Installing Stainless¶

General Requirement¶

Java 17 JRE It suffices to have headless OpenJDK JRE 17 (e.g. one that one gets with apt install openjdk-17-jre-headless on Debian/Ubuntu). Make sure that java -version reports a version starting with 1.17, such as openjdk version "1.17 or java version "1.17.

Stainless bundles Scala 3 compiler front-end and runs it before it starts compilation.

You can obtain Stainless:

via a package manager (see Section Obtain From A Package Manager)
via a standalone release (see Section Use Standalone Release)
by building it from source (see Section Build from Source on Linux & macOS)
by using it via the SBT plugin (see Section Usage Within An Existing Project)

Obtain From A Package Manager¶

Stainless is available via Snap and the AUR.

Snap¶

A package for Stainless is available on the Snap store as stainless with an experimental edge release. It can be used to install and run Stainless on any Snap enabled system (e.g. Ubuntu).

In a terminal, you can type:

$ sudo snap install stainless --edge

This exposes the stainless command and comes packaged with JDK 17 and z3, cvc5, and princess as SMT solvers. The edge build follows the latest commit on the main branch.

Arch User Repository (AUR)¶

A package for Stainless is available on the Arch User Repository (AUR) for ArchLinux as stainless-git, which follows the latest commit on the main branch. You can use your favorite AUR helper (we’ve tried yay, see AUR Helpers), or follow the detailed instructions as on the ArchWiki to install the package.

For quick reference, with yay (or other AUR helpers accordingly):

$ yay -S stainless-git

and manually:

$ git clone https://aur.archlinux.org/stainless-git.git
$ cd stainless-git
$ makepkg -si

The option -s acquires dependencies (java, git, sbt) using pacman, and -i installs Stainless system-wide. Omit -i to avoid installing system-wide, and only perform a local build in the directory.

The solver packages z3, cvc4, and cvc5^AUR can be added as optional dependencies, and having at least one is recommended for general use.

Issues with the package build should ideally be reported on the AUR package page itself.

Github Codespaces¶

To allow running Stainless with only a browser, we have provided a sample repository to use Stainless with Github Codespaces. Github Codespaces are cloud machines that can be access via Visual Studio Code locally or in the browser. In our experience (as of October 2023), this flow works well, given the provided Ubuntu Linux virtual machines with 16GB of RAM and substantial processing power. Please see this repository for further details.

You can also locally set up Stainless on a self-hosted machine and access it remotely over SSH with VSCode.

SSH and VSCode¶

Visual Studio Code offers a feature allowing to connect to a host over SSH and edit code located on this host. This is useful to edit code on a remote machine using the local Visual Studio Code editor and running Stainless on this remote machine. See this official documentation to learn more about this feature.

If you have access to a remote machine over SSH, this is a good way to use Stainless. Please note that you have to install Stainless on the remote machine following the instructions above.

Use Standalone Release¶

Download the latest Stainless release from the Releases page on GitHub, under the Assets section. Make sure to pick the appropriate ZIP for your operating system. The releases are bundled with z3 4.12.2+ and cvc5 1.0.8+.
Unzip the file you just downloaded to a directory.
(Optional) Add this directory to your PATH. This will let you invoke Stainless via the stainless command instead of its fully qualified path in step 5.
Paste the following code in a file named HelloStainless.scala:

import stainless.collection.*

object HelloStainless {
  def myTail(xs: List[BigInt]): BigInt = {
    require(xs.nonEmpty)
    xs match
      case Cons(h, _) => h // Match provably exhaustive
  }
}

In a terminal, type the following command, substituting the proper path to the directory where you unzipped the latest release:

$ /path/to/unzipped/directory/stainless HelloStainless.scala

The output should read:

