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File: asis_ug.info,  Node: Top,  Next: About This Guide,  Prev: (dir),  Up: (dir)

ASIS-for-GNAT User's Guide
**************************

   ASIS-for-GNAT User's Guide

   (C) Copyright 2000, Ada Core Technologies, Inc.

   Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

   ASIS-for-GNAT User's Guide

* Menu:

* About This Guide::
* Introduction::
* Getting Started::
* ASIS Overview::
* ASIS Context::
* ASIS Interpreter asistant::
* ASIS Application Templates::
* ASIS Tutorials::
* How to Build Efficient ASIS Applications::
* Processing an Ada Library by an ASIS-Based Tool::
* Compiling Binding and Linking Applications with ASIS-for-GNAT::
* ASIS-for-GNAT Warnings::
* File Naming Conventions and Applications Name Space::

 --- The Detailed Node Listing ---

About This Guide

* What This Guide Contains::
* What You Should Know Before Reading This Guide::
* Related Information::

Introduction

* What Is ASIS?::
* ASIS Scope What Kind of Tools Can Be Built with ASIS?::

Getting Started

* The Problem::
* An ASIS Application Which Solves the Problem::
* Required Sequence of Calls::
* Building the Executable for an ASIS application::
* Generating Trees for Input::
* Running an ASIS Application::

ASIS Overview

* Main ASIS Abstractions::
* ASIS Package Hierarchy::
* Structural and Semantic Queries::
* ASIS Error Handling Policy::
* Dynamic Validity Checking of the ASIS Queries::
* ASIS Iterator::
* How to Navigate through the Asis Specification::

ASIS Context

* ASIS Context and Tree Files::
* Creating Tree Files for Use by ASIS::
*   Creating Trees for Data Decomposition Annex::
* Different Ways to Define an ASIS Context in ASIS-for-GNAT::
* Consistency Problem::
*   Inconsistent versions of ASIS and GNAT::
*   Consistency of a set of tree and source files::
* Processing Several Contexts at a Time::

ASIS Interpreter `asistant'

* asistant introduction::
* asistant commands::
* asistant variables::
* Browsing an ASIS tree::
* Example::

ASIS Application Templates

ASIS Tutorials

How to Build Efficient ASIS Applications

* Tree Swapping as a Possible Cause of Poor Application Performance::
* Queries That Can Cause Tree Swapping::
* How to Avoid Unnecessary Tree Swapping::
* Using gnatmake to Create Tree Files::

Processing an Ada Library by an ASIS-Based Tool

Compiling, Building and Linking Applications with ASIS-for-GNAT

ASIS-for-GNAT Warnings

File Naming Conventions and Application's Name Space


File: asis_ug.info,  Node: About This Guide,  Next: Introduction,  Prev: Top,  Up: Top

About This Guide
****************

   This guide has two aims. The first one is to introduce you to the
Ada Semantic Interface Specification (ASIS) and show you how you can
build various useful tools on top of ASIS. The second is to describe
the ASIS implementation for the GNAT Ada 95 compiler.

* Menu:

* What This Guide Contains::
* What You Should Know Before Reading This Guide::
* Related Information::


File: asis_ug.info,  Node: What This Guide Contains,  Next: What You Should Know Before Reading This Guide,  Up: Top

What This Guide Contains
========================

This guide contains the following chapters:
   * *Note Introduction::, contains the general definition of ASIS and
     gives some examples of tools which can be built on top of ASIS;

   * *Note Getting Started::, contains a short guided tour through the
     development and use of ASIS-for-GNAT-based tools;

   * *Note ASIS Overview:: gives the general overview of the ASIS
     definition to help an ASIS newcomer to navigate through ASIS
     (readers already familiar with ASIS can just skip this section);

   * *Note ASIS Context:: explains what is the meaning of ASIS Context
     in the case of ASIS-for-GNAT and what should be done to prepare a
     set of Ada components to be processed by an ASIS application;

   * *Note ASIS Application Templates:: describes a set of Ada source
     components provided by the ASIS-for-GNAT distribution that may be
     used as a basis for developing simple ASIS applications;

   * *Note ASIS Tutorials:: describes some examples included in the
     ASIS-for-GNAT distribution that comprise a hands-on tutorial to
     get some initial experience with ASIS;

   * *Note How to Build Efficient ASIS Applications:: describes the
     problem of tree swapping as a possible source of a poor
     productivity of ASIS applications and explains how to avoid
     unnecessary tree swappings;

   * *Note Processing an Ada Library by an ASIS-Based Tool:: touches the
     specific issues of processing Ada programs which use the
     pre-compiled Ada libraries by an ASIS tool;

   * *Note Compiling Binding and Linking Applications with
     ASIS-for-GNAT:: explains how to compile an ASIS application with
     ASIS-for-GNAT and how to create an executable for it;

   * *Note File Naming Conventions and Applications Name Space::
     explains which names can and cannot be used as names of an ASIS
     application components.


