Joining forces vs. starting from scratch (was Re: Proposal to start a new implementation...)

Robert Kaiser kairo at
Sun Apr 16 14:36:59 UTC 2017

Magnus Melin schrieb:
> On 4/15/17 2:37 AM, Robert Kaiser wrote:
>> Magnus Melin schrieb:
>>> On 4/11/17 6:09 AM, R Kent James wrote:
>>>> I wonder if we would ever consider switching to GPL?
>>> Good question, the MPL really hasn't served Thunderbird very well, 
>>> with Postbox being the prime example, resulting in zero win for the 
>>> base project. This would not be possible with GPL.
>> Wrong. From all I heard, this is a common misconception. A fork of a 
>> GPLed project does not have to contribute code back to any upstream. 
>> They only need to make the code available to their customers under 
>> GPL as well.
> I did not mean to imply they have to upstream every change, they don't 
> have to do anything except release the code. But, with the *complete 
> code* available, the upstream project *could* fairly easily include 
> changes/features they like. With MPL a fork can easily make it very 
> difficult for anyone to do that.

They do not need to publicly make the code available (or make it 
available to upstream), they only have to make it available to anyone 
they give the binaries to, i.e. their customers. Of course, that needs 
to happen under GPL again, so any customer can make that code public or 
contribute it back, but the company changing the code doesn't have to do 
that themselves.

And IIRC, that is very much the same for MPL, just that it only affects 
the specific files that were under MPL in the first place and not any 
files they added to the code (unless they contain pieces of code copied 
or moved from MPLed files).

The GPL and the MPL are pretty much equivalent on the level of the files 
containing covered code, the differences are that GPL also "virally" 
applies to all added files of code and even code linked into the final 
executable - and that the GPL is much harder to read and potentially 
surprising while the MPL2 is easy to read and understand.


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