, the structure of the ASIS distribution and the ASIS building and installation process is based on project files. So, the same should be the case for ASIS application.

For your ASIS application you should create a project file that depends on the main ASIS project file asis.gpr. Here is the simplest version of such a project file:

with "asis";
project Example1 is
   for Main use ("example1.adb");
end Example1;

To get the executable for the ASIS application from An ASIS Application that Solves the Problem (assuming that it is located in your current directory as the Ada source file named example1.adb, and the corresponding project file is also located in the current directory), invoke gprbuid as follows:

$ gprbuild example1.gpr

For more details concerning compiling ASIS applications and building executables for them with ASIS-for-GNAT see Compiling, Binding, and Linking Applications with ASIS-for-GNAT.

3.5. Preparing Data for an ASIS Application — Generating Tree Files

The general ASIS implementation technique is to use some information generated by the underlying Ada compiler as the basis for retrieving information from the Ada environment. As a consequence, an ASIS application can process only legal (compilable) Ada code, and in most of the cases to make a compilation unit ‘visible’ for ASIS means to compile this unit (probably with some ASIS-specific options)

ASIS-for-GNAT uses tree output files (or, in short, tree files) to capture information about an Ada unit from an Ada environment. A tree file is generated by GNAT, and it contains a snapshot of the compiler’s internal data structures at the end of the successful compilation of the corresponding source file.

To create a tree file for a unit contained in some source file, you should compile this file with the -gnatct compiler option. If you want to apply the program described in section An ASIS Application that Solves the Problem to itself, compile the source of this application with the command:

$ gcc -c -gnatct example1.adb

and as a result, GNAT will generate the tree file named example1.adt in the current directory.

For more information on how to generate and deal with tree files, see ASIS Context, and ASIS Tutorials.

3.6. Running an ASIS Application

To complete our example, let’s execute our ASIS application. If you have followed all the steps described in this chapter, your current directory should contain the executable example1 (example1.exe on a Windows platform) and the tree file example1.adt. If we run our application, it will process an ASIS Context defined by one tree file example1.adt (for more details about defining an ASIS Context see ASIS Context, and the ASIS-for-GNAT Reference Manual). The result will be:

A Context contains the following compilation units:

   Standard (spec) - Ada predefined unit
   Example1 (body) - user-defined unit
   Ada (spec) - Ada predefined unit
   Ada.Wide_Text_IO (spec) - Ada predefined unit
   Ada.IO_Exceptions (spec) - Ada predefined unit
   Ada.Streams (spec) - Ada predefined unit
   System (spec) - Ada predefined unit
   System.File_Control_Block (spec) - implementation-specific unit
   Interfaces (spec) - Ada predefined unit
   Interfaces.C_Streams (spec) - implementation-specific unit
   System.Parameters (spec) - implementation-specific unit
   System.WCh_Con (spec) - implementation-specific unit
   Ada.Characters (spec) - Ada predefined unit
   Ada.Characters.Handling (spec) - Ada predefined unit
   Asis (spec) - user-defined unit
   A4G (spec) - user-defined unit
   A4G.A_Types (spec) - user-defined unit
   Ada.Characters.Latin_1 (spec) - Ada predefined unit
   GNAT (spec) - implementation-specific unit
   GNAT.OS_Lib (spec) - implementation-specific unit
   GNAT.Strings (spec) - implementation-specific unit
   Unchecked_Deallocation (spec) - Ada predefined unit
   Sinfo (spec) - user-defined unit
   Types (spec) - user-defined unit
   Uintp (spec) - user-defined unit
   Alloc (spec) - user-defined unit
   Table (spec) - user-defined unit
   Urealp (spec) - user-defined unit
   A4G.Int_Knds (spec) - user-defined unit
   Asis.Implementation (spec) - user-defined unit
   Asis.Errors (spec) - user-defined unit
   Asis.Ada_Environments (spec) - user-defined unit
   Asis.Compilation_Units (spec) - user-defined unit
   Asis.Ada_Environments.Containers (spec) - user-defined unit
   Asis.Exceptions (spec) - user-defined unit
   System.Unsigned_Types (spec) - implementation-specific unit

Note that the tree file contains the full syntactic and semantic information not only about the unit compiled by the given call to gcc, but also about all the units upon which this unit depends semantically; that is why you can see in the output list a number of units which are not mentioned in our example.

In the current version of ASIS-for-GNAT, ASIS implementation components are considered user-defined, rather than implementation-specific, units.