File: asis_ug.info,  Node: What You Should Know Before Reading This Guide,  Next: Related Information,  Prev: What This Guide Contains,  Up: About This Guide

What You Should Know Before Reading This Guide
==============================================

This User's Guide assumes that you are familiar with Ada 95 and that
you have some basic experience in Ada programming with GNAT.

   This User's Guide also assumes that you have ASIS-for-GNAT properly
installed for your GNAT compiler, and that you are familiar with the
structure of the ASIS-for-GNAT distribution (if not, see the top README
file from the distribution, section 2)

   This guide does not assume that you have any knowledge or experience
in ASIS.  If you indeed do not, you will learn some basic things about
ASIS when reading this Guide, doing exercises, playing with examples
and referring to the ASIS definition if needed.


File: asis_ug.info,  Node: Related Information,  Prev: What You Should Know Before Reading This Guide,  Up: About This Guide

Related Information
===================

To get to know more about GNAT, refer to the GNAT User's Guide.

   Refer to ASIS-for-GNAT Installation Guide to learn how to install
the ASIS implementation for your GNAT compiler.

   The ASIS 95 definition now exists as ISO/IEC International Standard
15291.

   To get more information about ASIS, visit the ASIS Working Group Web
Pages (http://www.acm.org/sigada/wg/asiswg).

   To read this Guide you will hardly need GNAT or ASIS-for-GNAT
Reference Manual.


File: asis_ug.info,  Node: Introduction,  Next: Getting Started,  Prev: About This Guide,  Up: Top

Introduction
************

* Menu:

* What Is ASIS?::
* ASIS Scope What Kind of Tools Can Be Built with ASIS?::


File: asis_ug.info,  Node: What Is ASIS?,  Next: ASIS Scope What Kind of Tools Can Be Built with ASIS?,  Up: Introduction

What Is ASIS?
=============

The Ada Semantic Interface Specification (ASIS) is an interface between
an Ada environment (as defined by ISO/IEC 8652:1995) and any tool
requiring information from it. An Ada environment includes valuable
semantic and syntactic information. ASIS is an open and published
callable interface which gives CASE tool and application developers
access to this information. ASIS has been designed to be independent of
underlying Ada environment implementations, thus supporting portability
of software engineering tools while relieving tool developers from
needing to understand the complexities of an Ada environment's
proprietary internal representation.

   Technically, ASIS is a hierarchy of the Ada package specifications.
These packages define a set of Ada private types which implement basic
notions needed to describe an Ada program. Operations for these types,
called ASIS queries, give you statically determinable information about
Ada compilation units in your environment.

   You may use ASIS as a third-part Ada library to implement a number
of useful program analysis tools.


File: asis_ug.info,  Node: ASIS Scope What Kind of Tools Can Be Built with ASIS?,  Prev: What Is ASIS?,  Up: Introduction

ASIS Scope: What Kind of Tools Can Be Built with ASIS?
======================================================

The following ASIS properties define the ASIS scope:

   bullet ASIS is a read-only interface;

   bullet ASIS provides only statically-determinable information about
     Ada programs;

   bullet ASIS provides all the syntax and the basic semantic
     information from/about Ada programs. If some semantic property of
     a program cannot be directly queried by means of ASIS queries, an
     ASIS application can compute the needed piece of information
     itself from the information available through ASIS queries;

   bullet Even though containing some implementation dependencies, ASIS
     provides information from/about Ada program in high-level terms
     which are well-conformed with RM 95 and which are
     Ada/ASIS-implementation-independent in their very nature.

Examples of tools that benefit from the ASIS interface include, but are
not limited by: automated code monitors, browsers, call tree tools, code
reformators, coding standards compliance tools, correctness verifiers,
debuggers, dependency tree analysis tools, design tools, document
generators, metrics tools, quality assessment tools, reverse
engineering tools, re-engineering tools, style checkers, test tools,
timing estimators, and translators.


