Allow packages to control handling of compiler flags (#4421)

* Initial work on flag trapping using functions called <flag>_handler and default_flag_handler

* Update packages so they do not obliterate flags

* Added append to EnvironmentModifications class

* changed EnvironmentModifications to have append_flags method

* changed flag_val to be a tuple

* Increased test coverage

* added documentation of flag handling

10 files changed, 34 insertions, 12 deletions

diff --git a/var/spack/repos/builtin/packages/clhep/package.py b/var/spack/repos/builtin/packages/clhep/package.py
index e9bf85c97f..7120fffac6 100644
--- a/var/spack/repos/builtin/packages/clhep/package.py
+++ b/var/spack/repos/builtin/packages/clhep/package.py
@@ -78,12 +78,18 @@ class Clhep(CMakePackage):
         cmake_args = []
 
         if '+cxx11' in spec:
-            env['CXXFLAGS'] = self.compiler.cxx11_flag
+            if 'CXXFLAGS' in env and env['CXXFLAGS']:
+                env['CXXFLAGS'] += ' ' + self.compiler.cxx11_flag
+            else:
+                env['CXXFLAGS'] = self.compiler.cxx11_flag
             cmake_args.append('-DCLHEP_BUILD_CXXSTD=' +
                               self.compiler.cxx11_flag)
 
         if '+cxx14' in spec:
-            env['CXXFLAGS'] = self.compiler.cxx14_flag
+            if 'CXXFLAGS' in env and env['CXXFLAGS']:
+                env['CXXFLAGS'] += ' ' + self.compiler.cxx14_flag
+            else:
+                env['CXXFLAGS'] = self.compiler.cxx14_flag
             cmake_args.append('-DCLHEP_BUILD_CXXSTD=' +
                               self.compiler.cxx14_flag)
 
diff --git a/var/spack/repos/builtin/packages/elpa/package.py b/var/spack/repos/builtin/packages/elpa/package.py
index 85d1706b2b..61e957c0c9 100644
--- a/var/spack/repos/builtin/packages/elpa/package.py
+++ b/var/spack/repos/builtin/packages/elpa/package.py
@@ -71,8 +71,8 @@ class Elpa(AutotoolsPackage):
         spack_env.set('FC', spec['mpi'].mpifc)
         spack_env.set('CXX', spec['mpi'].mpicxx)
 
-        spack_env.set('LDFLAGS', spec['lapack'].libs.search_flags)
-        spack_env.set('LIBS', spec['lapack'].libs.link_flags)
+        spack_env.append_flags('LDFLAGS', spec['lapack'].libs.search_flags)
+        spack_env.append_flags('LIBS', spec['lapack'].libs.link_flags)
         spack_env.set('SCALAPACK_LDFLAGS', spec['scalapack'].libs.joined())
 
     def configure_args(self):
diff --git a/var/spack/repos/builtin/packages/ferret/package.py b/var/spack/repos/builtin/packages/ferret/package.py
index f2a32fdd70..6a4c0902f6 100644
--- a/var/spack/repos/builtin/packages/ferret/package.py
+++ b/var/spack/repos/builtin/packages/ferret/package.py
@@ -98,7 +98,12 @@ class Ferret(Package):
         ln('-sf',
            libz_prefix + '/lib',
            libz_prefix + '/lib64')
-        os.environ['LDFLAGS'] = '-lquadmath'
+
+        if 'LDFLAGS' in env and env['LDFLAGS']:
+            env['LDFLAGS'] += ' ' + '-lquadmath'
+        else:
+            env['LDFLAGS'] = '-lquadmath'
+
         with working_dir('FERRET', create=False):
             os.environ['LD_X11'] = '-L/usr/lib/X11 -lX11'
             os.environ['HOSTTYPE'] = 'x86_64-linux'
diff --git a/var/spack/repos/builtin/packages/git/package.py b/var/spack/repos/builtin/packages/git/package.py
index f01cc37d7b..9dc9e460af 100644
--- a/var/spack/repos/builtin/packages/git/package.py
+++ b/var/spack/repos/builtin/packages/git/package.py
@@ -155,7 +155,7 @@ class Git(AutotoolsPackage):
     depends_on('m4',       type='build')
 
     def setup_environment(self, spack_env, run_env):
-        spack_env.set('LDFLAGS', '-L{0} -lintl'.format(
+        spack_env.append_flags('LDFLAGS', '-L{0} -lintl'.format(
             self.spec['gettext'].prefix.lib))
 
