[License-discuss] Intimacy in open source

John Cowan cowan at ccil.org
Mon Jan 14 18:42:47 UTC 2019

On Mon, Jan 14, 2019 at 1:02 PM Lawrence Rosen <lrosen at rosenlaw.com> wrote:

What is the relevance of "convoluted interaction" and "deep knowledge," and
> why should open source licenses care about independent implementations
> regardless of their design for utility?

I think (but don't actually know) that it was introduced in order to create
a somewhat-bright-line test for the real goal, which would be extremely
hard to establish directly; namely, if your program is designed to use a
GPLed program, it also must be GPLed.

The CLISP program was originally distributed as a binary-library-only
proprietary program along with binaries for readline (a GPLed library) and
an alternative noreadline without readline function, and it was up to the
user to link whichever library he chose.  The FSF advised the author that
this evasion would not pass muster with a judge, and he reluctantly
released the whole program under the GPL, because it was "designed to use"
readline, which added considerable value.

But a program designed to use one library can be used with a compatible
library instead: editline is a BSD-licensed drop-in replacement, and if
CLISP being written today it would probably be distributed as an executable
with editline.  Who's to say whether it was "designed to use" readline or
editline?  The FSF therefore takes the position that a program which has
always used editline is nonetheless "designed to use" readline, because
editline is a clean-room copy of readline.

Apparently, therefore, editline has been replaced by libedit, which lacks
the readline-compatible API.  Linenoise, a third library with the same
purpose, has a unique API.  Finally, rlwrap is a separate executable which
runs any interactive program and gives it readline services: the rlwrap
program uses readline and so is under the GPL, but the program it invokes
need not be, any more than the bash shell can only invoke programs that are
made available under the GPL.
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