Installation of custom eclipse plug-in available at github - eclipse

Question

I am trying to install a plug-in to eclipse from an update site. But, somehow that is not working (might be tool has ended support from update site). Although, i have found source code of plug-in from github(but it is not compiled version). I could download it as zip file. But, I am facing issues related to installation. It contains lot of plugin.xml files in different folders. But, i am not sure, which one to use.
This is the url for plug-in source code.
please help with the steps to install eclipse plugin from source code.
#ChandrayyaGK : I have followed steps mentioned in your answer.I am facing following error.
[INFO] Fetching org.eclipse.graphiti_0.11.4.v20150701-1432.jar.pack.gz from http://archive.eclipse.org/graphiti/updates/0.11.4/plugins/ (0B of 83.9kB at 0B/s)
[ERROR] Internal error: java.lang.NullPointerException -> [Help 1]
org.apache.maven.InternalErrorException: Internal error: java.lang.NullPointerException
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:164)
at org.apache.maven.cli.MavenCli.execute(MavenCli.java:555)
at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:214)
at org.apache.maven.cli.MavenCli.main(MavenCli.java:158)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)
Caused by: java.lang.NullPointerException
at org.eclipse.equinox.internal.p2.artifact.repository.simple.SimpleArtifactRepository.downloadArtifact(SimpleArtifactRepository.java:665)
at org.eclipse.equinox.internal.p2.artifact.repository.simple.SimpleArtifactRepository.downloadArtifact(SimpleArtifactRepository.java:590)
at org.eclipse.equinox.internal.p2.artifact.repository.simple.SimpleArtifactRepository.getArtifact(SimpleArtifactRepository.java:724)
at org.eclipse.tycho.repository.p2base.artifact.repository.RepositoryArtifactProvider.getArtifactFromOneMirror(RepositoryArtifactProvider.java:209)
at org.eclipse.tycho.repository.p2base.artifact.repository.RepositoryArtifactProvider.getArtifactFromAnyMirror(RepositoryArtifactProvider.java:192)
at org.eclipse.tycho.repository.p2base.artifact.repository.RepositoryArtifactProvider.access$1(RepositoryArtifactProvider.java:187)
at org.eclipse.tycho.repository.p2base.artifact.repository.RepositoryArtifactProvider$1.perform(RepositoryArtifactProvider.java:167)
at org.eclipse.equinox.internal.p2.artifact.repository.simple.SimpleArtifactRepository.getArtifact(SimpleArtifactRepository.java:708)
at org.eclipse.equinox.internal.p2.artifact.repository.simple.SimpleArtifactRepository.getArtifacts(SimpleArtifactRepository.java:779)
at org.eclipse.tycho.repository.p2base.artifact.repository.RepositoryArtifactProvider.getArtifactFromAnyChildRepository(RepositoryArtifactProvider.java:179)
at org.eclipse.tycho.repository.p2base.artifact.repository.RepositoryArtifactProvider.getArtifactFromAnyFormatAvailableInRepository(RepositoryArtifactProvider.java:149)
at org.eclipse.tycho.repository.p2base.artifact.repository.RepositoryArtifactProvider.getArtifactFromAnySource(RepositoryArtifactProvider.java:135)
at org.eclipse.tycho.repository.p2base.artifact.provider.CompositeArtifactProviderBaseImpl.getArtifact(CompositeArtifactProviderBaseImpl.java:50)
at org.eclipse.tycho.repository.local.MirroringArtifactProvider.downloadCanonicalArtifact(MirroringArtifactProvider.java:236)
at org.eclipse.tycho.repository.local.MirroringArtifactProvider.downloadMostSpecificNeededFormatOfArtifact(MirroringArtifactProvider.java:229)
at org.eclipse.tycho.repository.local.MirroringArtifactProvider.downloadArtifact(MirroringArtifactProvider.java:214)
at org.eclipse.tycho.repository.local.MirroringArtifactProvider.makeOneFormatLocallyAvailable(MirroringArtifactProvider.java:203)
at org.eclipse.tycho.repository.local.MirroringArtifactProvider.makeLocallyAvailable(MirroringArtifactProvider.java:174)
at org.eclipse.tycho.repository.local.MirroringArtifactProvider.getArtifactFile(MirroringArtifactProvider.java:118)
at org.eclipse.tycho.repository.p2base.artifact.provider.CompositeArtifactProvider.getArtifactFile(CompositeArtifactProvider.java:70)
at org.eclipse.tycho.p2.target.TargetPlatformBaseImpl.getLocalArtifactFile(TargetPlatformBaseImpl.java:93)
at org.eclipse.tycho.p2.resolver.P2ResolverImpl.addUnit(P2ResolverImpl.java:251)
at org.eclipse.tycho.p2.resolver.P2ResolverImpl.toResolutionResult(P2ResolverImpl.java:214)
at org.eclipse.tycho.p2.resolver.P2ResolverImpl.resolveDependencies(P2ResolverImpl.java:206)
at org.eclipse.tycho.p2.resolver.P2ResolverImpl.resolveDependencies(P2ResolverImpl.java:113)
at org.eclipse.tycho.p2.resolver.P2DependencyResolver.doResolveDependencies(P2DependencyResolver.java:360)
at org.eclipse.tycho.p2.resolver.P2DependencyResolver.resolveDependencies(P2DependencyResolver.java:333)
at org.eclipse.tycho.core.resolver.DefaultTychoResolver.resolveProject(DefaultTychoResolver.java:117)
at org.eclipse.tycho.core.maven.TychoMavenLifecycleParticipant.afterProjectsRead(TychoMavenLifecycleParticipant.java:77)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:271)
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:152)
... 11 more
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/InternalErrorException
After more investigation, i found reason was due to machine environment properties.
<environment>
<os>macosx</os>
<ws>cocoa</ws>
<arch>x86_64</arch>
</environment>
I have changed it to following , and it works.
<environment>
<os>win32</os>
<ws>win32</ws>
<arch>x86</arch>
</environment>

Answer 1

You have to have github account to clone or download sources from github. Create your github account then go to this project then click on clone or download button then download the sources as zip file.
You have to build these sources to get eclipse plugin, so unzip the content.
Location of graphiti p2 repo changed now so open the file
/Activiti-Designer-master/org.activiti.designer.parent/pom.xml
and change line from
<graphiti-site>http://download.eclipse.org/graphiti/updates/0.11.4</graphiti-site>
to
<graphiti-site> http://archive.eclipse.org/graphiti/updates/0.11.4</graphiti-site>
Go to Activiti-Designer-master/org.activiti.designer.parent folder in command prompt then run the command mvn clean install(Install maven if not installed).
I tried this and able to build this plugin successfully on my machine. By default it builds plugin for eclipse luna platform. So open eclipse luna and add /Activiti-Designer-master/org.activiti.designer.updatesite/target/repository folder as your update site then click install. Refer this for installing new software/plugin in luna.

Answer 2

About getting graphiti p2 repo.
Only solution worked for me, is to take graphiti site from a local folder.
Like it is described here Activiti Designer - build failures
download ZIP file: http://archive.eclipse.org/graphiti/archives/0.11.4/org.eclipse.graphiti.site_0.11.4.201507011432.zip
unzip it and set org.activiti.designer.parent/pom.xml <graphiti-site> value accordingly to point unzipped folder
in my case it was windows dir so e.g.:
<graphiti-site>file:///C:/temp/org.eclipse.graphiti.site_0.11.4.201507011432</graphiti-site>
after that i was able to build designer successfully.
ps. Sorry guys, I don't have enough reputation points to put this as a comment to a previous answer where it seems to be more obvious place.