File: asis_ug.info,  Node: Getting Started,  Next: ASIS Overview,  Prev: Introduction,  Up: Top

Getting Started
***************

In this section we go through the ASIS application development and
usage cycle in a very simplified way: we take a sample problem to be
solved with an ASIS application, then we present the code of the ASIS
application which gives the solution for our problem, then we show how
to compile it and build the executable for it 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.

* Menu:

* The Problem::
* An ASIS Application Which Solves the Problem::
* Required Sequence of Calls::
* Building the Executable for an ASIS application::
* Generating Trees for Input::
* Running an ASIS Application::


File: asis_ug.info,  Node: The Problem,  Next: An ASIS Application Which Solves the Problem,  Up: Getting Started

The Problem
===========

Suppose our goal is to process some set of Ada compilation units, and
for every unit to 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, a predefined unit as defined by RM 95 or an
implementation-specific unit (such as a part of a Run-Time Library).


File: asis_ug.info,  Node: An ASIS Application Which Solves the Problem,  Next: Required Sequence of Calls,  Prev: The Problem,  Up: Getting Started

An ASIS Application Which 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 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;
     
        --  then we define our Context by making association with
        --  "physical" environment:
        Asis.Ada_Environments.Associate
         (My_Context, "My Asis Context", "-CA");
        --  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 list 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);
           --  Compilation_Units query gives you 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,
              --  therefore we convert the result into String to use
              --  Ada.Text_IO
              Put (Asis.Compilation_Units.Unit_Full_Name (Next_Unit));
     
              --  to get more info about a unit, we ask about its class
              --  and about its 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 Context, to break its
        --  association with the external environment and to 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;


File: asis_ug.info,  Node: Required Sequence of Calls,  Next: Building the Executable for an ASIS application,  Prev: An ASIS Application Which Solves the Problem,  Up: Getting Started

Required Sequence of Calls
==========================

An ASIS application must use the following sequence of calls:

  1. `Asis.Implementation.Initialize (...);'

     This call initializes the ASIS implementation internal data
     structures and prepares the ASIS implementation for work. For most
     of the ASIS queries, it is erroneous to call them if an ASIS
     implementation is not initialized.

  2. `Asis.Ada_Environments.Associate (...);'

     This call is the only means to define a value of a variable of the
     ASIS limited private type Context. This value is 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.

  3. `Asis.Ada_Environments.Open (...);'

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

     After opening the Context, an ASIS application can start obtaining
     ASIS Compilation Units from it, further analyze Compilation Units
     by decomposing them into ASIS Elements etc.

     ASIS relies on the content of a Context being 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.

  4. `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.

  5. `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.

  6. `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.


File: asis_ug.info,  Node: Building the Executable for an ASIS application,  Next: Generating Trees for Input,  Prev: Required Sequence of Calls,  Up: Getting Started

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.

   To get the executable for the ASIS application from subsection 1.2
(assuming that it is located in your current directory as the Ada
source file named example1.adb), you have to call gnatmake as:

   `gnatmake example1[.adb] -largs -lasis'

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


File: asis_ug.info,  Node: Generating Trees for Input,  Next: Running an ASIS Application,  Prev: Building the Executable for an ASIS application,  Up: Getting Started

Generating Trees for Input
==========================

To get information from an Ada environment being processed,
ASIS-for-GNAT processes so-called tree files. A tree file is generated
by GNAT, and it contains a snapshot of a compiler's internal data
structures. For more details see section *Note ASIS Context and Tree
Files:: of this Guide

   To create a tree file for a unit contained in some source file, you
should compile this file with '-gnatc -gnatt' compiler options. If we
want to apply the application described in section *Note An ASIS
Application Which Solves the Problem:: to itself, we have to compile
the source of this application with a command

   `gcc -c -gnatc -gnatt example1.adb'

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

   For more explanation how to generate and how to deal with tree files
see chapters *Note ASIS Context:: and *Note ASIS Tutorials::.


File: asis_ug.info,  Node: Running an ASIS Application,  Prev: Generating Trees for Input,  Up: Getting Started

Running an ASIS Application
===========================

To complete our example, let's execute our ASIS application. If you have
followed all the steps described in chapter *Note Getting Started::,
now you should have in your current directory the executable `example1'
and the tree file `example1.atd'.  (Note that a tree file contains
information about a unit it was created for and about all the units
upon which this unit depends semantically). 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 chapter *Note ASIS
Context:: 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.Text_IO (spec) - Ada predefined unit
           Ada (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) - Ada predefined unit
           System.Parameters (spec) - Ada predefined unit
           Ada.Characters.Handling (spec) - Ada predefined unit
           Ada.Characters (spec) - Ada predefined unit
           Asis (spec) - user-defined unit
           A4G.A_Types (spec) - user-defined unit
           A4G (spec) - user-defined unit
           Ada.Characters.Latin_1 (spec) - Ada predefined unit
           A4G.Int_Knds (spec) - user-defined unit
           Types (spec) - user-defined unit
           Unchecked_Deallocation (spec) - Ada predefined 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

