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 ASISContext
with the ‘external world’. The way of making this association and the meaning of the corresponding parameters of theAssociate
query are implementation-specific, but as soon as this association has been made and aContext
variable is opened, the ASISContext
designated by this variable may be considered to be a set of ASISCompilation_Unit
s available through the ASIS queries.
Asis.Ada_Environments.Open (...);
Opening an ASIS
Context
variable makes the correspondingContext
accessible to all ASIS queries.After opening the
Context
, an ASIS application can start obtaining ASISCompilation_Unit
s from it, can further analyzeCompilation_Unit
s by decomposing them into ASISElement
s, etc. ASIS relies on the fact that the content of aContext
remains ‘frozen’ as long as theContext
remains open. It is erroneous to change through some non-ASIS program any data structures used by an ASIS implementation to define and implement thisContext
while theContext
is open.Now all the ASIS queries can be used. It is possible to access
Compilation_Unit
s from theContext
, to decompose units into syntacticElement
s, to query syntactic and semantic properties of theseElement
s 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 ofCompilation_Unit
,Element
andLine
types obtained when thisContext
was open become obsolete, and it is erroneous to use them after theContext
was closed. The content of thisContext
need not be frozen while theContext
remains closed. Note that a closedContext
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 ASISCompilation_Unit
s) of theContext
may be different from what was in theContext
before, because the external world may have changed while theContext
remained closed.Asis.Ada_Environments.Dissociate (...);
This query breaks the association between the corresponding ASIS
Context
and the ‘external world’, and the correspondingContext
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 Context
s opened at a time (the upper
limit is implementation-specific), and for each open Context
, an application
can process several Compilation_Unit
s 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 Context
s and on the
number of the ASIS Compilation_Unit
s 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.