Better debug support for Groovy-Eclipse

A short while ago, I wrote about the new debug support for GSP files inside the SpringSource Tool Suite. What I didn't describe is that this has coincided with enhanced debug support in Groovy-Eclipse.

There are a few tricks that you can do inside of Eclipse to vastly improve your debugging experience. Much of this is now automatically configured for you when you install the latest snapshot of Groovy-Eclipse, available at this update site: http://dist.codehaus.org/groovy/distributions/greclipse/snapshot/e3.6/.

Step filters

The Eclipse Java Development Tools supports the concept of step filters that enable a user to specify regular expressions of type names that should be ignored by the debugger. By this I mean that using any of the step commands (step into, step over, step out of...), the debugger falls through any types that match a filter.

This is particularly useful for stepping through Groovy MOP stack frames, including most stack frames that start org.codehaus.groovy.*, and many of the sun.reflect.* frames as well.

Groovy Eclipse now configures a reasonable set of default step-filters for you. These defaults can be viewed and edited in your Eclipse preferences:

Note that it is still possible to stop at a breakpoint set inside of a filtered type, but the next step-* command will step through to the first unfiltered type.

Show Logical Structure

At runtime, closure parameters are wrapped in groovy.lang.Reference objects. This makes for a bit of an annoyance when debugging and trying to browse variables. Take for example this simplified, but common debugging situation. You are debugging inside of a closure and you are using the variables view to explore the current value of your closure parameter:

Unfortunately as you can see, you have to dig 3 levels deep to see the contents of the list.

Again, Eclipse offers a solution. You can select the Show Logical Structure button . The result is a significantly more concise way to browse your variables:

Groovy-Eclipse has added a custom logical structure for Reference objects so that they are automatically dereferenced inside of the variables view. You can edit existing and add new logical structures in your Java Debug preferences:

Stack frame emphasis

Another common complaint about debugging Groovy code is that the extra stack frames from Groovy's MOP hides the application stack frames from view. As an exercise, try to find the application stack frames in the following code (hint: the name of the script is Script.groovy):

On second thought...don't try.  Groovy-Eclipse automatically greys-out MOP and related stack frames, making it easy to see application stack frames (without actually hiding Groovy magic):

This feature, combined with step filtering above makes stepping through Groovy code significantly more efficient.

By default, Groovy-Eclipse de-emphasizes some of the most common MOP stack frames, but this can be changed in the Eclipse preferences:

What's next?

Two of the most requested debugging features are Groovy-aware hotswapping (so that Groovy code can be edited, compiled, and loaded without needing to restart a debugging session) and a Groovy-aware Display view (so that Groovy snippets can be executed in the context of a paused application).

We've had some success with hotswapping, but more work needs to be done before it can be generally useful. Specifically, we've hit some limitations due to the class files produced by groovyc and are awaiting a fix for GROOVY-4152.

A Groovy-aware display view is something that we need to work on and I hope to have initial support for this for the 2.1.0 release in late October.

Clearly, we have work to do, but the existing debug support provides significant improvements over what was available even a few months ago.

Where are all my stubs?

Update: you must also include a pluginRepositories section. See below for XML snippet.



Update: See here for a sample project and the source code of the compiler integration.




The standard way of compiling joint Groovy-Java code outside of Eclipse has always been through the use of stubs:

1. Generate Java stub files for the Groovy files
2. Compile the Java files using the stubs to compile against
3. Compile the Groovy files

Although this works reasonably well in many situations, there are some complications and problems with this approach, most of which have already been described recently in detail on the groovy-dev mailing list here and here, so I won't go into them in this post.

About a year ago, we introduced Groovy-Eclipse 2.0, which compiles Groovy code by plugging into the JDT compiler and does not need to generate stub files. And as Andy Clement describes, it is possible to run the compiler in batch mode on the command line.

And now, with a little bit of glue code required, I have released a snapshot of the compiler with both ant and maven integration. Although, this is still early work, I do hope that this approach will solve many of the problems that Groovy programmers are having with stub generation. I'll describe below how they both work.

Ant integration for Groovy-Eclipse

Ant integration for the batch compiler is fairly simple.

1. Download the groovy-eclipse-batch-0.5.0.jar from its temporary location.
2. Add this jar to your ~/.ant/lib directory.
3. Once you have that, you need to set the build.compiler property to org.codehaus.groovy.eclipse.ant.GroovyCompilerAdapter.