In the current implementation, ASIS implementation components are
considered user-defined, not implementation-specific, units. Note also,
that some components of the GNAT Run-Time Library may be implicitly
"withed" by some Ada units, and therefore they may be presented by a
tree file, that is why you can see System.File_Control_Block in the
list above.


File: asis_ug.info,  Node: ASIS Overview,  Next: ASIS Context,  Prev: Getting Started,  Up: Top

ASIS Overview
*************

This chapter contains a short overview of the ASIS definition as given
in the ISO/IEC 15291:1999 ASIS Standard. This overview is aimed at
helping an ASIS newcomer to find needed information in the ASIS
definition and to navigate himself in it.

   For more details look into the ASIS definition itself. To get some
initial experience with ASIS, go through the ASIS Tutorials (see *Note
ASIS Tutorials::).

* Menu:

* Main ASIS Abstractions::
* ASIS Package Hierarchy::
* Structural and Semantic Queries::
* ASIS Error Handling Policy::
* Dynamic Validity Checking of the ASIS Queries::
* ASIS Iterator::
* How to Navigate through the Asis Specification::


File: asis_ug.info,  Node: Main ASIS Abstractions,  Next: ASIS Package Hierarchy,  Up: ASIS Overview

Main ASIS Abstractions
======================

ASIS is based on the three main abstractions used to describe Ada
programs:

Context
     an ASIS Context is a logical handle to an Ada environment, as
         defined in RM 95 Chapter 10. To avoid the language-lawyer
          difficulties when trying to understand the formal relation
            between an ASIS Context and an Ada environment, an ASIS
           application developer may view an ASIS Context as a way
          to define a set of compilation units available through the
            ASIS queries.

Compilation Unit
     an ASIS Compilation Unit is a logical handle to an Ada
     compilation unit. It reflects practically one-to-one all the
        properties of compilation units defined by RM 95, and it also
             reflects some properties of "physical objects" treated by
     an           underlying Ada implementation as compilation units
     (such as time of           last update, the name of some object
     treated as containing the           source text for a unit). An
     ASIS Compilation Unit provides the           black-box view of a
     compilation unit, considering a unit as a whole.            It may
     be decomposed and analyzed as a white-box by means of ASIS
      Elements.

Element
     an ASIS Element is a logical handle to syntax components of ASIS
            Compilation Units (both explicit and implicit).

   Some ASIS components use additional abstractions needed for specific
pieces of functionality provided by these components:

Container
     an ASIS Container (defined and used by the
     Asis.Ada_Environments.Containers package) provides means for
        structuring the content of an ASIS Context by grouping ASIS
           Compilation units into Containers.

Line
     an ASIS Line (defined and used by the Asis.Text package) is the
           abstraction of a line in an Ada source text. An ASIS Line
     has a           length, a string image and a number.

Span
     an ASIS Span (defined and used by the Asis.Text package) defines
     the           location of an Element, a Compilation Unit or a
     whole compilation in           the corresponding source text.

Id
     An ASIS Id (defined and used by the Asis.Ids package) provides a
            way to store some "image" of an ASIS Element outside an
     ASIS           application. An application may create an Id value
     from an Element           value and store it in a file. After
     that, the same or another           application may read this Id
     value in and try to convert it back           into the
     corresponding Element value.


File: asis_ug.info,  Node: ASIS Package Hierarchy,  Next: Structural and Semantic Queries,  Prev: Main ASIS Abstractions,  Up: ASIS Overview

ASIS Package Hierarchy
======================

ASIS is defined as a hierarchy of Ada package specifications. Below is
the short description of this hierarchy.

