[MNG-5523] support actual incremental build

**[Jigar Joshi](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=jigar.joshi)** opened **[MNG-5523](https://issues.apache.org/jira/browse/MNG-5523?redirect=false)** and commented

## Background:

We have project structure of around 200 project in the maven tree, every single build takes around 13 minute of time (clean, compile, test install, deploy)

With current version of maven `3.1`, you can skip clean phase and it will do incremental build, which is not bullet proof incremental build actually

## Problem example

```
----------root (module)
\
|
|---foo (jar project)
|
|---bar (jar project, it consumes foo as dependency)
```

before

```
public class Foo{
public static void sayHello(){
System.out.println("hello from foo");
}
}

public class Bar{
public static void main(String arg[]){
Foo.sayHello();
}
}
```

I do `mvn clean install` from root module, it would go successful, I launch the `main()` method of `Bar` now, it will be succesful

now I modify `sayHello()` to

```
public static void sayHello(String name){
System.out.println("hello from foo to " + name);
}
```

and I execute `mvn install` (incremental build) from root module, it will still compile and execute successfully because it takes previously built artifact for `Foo` at compile phase, now if I attempt to run it in IDE or in a packaged build it will fail with

```
Exception in thread "main" java.lang.NoSuchMethodError:
```

## Proposal:

- somewhere in pre execution phase, it needs to calculate the modified source and artifacts and it should be able to detect all the consumers in dependency tree (compile, runtime, test all scopes) and flag all the artifacts to treat as modified and it should re do build for those

- all the maven plugins should support incremental build as well

- plugin needs to be marked to execute incrementally by adding a `boolean` parameter to `AbstractMOJO` to declare that plugin execution needs to be calculated in effective incremental way

- all plugins which are marked as `incremental` needs to take the same approach as mentioned in first point

- also in parallel build when it fans out in multiple threads it should have knowledge of what plugins to execute effectively

It would be totally useful to have this feature corrected

Some other people who wants this as well

- http://stackoverflow.com/questions/6281699/maven-incremental-building
- http://stackoverflow.com/questions/8918165/does-maven-support-incremental-builds

**Also See**

- http://jira.codehaus.org/browse/MCOMPILER-213
- http://blog.jetbrains.com/teamcity/2012/03/incremental-building-with-maven-and-teamcity/

Thanks!
Jigar

---

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**Issue Links:**
- [MBUILDCACHE-1](https://issues.apache.org/jira/browse/MBUILDCACHE-1) [Deutsche Bank contribution] Incremental build with local and remote(shared) cache

6 votes, 12 watchers