BUILD, DOC: remove the std=c99 flag from docs, builds, add release note

5 files changed, 13 insertions, 18 deletions

diff --git a/INSTALL.rst.txt b/INSTALL.rst.txt
index bd2f4f92c..d6c42bad7 100644
--- a/INSTALL.rst.txt
+++ b/INSTALL.rst.txt
@@ -28,7 +28,7 @@ Building NumPy requires the following installed software:
 
 2) Cython >= 0.29.2 (for development versions of numpy, not for released
                      versions)
-                     
+
 3) pytest__ (optional) 1.15 or later
 
    This is required for testing numpy, but not for using it.
@@ -37,7 +37,7 @@ Python__ http://www.python.org
 pytest__ http://pytest.readthedocs.io
 
 
-.. note:: 
+.. note::
 
    If you want to build NumPy in order to work on NumPy itself, use
    ``runtests.py``.  For more details, see
@@ -77,11 +77,7 @@ skipped when running the test suite if no Fortran compiler is available.  For
 building Scipy a Fortran compiler is needed though, so we include some details
 on Fortran compilers in the rest of this section.
 
-On OS X and Linux, all common compilers will work.  Note that C99 support is
-required.  For compilers that don't support the C99 language standard by
-default (such as ``gcc`` versions < 5.0), it should be enabled.  For ``gcc``::
-
-    export CFLAGS='-std=c99'
+On OS X and Linux, all common compilers will work.
 
 For Fortran, ``gfortran`` works, ``g77`` does not.  In case ``g77`` is
 installed then ``g77`` will be detected and used first.  To explicitly select
@@ -117,9 +113,9 @@ details.
 Windows
 -------
 
-The Intel compilers work with Intel MKL, see the application note linked above. 
+The Intel compilers work with Intel MKL, see the application note linked above.
 MingwPy__ works with OpenBLAS.
-For an overview of the state of BLAS/LAPACK libraries on Windows, see 
+For an overview of the state of BLAS/LAPACK libraries on Windows, see
 `here <https://mingwpy.github.io/blas_lapack.html>`_.
 
 OS X
diff --git a/azure-pipelines.yml b/azure-pipelines.yml
index c5ae65dbf..bfb033bb8 100644
--- a/azure-pipelines.yml
+++ b/azure-pipelines.yml
@@ -46,7 +46,7 @@ stages:
             python3 -m pip install --user -r test_requirements.txt && \
             python3 -m pip install . && \
             F77=gfortran-5 F90=gfortran-5 \
-            CFLAGS='-UNDEBUG -std=c99' python3 runtests.py -n --debug-info --mode=full -- -rsx --junitxml=junit/test-results.xml && \
+            CFLAGS=-UNDEBUG python3 runtests.py -n --debug-info --mode=full -- -rsx --junitxml=junit/test-results.xml && \
             python3 tools/openblas_support.py --check_version $(OpenBLAS_version)"
       displayName: 'Run 32-bit Ubuntu Docker Build / Tests'
     - task: PublishTestResults@2
diff --git a/doc/release/upcoming_changes/14771.improvement.rst b/doc/release/upcoming_changes/14771.improvement.rst
new file mode 100644
index 000000000..847f21b5e
--- /dev/null
+++ b/doc/release/upcoming_changes/14771.improvement.rst
@@ -0,0 +1,6 @@
+``std=c99`` added if compiler is named ``gcc``
+----------------------------------------------
+
+GCC before version 5 requies the ``-std=c99`` command line argument. Newer
+compilers automatically turn on C99 mode. The compiler setup code will
+automatically add the code if the compiler name has ``gcc`` in it.
diff --git a/doc/source/dev/development_environment.rst b/doc/source/dev/development_environment.rst
index 9d618cc9f..297502b31 100644
--- a/doc/source/dev/development_environment.rst
+++ b/doc/source/dev/development_environment.rst
@@ -11,8 +11,7 @@ Recommended development setup
 Since NumPy contains parts written in C and Cython that need to be
 compiled before use, make sure you have the necessary compilers and Python
 development headers installed - see :ref:`building-from-source`. Building
-NumPy as of version ``1.17`` requires a C99 compliant compiler. For
-some older compilers this may require ``export CFLAGS='-std=c99'``.
+NumPy as of version ``1.17`` requires a C99 compliant compiler.
 
 Having compiled code also means that importing NumPy from the development
 sources needs some additional steps, which are explained below.  For the rest
diff --git a/tools/travis-test.sh b/tools/travis-test.sh
index 6094f0ee6..e04a33143 100755
--- a/tools/travis-test.sh
+++ b/tools/travis-test.sh
@@ -36,8 +36,6 @@ setup_base()
   sysflags="$($PYTHON -c "from distutils import sysconfig; \
     print (sysconfig.get_config_var('CFLAGS'))")"
   export CFLAGS="$sysflags $werrors -Wlogical-op -Wno-sign-compare"
-  # use c99
-  export CFLAGS=$CFLAGS" -std=c99"
   # We used to use 'setup.py install' here, but that has the terrible
   # behaviour that if a copy of the package is already installed in the
   # install location, then the new copy just gets dropped on top of it.
@@ -141,8 +139,6 @@ if [ -n "$USE_WHEEL" ] && [ $# -eq 0 ]; then
   $PIP install -U virtualenv
   # ensure some warnings are not issued
   export CFLAGS=$CFLAGS" -Wno-sign-compare -Wno-unused-result"
-  # use c99
-  export CFLAGS=$CFLAGS" -std=c99"
   # adjust gcc flags if C coverage requested
   if [ -n "$RUN_COVERAGE" ]; then
      export NPY_DISTUTILS_APPEND_FLAGS=1
@@ -169,8 +165,6 @@ elif [ -n "$USE_SDIST" ] && [ $# -eq 0 ]; then
   $PYTHON -c "import fcntl; fcntl.fcntl(1, fcntl.F_SETFL, 0)"
   # ensure some warnings are not issued
   export CFLAGS=$CFLAGS" -Wno-sign-compare -Wno-unused-result"
-  # use c99
-  export CFLAGS=$CFLAGS" -std=c99"
   $PYTHON setup.py sdist
   # Make another virtualenv to install into
   virtualenv --python=`which $PYTHON` venv-for-wheel