   Asis - this is the top package of the hierarchy. It defines the main
ASIS        abstractions - Context, Compilation_Unit and Element - as
Ada private        types. It also contains a set of enumeration types
that define the        classification hierarchy for ASIS Elements
(which closely reflects the        Ada syntax defined in RM 95) and
classification of ASIS Compilation        Units. This package does not
contain any queries;

   Asis.Implementation - contains subprograms that control an ASIS
 implementation: initializing and finalizing it, retrieving and
resetting the diagnosis information. Its child package
Asis.Implementation.Permissions contains boolean queries which tells
   you how ASIS implementation-specific features are implemented in
your        ASIS implementation;

   Asis.Ada_Environments - contains queries that deal with an ASIS
Context:        associating and dissociating, opening and closing a
Context;

   Asis.Compilation_Units - contains queries that work with ASIS
Compilation        Units: obtaining units from a Context, getting
semantic dependencies        between Units and black-box Unit
properties;

   Asis.Compilation_Units.Relations - contains queries that return
integrated        semantic dependencies among ASIS Compilation Units,
e.g. all the Units        needed by a given Unit to be included in a
partition;

   Asis.Elements - contains queries working on Elements and
implementing general        Element properties: gateway queries from
ASIS Compilation Units to        ASIS Elements, queries defining the
position of an Element in the        Element classification hierarchy,
queries which define for a given        Element its Enclosing
Compilation Unit and its Enclosing Element.         It also contains
queries that work on pragmas;

   Asis.Declarations, Asis.Definitions, Asis.Statements,
Asis.Expressions and ASIS.Clauses - each of these packages contains
queries working on Elements of        the corresponding kind - that is,
representing Ada        declarations, definitions, statements,
expressions and clauses        respectively;

   Asis.Text - contains queries returning information about the source
     representation of ASIS Compilation Units and ASIS Elements;

   Asis.Exceptions - defines ASIS exceptions;

   Asis.Errors - defines possible ASIS error statuses.


File: asis_ug.info,  Node: Structural and Semantic Queries,  Next: ASIS Error Handling Policy,  Prev: ASIS Package Hierarchy,  Up: ASIS Overview

Structural and Semantic Queries
===============================

Queries working on Elements and returning Elements or Element Lists are
divided into structural and semantic queries.

   Each structural query (except Enclosing_Element) implements one step
of the parent-to-child decomposition of an Ada program according to the
ASIS Element classification hierarchy. Asis.Elements.Enclosing_Element
query implements the reverse child-to-parent step. (For implicit
Elements obtained as results of semantic queries, Enclosing Element may
not correspond to what could be expected from the Ada syntax and
semantics as defined in RM 95, in this case the documentation of a
semantic query also defines the effect of Enclosing_Element applied to
its result).

   A semantic query for a given Element returns the Element representing
some semantic property of the first - e.g. type declaration for an
expression as expression's type, a defining identifier as a definition
for a simple name etc.

   For example, if we have Element El representing an assignment
statement:

         X := A + B;

then we can get the structural components of this assignment statements
by applying the appropriate structural queries:

        El_Var  := Asis.Statements.Assignment_Variable_Name (El); --  X
        El_Expr := Asis.Statements.Assignment_Expression    (El); --  A + B

And then we can analyze semantic properties of the variable name
represented by El_Var and of the expression represented by El_Expr by
means of appropriate semantic queries:

        El_Var_Def   :=
           Asis.Expressions.Corresponding_Name_Definition (El_Var);
        El_Expt_Type :=
           Asis.Expressions.Corresponding_Expression_Type (El_Expr);

As the result, El_Var_Def will be of A_Defining_Identifier kind and
will represent the defining occurrence of X, while El_Expt_Type of a
kind An_Ordinary_Type_Declaration will represent the declaration of the
type of the expression   A + B.

   If we apply Asis.Elements.Enclosing_Element to El_Var or to El_Expr,
we will get back to the Element representing the assignment statement.

   An important thing about classifying queries working on Elements as
structural and semantic is that all the structural queries cannot go
outside one ASIS Compilation Unit, but for semantic queries it is quite
usual that the argument of a query is in one ASIS Compilation Unit, but
the result of this query is in another ASIS Compilation Unit.


File: asis_ug.info,  Node: ASIS Error Handling Policy,  Next: Dynamic Validity Checking of the ASIS Queries,  Prev: Structural and Semantic Queries,  Up: ASIS Overview

ASIS Error Handling Policy
==========================

Only ASIS-defined exceptions (and the Ada predefined Storage_Error
exception) are allowed to propagate outside the ASIS queries. ASIS
exceptions are defined in the Asis.Exceptions package.

   When an ASIS exception is raised, ASIS sets the Error Status (the
possible ASIS error conditions are defined as the values of the
Asis.Errors.Error_Kinds type) and forms the Diagnosis string. An
application can query the current value of the ASIS Error Status by
Asis.Implementation.Status query, and the current content of the
Diagnosis string by Asis.Implementation.Diagnosis query. An application
can reset the Error Status and Diagnosis by
Asis.Implementation.Set_Status procedure.


