try using nox from nixpkgs (#15857)

* try using nox from nixpkgs

* release.nix: block on nox since otherwise travis-ci will fail hard

.travis.yml

@@ -1,16 +1,12 @@
 matrix:
     include:
         - os: linux
-          language: python
-          python: "3.4"
+          language: generic
           sudo: required
           dist: trusty
-          before_install: ./maintainers/scripts/travis-nox-review-pr.sh nix
         - os: osx
           language: generic
           osx_image: xcode7.3
-          before_install:
-              - brew upgrade && brew install python
-              - ./maintainers/scripts/travis-nox-review-pr.sh nix
+before_install: ./maintainers/scripts/travis-nox-review-pr.sh nix
 install: ./maintainers/scripts/travis-nox-review-pr.sh nox
 script: ./maintainers/scripts/travis-nox-review-pr.sh build

maintainers/scripts/travis-nox-review-pr.sh

@@ -17,9 +17,9 @@ if [[ $1 == nix ]]; then
     echo "=== Verifying that nixpkgs evaluates..."
     nix-env -f. -qa --json >/dev/null
 elif [[ $1 == nox ]]; then
+    source $HOME/.nix-profile/etc/profile.d/nix.sh
     echo "=== Installing nox..."
-    git clone -q https://github.com/madjar/nox
-    pip --quiet install -e nox
+    nix-build -A nox '<nixpkgs>'
 elif [[ $1 == build ]]; then
     source $HOME/.nix-profile/etc/profile.d/nix.sh
 
@@ -38,7 +38,7 @@ elif [[ $1 == build ]]; then
     else
         echo "=== Checking PR"
 
-        if ! nox-review pr ${TRAVIS_PULL_REQUEST}; then
+        if ! nix-shell -p nox --run "nox-review pr ${TRAVIS_PULL_REQUEST}"; then
             if sudo dmesg | egrep 'Out of memory|Killed process' > /tmp/oom-log; then
                 echo "=== The build failed due to running out of memory:"
                 cat /tmp/oom-log

pkgs/top-level/release.nix

@@ -49,6 +49,10 @@ let
               jobs.python3.x86_64-linux
               jobs.python3.i686-linux
               jobs.python3.x86_64-darwin
+              # Needed by travis-ci to test PRs
+              jobs.nox.i686-linux
+              jobs.nox.x86_64-linux
+              jobs.nox.x86_64-darwin
               # Ensure that X11/GTK+ are in order.
               jobs.thunderbird.x86_64-linux
               jobs.thunderbird.i686-linux