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Eclipse: reference local code instead of cached gradle dependency

I have two gradle java projects imported into Eclipse, one being a dependency of the other.
I would like for Eclipse to use the local dependency code, instead of the compiled dependency in the gradle cache folders, so I can modify and debug both projects simultaneously.
How do I force Eclipse to use a local dependency code?

The feature you are referring to is known as Composite Builds:
Importing into the IDE
One of the most useful features of composite builds is IDE integration. By applying the idea or eclipse plugin to your build, it is possible to generate a single IDEA or Eclipse project that permits all builds in the composite to be developed together.
In addition to these Gradle plugins, recent versions of IntelliJ IDEA and Eclipse Buildship support direct import of a composite build.
Importing a composite build permits sources from separate Gradle builds to be easily developed together. For every included build, each sub-project is included as an IDEA Module or Eclipse Project. Source dependencies are configured, providing cross-build navigation and refactoring.
The most simple way of achieving this is to use includeBuild in your settings.gradle.
rootProject.name = 'my-composite'
includeBuild 'my-app'
includeBuild 'my-utils'
With that in place, there's no need to configure the build path manually in Eclipse.

Gosh this was a trivial one and it took me way too long to figure it out.
Solved the issue by creating a file named external-projects.properties in the root folder of the parent project with the relative or full path to the dependency project folder.
To be precise, for me the folders tree ends up like this:
git-folder/
|__parent-project/
|__external-projects.properties
|__build.gradle.kts
|__rest (src/main, etc)
|__dependency-project/
|__build.gradle.kts
|__rest (src/main, etc)
And the contents of the external-projects.properties file:
dependency-project = ../dependency-project
The dependency project must also be in the build path of the parent project (done by "Right-Click project > Build Path > Configure Build Path" and adding it in the "Projects" tab).
After that, a "Right Click > Gradle > Refresh Gradle Project" did the trick.

Adding Javadoc of dependencies of a library from Maven in IntelliJ IDEA

When I want to add a library from Maven, I go to Project Settings -> Libraries -> New Project Library -> From Maven... then search for the right library version and tick the JavaDocs checkbox. IntelliJ IDEA will download the library, its Javadocs and its dependencies jar files to the repository folder.
Is there any way to also download its dependencies's Javadocs?

For this to work, you need to add the library to the POM file instead of using the project settings in IntelliJ and make sure that the following setting is checked:
Settings -> Build -> Build Tools -> Maven -> Importing -> Automatically download: Documentation

Intellij not importing dependencies of modules

IntelliJ is not importing my modules dependencies for some reason. Like it's not taking into account my modules pom.xml. The dependencies added for example in the core module don't figure in the External library of the subject. As I'm not yet that familiar with intelliJ I assume the problem comes from the project structure so here it is:

You need to import the project as a "Maven Project".
Remove the "wallbang" module with the "-" button.
Click "+" -> "Import Module", then select the pom.xml.
Configure it using the wizard.
Click "Ok"
That should open up the Maven view and automatically include all dependencies.

Intellij - Add project dependency like in Eclipse

I'm switching to Intellij and trying to do the same thing as in Eclipse. In Eclipse, you can add a project as a dependency in another project (project properties -> "Java Build Path" -> "Projects" -> Click on my library project).
The current situation is that I'm developing a library and I can test the features in another project without building the jar file every time I add new stuff to the library.
I'm trying to achieve this with Intellij but without success (the projects are both imported in Intellij).
How can I do that?

File > Project Structure. Then choose your module, and add any dependency, either Jar, Library or Module:
Larger image here: http://i.imgur.com/rjdxJHx.png

From File -> project structure, select Modules. You will be presented with all the added projects. Click a project and from the right hand side select Dependencies tab. This will show you projects that are not imported in red coloured text. HTH

File > Project Structure > Project Settings > Modules
Add the module you want to add as dependency.
Add your module dependency in your project.
If you use Maven you'll see the following message:
Module 'your-module' is imported from Maven. Any changes made in its
configuration may be lost after reimporting.
→ Add your project to your pom.xml
If you don't do that, your dependency will be removed each time you reimport/refresh maven projects.

Adding POM Dependency in Eclipse build path

I have a project with a number of POM files. I have done a clean install and eclipse:eclipse. I would like to import the project as a normal project rather than Maven project. When I imported the project as normal project , I was not able to see the Maven dependencies present in POM in eclipse's build path. Is importing the project as Maven project only way of doing it? When I import the project as Maven project I see a number projects in eclipse workspace (one for each POM). However I would like to view this as a single project in eclipse workspace.
UPDATE: The classpath files of the child projects contain the dependent jar files , however it is not added to build path when the main project is added. Only the entries in classpath file of the main project is being added.

Given that you refer to "Maven project", are you using an eclipse plugin for Maven like M2Eclipse?
Assuming you are using M2Eclipse, the Maven Dependencies Library is automatically enabled for a Maven project. For a normal Java project, importing the library would force you to configure the project as a Maven project (On the context menu for the project, select Configure -> Convert to Maven Project).
Having said that, while you import your Maven project, you will notice an "Advanced" option (towards the lower section of the "Import Maven Projects" dialog). When you expand this option, there will be a checkbox to "Resolve Workspace Projects" - this is checked by default and is hence responsible for importing the child modules as separate projects. If you uncheck this, it will import only the parent module as the project and all children modules will be in sb folders under the parent module.
IMO, resolving the projects provides greater clarity, but then again this is very much a personal choice.
Hope that helps.

Eclipse doesn't support nested projects, and Maven kinda forces you to. So you can't really push everything into one project.
Doing a cursory google search led me to this, which might be helpful: http://warpedjavaguy.wordpress.com/2011/08/08/how-i-defeated-the-maven-release-plugin-in-a-flat-structured-multi-module-project/
You might also check out the following two online books from Sonatype:
Maven: The Complete Reference and Developing with Eclipse and Maven

Personally, I create Working Sets for each multi-module project and add all the individual projects to it. This enables me to see them all grouped together, this might be to your liking.
http://help.eclipse.org/indigo/index.jsp?topic=%2Forg.eclipse.platform.doc.user%2Fconcepts%2Fcworkset.htm
Once you have created the working set you can enable/disable them in the menu in Project Explorer and configure the project explorer to display the working set as the root element in the tree rather than the project.