ChronoLens

Features

History analysis and extraction

• an abstract model to represent the history of a system (sources and differences between two versions of the same source)
• JSON serialization utilities for the defined model
• a Git proxy module
• a Java parser that extracts the source model from Java files
• utilities for building command-line interfaces

Anti-pattern detection

• an analyzer that detects decapsulations of fields
• an analyzer that detects churners of a system
• an analyzer that detects instances of the Divergent Change code smell
• an analyzer that detects instances of the Feature Envy code smell

Using ChronoLens

Environment requirements

In order to use ChronoLens you need to have JDK 11 or newer.

Using the command line

Download the most recently released distribution from here and run the executable from the bin directory: ./chronolens-cli help.

The following is an example session of commands that inspect a remote git repository:

# Clones the repository to the current working directory.
git clone $URL .

# Prints help and lists the available commands.
chronolens-cli help

# Prints usage information for the 'model' command.
chronolens-cli help model

# Prints the source model for the specified file as it is found in the 'HEAD'
# revision.
chronolens-cli model --id $PATH

# Persists the history model.
chronolens-cli persist

# Run the 'decapsulations' analysis that makes use of the persisted model.
chronolens-cli decapsulations | less

# Deletes the persisted model.
chronolens-cli clean

Using Gradle

Add the JitPack repository to your build file:

repositories {
    maven { url 'https://jitpack.io' }
}

Add the dependencies:

dependencies {
    compile "com.github.andreihh.chronolens:chronolens-core:$version"
    testCompile "com.github.andreihh.chronolens:chronolens-test:$version"
}

Using Maven

Add the JitPack repository to your build file:

<repositories>
  <repository>
    <id>jitpack.io</id>
    <url>https://jitpack.io</url>
  </repository>
</repositories>

Add the dependencies:

<dependencies>
  <dependency>
    <groupId>com.github.andreihh.chronolens</groupId>
    <artifactId>chronolens-core</artifactId>
    <version>$version</version>
    <scope>compile</scope>
  </dependency>
  <dependency>
    <groupId>com.github.andreihh.chronolens</groupId>
    <artifactId>chronolens-test</artifactId>
    <version>$version</version>
    <scope>test</scope>
  </dependency>
</dependencies>

Example Java usage

There are three ways to interact with a repository from Java:

// Connect to the repository directly, without persisting anything. All method
// calls are delegated to a VCS proxy.
Repository repository = InteractiveRepository.connect();
// ...

// Connect to the previously persisted data from the repository. All method
// calls read the persisted data from the disk.
Repository repository = PersistentRepository.load();
// ...

// Connect to the repository directly, persist the data and then interact with
// the persisted data. The repository will be analyzed and persisted to disk.
SourceTree sourceTree = InteractiveProject.connect().persist();
// ...

There are three ways to process data from a repository:

// Process all sources individually.
for (String path : repository.listSources()) {
    SourceFile source = repository.getSource(path);
    // ...
}

// Process the latest snapshot.
SourceTree sourceTree = repository.getSnapshot();
// ...

// Process the transaction history.
Stream<Transaction> history = repository.getHistoryStream();
// ...

Processing a SourceNode can be achieved using the Visitor pattern:

abstract class NodeVisitor {
    public abstract void visit(SourceFile sourceFile);
    public abstract void visit(Type type);
    public abstract void visit(Function function);
    public abstract void visit(Variable variable);
    public final void visit(SourceNode node) {
        // safe to use `instanceof` because the class hierarchy is sealed
        if (node instanceof SourceFile) {
            visit((SourceFile) node);
        } else if (node instanceof Type) {
            visit((Type) node);
        } else if (node instanceof Function) {
            visit((Function) node);
        } else if (node instanceof Variable) {
            visit((Variable) node);
        } else {
            // should never be executed
            throw new AssertionError("Unknown node type!");
        }
    }
}

Processing a Transaction can also be achieved using the Visitor pattern:

abstract class TransactionVisitor {
    /** The current snapshot of the repository. */
    protected final SourceTree sourceTree = SourceTree.empty();

    protected abstract void visit(AddNode edit);
    protected abstract void visit(RemoveNode edit);
    protected abstract void visit(EditType edit);
    protected abstract void visit(EditFunction edit);
    protected abstract void visit(EditVariable edit);
    protected final void visit(SourceTreeEdit edit) {
        // safe to use `instanceof` because the class hierarchy is sealed
        if (edit instanceof AddNode) {
            visit((AddNode) edit);
        } else if (edit instanceof RemoveNode) {
            visit((RemoveNode) edit);
        } else if (edit instanceof EditType) {
            visit((EditType) edit);
        } else if (edit instanceof EditFunction) {
            visit((EditFunction) edit);
        } else if (edit instanceof EditVariable) {
            visit((EditVariable) edit);
        } else {
            // should never be executed
            throw new AssertionError("Unknown edit type!");
        }
    }

    public final void visit(Transaction transaction) {
        for (SourceTreeEdit edit : transaction.getEdits()) {
            visit(edit); // process this edit
            sourceTree.apply(edit); // update the snapshot with this edit
        }
    }
}

Implementing a analyzer for the main executable can be done as follows:

import org.chronolens.core.analysis.AnalyzerSpec;
import org.chronolens.core.analysis.Analyzer;
import org.chronolens.core.analysis.OptionsProvider;
import org.chronolens.core.analysis.Report;
import org.chronolens.core.repository.RepositoryConnector.AccessMode;

public final class SampleAnalyzerSpec implements AnalyzerSpec {
    @Override
    public String getName() { return "sample-analyzer"; }

    @Override
    public String getDescription() { return "An example analyzer implementation."; }

    @Override
    public SampleAnalyzer create(OptionsProvider optionsProvider) {
        return new SampleAnalyzer(optionsProvider);
    }
}

public final class SampleAnalyzer extends Analyzer {
    public SampleAnalyzer(OptionsProvider optionsProvider) {
        super(optionsProvider);
    }

    @Override
    public AccessMode getAccessMode() { return AccessMode.ANY; }

    private final Option<String> message =
        untypedOption()
            .name("message")
            .type(String.class)
            .description("The message to display to standard output.")
            .defaultValue("Hello, world!");

    private String getMessage() { return message.getValue(); }

    @Override
    public SampleReport analyze(Repository repository) {
        return getMessage();
    }
}

public final class SampleReport implements Report {
    private final String message;

    public SampleReport(String message) {
        this.message = message;
    }

    @Override
    public String toString() {
      return message;
    }
}

Building

To build the project, run ./gradlew build.

To build the distribution zip in the build/distributions directory, run ./gradlew distZip.

Documentation

To generate the documentation, run ./gradlew dokka.

Licensing

The code is available under the Apache V2.0 License.