error with d28016d16e9a (change to jsonencode.cc)

[Benjamin Abbott]

Rik

I’m seeing a build problem on the default branch when building on macOS 
(10.15.6) using Homebrew for dependencies and Apple’s clang version 12.0.0 
(clang-1200.0.32.2).

If I revert the change below, I’m able to build.

http://hg.savannah.gnu.org/hgweb/octave/rev/d28016d16e9a

libtool: compile:  g++ -std=gnu++11 -DHAVE_CONFIG_H -I. -Iliboctave 
-I./liboctave -I./liboctave/array -Iliboctave/numeric -I./liboctave/numeric 
-Iliboctave/operators -I./liboctave/operators -I./liboctave/system 
-I./liboctave/util -I./libinterp/octave-value -Ilibinterp -I./libinterp 
-I./libinterp/operators -Ilibinterp/parse-tree -I./libinterp/parse-tree 
-Ilibinterp/corefcn -I./libinterp/corefcn -I./liboctave/wrappers 
-I/usr/local/opt/hdf5/include 
-I/usr/local/Cellar/graphicsmagick/1.3.35/include/GraphicsMagick 
-I/usr/local/Cellar/fftw/3.3.8_2/include 
-I/usr/local/Cellar/fftw/3.3.8_2/include 
-I/usr/local/Cellar/fontconfig/2.13.1/include 
-I/usr/local/opt/freetype/include/freetype2 
-I/usr/local/opt/freetype/include/freetype2 -I/usr/local/opt/hdf5/include 
-I/usr/local/opt/readline/include -I/usr/local/opt/sqlite/include 
-I/usr/local/opt/openssl/include -I/usr/local/opt/gettext/include 
-I/usr/local/opt/icu4c/include -I/usr/local/opt/qt5/include 
-I/usr/local/opt/sundials27/include -I/usr/local/opt/zlib/include -fPIC 
-D_THREAD_SAFE -pthread -Wall -W -Wshadow -Woverloaded-virtual -Wold-style-cast 
-Wformat -Wpointer-arith -Wwrite-strings -Wcast-align -Wcast-qual -g -O2 -MT 
libinterp/corefcn/libcorefcn_la-jsonencode.lo -MD -MP -MF 
libinterp/corefcn/.deps/libcorefcn_la-jsonencode.Tpo -c 
libinterp/corefcn/jsonencode.cc  -fno-common -DPIC -o 
libinterp/corefcn/.libs/libcorefcn_la-jsonencode.o
libinterp/corefcn/jsonencode.cc:414:20: error: 'auto' not allowed in lambda 
parameter
        ([] (const auto& old_warning_state)
                   ^~~~
libinterp/corefcn/jsonencode.cc:414:26: warning: unused parameter 
'old_warning_state' [-Wunused-parameter]
        ([] (const auto& old_warning_state)
                         ^
libinterp/corefcn/jsonencode.cc:425:20: error: 'auto' not allowed in lambda 
parameter
        ([] (const auto& old_warning_state)
                   ^~~~
libinterp/corefcn/jsonencode.cc:425:26: warning: unused parameter 
'old_warning_state' [-Wunused-parameter]
        ([] (const auto& old_warning_state)
                         ^
In file included from libinterp/corefcn/jsonencode.cc:32:
In file included from libinterp/corefcn/error.h:35:
./liboctave/util/unwind-prot.h:171:9: error: no matching constructor for 
initialization of 'std::function<void ()>'
      : m_fcn (std::bind (fcn, args...))
        ^      ~~~~~~~~~~~~~~~~~~~~~~~~

Ben