LICENCE.txt: Discuss incorporated and related works

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

diff --git a/LICENCE.txt b/LICENCE.txt
index 22f126c3f3e853a676f78510bd3cc4580f65baef..3cb3691c0d15d13f7f884dc29bf22b9ead35dd2e 100644 (file)
--- a/LICENCE.txt
+++ b/LICENCE.txt
@@ -45,8 +45,53 @@ header.  In the main parts of innduct this should be something like:
  *  SPDX-License-Identifier: GPL-3.0-or-later
 
 
+Incorporated and related works
+==============================
 
-(I believe that when you compile and link this as part of the inn2
-build, with the Makefile runes I have provided, all the libraries
-and files which end up included in innduct are licence-compatible
-with GPLv3.  If not then please let me know.  -Ian Jackson.
+The source tree contains a handful of build system related files that
+aren't part of innduct proper, and have a separate copyright status.
+And, we link against libraries supplied by INN2.
+
+autoconf-aux/*
+--------------
+
+  Used for building, but none of this ends up in the binaries.
+  Manually copied from Debian's automake-1.16 package.
+
+  Copyright (C) 1992-2018 Free Software Foundation, Inc.
+  Copyright (C) 1994 X Consortium
+  Listed authors: Tom Tromey, Per Bothner, Ben Elliston,
+  Alexandre Oliva, Fran,cois Pinard, Noah Friedman.
+
+  Licence is GPLv3+; see autoconf-aux/COPYING.
+
+Makefile.in, configure
+----------------------
+
+  Used for building, but none of this ends up in the binaries.
+  Generated by autogen.sh, which copies parts of the system's autoconf
+  and automake into the innduct source tree, combining it with the
+  "source code proper" eg configure.ac.  (In the Debian package build,
+  dh will rerun autogen.sh, overwriting the supplied version.)
+
+  As of January 2024, the versions here are:
+
+  Copyright (C) 1992-1996, 1998-2012 Free Software Foundation, Inc.
+  Copyright authors and contributors to innduct (see above)
+
+  Licence of each from the Free Software Foundation is as follows:
+    The Free Software Foundation gives unlimited permission
+    to copy, distribute and modify [this file].
+  But the overall licence is GPLv3+ since each file also contains
+  GPLv3+ code from innduct's build system.
+
+INN2
+----
+
+  Nothing from INN2 is included in the innduct source tree.
+  But when you build innduct, you link with libraries from inn2
+  (currently, statically, since those libraries have no stable ABI).
+
+  INN2 is under a variety of licences.  At the time of writing,
+  MIT, and GPLv2+.  So the effective licence of the resulting
+  binaries is GPLv3+ - the licence of innduct itself.