buffer.c/buffer.h: How to add new buffer-local variables?

[Keith David Bershatsky <esq@lawlist.com>]

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I am working on feature requests #22873 (multiple fake cursors) and #17684 (crosshairs that track the cursor position).

In an earlier version of the Emacs master branch from a few months ago, I was able to increase the number of buffer-local variables in buffer.c/buffer.h by changing the value of MAX_PER_BUFFER_VARS from 50 to 60.  That approach does not permit me to build a current version of the Emacs master branch, which fails with the following error:

    Dumping under the name bootstrap-emacs.pdmp
    dumping fingerprint: 50894efcc2cdb17747a4536c9f53c4d093895712c3604daa88d068c383ea4780

    pdumper.c:1786: Emacs fatal error: assertion failed: relpos < 1024
    Fatal error 6: Abort trapmake[1]: *** [bootstrap-emacs.pdmp] Abort trap
    make[1]: *** Deleting file `bootstrap-emacs.pdmp'
    make: *** [src] Error 2

    Compilation exited abnormally with code 2 at Sat Mar 30 15:53:18

I have narrowed the issue down to adding just one (1) more buffer local variable, which breaks the camel's back.  Attached are git diffs for a working build and a broken build.  I am using Emacs master branch from 03/28/2019:  2da9f8bf4222fda504f43b4757e154999cdbbf2c

My config options are as follows:

CFLAGS='-Wall -O0 -g3' ./configure \
--with-ns \
--enable-checking='yes,glyphs' \
--enable-check-lisp-object-type \
--without-compress-install \
--without-makeinfo \
--with-gnutls=no \
--with-mailutils \
--without-makeinfo

How can I increase the number of buffer local variables in buffer.c/buffer.h without breaking the ability to build Emacs?

Keith


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