# Chapter 37. The IDEA Plugin

The IDEA plugin generates files that are used by IntelliJ IDEA, thus making it possible to open the project from IDEA (File - Open Project). Both external dependencies (including associated source and javadoc files) and project dependencies are considered.

What exactly the IDEA plugin generates depends on which other plugins are used:

Table 37.1. IDEA plugin behavior

Plugin | Description
None | Generates an IDEA module file. Also generates an IDEA project and workspace file if the project is the root project.
Java | Adds Java configuration to the module and project files.

One focus of the IDEA plugin is to be open to customization. The plugin provides a standardized set of hooks for adding and removing content from the generated files.

## 37.1. Usage

To use the IDEA plugin, include this in your build script:

Example 37.1. Using the IDEA plugin

`build.gradle`

    apply plugin: 'idea'

The IDEA plugin adds a number of tasks to your project. The main tasks that you will use are the `idea` and `cleanIdea` tasks.

## 37.2. Tasks

The IDEA plugin adds the tasks shown below to a project. Notice that `clean` does not depend on `cleanIdeaWorkspace`. It's because workspace contains a lot of user specific temporary data and typically it is not desirable to manipulate it outside IDEA.

Table 37.2. IDEA plugin - Tasks

Task name | Depends on | Type | Description
`idea` | `ideaProject`, `ideaModule`, `ideaWorkspace` | `-` | Generates all IDEA configuration files
`cleanIdea` | `cleanIdeaProject`, `cleanIdeaModule` | `Delete` | Removes all IDEA configuration files
`cleanIdeaProject` | `-` | `Delete` | Removes the IDEA project file
`cleanIdeaModule` | `-` | `Delete` | Removes the IDEA module file
`cleanIdeaWorkspace` | `-` | `Delete` | Removes the IDEA workspace file
`ideaProject` | `-` | `GenerateIdeaProject` | Generates the `.ipr` file. This task is only added to the root project.
`ideaModule` | `-` | `GenerateIdeaModule` | Generates the `.iml` file
`ideaWorkspace` | `-` | `GenerateIdeaWorkspace` | Generates the `.iws` file. This task is only added to the root project.

## 37.3. Configuration

Table 37.3. Configuration of the idea plugin

Model | Reference name | Description
`IdeaModel` | `idea` | Top level element that enables configuration of the idea plugin in a DSL-friendly fashion
`IdeaProject` | `idea.project` | Allows configuring project information
`IdeaModule` | `idea.module` | Allows configuring module information
`IdeaWorkspace` | `idea.workspace` | Allows configuring the workspace xml

## 37.4. Customizing the generated files

IDEA plugin provides hooks and behavior for customizing the generated content. The workspace file can effectively only be manipulated via the `withXml` hook because its corresponding domain object is essentially empty.

The tasks recognize existing IDEA files, and merge them with the generated content.

### 37.4.1. Merging

Sections of existing IDEA files that are also the target of generated content will be amended or overwritten, depending on the particular section. The remaining sections will be left as-is.

#### 37.4.1.1. Disabling merging with a complete overwrite

To completely overwrite existing IDEA files, execute a clean task together with its corresponding generation task, for example `gradle cleanIdea idea` (in that order). If you want to make this the default behavior, add `tasks.idea.dependsOn(cleanIdea)` to your build script. This makes it unnecessary to execute the clean task explicitly.

Complete overwrite works equally well for individual files, for example by executing `gradle cleanIdeaModule ideaModule`.

### 37.4.2. Hooking into the generation lifecycle

The plugin provides objects modeling the sections of the metadata files that are generated by Gradle. The generation lifecycle is as follows:

1. The file is read; or a default version provided by Gradle is used if it does not exist
2. The `beforeMerged` hook is executed with a domain object representing the existing file
3. The existing content is merged with the configuration inferred from the Gradle build or defined explicitly in the eclipse DSL
4. The `whenMerged` hook is executed with a domain object representing contents of the file to be persisted
5. The `withXml` hook is executed with a raw representation of the xml that will be persisted
6. The final XML is persisted

The following table lists the domain object used for each of the model types:

Table 37.4. Idea plugin hooks

Model | `beforeMerged { arg -> }` argument type | `whenMerged { arg -> }` argument type | `withXml { arg -> }` argument type
`IdeaProject` | `Project` | `Project` | `XmlProvider`
`IdeaModule` | `Module` | `Module` | `XmlProvider`
`IdeaWorkspace` | `Workspace` | `Workspace` | `XmlProvider`

#### 37.4.2.1. Partial overwrite of existing content

A complete overwrite causes all existing content to be discarded, thereby losing any changes made directly in the IDE. The `beforeMerged` hook makes it possible to overwrite just certain parts of the existing content. The following example removes all existing dependencies from the `Module` domain object:

Example 37.2. Partial Overwrite for Module

`build.gradle`

    idea.module.iml {
        beforeMerged { module ->
            module.dependencies.clear()
        }
    }

The resulting module file will only contain Gradle-generated dependency entries, but not any other dependency entries that may have been present in the original file. (In the case of dependency entries, this is also the default behavior.) Other sections of the module file will be either left as-is or merged. The same could be done for the module paths in the project file:

Example 37.3. Partial Overwrite for Project

`build.gradle`

    idea.project.ipr {
        beforeMerged { project ->
            project.modulePaths.clear()
        }
    }

#### 37.4.2.2. Modifying the fully populated domain objects

The `whenMerged` hook allows to manipulate the fully populated domain objects. Often this is the preferred way to customize IDEA files. Here is how you would export all the dependencies of an IDEA module:

Example 37.4. Export Dependencies

`build.gradle`

    idea.module.iml {
        whenMerged { module ->
            module.dependencies*.exported = true
        }
    }

#### 37.4.2.3. Modifying the XML representation

The `withXml`hook allows to manipulate the in-memory XML representation just before the file gets written to disk. Although Groovy's XML support makes up for a lot, this approach is less convenient than manipulating the domain objects. In return, you get total control over the generated file, including sections not modeled by the domain objects.

Example 37.5. Customizing the XML

`build.gradle`

    idea.project.ipr {
        withXml { provider ->
            provider.node.component.find { it.@name == 'VcsDirectoryMappings' }.mapping.@vcs = 'Git'
        }
    }

## 37.5. Further things to consider

The paths of the dependencies in the generated IDEA files are absolute. If you manually define a path variable pointing to the Gradle dependency cache, IDEA will automatically replace the absolute dependency paths with this path variable. If you use such a path variable, you need to configure this path variable via `idea.pathVariables`, so that it can do a proper merge without creating duplicates.