0. emacs -Q
1. C-x C-+ (i.e. M-x text-scale-adjust)
2. M-x variable-pitch-mode or M-x buffer-face-mode
=> Args out of range: [nil :family :foundry :swidth :height :weight :slant :underline :inverse :foreground ...], 19

The error happens because the vector of face attributes defined in
face-remap.el is missing the recently added :extend attribute, so it is
too short.  This also breaks the MELPA package charmap.el (that's where
I hit the error).  The patch below fixes this, though perhaps now would
be a good time to do what the comment above the definition of the vector
says: "This variable should probably be defined in C code where the
actual definitions are available."  Or is this simple fix good enough?

(The vector is also missing the :distant-foreground attribute, so the
patch adds that as well.  This absence happened to be innocuous because
the first element of the vector is nil, in order to make the attribute
indices match those of the enum lface_attribute_index defined in
dispextern.h, so the vector was long enough; but after the addition of
the :extend attribute, it wasn't anymore (only the indices of the vector
are used in face-remap.el).)

In GNU Emacs 27.0.50 (build 17, x86_64-pc-linux-gnu, GTK+ Version 3.24.5, cairo version 1.16.0)
 of 2019-10-18 built on strobe-lfs84
Repository revision: 2d13a3f68d4724af52e47675bedf60709c7b5171
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12003000
System Description: Linux From Scratch