quiltflower: A Java repository from QuiltMC

Quiltflower

Quiltflower is a modern, general purpose decompiler focused on improving code quality, speed, and usability. Quiltflower is a fork of Fernflower and Forgeflower.

Changes include:

New language features (Try with resources, switch expressions, pattern matching, and more)
Better control flow generation (loops, try-catch, and switch, etc.)
More configurability
Better error messages
Javadoc application
Multithreading
Optimization
Many other miscellaneous features and fixes

Use

Want to use Quiltflower? There are a few ways! For Fabric and Architectury projects, Loom Quiltflower allows you to run genSources with Quiltflower. The Quiltflower Intellij IDEA plugin replaces Fernflower in IDEA with Quiltflower, and allows you to modify its settings. Or, if you want to run Quiltflower from the commandline, head over to the Releases tab and grab the latest, and then follow the instructions further down the readme. Make sure to report any issues to the Issues tab!

For support or questions, please join the Quilt toolchain discord.

Contributing

To contribute, please check out CONTRIBUTING.md and ARCHITECTURE.md!

When pulling from upstream, use https://github.com/fesh0r/fernflower

Special Thanks

Jetbrains- For maintaining Fernflower
Forge Team- For maintaining ForgeFlower
CFR- For it's large suite of very useful tests

Fernflower's readme is preserved below:

About Fernflower

Fernflower is the first actually working analytical decompiler for Java and probably for a high-level programming language in general. Naturally it is still under development, please send your bug reports and improvement suggestions to the issue tracker.

Licence

Fernflower is licenced under the Apache Licence Version 2.0.

Running from command line

java -jar quiltflower.jar [-<option>=<value>]* [<source>]+ <destination>

* means 0 or more times
+ means 1 or more times

<source>: file or directory with files to be decompiled. Directories are recursively scanned. Allowed file extensions are class, zip and jar. Sources prefixed with -e= mean "library" files that won't be decompiled, but taken into account when analysing relationships between classes or methods. Especially renaming of identifiers (s. option 'ren') can benefit from information about external classes.

<destination>: destination directory

<option>, <value>: a command-line option with the corresponding value (see "Command-line options" below).

Examples:

java -jar quiltflower.jar -hes=0 -hdc=0 c:\Temp\binary\ -e=c:\Java\rt.jar c:\Temp\source\

java -jar quiltflower.jar -dgs=1 c:\Temp\binary\library.jar c:\Temp\binary\Boot.class c:\Temp\source\

Command-line options

To force saving as a file or folder, --file and --folder can be provided. If not specified, Quiltflower will try to guess based on the file name.

With the exception of mpm, urc, ind, thr and log, the value of 1 means the option is activated, 0 - deactivated. Default value, if any, is given between parentheses.

Typically, the following options will be changed by user, if any: hes, hdc, dgs, mpm, ren, urc, ind, thr, tlf, tco The rest of options can be left as they are: they are aimed at professional reverse engineers.

rbr (1): Hide bridge methods
rsy (1): Hide synthetic class members
din (1): Decompile inner classes
dc4 (1): Collapse 1.4 class references
das (1): Decompile assertions
hes (1): Hide empty super invocation
hdc (1): Hide empty default constructor
dgs (1): Decompile generic signatures
ner (1): Assume return not throwing exceptions
esm (1): Ensure synchronized ranges are complete
den (1): Decompile enumerations
rgn (1): Remove getClass() invocation, when it is part of a qualified new statement
lit (0): Output numeric literals "as-is"
bto (1): Interpret int 1 as boolean true (workaround to a compiler bug)
asc (0): Encode non-ASCII characters in string and character literals as Unicode escapes
nns (0): Allow for not set synthetic attribute (workaround to a compiler bug)
uto (1): Consider nameless types as java.lang.Object (workaround to a compiler architecture flaw)
udv (1): Reconstruct variable names from debug information, if present
ump (1): Use method parameter names from the MethodParameter attribute.
rer (1): Remove empty exception ranges
fdi (1): De-inline finally structures
inn (1): Check for IntelliJ IDEA-specific @NotNull annotation and remove inserted code if found
lac (0): Decompile lambda expressions to anonymous classes
bsm (0): Add mappings for source bytecode instructions to decompiled code lines
dcl (0): Dump line mappings to output archive zip entry extra data
iib (0): Ignore invalid bytecode
vac (0): Verify that anonymous classes can be anonymous
tcs (0): Simplify boolean constants in ternary operations
pam (1): Decompile pattern matching
tlf (1): loop-in-try fixes
tco (1): Allow ternaries to be generated in if and loop conditions
swe (1): Decompile Switch Expressions in modern Java
shs (0): Display code blocks hidden, for debugging purposes
ovr (1): Show override annotations for methods known to the decompiler.
ssp (1): Second-Pass Stack Simplficiation
vvm (0): Verify variable merges before remapping them
iec (0): Give the decompiler information about every jar on the classpath.
jrt (0/if running from CLI, current): The path to a java runtime to add to the classpath, or 1 or current to add the java runtime of the active JVM to the classpath.
ega (0): Explicit Generic Arguments
isl (1): Inline simple lambdas
log (INFO): A logging level, possible values are TRACE, INFO, WARN, ERROR
mpm (0): [DEPRECATED] max processing time per decompiled method, in seconds. 0 means no upper limit
ren (0): Rename ambiguous (resp. obfuscated) classes and class elements
urc (-): Full name of a user-supplied class implementing IIdentifierRenamer interface. It is used to determine which class identifiers should be renamed and provides new identifier names (see "Renaming identifiers")
nls (0): define new line character to be used for output. 0 - '\r\n' (Windows), 1 - '\n' (Unix), default is OS-dependent
ind (3 spaces): Indentation string
pll (160): Max line length before formatting
ban (-): Banner to display before every root class definition
erm (-): Message to display when a decomplication error occurs
thr: maximum number of threads (default is number of threads available to the JVM)
jvn (0): Use jad variable naming for local variables
sef (0): Skip copying non-class files from the input folder or file to the output
win (1): Warn about inconsistent inner class attributes
dbe (1): Dump bytecode on errors
dee (1): Dump exceptions on errors
dec (1): Decompiler error comments
sfc (0): Debug comments showing the class SourceFile attribute if present
dcc (0): Decompile complex constant-dynamic bootstraps, that might have different or slower run-time behaviour when recompiled
dpr (1): Decompile preview features in latest Java versions

Renaming identifiers

Some obfuscators give classes and their member elements short, meaningless and above all ambiguous names. Recompiling of such code leads to a great number of conflicts. Therefore it is advisable to let the decompiler rename elements in its turn, ensuring uniqueness of each identifier.

Option 'ren' (i.e. -ren=1) activates renaming functionality. Default renaming strategy goes as follows:

rename an element if its name is a reserved word or is shorter than 3 characters
new names are built according to a simple pattern: (class|method|field)_<consecutive unique number>
You can overwrite this rules by providing your own implementation of the 4 key methods invoked by the decompiler while renaming. Simply pass a class that implements org.jetbrains.java.decompiler.main.extern.IIdentifierRenamer in the option 'urc' (e.g. -urc=com.example.MyRenamer) to Fernflower. The class must be available on the application classpath.

The meaning of each method should be clear from naming: toBeRenamed determine whether the element will be renamed, while the other three provide new names for classes, methods and fields respectively.

QuiltMC/quiltflower