Error Prone Workshop

Download the slides here.

Initial setup of the workshop

Start by cloning this repository locally from GitHub.
Checkout the workshop branch.
Make sure to run mvn clean install in the root of this repository.
Open your code editor and familiarize yourself with the project structure.

In IntelliJ IDEA (or your preferred editor), try to run the WorkshopRefasterRulesTest test. You might see the following error:

java: exporting a package from system module jdk.compiler is not allowed with --release

If this happens, go to File -> Settings... -> Build, Execution, Deployment -> Compiler -> Java Compiler and deselect the option Use '--release' option for cross-compilation (Java 9 and later).

If you encounter any other bugs when running mvn clean install, make sure you are using a recent release of JDK 17.

Now the project is ready for the workshop.

Part 1: Writing Refaster rules

During this part of the workshop we will implement multiple Refaster rules.

Go to the workshop module and navigate to the tech.picnic.errorprone.workshop.refasterrules package. There you can find one example and five different exercises to do. Make sure to open the WorkshopRefasterRulesTest class where you can enable tests. Per assignment there is a test in this class that you can enable (by dropping the @Disabled annotation) to validate your changes. The goal is to implement or improve the Refaster rules such that the enabled tests pass.

Tips:

Go through the exercises in the proposed order.
The XXX: comments explain what needs to happen.
Find the test case for each Refaster rule by looking for the name of the Refaster rule, prefixed with test. For example, the WorkshopAssignment0Rules.java rule collection has a Refaster rule named ExampleStringIsEmpty. In the WorkshopAssignment0RulesTestInput.java and WorkshopAssignment0RulesTestOutput.java files there is a testExampleStringIsEmpty method that shows the input and output to test the Refaster rule.

Part 2: Writing Error Prone checks

During this part of the workshop we will implement parts of multiple Error Prone BugCheckers. Each of these classes contain XXX comments explaining what needs to be implemented. However, before diving in, make sure to first navigate to a check's associated test class to drop the class-level @Disabled annotation. Upon initial execution the tests will fail; the goal is to get then to pass.

Some utility classes that you can use:

com.google.errorprone.util.ASTHelpers: contains many common operations on the Abstract Syntax Tree.
com.google.errorprone.fixes.SuggestedFixes: contains helper methods for creating Fixes.

Tips and tricks

If you are working from the command line, it is suggested to run commands in the workshop directory. To do this, navigate to the root of the repository and run:

cd workshop

In case you want to do a fast build to just compile the project, run:

mvn clean install -DskipTests -Dverification.skip

In case you want to run one test from the command line, run the following commands:

mvn clean install -Dtest=WorkshopRefasterRulesTest -Dverification.skip

Troubleshooting

Make sure to use the latest version of JDK 21 or 17.

In some specific cases the -Dverification.skip is not correctly processed. In that case, use -D"verification.skip".

In case there is an error mentioning the BetaApi check, please rebuild or try to Reload All Maven projects.