[  Info  ] Finished compiling
[  Info  ] Preprocessing finished
[  Info  ] Finished lowering the symbols
[  Info  ] Finished generating VCs
[  Info  ] Starting verification...
[  Info  ]  Verified: 0 / 1
[  Info  ]  Verified: 1 / 1
[  Info  ] Done in 2.59s
[  Info  ]   ┌───────────────────┐
[  Info  ] ╔═╡ stainless summary ╞═════════════════════════════════════════════════════════════════════════════════╗
[  Info  ] ║ └───────────────────┘                                                                                 ║
[  Info  ] ║ HelloStainless.scala:6:9:     myTail  body assertion: match exhaustiveness     valid   nativez3   0.1 ║
[  Info  ] ╟┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄╢
[  Info  ] ║ total: 1    valid: 1    (0 from cache, 0 trivial) invalid: 0    unknown: 0    time:    0.15           ║
[  Info  ] ╚═══════════════════════════════════════════════════════════════════════════════════════════════════════╝
[  Info  ] Verification pipeline summary:
[  Info  ]   nativez3, non-batched
[  Info  ] Shutting down executor service.

Usage Within An Existing Project¶

Stainless can also be used within an existing SBT >=1.7.0 project.

Start by installing an external solver (see Section “External Solver Binaries”).
Download sbt-stainless from the GitHub releases, and move it to the directory of the project. Starting from the following project structure:

MyProject
├── build.sbt
├── project
│   └── build.properties
├── sbt-stainless.zip
└── src/

Unzipping sbt-stainless.zip should yield the following:

MyProject
├── build.sbt
├── project
│   ├── build.properties
│   └── lib                     <--------
│       └── sbt-stainless.jar   <--------
├── sbt-stainless.zip
├── src/
└── stainless/                  <--------

That is, it should create a stainless/ directory and a lib/ directory with project/. If, instead, the unzipping process creates a sbt-stainless/ directory containing the lib/project/ and stainless/ directories, these should be moved according to the above structure.

Finally, the plugin must be explicitly enabled for intended projects in build.sbt with .enablePlugins(StainlessPlugin). For instance:

// build.sbt
lazy val algorithm = project
    .in(file("algorithm"))
    .enablePlugins(StainlessPlugin) // <-- Enabling Stainless verification on this module!
    .settings(...)

Note that if you are using .scala build files you need to use the fully qualified name ch.epfl.lara.sbt.stainless.StainlessPlugin. Also, because Stainless accepts a subset of the Scala language, you may need to refactor your build and code somewhat to successfully run Stainless on a module.

After modifying the build, type reload if inside the sbt interactive shell. From now on, when executing compile on a module where the StainlessPlugin is enabled, Stainless will check your Scala code and report errors in the shell (just like any other error that would be reported during compilation).

That’s all there is to it. Note that the sbt-stainless plugin is a more recent addition to Stainless compared to command-line script and is still evolving. For now, there is no incremental compilation support.

Also, note that the plugin offers a stainlessEnabled setting that can help in experimenting with Stainless. The stainlessEnabled setting is set to true by default, but you can flip the flag to false by typing set every stainlessEnabled := false while inside the sbt interactive shell to temporarily bypass checking.

If you need to run your code with the Stainless SBT plugin, you can create a Main.scala file as follows in the correct source directory (e.g. src/main/scala/your/package/example/Main.scala):

package your.package.example

object Main:
  def main(args: Array[String]): Unit =
    println("Hello, World!")

and then you can run it with:

$ sbt "runMain your.package.example.Main"

Note that you Main object cannot extend App and the main function must take args: Array[String] as parameter.

Running Code with Stainless dependencies¶

If you are debugging your scala code before running stainless on it (e.g. using a simple editor with scala-cli --watch), you can use this workflow with stainless as well; you just need to make sure that Stainless libraries are visible to the Scala compiler.

The simplest way is to use the release package, which contains stainless-cli script, a simple wrapper around scala-cli that adds the jar dependency on the compiled and source version of stainless library.

Building a jar:

You can package the Stainless library into a jar like this:

$ cd path/to/stainless/
$ sbt stainless-library/packageBin

Add the generated Stainless library jar file when invoking the compiler with scalac and the JVM with scala or java. For instance:

$ mkdir -p ~/.scala_objects
$ scalac -d ~/.scala_objects -cp /path/to/stainless/frontends/library/target/scala-3.3.3/stainless-library_3-X.Y.Z-A-BCDEFGHI.jar MyFile1.scala MyFile2.scala # and so on
$ scala -cp ~/.scala_objects:/path/to/stainless/frontends/library/target/scala-3.3.3/stainless-library_3-X.Y.Z-A-BCDEFGHI.jar MyMainClass

where X.Y.Z is the Stainless version and A-BCDEFGHI is some hash (which can be autocompleted by the terminal).