File: asis_ug.info,  Node: Dynamic Validity Checking of the ASIS Queries,  Next: ASIS Iterator,  Prev: ASIS Error Handling Policy,  Up: ASIS Overview

Dynamic Validity Checking of the ASIS Queries
=============================================

ASIS has just one type (Element) for all kinds of Ada syntax constructs,
and just one type (Compilation_Unit) for all kinds of Ada compilation
units.  However, many of the queries working on Elements and
Compilation Units can be applied only to specific kinds of Elements and
Compilation units respectively. (For example, it does not make sense
and is illegal to query Assignment_Variable_Name for an Element of
An_Ordinary_Type_Declaration kind).

   ASIS is a dynamic validity checking interface. If a query working on
Elements has a list of appropriate Element kinds in its documentation,
this means that this query can work only on Elements of the kinds from
this list. Such a query should raise
Asis.Exceptions.ASIS_Inappropriate_Element exception with
Asis.Errors.Value_Error error status set when called for any Element
with a kind not from the list of the appropriate Element kinds.

   If a query working on Compilation Units has a list of appropriate
unit kinds in its documentation, then this query can work only on
Compilation Units of the kinds from this list. Such a query should raise
Asis.Exceptions.ASIS_Inappropriate_Compilation_Unit with
Asis.Errors.Value_Error error status set when called for any
Compilation_Unit with a kind not from the list of the appropriate unit
kinds.

   If a query has a list of expected Element kinds or expected
Compilation Unit kinds in its documentation, this query does not raise
any exception when called with any argument, but it produces a
meaningful result only when called with an argument with the kind from
this list. For example, if Asis.Elements.Statement_Kind query is called
for an argument of A_Declaration kind, it just returns Not_A_Statement,
but without raising any exception.


File: asis_ug.info,  Node: ASIS Iterator,  Next: How to Navigate through the Asis Specification,  Prev: Dynamic Validity Checking of the ASIS Queries,  Up: ASIS Overview

ASIS Iterator
=============

ASIS provides a powerful mechanism to traverse an Ada code, the generic
procedure Asis.Iterator.Traverse_Element. This procedure makes top-down
left-to-right (or depth-first) traversal of the ASIS tree (that is, of
the syntax structure of the Ada code represented by the hierarchy of
ASIS Elements). In the course of this traversal, it applies to each
Element the formal Pre_Operation procedure when visiting this element
for the first time, and the formal Post_Operation procedure when
leaving this Element.  By providing his own instantiations for Pre_-
and Post_Operation, the user gains the ability to automatically process
all ASIS Elements found in a given ASIS tree.

   For example, suppose we have an assignment statement:

         X := F (Y);

When called for an Element representing this statement, a
Traverse_Element instantiation does the following (below Pre_Op and
Post_Op stand for actual procedures provided for formal Pre_Operation
and Post_Operation, and numbers indicate the sequence of calls to
Pre_Op and Post_Op during traversal):

                  (1 Pre_Op)  X := F (Y) (10 Post_Op)
                                  |
                                  |
                -----------------------------------
                |                                 |
     (2 Pre_Op) X (3 Post_Op)                     |
                                                  |
                                     (4 Pre_Op) F(Y) (9 Post_Op)
                                                  |
                                                  |
                                     ---------------------------
                                     |                         |
                         (5 Pre_Op)  F (6 Post_Op)  (7 Pre_Op) Y (8 Post_Op)

To see in more detail how Traverse_Element may be used for fast-and-easy
development of a number of useful ASiS applications, see ASIS tutorials
provided as a part of ASIS-for-GNAT distribution (Section 4).


File: asis_ug.info,  Node: How to Navigate through the Asis Specification,  Prev: ASIS Iterator,  Up: ASIS Overview

How to Navigate through the Asis Specification
==============================================

The following hints and tips may be useful when looking for some
specific information in the ASIS definition:

  1.  Use the short overview of the ASIS packages given in section
     *Note ASIS Package Hierarchy:: to limit     your browsing to a
     smaller set of ASIS packages (e.g. if you are     interested in
     what can be done with Compilation_Units - look only in
     Asis.Compilation_Units, if you are looking for queries which can
     be used     to decompose and analyze declarations, limit your
     search to     Asis.Declarations).

