Change apt-get to allow external repository

Author: sethrj

.travis.yml

@@ -1,7 +1,7 @@
 language: cpp
 dist: bionic
 compiler: gcc
-sudo: false
+sudo: required # apt-get done in before_install.sh
 
 # Only build master or PRs merging into master
 branches:
@@ -16,33 +16,16 @@ matrix:
         addons:
           apt:
             packages:
-            - gfortran
             - python3-sphinx
             - valgrind
       - os: linux
         env: FLIBCPP_DEV=OFF GENERATOR=make
              FLIBCPP_FORTRAN_STD=f2003
-             CC=gcc-8 CXX=g++-8 FC=gfortran-8 
-        addons:
-          apt:
-            packages:
-            - gcc-8
-            - g++-8
-            - gfortran-8
+             GCC_VERSION=8
       - os: linux
         env: FLIBCPP_DEV=OFF GENERATOR=make
              FLIBCPP_FORTRAN_STD=f2008
-             CC=gcc-9 CXX=g++-9 FC=gfortran-9 
-        sudo: required
-        addons:
-          apt:
-            sources:
-            - ubuntu-toolchain-r-test
-            packages:
-            - gcc-9
-            - g++-9
-            - gfortran-9
-
+             GCC_VERSION=9
 # Build phases
 before_install:
   - source ./scripts/travis/before_install.sh

scripts/travis/before_install.sh

@@ -3,12 +3,46 @@
 # File  : example/before_install.sh
 ###############################################################################
 
+###############################################################################
+# APT PACKAGE INSTALLS
+#
+# see https://docs.travis-ci.com/user/installing-dependencies
+###############################################################################
+
+set -x
+
+if [ "${GCC_VERSION}" = "9" ]; then
+  # Special repo needed for new GCC version
+  sudo add-apt-repository ppa:ubuntu-toolchain-r/test -y
+  sudo apt-get update -q
+fi
+
+if [ -n "${GCC_VERSION}" ]; then
+  # Suffix for compilers and packages
+  _GCCV="-${GCC_VERSION}"
+fi
+
+sudo apt-get install gfortran${_GCCV} -y
+
+if [ -n "${GCC_VERSION}" ]; then
+  sudo apt-get install gcc${_GCCV} -y
+  sudo apt-get install g++${_GCCV} -y
+fi
+
+set +x
+
+###############################################################################
+# ENVIRONMENT VARIABLES
+###############################################################################
+
 export SOURCE_ROOT=${PWD}
 export BUILD_ROOT=${SOURCE_ROOT}/build
 export INSTALL_ROOT=${HOME}/install
 export CMAKE_PREFIX_PATH=${INSTALL_ROOT}:${CMAKE_PREFIX_PATH}
 export PATH=${INSTALL_ROOT}/bin:${PATH}
-export FC=${FC:-gfortran}
+export FC=${FC:-gfortran${_GCCV}}
+export CC=${CC:-gcc${_GCCV}}
+export CXX=${CXX:-g++${_GCCV}}
 
 mkdir -p ${BUILD_ROOT}