Add CPyChecker for a bit of static analysis of C code

Refcounting correctly is hard...

The plugin will bail out before it successfully compiles. Allow the
check to fail but I want to see the warnings.

.travis.yml

@@ -55,6 +55,18 @@ matrix:
       python: 3.7
       env:
         - ACTION=codecov
+    - name: "Python 3.7 on Linux (CPyChecker)"
+      dist: bionic
+      python: 3.7
+      addons:
+        apt:
+          sources:
+            - ubuntu-toolchain-r-test
+          packages:
+            # Old GCC needed for refcounting verification
+            - g++-6 gcc-6-plugin-dev libpython3.7 libpython3.7-dev
+      env:
+        - ACTION=cpychecker
 install:
   - which python3 &> /dev/null && export PYTHON=python3 || export PYTHON=python
   - pip3 install --upgrade pip

travis.sh

@@ -57,4 +57,21 @@ EOF
     esac
     ;;
 
+cpychecker)
+    case "$1" in
+    install)
+        pip install six
+        pushd /tmp
+        git clone --branch v0.17 https://github.com/davidmalcolm/gcc-python-plugin.git gcc-python-plugin
+        cd gcc-python-plugin
+        CC=gcc-6 CXX=g++-6 make plugin
+        popd
+        ;;
+    script)
+        # Not ready yet, permit failure
+        CC_FOR_CPYCHECKER=gcc-6 CC=/tmp/gcc-python-plugin/gcc-with-cpychecker CFLAGS=--cpychecker-verbose pip install -ve . || true
+        ;;
+    esac
+    ;;
+
 esac