This will cause ant's javac task to delegate the Groovy-Eclipse compiler for the actual compilation. This means that it is possible to pass any combination of Groovy and Java files to the compiler and most parameters applicable for javac are still available when using the compiler adapter.

A very simple script that uses the Groovy compiler adapter looks like this:

<target name="compile">
  <property name="build.compiler"
           value="org.codehaus.groovy.eclipse.ant.GroovyCompilerAdapter">
  <javac srcdir="src" destdir="bin"/>
</target>

This script sets compiler adapter and compiles all source files in src, placing the resulting class files in bin. Both *.java files and *.groovy files are included in the compilation.

Maven integration for Groovy-Eclipse

Groovy-Eclipse can now also be used from maven. To do so, add the following to your pom.xml.

The artifacts are currently in the SpringSource snapshot maven repo. You must add it as a regular repository:

<repositories>
  <repository>
  <id>springsource</id>
  <url>http://maven.springframework.org/snapshot</url>
  <releases><enabled>true</enabled></releases>
  <snapshots><enabled>true</enabled></snapshots>
  </repository>
</repositories>

as well as a plugin repository:

<pluginRepositories>
  <pluginRepository>
  <id>springsource</id>
  <url>http://maven.springframework.org/snapshot</url>
  </pluginRepository>
</pluginRepositories>

And in your plugin section, you must change the compiler used by the maven-compiler-plugin. Like the javac ant task, the maven-compiler-plugin does not actually compile, but rather delegates the compilation to a different artifact:

<build>
...
<plugins>
  <plugin>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>2.3.1</version>
    <configuration>
      <compilerId>groovy-eclipse-compiler</compilerId>
      <verbose>true</verbose>
    </configuration>
    <dependencies>
      <dependency>
        <groupId>org.codehaus.groovy</groupId>
        <artifactId>groovy-eclipse-compiler</artifactId>
        <version>0.0.1-SNAPSHOT</version>
      </dependency>
    </dependencies>
  </plugin>
  ...
</plugins>
</build>

This will allow Groovy files to be compiled. The maven-compiler-plugin prefers all source files to be in src/main/java and src/test/java, but if you prefer you can use the standard Groovy convention and keep your files in src/main/groovy and src/test/groovy. You can do so by adding the following plugin to your build section of the pom:

<plugin>
  <groupId>org.codehaus.mojo</groupId>
  <artifactId>build-helper-maven-plugin</artifactId>
  <version>1.5</version>
  <executions>
    <execution>
      <id>add-source</id>
      <phase>generate-sources</phase>
      <goals>
        <goal>add-source</goal>
      </goals>
      <configuration>
        <sources>
          src/main/groovy
          src/test/groovy
        </sources> 
      </configuration>
    </execution>
  </executions>
</plugin>

This approach is still in an alpha state and has not been widely tested. It was hard to find reasonably large Groovy-Java projects that use maven for me to try this on. The largest project I have compiled in this way is the GPars project (GPars uses gradle for its build, but I adapted its build.gradle to a pom.xml and successfully ran maven on it). This project includes 168 Java and Groovy files in main as well as 338 Groovy files in test. In a not particularly scientific manner, I did a few runs of building the main and test classes using both Groovy-Eclipse and GMaven and the results are that Groovy-Eclipse is reasonably faster than GMaven for this project:

• Time to compile main and test classes using GMaven: 36s
• Time to compile main and test classes using Groovy-Eclipse: 28s

In addition to being largely untested in the wild, there are a few caveats when using Groovy-Eclipse:

• Since stubs are not generated, GroovyDoc and any other artifacts that rely on stubs cannot be generated.
• This only supports Groovy 1.7.
• Third (ant only), your project must have at least one Java file in it (this can be an empty stub), or else ant will finish without compiling anything. There is a patch for this (Bug 48829), but I am waiting for it to be contributed back to ant.
• Fourth (maven only), your maven project must have at least one groovy file or else compilation will not occur. (Though, if your project doesn't have any Groovy files, then why are you using a Groovy compiler?)

There is still some work to be done, but it is ready enough for people to start trying it out. Feedback is greatly appreciated. You can reply to this blog post, send a message to the mailing list, or raise an issue on jira.