Move variable substitution to be independent

3 files changed, 56 insertions, 18 deletions

diff --git a/coverage/config.py b/coverage/config.py
index 061fa304..69c929b4 100644
--- a/coverage/config.py
+++ b/coverage/config.py
@@ -10,6 +10,7 @@ import re
 from coverage import env
 from coverage.backward import configparser, iitems, string_class
 from coverage.misc import contract, CoverageException, isolate_module
+from coverage.misc import substitute_variables
 
 os = isolate_module(os)
 
@@ -85,23 +86,7 @@ class HandyConfigParser(configparser.RawConfigParser):
             raise configparser.NoOptionError
 
         v = configparser.RawConfigParser.get(self, real_section, option, *args, **kwargs)
-        def dollar_replace(m):
-            """Called for each $replacement."""
-            # Only one of the groups will have matched, just get its text.
-            word = next(w for w in m.groups() if w is not None)     # pragma: part covered
-            if word == "$":
-                return "$"
-            else:
-                return os.environ.get(word, '')
-
-        dollar_pattern = r"""(?x)   # Use extended regex syntax
-            \$(?:                   # A dollar sign, then
-            (?P<v1>\w+) |           #   a plain word,
-            {(?P<v2>\w+)} |         #   or a {-wrapped word,
-            (?P<char>[$])           #   or a dollar sign.
-            )
-            """
-        v = re.sub(dollar_pattern, dollar_replace, v)
+        v = substitute_variables(v)
         return v
 
     def getlist(self, section, option):
diff --git a/coverage/misc.py b/coverage/misc.py
index ab950846..e2031852 100644
--- a/coverage/misc.py
+++ b/coverage/misc.py
@@ -8,6 +8,7 @@ import hashlib
 import inspect
 import locale
 import os
+import re
 import sys
 import types
 
@@ -250,6 +251,42 @@ def _needs_to_implement(that, func_name):
         )
 
 
+def substitute_variables(text, variables=os.environ):
+    """Substitute ``${VAR}`` variables in `text` with their values.
+
+    Variables in the text can take a number of shell-inspired forms::
+
+        $VAR
+        ${VAR}
+
+    A dollar can be inserted with ``$$``.
+
+    `variables` is a dictionary of variable values, defaulting to the
+    environment variables.
+
+    Returns the resulting text with values substituted.
+
+    """
+    def dollar_replace(m):
+        """Called for each $replacement."""
+        # Only one of the groups will have matched, just get its text.
+        word = next(w for w in m.groups() if w is not None)     # pragma: part covered
+        if word == "$":
+            return "$"
+        else:
+            return variables.get(word, '')
+
+    dollar_pattern = r"""(?x)   # Use extended regex syntax
+        \$(?:                   # A dollar sign, then
+        (?P<v1>\w+) |           #   a plain word,
+        {(?P<v2>\w+)} |         #   or a {-wrapped word,
+        (?P<char>[$])           #   or a dollar sign.
+        )
+        """
+    text = re.sub(dollar_pattern, dollar_replace, text)
+    return text
+
+
 class BaseCoverageException(Exception):
     """The base of all Coverage exceptions."""
     pass
diff --git a/tests/test_misc.py b/tests/test_misc.py
index 1d01537b..77200b3c 100644
--- a/tests/test_misc.py
+++ b/tests/test_misc.py
@@ -6,7 +6,7 @@
 import pytest
 
 from coverage.misc import contract, dummy_decorator_with_args, file_be_gone
-from coverage.misc import format_lines, Hasher, one_of
+from coverage.misc import format_lines, Hasher, one_of, substitute_variables
 
 from tests.coveragetest import CoverageTest
 
@@ -135,3 +135,19 @@ class ContractTest(CoverageTest):
 ])
 def test_format_lines(statements, lines, result):
     assert format_lines(statements, lines) == result
+
+
+@pytest.mark.parametrize("before, after", [
+    ("Nothing to do", "Nothing to do"),
+    ("Dollar: $$", "Dollar: $"),
+    ("Simple: $FOO is fooey", "Simple: fooey is fooey"),
+    ("Braced: X${FOO}X.", "Braced: XfooeyX."),
+    ("Missing: x$NOTHING is x", "Missing: x is x"),
+    ("Multiple: $$ $FOO $BAR ${FOO}", "Multiple: $ fooey xyzzy fooey"),
+])
+def test_substitute_variables(before, after):
+    variables = {
+        'FOO': 'fooey',
+        'BAR': 'xyzzy',
+    }
+    assert substitute_variables(before, variables) == after