Using sources:

Clone the sources from https://github.com/epfl-lara/stainless
Create a folder to put compiled Scala objects: mkdir -p ~/.scala_objects
Compile your code (here in MyFile.scala, though you can have more than one file) while referring to the Stainless library sources: scalac -d ~/.scala_objects $(find /path/to/stainless/frontends/library/stainless/ -name "*.scala") MyFile.scala
Run your code (replace MyMainClass with the name of your main object): scala -cp ~/.scala_objects MyMainClass

External Solver Binaries¶

If no external SMT solvers (such as z3 or cvc5) are found, Stainless will use the bundled Scala-based Princess solver

To improve performance, we highly recommend that you install the following two additional external SMT solvers for your platform:

cvc5, https://cvc5.github.io/
z3, https://github.com/Z3Prover/z3

The simplest and recommended way to obtain these solvers is from your package manager. They are available under their respective names z3 and cvc5 for Ubuntu, Debian, Fedora, ArchLinux (+ AUR), nixOS, and macOS (via brew), to name a few.

You can enable these solvers using --solvers=smt-z3 and --solvers=smt-cvc5 flags. Multiple solvers can be used in portfolio mode, as with the options --timeout=15 --solvers=smt-z3,smt-cvc5, where verification succeeds if at least one of the solvers proves (within the given number of seconds) each of the verification conditions. We suggest ordering solvers starting from the one perceived most likely to succeed quickly.

Note that most recent versions of the solvers should work well and might even have different sets of soundness-related issues.

For final verification runs of highly critical software, we recommend that (instead of the portfolio mode) you obtain several solvers and their versions, then try a single solver at a time and ensure that each verification run succeeds (thus applying N-version programming to SMT solver implementations).

If needed, the solver binaries are published for various platforms on their GitHub releases pages. Example installation instructions for chosen versions follow. They should be similar for other versions and platforms.

Install z3 4.12.2¶

Download z3 4.12.2 from https://github.com/Z3Prover/z3/releases/tag/z3-4.12.2
Unzip the downloaded archive
Copy the z3 binary found in the bin/ directory of the inflated archive to a directory in your $PATH, eg., /usr/local/bin.
Make sure z3 can be found, by opening a new terminal window and typing:

$ z3 --version

The output should read:

z3 version 4.12.2 - 64 bit

Install cvc5 1.2.0¶

Download cvc5 1.2.0 from https://github.com/cvc5/cvc5/releases/tag/cvc5-1.2.0 for your platform. Make sure to pick one of the zip files labeled “static”.
Unzip the downloaded archive.
Copy the cvc5 binary found in the bin/ directory of the inflated archive to a directory in your $PATH, eg., /usr/local/bin.
Make sure cvc5 can be found, by opening a new terminal window and typing:

$ cvc5 --version | head

The output should begin with:

This is cvc5 version 1.0.8

Build from Source on Linux & macOS¶

To build Stainless from source, you need:

For Java and sbt, you can follow their individual installation instructions for your platform, or use the standard Scala setup guide here, which uses Coursier.

With dependencies in place, you can clone the repository (recursively) and build Stainless:

git clone --recursive https://github.com/epfl-lara/stainless
cd stainless
sbt Universal/stage

If all goes well, a script is generated for the front end at frontends/dotty/target/universal/stage/bin/stainless-dotty.

It can be useful to introduce a soft-link from this script to a file called stainless to shorten the reference:

$ ln -s frontends/dotty/target/universal/stage/bin/stainless-dotty stainless

Use this script as you would use the Scala compiler scalac to compile Scala files. The default behavior of Stainless is to formally verify files, instead of generating JVM class files.

