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https://github.com/leibnitz27/cfr

This is the public repository for the CFR Java decompiler
https://github.com/leibnitz27/cfr

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This is the public repository for the CFR Java decompiler

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# CFR - Another Java Decompiler \o/



This is the public repository for the CFR decompiler, main site hosted at benf.org/other/cfr



CFR will decompile modern Java features - including much of Java 9, 12 & 14, but is written entirely in Java 6, so will work anywhere!  (FAQ) - It'll even make a decent go of turning class files from other JVM languages back into java!



To use, simply run the specific version jar, with the class name(s) you want to decompile (either as a path to a class file, or as a fully qualified classname on your classpath).

(`--help` to list arguments).



Alternately, to decompile an entire jar, simply provide the jar path, and if you want to emit files (which you probably do!) add `--outputdir /tmp/putithere`.



# Getting CFR



The main site for CFR is benf.org/other/cfr, where releases are available with a bunch of rambling musings from the author.



Since 0.145, Binaries are published on github along with release tags.



You can also download CFR from your favourite maven repo, though releases are published a few days late usually, to allow for release regret.



# Issues



If you have an issue, please **_DO NOT_** include copyright materials.  I will have to delete your issue.



# Building CFR



Dead easy!



Just ensure you have [Maven](https://maven.apache.org/) installed. Then `mvn compile` in the root directory of this project will get you what you need.



Note: If you encounter a `maven-compiler-plugin...: Compilation failure` error while trying to compile the project then your `JAVA_HOME` environment variable is probably pointing to a JDK version that doesn't support `6` for the `source` or `target` compile options.

Fix this by pointing `JAVA_HOME` to a JDK version that still supports compiling to Java 1.6 such as JDK 11. Also note, the version of Java on your `JAVA` may need to be greater than 1.6 if you are using Maven version `>=3.3.1` which requires Java 1.7. The best solution is to use JDK 8, 9, 10 or 11 for both your `PATH` and `JAVA_HOME`.



The main class is `org.benf.cfr.reader.Main`, so once you've built, you can test it out (from `target/classes`)

```

java org.benf.cfr.reader.Main java.lang.Object

```

to get CFR to decompile `java.lang.Object`.



## Decompilation tests



As part of the Maven build automatic decompilation tests are performed. They verify that the current decompiled output of CFR matches the expected previous output. The test data (Java class and JAR files) are part of a separate Git repository; it is therefore necessary to clone this repository with `git clone --recurse-submodules`. The expected output and CFR test configuration is however part of this repository to allow altering it without having to modify the corresponding test data. The test data is in the `decompilation-test/test-data` directory, and the respective expected data and custom configuration is in the `decompilation-test/test-data-expected-output` directory (with a similar directory structure, see [Expected data structure](#expected-data-structure) below).



The decompilation tests are also performed by the GitHub workflow, and in case of test failures the unified diff is available in a [workflow artifact](https://docs.github.com/en/actions/managing-workflow-runs/downloading-workflow-artifacts) called "decompilation-test-failures-diff".



**The expected output is not the gold standard**, it merely describes the currently expected output. There is nothing wrong with adjusting the expected output, if the changes to the decompilation results are reasonable.



The test class is [`org.benf.cfr.test.DecompilationTest`](decompilation-test/src/org/benf/cfr/test/DecompilationTest.java). It can be modified to adjust the test directories, or to ignore certain class files or JARs. Additionally it is possible to directly execute the tests there from the IDE. This usually gives better output than what is shown by Maven, and allows using the built-in IDE functionality for showing differences between the expected and the actual data.



### Options file



The decompilation process can be customized by adding an options file. Each line of it specifies a CFR option, with key and value separated by a space. Empty lines and lines starting with `#` are ignored and can be used for comments.



Example:

```

# Enable identifier renaming

renameillegalidents true

```



See [Expected data structure](#expected-data-structure) below for how to name the file and where to place it.



### Expected data structure



#### Class files



For class files the expected data and custom configuration is in the same respective location under `test-data-expected-output`, with the file names being based on the class file name.



For example, for the class file `test-data/classes/subdir/MyClass.class` the following files can be used:



- `test-data-expected-output/classes/subdir/`

    - `MyClass.expected.java`  

      Contains the expected decompiled Java output, optionally with [decompilation notes](#decompilation-note-comments).

    - `MyClass.options`  

      An optional [options file](#options-file) customizing decompilation.

    - `MyClass.expected.summary`  

      Contains the expected summary reported by the CFR API. Can be omitted when no summary is produced.

    - `MyClass.expected.exceptions`  

      Contains the expected exceptions reported by the CFR API. Can be omitted when no exception is reported.



#### JAR files



For JAR files the expected data and custom configuration is inside a directory with the name of the JAR file in the respective location under `test-data-expected-output`. Expected Java output files include the package name in their file name, for example `mypackage.MyClass.java`. The options file and the expected summary and exceptions file use the "file name" `_`. For [multi-release JARs](https://openjdk.java.net/jeps/238) the directory contains subdirectories for version specific classes. The directory name has the form `java-`.



For example, for the multi-release JAR file `test-data/jars/subdir/MyJar.jar` the following files can be used:

- `test-data-expected-output/jars/subdir/MyJar/`

    - `mypackage.MyClass.java`  

      Contains the expected decompiled Java output for the class `mypackage.MyClass`, optionally with [decompilation notes](#decompilation-note-comments).

    - `java-11/mypackage.MyClass.java`  

      Contains the expected decompiled Java output for a class file specific to Java 11 and higher (for multi-release JARs).

    - `_.options`  

      An optional [options file](#options-file) customizing decompilation.

    - `_.expected.summary`  

      Contains the expected summary reported by the CFR API. Can be omitted when no summary is produced.

    - `_.expected.exceptions`  

      Contains the expected exceptions reported by the CFR API. Can be omitted when no exception is reported.



### Decompilation note comments



The expected Java output files support comments representing _decompilation notes_. They are ignored during comparison with the actual Java output and can for example be used to indicate incorrect or improvable CFR output. There are two kinds of decompilation notes:



- Line: Start with `//#` (optionally prefixed with whitespace)

- Inline: `/*# ... #*/`



Line decompilation notes should be used sparingly, especially in large files, because they shift line numbers for the diff files (due to being removed during comparison), which can be confusing.



Example:

```java

//# Line decompilation note

public class MyClass {

    public static void main(String[] stringArray/*# Inline decompilation note #*/) {

        ...

    }

}

```



### Updating / creating expected data



When adding a lot of new classes or JAR files for the decompilation tests or when a change to CFR affects the output for a lot of classes or JAR files, manually creating or updating the expected output can be rather cumbersome. For these cases the following system properties exist which help with this. They can be set with `-D` when running tests. However, when these system properties are set, the respective tests will still fail (but the expected data is updated) to prevent accidentally using them for regular test execution.



- `cfr.decompilation-test.create-expected`  

Generates all missing expected test data based on the current CFR output.

- `cfr.decompilation-test.update-expected`  

Updates the expected test data to match the actual data produced by CFR. Note that this does not work for expected Java output using [decompilation notes](#decompilation-note-comments) because those comments would get lost. The affected tests have to be updated manually.