     def configure_args(self):
diff --git a/var/spack/repos/builtin/packages/libint/package.py b/var/spack/repos/builtin/packages/libint/package.py
index d267a8ea88..34600e742a 100644
--- a/var/spack/repos/builtin/packages/libint/package.py
+++ b/var/spack/repos/builtin/packages/libint/package.py
@@ -85,6 +85,7 @@ class Libint(AutotoolsPackage):
     def configure_args(self):
 
         config_args = ['--enable-shared']
+
         optflags = self.optflags
 
         # Optimization flag names have changed in libint 2
diff --git a/var/spack/repos/builtin/packages/libxc/package.py b/var/spack/repos/builtin/packages/libxc/package.py
index f018bacfa3..e2fe25c455 100644
--- a/var/spack/repos/builtin/packages/libxc/package.py
+++ b/var/spack/repos/builtin/packages/libxc/package.py
@@ -71,8 +71,15 @@ class Libxc(Package):
             if which('xiar'):
                 env['AR'] = 'xiar'
 
-        env['CFLAGS']  = optflags
-        env['FCFLAGS'] = optflags
+        if 'CFLAGS' in env and env['CFLAGS']:
+            env['CFLAGS'] += ' ' + optflags
+        else:
+            env['CFLAGS'] = optflags
+
+        if 'FCFLAGS' in env and env['FCFLAGS']:
+            env['FCFLAGS'] += ' ' + optflags
+        else:
+            env['FCFLAGS'] = optflags
 
         configure('--prefix={0}'.format(prefix),
                   '--enable-shared')
diff --git a/var/spack/repos/builtin/packages/libxpm/package.py b/var/spack/repos/builtin/packages/libxpm/package.py
index 09d0b0ec61..40234b1b2d 100644
--- a/var/spack/repos/builtin/packages/libxpm/package.py
+++ b/var/spack/repos/builtin/packages/libxpm/package.py
@@ -46,5 +46,5 @@ class Libxpm(AutotoolsPackage):
     depends_on('util-macros', type='build')
 
     def setup_environment(self, spack_env, run_env):
-        spack_env.set('LDFLAGS', '-L{0} -lintl'.format(
+        spack_env.append_flags('LDFLAGS', '-L{0} -lintl'.format(
             self.spec['gettext'].prefix.lib))
diff --git a/var/spack/repos/builtin/packages/llvm-lld/package.py b/var/spack/repos/builtin/packages/llvm-lld/package.py
index 4624451e69..0ebe2e6b89 100644
--- a/var/spack/repos/builtin/packages/llvm-lld/package.py
+++ b/var/spack/repos/builtin/packages/llvm-lld/package.py
@@ -38,7 +38,10 @@ class LlvmLld(Package):
     depends_on('cmake', type='build')
 
     def install(self, spec, prefix):
-        env['CXXFLAGS'] = self.compiler.cxx11_flag
+        if 'CXXFLAGS' in env and env['CXXFLAGS']:
+            env['CXXFLAGS'] += ' ' + self.compiler.cxx11_flag
+        else:
+            env['CXXFLAGS'] = self.compiler.cxx11_flag
 
         with working_dir('spack-build', create=True):
             cmake('..',
diff --git a/var/spack/repos/builtin/packages/llvm/package.py b/var/spack/repos/builtin/packages/llvm/package.py
index 1f88d94882..fc8823f1a8 100644
--- a/var/spack/repos/builtin/packages/llvm/package.py
+++ b/var/spack/repos/builtin/packages/llvm/package.py
@@ -325,7 +325,7 @@ class Llvm(CMakePackage):
     conflicts('+lldb',        when='~clang')
 
     def setup_environment(self, spack_env, run_env):
-        spack_env.set('CXXFLAGS', self.compiler.cxx11_flag)
+        spack_env.append_flags('CXXFLAGS', self.compiler.cxx11_flag)
 
     def build_type(self):
         if '+debug' in self.spec:
diff --git a/var/spack/repos/builtin/packages/zlib/package.py b/var/spack/repos/builtin/packages/zlib/package.py
index 0d9822f287..30fcef95e1 100644
--- a/var/spack/repos/builtin/packages/zlib/package.py
+++ b/var/spack/repos/builtin/packages/zlib/package.py
@@ -57,7 +57,7 @@ class Zlib(Package):
 
     def setup_environment(self, spack_env, run_env):
         if '+pic' in self.spec:
-            spack_env.set('CFLAGS', self.compiler.pic_flag)
+            spack_env.append_flags('CFLAGS', self.compiler.pic_flag)
 
     def install(self, spec, prefix):
         config_args = []