  2.  Inside Asis packages working with particular kinds of Elements
     (Asis.Declarations, Asis.Definitions, Asis.Statements,
     Asis.Expressions     and ASIS.Clauses) queries are ordered
     according to the order of the     description of the corresponding
     constructions in RM 95 (e.g., package     Asis.Statements starts
     from a query retrieving labels and ends with the     query
     decomposing a code statement).

  3.  The names of all the semantic queries (and only ones) start from
       Corresponding_... or Implicit_...

  4.  Use comment sentinels given in the specification of the ASIS
     packages. A     sentinel of the form "-|ER" (from "Element
     Reference") introduces a new     element kind, and it is followed
     by a group of sentinels of the form     "-|CR" (from "Child
     Reference") which list queries yielding the child     Elements for
     the Element just introduced.


File: asis_ug.info,  Node: ASIS Context,  Next: ASIS Interpreter asistant,  Prev: ASIS Overview,  Up: Top

ASIS Context
************

* Menu:

* ASIS Context and Tree Files::
* Creating Tree Files for Use by ASIS::
* Different Ways to Define an ASIS Context in ASIS-for-GNAT::
* Consistency Problem::
* Processing Several Contexts at a Time::


File: asis_ug.info,  Node: ASIS Context and Tree Files,  Next: Creating Tree Files for Use by ASIS,  Up: ASIS Context

ASIS Context and Tree Files
===========================

From an ASIS application viewpoint we may view an ASIS Context as a set
of ASIS Compilation Units accessible through the ASIS queries. The
common ASIS implementation technique is to base an implementation of an
ASIS Context on some persistent data structures created by the
underlying Ada compiler when compiling Ada compilation units maintained
by this compiler. An ASIS Context can only contain compilable (that is,
legal) compilation units.

   In case of ASIS-for-GNAT, an ASIS implementation is based on tree
output files, or, simply, tree files. When called with the special
option (-gnatt), GNAT creates and outputs a tree file in case if no
error was detected during the compilation. The tree file is a kind of
the snapshot of the compiler internal data structures (basically, of
the Abstract Syntax Tree (AST)) in the very end of the successful
compilation. ASIS then inputs tree files and recreates in its internal
data structures just the same picture as the compiler had in the end of
the corresponding successful compilation.

   An important consequence of the GNAT source-based compilation model
is that AST contains full information not only about the unit being
compiled, but also about all the units upon which this unit depends
semantically. Therefore, having read a tree file, ASIS can in general
provide information about more than one unit. By processing a tree file
information can be provided about the unit for which this tree was
created and about all the units upon which it depends semantically.
However, to process several units, ASIS sometimes has to change the
tree being processed (in particular, it is the case when an application
switches between units which do not semantically depend on each other).
Therefore, in the course of an ASIS application, ASIS may read
different tree files and it may read the same tree file more then once.

   The name of a tree file is obtained from the name of the source file
being compiled by replacing its suffix with '`.adt''. For example, the
tree file for `foo.adb' is named `foo.adt'.


File: asis_ug.info,  Node: Creating Tree Files for Use by ASIS,  Next: Different Ways to Define an ASIS Context in ASIS-for-GNAT,  Prev: ASIS Context and Tree Files,  Up: ASIS Context

Creating Tree Files for Use by ASIS
===================================

* Menu:

* Creating Trees for Data Decomposition Annex::

Neither GNAT nor `gnatmake' will create tree files automatically when
you are working with your Ada program. It is the responsibility of a
user of an ASIS application to create a set of tree files which would
correctly reflect the set of the Ada components to be processed by
ASIS/ASIS applications, as well as to maintain the consistency of the
trees and the related source files.

   To create a tree file for a certain source file, the corresponding
source file must be compiled with -gnatc -gnatt flags:

         gcc -c -gnatc -gnatt foo.adb

will produce foo.adt, provided that foo.adb contains the source of a
legal Ada compilation unit. -gnatt generates a tree file, and -gnatc
turns off tree expansion. ASIS needs tree files created without tree
expansion, whereas to create an object file, GNAT needs expanded AST.
Therefore it is impossible to produce tree files together with
producing object files.

   The following things are important to remember when generating and
dealing with tree files:

  1.  ASIS-for-GNAT is distributed for a particular version of
     GNAT. All the trees to be processed by an ASIS application should
     be      generated by this specific version of the compiler.

  2.  When creating a tree file for ASIS, use two options -gnatc and
     -gnatt      separately, do not combine them into a single -gnatct
     or -gnattc option      or it will result in a generation of a
     bogus object file.

