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I've been looking at the web articles, and following statement seems to be true:

  • When there is an application source code which just uses some GPL library, but does not contain any part of the library within the codebase, the developer of the application still needs to publish the application in GPL (if he/she is to publish the source code).

Reference, for example, https://softwareengineering.stackexchange.com/questions/317284/licensing-on-github

Given my assumption is true, here's my question:

Here, I think the to-be-published source code is not "translated" or in anyway interacted with the GPL library per se (as it is merely a source code), so I'm wondering how the above restriction gets logically deduced from the License statements.

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The relevant section is GPLv3 s5, which says that

You may convey a work based on the Program [...] provided that you also meet all of these conditions:

[...]

c) You must license the entire work, as a whole, under this License to anyone who comes into possession of a copy.

The question of whether linking to a library is enough to produce a derivative work of that library, and thus engage the GPL, is an open one. The FSF believes that dynamic (and static) linking does produce a derivative work, and therefore that code that uses a GPLed library must therefore be released under the GPL (or a less-restrictive, but compatible, licence). Others have different beliefs; Wikipedia has a fairly well-referenced summary of various different points of view that people have held on the subject.

Until a court of significance rules persuasively on the issue, we simply don't know for sure.

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  • FSF contends that if writing program P that depends on GPLed library L, P is a derivative and thus must be GPLed. Thus the readline (GPL) library was cloned as libedit (BSD), now I can write programs using readline, but they aren't automatically GPLed anymore (as they work with libedit, a drop-in replacement). – vonbrand Feb 20 '20 at 11:19
  • @vonbrand an interesting line of argument. Do you know of anyone that's tried it in court? – MadHatter♦ Feb 20 '20 at 11:22
  • Mad Hatter, none whatsoever. And as far as I understand, not everybody agrees that that is correct. I for one would contend that e.g. using libreadline (GPL) though it's public interface is exactly the use it is meant to get, it shouldn't affect my independent code. – vonbrand Feb 20 '20 at 13:35

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