Implement method call nodes

[jacosro]

Currently, method call nodes (i.e. nodes which contain an expression corresponding to a method call) are not represented as different nodes (they are GraphNodes). Maybe, it would be a good idea to represent them separately in SDG, in order to build in/out variable nodes and work with them easily. This way, a new class MethodCallNode extending the GraphNode class would be created, containing references to in/out variable nodes.

This would only exist in the SDG, so this also implies, as the SDG is built by a composition of PDGs, that there should exist a visitor which converts GraphNodes from the PDG into MethodCallNodes

@cargaji What do you think? Any alternatives?

To do:

• [x] In and out nodes
• [x] handle data dependency with new nodes
• [x] Accept variables (NameExpr) as arguments
• [x] return node?
• [x] ~Accept all types of expressions as arguments (including nested method calls) (as new issue)~
• [ ] Review for errors/improve nodes generation

[cargaji]

The alternative would be to add extra parameter input and output to method calls. This would be done in the PDG:

• Each GraphNode<MethodDeclaration> should be split into n nodes: a GraphNode<MethodDeclaration> and as many GraphNode<VariableDeclarator> as needed (each parameter and global variable used, and each parameter and variable modified in such a way that the change can be seen when querying from the original position).
• In a similar fashion, all GraphNode<? extends Statement> needs to be traversed to find all MethodCallExpr objects, so that input and output nodes can be generated and then connected to the corresponding method call.

The "creation" of the SDG is as simple as connecting each method call and its in/out nodes to all the matching method declarations (and their in/out nodes), plus adding summary arcs between in/out nodes.

[cargaji]

Useful material (papers):

• Slicing Java Programs that Throw and Catch Exceptions by Allen and Horwitz: section 2, steps 2 and 3.
• An Approach of Slicing for Object-oriented Language with Exception Handling by Jiang and Jie.
• Carlos' Master Thesis report: download here. Specifically, section 3.1, which details the creation of the SDG from scratch.

[cargaji]

Locating which method call has been executed with JavaParser + JavaSymbolSolver: https://tomassetti.me/resolve-method-calls-using-java-symbol-solver/

[jacosro]

Closing this issue since it is completed for now. Opening new issues to refine it