Make optionalenv defenv to support default values

Change the 'optionalenv' substitution to 'defenv' and support providing
a default substitution value. Format is "defenv:DEFAULTVALUE:KEY".

3 files changed, 38 insertions, 20 deletions

diff --git a/doc/config.txt b/doc/config.txt
index 971ca68..5a9134d 100644
--- a/doc/config.txt
+++ b/doc/config.txt
@@ -293,16 +293,24 @@ and raise an Error if the environment variable
 does not exist.
 
 
-optional environment variable substitutions
-++++++++++++++++++++++++++++++++++
+environment variable substitutions with default values
+++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+If you specify a substitution string like this::
+
+    {defenv:DEFAULTVALUE:KEY}
+
+then the value will be retrieved as ``os.environ['KEY']``
+and replace with DEFAULTVALUE if the environment variable does not
+exist.
 
 If you specify a substitution string like this::
 
-    {optionalenv:KEY}
+    {defenv::KEY}
 
 then the value will be retrieved as ``os.environ['KEY']``
-and replace with '' if the environment variable does not
-exist
+and replace with and empty string if the environment variable does not
+exist.
 
 .. _`command positional substitution`:
 .. _`positional substitution`:
diff --git a/tests/test_config.py b/tests/test_config.py
index 419d021..3084001 100644
--- a/tests/test_config.py
+++ b/tests/test_config.py
@@ -242,17 +242,20 @@ class TestIniParser:
         py.test.raises(tox.exception.ConfigError,
             'reader.getdefault("section", "key2")')
 
-    def test_getdefault_environment_optional_sub(self, monkeypatch, newconfig):
+    def test_getdefault_environment_substitution_with_default(self, monkeypatch, newconfig):
         monkeypatch.setenv("KEY1", "hello")
         config = newconfig("""
             [section]
-            key1={optionalenv:KEY1}
-            key2={optionalenv:KEY2}
+            key1={defenv:DEFAULT_VALUE:KEY1}
+            key2={defenv:DEFAULT_VALUE:KEY2}
+            key3={defenv::KEY3}
         """)
         reader = IniReader(config._cfg)
         x = reader.getdefault("section", "key1")
         assert x == "hello"
         x = reader.getdefault("section", "key2")
+        assert x == "DEFAULT_VALUE"
+        x = reader.getdefault("section", "key3")
         assert x == ""
 
     def test_getdefault_other_section_substitution(self, newconfig):
diff --git a/tox/_config.py b/tox/_config.py
index 4f6fa33..468af5f 100644
--- a/tox/_config.py
+++ b/tox/_config.py
@@ -595,25 +595,32 @@ class IniReader:
         #print "getdefault", section, name, "returned", repr(x)
         return x
 
-    def _do_replace_env(self, match, error=True):
-        envkey = match.group('substitution_value')
+    def _do_replace_env(self, envkey, default=None):
         if not envkey:
             raise tox.exception.ConfigError(
                 'env: requires an environment variable name')
 
-        if not envkey in os.environ:
-            if error:
-                raise tox.exception.ConfigError(
-                    "substitution env:%r: unkown environment variable %r" %
-                    (envkey, envkey))
+        if not envkey in os.environ and default is None:
+            raise tox.exception.ConfigError(
+                "substitution env:%r: unkown environment variable %r" %
+                (envkey, envkey))
 
-        return os.environ.get(envkey, '')
+        return os.environ.get(envkey, default)
 
     def _replace_env(self, match):
-        return self._do_replace_env(match)
+        envkey = match.group('substitution_value')
+        return self._do_replace_env(envkey)
+
+    def _replace_env_with_default(self, match):
+        envkey = match.group('substitution_value')
+        try:
+            default, envkey = envkey.split(':', 1)
+        except ValueError:
+            raise tox.exception.ConfigError(
+                "substitution 'defenv:%r': malformed, expected "
+                "'defenv:DEFAULTVALUE:KEY'" % match)
 
-    def _replace_env_no_error(self, match):
-        return self._do_replace_env(match, error=False)
+        return self._do_replace_env(envkey, default=default)
 
     def _substitute_from_other_section(self, key):
         if key.startswith("[") and "]" in key:
@@ -654,7 +661,7 @@ class IniReader:
 
         handlers = {
             'env' : self._replace_env,
-            'optionalenv' : self._replace_env_no_error,
+            'defenv' : self._replace_env_with_default,
             None : self._replace_substitution,
             }
         try: