PyYAML: fix linking to libyaml (#16682)

var/spack/repos/builtin/packages/py-pyyaml/package.py

@@ -11,6 +11,9 @@ class PyPyyaml(PythonPackage):
 
     homepage = "https://pyyaml.org/wiki/PyYAML"
     url      = "https://pypi.io/packages/source/P/PyYAML/PyYAML-5.3.1.tar.gz"
+    git      = "https://github.com/yaml/pyyaml.git"
+
+    maintainers = ['adamjstewart']
 
     version('5.3.1', sha256='b8eac752c5e14d3eca0e6dd9199cd627518cb5ec06add0de9d32baeee6fe645d')
     version('5.1.2', sha256='01adf0b6c6f61bd11af6e10ca52b7d4057dd0be0343eb9283c878cf3af56aee4')
@@ -24,6 +27,17 @@ class PyPyyaml(PythonPackage):
     depends_on('python@2.7:2.8,3.5:', type=('build', 'run'))
     depends_on('libyaml', when='+libyaml')
 
+    phases = ['build_ext', 'install']
+
+    @property
+    def import_modules(self):
+        modules = ['yaml']
+
+        if '+libyaml' in self.spec:
+            modules.append('yaml.cyaml')
+
+        return modules
+
     def setup_py(self, *args, **kwargs):
         # Cast from tuple to list
         args = list(args)
@@ -34,3 +48,21 @@ def setup_py(self, *args, **kwargs):
             args.insert(0, '--without-libyaml')
 
         super(PyPyyaml, self).setup_py(*args, **kwargs)
+
+    def build_ext_args(self, spec, prefix):
+        args = []
+
+        if '+libyaml' in spec:
+            args.extend([
+                spec['libyaml'].libs.search_flags,
+                spec['libyaml'].headers.include_flags,
+            ])
+
+        return args
+
+    # Tests need to be re-added since `phases` was overridden
+    run_after('build_ext')(
+        PythonPackage._run_default_build_time_test_callbacks)
+    run_after('install')(
+        PythonPackage._run_default_install_time_test_callbacks)
+    run_after('install')(PythonPackage.sanity_check_prefix)