Support tag specific environment variables

This makes it possible to specify an environment variable for a tag
that will be used during builds. e.g.

koji edit-tag -x rpm.env.CC=clang

builder/kojid

@@ -293,10 +293,13 @@ class BuildRoot(object):
         if self.internal_dev_setup is not None:
             opts['internal_dev_setup'] = bool(self.internal_dev_setup)
         opts['tag_macros'] = {}
+        opts['tag_envvars'] = {}
         for key in self.config['extra']:
             if key.startswith('rpm.macro.'):
                 macro = '%' + key[10:]
                 opts['tag_macros'][macro] = self.config['extra'][key]
+            elif key.startswith('rpm.env.'):
+                opts['tag_envvars'][key[8:]] = self.config['extra'][key]
         output = koji.genMockConfig(self.name, self.br_arch, managed=True, **opts)
 
         # write config

docs/source/using_the_koji_build_system.rst

@@ -395,6 +395,15 @@ environment follows:
   `--old-chroot` option is appended to any mock call. If it is not set,
   mock's default behavior is used.
 
+You may also specify per-tag environment variables for mock to use.
+For example, to set the CC environment variable to clang, you could
+do:
+
+::
+
+    koji edit-tag dnf-fedora-tag -x rpm.env.CC=clang
+
+
 Using Koji to control tasks
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 

koji/__init__.py

@@ -1697,6 +1697,13 @@ name=build
         value = macros[key]
         parts.append("config_opts['macros'][%r] = %r\n" % (key, value))
     parts.append("\n")
+    envvars = opts.get('tag_envvars', {})
+    for key in sorted(envvars):
+        value = envvars[key]
+        parts.append("config_opts['environment'][%r] = %r\n" % (key, value))
+    if len(envvars):
+        parts.append("\n")
+
     for key in sorted(files):
         value = files[key]
         parts.append("config_opts['files'][%r] = %r\n" % (key, value))