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https://github.com/AdaCore/libadalang

Ada semantic analysis library.
https://github.com/AdaCore/libadalang

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Ada semantic analysis library.

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README 

        
Libadalang

==========



Libadalang is a library for parsing and semantic analysis of Ada code. It is

meant as a building block for integration into other tools. (IDE, static

analyzers, etc.)



Libadalang provides mainly the following services to users:



* Complete syntactic analysis with error recovery, producing a precise syntax

  tree when the source is correct, and a best effort tree when the source is

  incorrect.



* Semantic queries on top of the syntactic tree, such as, but not limited to:

  * Resolution of references (what a reference corresponds to)

  * Resolution of types (what is the type of an expression)

  * General cross references queries (find all references to this entity)



Libadalang does not (at the moment) provide full legality checks for the Ada

language.  If you want such a functionality, you’ll need to use a full Ada

compiler, such as GNAT.



While it can be used in Ada (2012+) and Python (3.9 or Python 3.10) Libadalang

also provides a low-level C API (meant to write bindings to other languages)

and an experimental OCaml API.



If you have problems building or using Libadalang, or want to suggest

enhancements, please open [a GitHub

issue](https://github.com/AdaCore/libadalang/issues/). We also gladly accept

[pull requests](https://github.com/AdaCore/libadalang/pulls)!



Status of the project

---------------------



Libadalang is still in development and we allow ourselves some headroom in

terms of breaking backwards compatibility. If you want to use a stable version

of Libadalang, you'll need to build from one of the stable branches, such as

[19.1](https://github.com/AdaCore/libadalang/tree/19.1).



Libadalang currently:



* Is able to parse 100% of Ada 2012 syntax, and presents a well formed tree for

  it. Support for Ada 2022 constructs is a work in progress.



* Is able to recover most common syntax errors. The error messages are

  behind those of GNAT, but the recovery will potentially work better in many

  situations.



* Provides name resolution/navigation.



* Is able to handle some very simple incremental processing. Reparsing a source

  A and querying xref on a source B that depends on A is handled efficiently.



How to use Libadalang

---------------------



There are several ways to get Libadalang:



* Build it using the [Libadalang Alire

  crate](https://alire.ada.dev/crates/libadalang).  This will only let you

  build the current and the previous releases (i.e. not the development

  version), but is by far the easiest way, as [Alire](https://alire.ada.dev/)

  automatically deals with dependencies.



* Build it from Git repository sources: install all dependencies, generate its

  code and to build it. Please refer to the [User

  Manual](user_manual/building.rst) for detailed instructions.



* **Important**: if you are an AdaCore customer with a GNAT Pro subscription,

  please get Libadalang through GNATtracker, as this is the only version of

  Libadalang that is covered by your support contract.



To learn how to use the API from Libadalang's the development branch, you can

read the [AdaCore Live

Docs](http://docs.adacore.com/live/wave/libadalang/html/libadalang_ug/index.html)

(updated daily).



Quick overview

--------------



Libadalang has a Python API, for easy prototyping and explorative programming.

It ships with an executable named `playground`, that allows you to analyze Ada

files and play with them in an interactive Python console.



Given the following `main.adb` Ada file:



~~~ada

with Ada.Text_IO; use Ada.Text_IO;



procedure Main is

begin

    Put_Line ("Hello World");

end Main;

~~~



You can start the playground on it:



~~~sh

% playground main.adb



--

-- libadalang playground

--



The file(s) passed as argument have been put into the `u` variable, or units if

there are multiple.



Enjoy!



In [1]: print(u.root.text)

with Ada.Text_IO; use Ada.Text_IO;



procedure Main is

begin

    Put_Line ("Hello World");

end Main;



In [2]: print(u.root.findall(mdl.CallExpr))

[]



In [3]: print(u.root.findall(mdl.CallExpr)[0].text)

Put_Line ("Hello World")

~~~



The playground embeds the [IPython](https://ipython.org/) interactive Python

console, so you have a modern interactive programming environment. You can use

tab completion to explore the Libadalang API.



Libadalang and ASIS

-------------------



ASIS is widely used for static analysis of Ada code, and is an ISO standard. It

is still the go-to tool if you want to create a tool that analyses Ada code.

Also, as explained above, Libadalang is not mature yet, and cannot replace ASIS

in tools that require semantic analysis.



However, there are a few reasons you might eventually choose to use Libadalang

instead of ASIS:



1. The ASIS standard has not yet been updated to the 2012 version of Ada. More

   generally, the advantages derived from ASIS being a standard also means that

   it will evolve very slowly.



2. Syntax only tools will derive a lot of advantages on being based on

   Libadalang:



   * Libadalang will be completely tolerant to semantic errors. For example, a

     pretty-printer based on Libadalang will work whether your code is

     semantically correct or not, as long as it is syntactically correct.



   * Provided you only need syntax, Libadalang will be much faster than ASIS'

     main implementation (AdaCore's ASIS), because ASIS always does complete

     analysis of the input Ada code.



3. The design of Libadalang's semantic analysis is lazy. It will only process

   semantic information on-demand, for specific portions of the code. It means

   that you can get up-to-date information for a correct portion of the code

   even if the file contains semantic errors.



4. Libadalang has bindings to C and Python, and its design makes it easy to

   bind to new languages.



5. Libadalang is suitable to write tools that work on code that is evolving

   dynamically. It can process code and changes to code incrementally. Thus, it

   is suitable as an engine for an IDE, unlike AdaCore's ASIS implementation.



6. Libadalang is not tied to a particular compiler version. This combined with

   its staged and error tolerant design means that you can use it to detect

   bugs in Ada compilers/tools.



Implementation

--------------



The Libadalang project is based on the

[Langkit](https://github.com/AdaCore/langkit) framework, so its

Ada/Python/C/OCaml source code is not checked in this repository: it is instead

generated from the Langkit language specification that you can find in

[ada/](ada/). This language specification, while embedded in Python syntax, is

mostly its own language, the Langkit DSL, that is used to specify the part of

Ada syntax and semantics that are of interest to us.



See the [Developer Manual](dev_manual) for more information about Libadalang's

development.