Analogous scripts work for various platforms and allow additional control over the execution, such as passing JVM arguments or system properties:

$ stainless -Dscalaz3.debug.load=true -J-Xmx6G --help

Note that Stainless is organized as a structure of several projects. The main project lives in core while the Scala 3 frontend can be found in frontends/dotty. From a user’s point of view, this should be largely transparent, and the build command should take care of everything.

Build from Source on Windows¶

Before following the infrequently updated instructions in this section, considering running Ubuntu on Windows via Windows Subsystem for Linux (WSL2) and following the instructions for Linux.

Get the sources of Stainless by cloning the official Stainless repository. You will need a Git shell for windows, e.g. Git for Windows. On Windows, please do not use sbt Universal/stage as this generates a Windows batch file which is unusable, because it contains commands that are too long for Windows. Instead, please use sbt stainless-dotty-standalone/assembly as follows:

$ git clone --recursive https://github.com/epfl-lara/stainless.git
Cloning into 'stainless'...
// ...
$ cd stainless
$ git submodule update --init --recursive
$ sbt stainless-dotty-standalone/assembly // takes about 1 minutes

Stainless can then be run with the command:

$ java -jar frontends\stainless-dotty-standalone\target\scala-{SCALA_VERSION}\stainless-dotty-standalone-{VERSION}.jar --help

where SCALA_VERSION denotes the Scala version and VERSION denotes Stainless version and should be replaced with the actual versions. The paths should be unique, and auto-completion is recommended.

Running Tests¶

Stainless comes with a test suite. Use the following commands to invoke different test suites:

$ sbt test
$ sbt IntegrationTest/test

It’s also possible to run tests in isolation, for example, the following command runs Extraction tests on all files in termination/looping:

$ sbt 'IntegrationTest/testOnly *ExtractionSuite* -- -z "in termination/looping"'

Building Stainless Documentation¶

Stainless documentation is available at https://epfl-lara.github.io/stainless/. To build the documentation locally, you will need Sphinx (http://sphinx-doc.org/), a restructured text toolkit that was originally developed to support Python documentation.

On Ubuntu 24, you can use sudo apt install sphinx-common

The documentation resides in the core/src/sphinx/ directory and can be built using the provided Makefile. To do this, in a Linux shell, type make html, and open in your web browser the generated top-level local HTML file, by default stored in core/src/sphinx/_build/html/index.html. Also, you can open the *.rst documentation files in a text editor, as they are human-readable in their source form as well.

Note for project maintainers: to build documentation on GitHub Pages, use make gh-pages in the same Makefile, or adapt it to your needs.

Using IDEs with –no-colors option. Emacs illustration¶

Using command line option --no-colors asks Stainless to produce clear 7-bit ASCII output with error messages in a standardized format:

FileName.scala:LineNo:ColNo: text of the error message

This helps IDEs to pick up line numbers and show error location in the source file.

In emacs editor, you can invoke ansi-term and compilation-shell-minor-mode. Then, run

stainless --no-colors <InputFilesAndOptions>

You may also consider using the --watch option, which reruns Stainless and updates the report whenever you save one of the input files.

You should now be able to click on a message for verification condition to jump to the appropriate position in the appropriate file, as well as to use emacs commands previous-error and next-error to navigate through errors and other verification-condition outcomes.

Here is a very simple illustration that introduces an interactive comp-ansi-term command that creates new window with ansi-term and minor compilation mode:

(setq comp-terminal-current-number 1)
(defun create-numbered-comp-terminal ()
  (ansi-term "/bin/bash")
  (rename-buffer (concat "q" (number-to-string comp-terminal-current-number)) 1)
  (setq comp-terminal-current-number (+ comp-terminal-current-number 1))
  (compilation-shell-minor-mode)
)
(defun comp-ansi-term (arg)
  "Run ansi-term with bash and compilation-shell-minor-mode in buffer named q_N for increasing N" (interactive "P")
  (create-numbered-comp-terminal)
  (split-window-vertically)
  (previous-buffer)
  (other-window 1)
)

The following globally binds the above command to the F3 key and binds F7 and F8 to commands for navigating reports:

(global-set-key [f3] 'comp-ansi-term)
(global-set-key [f7] 'previous-error)
(global-set-key [f8] 'next-error)

For more information, please consult the documentation for emacs.