Travis CI build matrix contains spurious entry? - c++

Question

I've a Travis CI build matrix intended to test recent g++ and clang. In addition to those two intended entries, I see an entry, AFAIK, not specified in the include matrix. How can I either suppress or remove this third build configuration?
The .travis.yml:
language: generic
os: linux
script: ./bootstrap && ./configure && make all && make check && make distcheck
matrix:
include:
- env: COMPILER_NAME=gcc CXX=g++-5 CC=gcc-5
addons:
apt:
sources:
- ubuntu-toolchain-r-test
packages:
- autotools-dev
- g++-5
- env: COMPILER_NAME=clang CXX=clang++-3.8 CC=clang-3.8
addons:
apt:
sources:
- ubuntu-toolchain-r-test
- llvm-toolchain-precise-3.8
packages:
- autotools-dev
- clang-3.8
Snippet of Travis' output taken from the full details:

Answer 1

From the docs, "the os key also multiplies the matrix":
If your code is used on multiple operating systems it probably should
be tested on multiple operating systems. Travis CI can test on Linux
and OS X.
To enable testing on multiple operating systems add the os key to your
.travis.yml:
os:
linux
osx
The value of the $TRAVIS_OS_NAME variable is set to linux or osx
according to the operating system a particular build is running on, so
you can use it to conditionalize your build scripts.
If you are already using a build matrix to test multiple versions, the
os key also multiplies the matrix.
Source: https://docs.travis-ci.com/user/multi-os/
Builds with multiple os keys:
For example, for each separate "os" key, it creates another build. See here: https://github.com/jaredsburrows/cplusplus-cmake-template/blob/master/.travis.yml#L3 or https://github.com/jaredsburrows/open-virus/blob/master/.travis.yml#L3.
Since the default "os" is linux, it is implied in your own question that you have 3 separate builds, that are all use "os: linux".
Matrix builds with different os keys:
For example, each key is now specified in the matrix on separate lines. See here: https://github.com/jaredsburrows/cs-interview-questions/blob/master/.travis.yml#L3 and https://github.com/jaredsburrows/android-gif-example/blob/master/.travis.yml#L8.
In your question, you are not only specifying a "matrix" build but also a plain build with a different os. When specifying "matrix", you are overriding the default "os" build. But you explicitly wrote both "os" and "matrix", implying that you wanted 3 separate builds.

Answer 2

Moving the language and os portions into the matrix include works. I've still no insight as to why, however.
https://github.com/RhysU/descendu/commit/ab275ea79b4ff315f99604d6d7f26dd2488aa266