looks like the latest Xcode release has a new version of clang - tried to compile a model and got the PCH warning:
make examples/bernoulli/bernoulli
--- Compiling, linking C++ code ---
clang++ -std=c++1y -Wno-unknown-warning-option -Wno-tautological-compare -Wno-sign-compare -D_REENTRANT -Wno-ignored-attributes -I stan/lib/stan_math/lib/tbb_2019_U8/include -O3 -I src -I stan/src -I lib/rapidjson_1.1.0/ -I stan/lib/stan_math/ -I stan/lib/stan_math/lib/eigen_3.3.7 -I stan/lib/stan_math/lib/boost_1.72.0 -I stan/lib/stan_math/lib/sundials_5.2.0/include -DBOOST_DISABLE_ASSERTS -c -include-pch stan/src/stan/model/model_header.hpp.gch -x c++ -o examples/bernoulli/bernoulli.o examples/bernoulli/bernoulli.hpp
error: PCH file built from a different branch ((clang-1200.0.32.21)) than the compiler ((clang-1200.0.32.27))
1 error generated.
make: *** [examples/bernoulli/bernoulli] Error 1
to fix run commands make clean-all
followed by make build
(better yet, make -j4 build
, if you’ve got the cores)