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# Spoon-smpl: Semantic Patches for Java

This Spoon module implements the Semantic Patch Language called [SmPL](https://en.wikipedia.org/wiki/Coccinelle_(software)#Semantic_Patch_Language "Wikipedia entry"). The Semantic Patch Language, invented for C by the seminal tool [Coccinelle](https://github.com/coccinelle/coccinelle) enables to apply transformations in an automated way, where the transformation itself is a patch written in a special syntax.

Here is an example  of a semantic patch that replaces all calls to a specific method by another one.

```java
@@
Context ctx;
expression E;
@@
- ctx.getResources().getColor(E)
+ ContextCompat.getColor(ctx , E)
``` 

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Spoon-SmPL's initial version has been implemented by Mikael Forsberg as part of his master's thesis ["Design and Implementation of Semantic Patch Support for the Spoon Java Transformation Engine' at KTH Royal Institute of Technology"](http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-291226).
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References:
* [SmPL: A Domain-Specific Language for Specifying Collateral Evolutions in Linux Device Drivers](http://coccinelle.lip6.fr/papers/ercim.pdf)
* [A Foundation for Flow-Based Program Matching Using Temporal Logic and Model Checking](http://coccinelle.lip6.fr/papers/popl09.pdf)
* [Semantic Patches for Java Program Transformation](https://drops.dagstuhl.de/opus/volltexte/2019/10814/pdf/LIPIcs-ECOOP-2019-22.pdf)
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* [Semantic Patches for Java Program Transformation](https://drops.dagstuhl.de/opus/volltexte/2019/10814/pdf/LIPIcs-ECOOP-2019-22.pdf)
* [Design and Implementation of Semantic Patch Support for the Spoon Java Transformation Engine' at KTH Royal Institute of Technology](http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-291226)
 
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## Architecture Notes

* Parsing SMPL: see SmPLLexer
    *  SmPLLexer is used by SmPLParser, whose main method is method `parse`. Next, method `rewrite` transforms the SmPL code into the Java DSL.
* class `SmPLRule` encapsulates a single rule, it is created by method `SmPLParser#compile`
* class `FormulaCompiler` generates the CTL formula, method `compileFormula()` returns a `Formula`
* `ModelChecker` takes a `CFGModel` as input (there is one `CFGModel` instance per method in the project to be analyzed) (there are many `CFGModel` and only one `Formula`, and then evaluates the formula on the model. The evaluation is done through interpretation with a visitor over the formula code. It returns a `Result` containing a set of `Witness` that encode the metavariable bindings and transformation operations, and this set is taken as input by `Transformer`.
* `Transformer` takes the CFG model and a set of `Witness`
* package `spoon.smpl.operation` contains reified operations and a way to execute them
* `Substitutor` substitutes meta-variables by their bound values
* The full loop can be seen in method `spoon.smpl.SmPLProcessor#tryApplyPatch`

## Ideas

* CFGModel could be merged SmPLMethodCFG
* The Operation hierarchy could be merged with that of Gumtree-Spoon
* Substitutor could be unified with the existing Pattern architecture.