  3.  The tree file is not created if an error has been detected during
     the      compilation.

  4.  Opposite to object files, a tree file may be generated for any
     legal Ada      compilation unit, including a library package
     declaration requiring a body      and a subunit.

  5.  A set of tree files processed by ASIS (ASIS application) may be
       inconsistent, for example two tree files may have been created
     with the      different versions of the source of the same unit.
     This will lead to      inconsistencies in the corresponding ASIS
     Context. See section *Note Consistency Problem:: for      more
     details.

  6.  Do not move tree, object and source files among directories in the
         underlying file system! It may confuse ASIS, and it may detect
         inconsistency between tree and source files when opening a
     Context or you      may get wrong results when asking about the
     source or object file for a      given ASIS Compilation Unit.

  7.  When calling `gcc' or `gnatmake' to create tree files, all file
     and      directory names containing relative path information
     should start from      "./" or "../" (".\" and "..\" respectively
     in Windows NT/95). That is, to      create a tree file for the
     source file `foo.adb' located in the inner      directory named
     "inner", you should call gcc as:

               >gcc -c -gnatc -gnatt .\inner\foo.adb

     but not as

               >gcc -c -gnatc -gnatt inner\foo.ads

     otherwise ASIS will get confused.

  8.  When reading in a tree file, ASIS checks that this tree file was
     created      with '-gnatc' option, and it does not accept trees
     created without      '-gnatc'.

  9.  Tree and ALI files. If called to create a tree, GNAT does not
     destroy      an ALI file if the ALI file already exists for the
     unit being compiled      and if this ALI file is up-to-date.
     Moreover, GNAT may use some      information from the existing ALI
     file to put it into the tree file. So      if you would like to
     have both object and tree files for your program,      first
     create object files and then - tree files.

 10.  There is only one extension for tree files - .adt, whereas the
     standard      GNAT name convention for the Ada source files uses
     two different      extensions for a spec (.ads) and for a body
     (.adb). This means that if      you first compile the body for the
     tree:

               >gcc -c -gnatc -gnatt foo.adb

     and then - compile the corresponding spec for the tree:

               >gcc -c -gnatc -gnatt foo.ads

     then the tree file `foo.adt' will be created twice - first for the
         body, and then - for the spec, the tree for the spec will
     override      the tree for the body, and the information about the
     body will be lost      for ASIS. If you first create the tree for
     a spec, and then for a body,      the second tree will also
     override the first one, but no information will      be lost for
     ASIS, because the tree for a body contains full      information
     about the corresponding spec.

     To avoid losing information when creating trees for a set of Ada
     sources,      use the following rules:

     - if a set of Ada components to process makes up a complete
     partition,        use `gnatmake' (see section *Note Using gnatmake
     to Create Tree Files:: for more details);

     - otherwise first create trees for specs, and then - for bodies:

                 >gcc -c -gnatc -gnatt *.ads
                 >gcc -c -gnatc -gnatt *.adb

 11.  Reading tree files is a time-consuming operation. Try to minimize
     the      number of tree files to be processed by your application
     and to avoid      unnecessary tree swappings. (See chapter *Note
     How to Build Efficient ASIS Applications:: for some tips).

Note that between opening and closing a Context, an ASIS application
should not change its working directory (or restore it before making an
ASIS call), otherwise application behavior may be erroneous.


File: asis_ug.info,  Node: Creating Trees for Data Decomposition Annex,  Up: Creating Tree Files for Use by ASIS

Creating Trees for Data Decomposition Annex
-------------------------------------------

Using the ASIS Data Decomposition Annex (DDA) does not require anything
special to be done by an ASIS user, except one thing. The
implementation of the ASIS DDA is based on some special annotation
added by the compiler to the trees used by ASIS. An ASIS user should be
aware of the fact, that trees created for subunits does not have this
special annotation, therefore ASIS DDA queries do not work correctly on
trees created for subunits (and these queries may not work correctly if
a set of tree files making up a Context contain a tree created for a
subunit).

   So, when working with ASIS DDA, a user should avoid creating
separate trees for subunits. Actually, it is not a limitation - to
create a tree for a subunit, a user should also have the source of the
parent body around. If in this situation a user creates the tree for
the parent body, it will contain the full information (including
DDA-specific annotation) for all the subunits which are around. From
the other side, a tree created for a single subunit has to contain
information about the parent body, so it is about of the same size as
the tree for the parent body.

   The best way to create trees when using ASIS DDA is to use gnatmake
- it will never create separate trees for subunits.

