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SSLR stands for SonarSource Language Recognizer, this is a lightweight Java library which provides all the required material to analyse any piece of source code. For the time being, by using SSLR you can quickly create a lexer, a parser and some AST visitors to implement for instance some quality rules or to compute some measures. This library is already used in Sonar used in SonarQubeTM by the Java, JavaScript, COBOL, C#, Python, PL/SQL, C/C++, Flex, etc. plugins.

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Community support: feel free to ask any question on the Sonar Dev SonarQubeTM developer mailing-list

License: LGPLv3

Motivations

Why yet another tool for language recognition ? Why not reusing open source and well-know libraries like ANTLR or JavaCC ? This is the first question asked by any developer discovering SSLR. Of course this option was seriously studied and had big advantages but we decided to start from scratch for the following reasons :

  • The Sonar SonarQubeTM team is TDD addict and we think that existing tools don't fit well with TDD as they require some code generation and doesn't provide any simple and quick way to unit test all part of a source code analyser like a parsing rule for instance. 
  • The Sonar SonarQubeTM team is KISS addict and so we think that a Java developer should be able to do anything from its favorite IDE.
  • This technology is also used to analyse some legacy languages like COBOL for instance which require some very specific lexing and preprocessing features. Implementing those features would have required to fully master the implementation of those existing tools and so we didn't benefit from a black box approach.
  • In any case, the ultimate goal of SSLR is to provide a complete compiler front-end stack, which goes well beyond the parsing. SSLR will sooner or later provide the required material to fully implement a:
    • Symbolic table (currently in beta)
    • Control flow graph
    • Data flow analysis
    • LLVM IR emitter
    • ...

Features

Here are the main features of SSLR :

  • Easy integration and use
    • Just add a dependency on a jar file (or several jar according to what you want to use : lexer/parser, xpath, common rules, symbol table, ...)
    • No special step to add to the build process
    • No "untouchable" generated code
  • Everything in java
    • Definition of grammar and lexer directly in code using Java
    • No break in IDE support (syntax highlighting, code navigation, refactoring, etc)
  • Mature and production ready
    • This technology is already used in production to analyse millions of COBOL, PL/SQL, Java, C, C#, ... lines of code
    • Awesome performances
  • Some common rules and basic metric computations available out-of-the-box
  • XPath library to query the AST
  • Toolkit to browse the AST of any source code and to evaluate XPath expressions on it

Limitations

SSLR evolves pretty quickly and we hope to remove those limitations sooner or later :

  • No way to inject some semantic actions
  • No way to tune the AST generation 

SSLR in Action

If you want to start working with SSLR, you must be familiar with the following standard concepts : Lexical Analysis, Parsing Expression Grammar and AST(Abstract Syntax Tree). From there you can directly have a look to the source code of the JavaScript (lexer/parser, rules), Flex (lexer/parser, rules) or Python (lexer/parser, rules) plugins to see how those languages are analysed with help of SSLR. 

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