Speed up Travis CI build (#1056)

* Update Python 3 osx image to xcode8.3 to speed up brew install. 
  The Python 2 osx image remains xcode7.3.

* Have one osx config run in debug mode to improve coverage.

* Only run CMake build tests on two configs to speed up overall build.

  The CMake tests take ~30 seconds on each configuration, but we really 
  only need to them to run on two: one on Linux and one on macOS. This
  mirrors the recent change on AppVeyor.

* Merge the style/docs/pip tests with the barebones build.

* Merge 32-bit and CMake install configurations.

  This removes clang 3.9 from testing, but there are already 3 other clang 
  versions being tested on Travis and the new xcode8.3 image should be 
  close to clang 3.9.

[skip appveyor]

.travis.yml

@@ -16,7 +16,7 @@ matrix:
         packages: [python3.6-dev python3.6-venv, cmake=2.\*, cmake-data=2.\*]
   - sudo: true
     services: docker
-    env: PYTHON=2.7 CPP=14 GCC=6
+    env: PYTHON=2.7 CPP=14 GCC=6 CMAKE=1
   - sudo: true
     services: docker
     env: PYTHON=3.5 CPP=14 GCC=6 DEBUG=1
@@ -31,23 +31,20 @@ matrix:
         packages: [python3.6-dev python3.6-venv clang-5.0 llvm-5.0-dev, lld-5.0]
   - os: osx
     osx_image: xcode7.3
-    env: PYTHON=2.7 CPP=14 CLANG
+    env: PYTHON=2.7 CPP=14 CLANG CMAKE=1
   - os: osx
-    osx_image: xcode7.3
-    env: PYTHON=3.6 CPP=14 CLANG
+    osx_image: xcode8.3
+    env: PYTHON=3.6 CPP=14 CLANG DEBUG=1
   # Test a PyPy 2.7 build
   - os: linux
     env: PYPY=5.8 PYTHON=2.7 CPP=11 GCC=4.8
     addons:
       apt:
         packages: [libblas-dev, liblapack-dev, gfortran]
+  # Build in 32-bit mode and tests against the CMake-installed version
   - sudo: true
     services: docker
-    env: ARCH=i386 PYTHON=3.5 CPP=14 GCC=6
-  # This next one does a make install *before* testing, then builds the tests against the installed version:
-  - sudo: true
-    services: docker
-    env: PYTHON=3.5 CPP=14 CLANG=3.9 INSTALL=1
+    env: ARCH=i386 PYTHON=3.5 CPP=14 GCC=6 INSTALL=1
     script:
       - |
         $SCRIPT_RUN_PREFIX sh -c "set -e
@@ -57,32 +54,36 @@ matrix:
         mkdir /build-tests && cd /build-tests
         cmake ../pybind11-tests ${CMAKE_EXTRA_ARGS} -DPYBIND11_WERROR=ON
         make pytest -j 2"
-  # A barebones build makes sure everything still works without optional deps (numpy/scipy/eigen)
-  # and also tests the automatic discovery functions in CMake (Python version, C++ standard).
+  # This config does a few things:
+  # - Checks C++ and Python code styles (check-style.sh and flake8).
+  # - Makes sure sphinx can build the docs without any errors or warnings.
+  # - Tests setup.py sdist and install (all header files should be present).
+  # - Makes sure that everything still works without optional deps (numpy/scipy/eigen) and
+  #   also tests the automatic discovery functions in CMake (Python version, C++ standard).
   - os: linux
-    env: BAREBONES PYTHON=3.5
-    install: $PY_CMD -m pip install --user --upgrade pytest
-  # Documentation build:
-  - os: linux
-    language: docs
-    env: DOCS STYLE LINT PIP
+    env: STYLE DOCS PIP PYTHON=3.5
     cache: false
     install:
     - export PATH="~/.local/bin:$PATH"
-    - $PY_CMD -m pip install --user --upgrade sphinx sphinx_rtd_theme breathe flake8 pep8-naming
+    - $PY_CMD -m pip install --user --upgrade sphinx sphinx_rtd_theme breathe flake8 pep8-naming pytest
     - |
       curl -fsSL ftp://ftp.stack.nl/pub/users/dimitri/doxygen-1.8.12.linux.bin.tar.gz | tar xz
       export PATH="$PWD/doxygen-1.8.12/bin:$PATH"
     script:
-    - $PY_CMD -m sphinx -W -b html docs docs/.build
     - tools/check-style.sh
     - flake8
+    - $PY_CMD -m sphinx -W -b html docs docs/.build
     - |
       # Make sure setup.py distributes and installs all the headers
       $PY_CMD setup.py sdist
       $PY_CMD -m pip install --user -U ./dist/*
       installed=$($PY_CMD -c "import pybind11; print(pybind11.get_include(True) + '/pybind11')")
       diff -rq $installed ./include/pybind11
+    - |
+      # Barebones build
+      cmake -DCMAKE_BUILD_TYPE=Debug -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON
+      make pytest -j 2
+      make cpptest -j 2
 cache:
   directories:
   - $HOME/.local/bin
@@ -102,7 +103,7 @@ before_install:
       fi
       export CXX=g++-$GCC CC=gcc-$GCC
     fi
-    if [ "$GCC" = "6" ] || [ "$CLANG" = "3.9" ]; then DOCKER=${ARCH:+$ARCH/}debian:stretch
+    if [ "$GCC" = "6" ]; then DOCKER=${ARCH:+$ARCH/}debian:stretch
     elif [ "$GCC" = "7" ]; then DOCKER=debian:buster
     fi
   elif [ "$TRAVIS_OS_NAME" = "osx" ]; then
@@ -133,7 +134,7 @@ before_install:
       PY_CMD=python$PYTHON
       if [ "$TRAVIS_OS_NAME" = "osx" ]; then
         if [ "$PY" = "3" ]; then
-          brew update; brew install python$PY;
+          brew install python$PY;
         else
           curl -fsSL https://bootstrap.pypa.io/get-pip.py | $PY_CMD - --user
         fi
@@ -169,9 +170,9 @@ install:
         git clone https://github.com/llvm-mirror/libcxxabi.git llvm-source/projects/libcxxabi -b release_50
         mkdir llvm-build && cd llvm-build
         # Building llvm requires a newer cmake than is provided by the trusty container:
-        CMAKE=cmake-3.8.0-Linux-x86_64
-        curl https://cmake.org/files/v3.8/$CMAKE.tar.gz | tar xz
-        ./$CMAKE/bin/cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=~/.local ../llvm-source
+        CMAKE_VER=cmake-3.8.0-Linux-x86_64
+        curl https://cmake.org/files/v3.8/$CMAKE_VER.tar.gz | tar xz
+        ./$CMAKE_VER/bin/cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=~/.local ../llvm-source
         make -j2 install-cxxabi install-cxx
         cp -a include/c++/v1/*cxxabi*.h ~/.local/include/c++/v1
         cd ..
@@ -201,7 +202,7 @@ script:
     -DDOWNLOAD_CATCH=ON
 - $SCRIPT_RUN_PREFIX make pytest -j 2
 - $SCRIPT_RUN_PREFIX make cpptest -j 2
-- $SCRIPT_RUN_PREFIX make test_cmake_build
+- if [ -n "$CMAKE" ]; then $SCRIPT_RUN_PREFIX make test_cmake_build; fi
 after_failure: cat tests/test_cmake_build/*.log*
 after_script:
 - if [ -n "$DOCKER" ]; then docker stop "$containerid"; docker rm "$containerid"; fi