diff --git a/src/pip/_internal/index.py b/src/pip/_internal/index.py
index 5dafd1c7e..aac93cdb6 100644
--- a/src/pip/_internal/index.py
+++ b/src/pip/_internal/index.py
@@ -413,7 +413,9 @@ class CandidateEvaluator(object):
             return (False, 'No sources permitted for %s' % search.supplied)
 
         if not version:
-            version = _egg_info_matches(egg_info, search.canonical)
+            version = _extract_version_from_fragment(
+                egg_info, search.canonical,
+            )
         if not version:
             return (False, 'Missing project version for %s' % search.supplied)
 
@@ -1117,45 +1119,47 @@ class PackageFinder(object):
         return result
 
 
-def _find_name_version_sep(egg_info, canonical_name):
+def _find_name_version_sep(fragment, canonical_name):
     # type: (str, str) -> int
     """Find the separator's index based on the package's canonical name.
 
-    `egg_info` must be an egg info string for the given package, and
-    `canonical_name` must be the package's canonical name.
+    :param fragment: A <package>+<version> filename "fragment" (stem) or
+        egg fragment.
+    :param canonical_name: The package's canonical name.
 
     This function is needed since the canonicalized name does not necessarily
     have the same length as the egg info's name part. An example::
 
-    >>> egg_info = 'foo__bar-1.0'
+    >>> fragment = 'foo__bar-1.0'
     >>> canonical_name = 'foo-bar'
-    >>> _find_name_version_sep(egg_info, canonical_name)
+    >>> _find_name_version_sep(fragment, canonical_name)
     8
     """
     # Project name and version must be separated by one single dash. Find all
     # occurrences of dashes; if the string in front of it matches the canonical
     # name, this is the one separating the name and version parts.
-    for i, c in enumerate(egg_info):
+    for i, c in enumerate(fragment):
         if c != "-":
             continue
-        if canonicalize_name(egg_info[:i]) == canonical_name:
+        if canonicalize_name(fragment[:i]) == canonical_name:
             return i
-    raise ValueError("{} does not match {}".format(egg_info, canonical_name))
+    raise ValueError("{} does not match {}".format(fragment, canonical_name))
 
 
-def _egg_info_matches(egg_info, canonical_name):
+def _extract_version_from_fragment(fragment, canonical_name):
     # type: (str, str) -> Optional[str]
-    """Pull the version part out of a string.
+    """Parse the version string from a <package>+<version> filename
+    "fragment" (stem) or egg fragment.
 
-    :param egg_info: The string to parse. E.g. foo-2.1
+    :param fragment: The string to parse. E.g. foo-2.1
     :param canonical_name: The canonicalized name of the package this
         belongs to.
     """
     try:
-        version_start = _find_name_version_sep(egg_info, canonical_name) + 1
+        version_start = _find_name_version_sep(fragment, canonical_name) + 1
     except ValueError:
         return None
-    version = egg_info[version_start:]
+    version = fragment[version_start:]
     if not version:
         return None
     return version
diff --git a/tests/unit/test_index.py b/tests/unit/test_index.py
index 83531d4d2..4c07d052f 100644
--- a/tests/unit/test_index.py
+++ b/tests/unit/test_index.py
@@ -9,7 +9,7 @@ from pip._internal.download import PipSession
 from pip._internal.index import (
     CandidateEvaluator, HTMLPage, Link, PackageFinder, Search,
     _check_link_requires_python, _clean_link, _determine_base_url,
-    _egg_info_matches, _find_name_version_sep, _get_html_page,
+    _extract_version_from_fragment, _find_name_version_sep, _get_html_page,
 )
 from pip._internal.models.candidate import InstallationCandidate
 from pip._internal.models.search_scope import SearchScope
@@ -510,7 +510,7 @@ def test_secure_origin(location, trusted, expected):
 
 
 @pytest.mark.parametrize(
-    ("egg_info", "canonical_name", "expected"),
+    ("fragment", "canonical_name", "expected"),
     [
         # Trivial.
         ("pip-18.0", "pip", 3),
@@ -539,13 +539,13 @@ def test_secure_origin(location, trusted, expected):
         ("zope.interface-", "zope-interface", 14),
     ],
 )
-def test_find_name_version_sep(egg_info, canonical_name, expected):
-    index = _find_name_version_sep(egg_info, canonical_name)
+def test_find_name_version_sep(fragment, canonical_name, expected):
+    index = _find_name_version_sep(fragment, canonical_name)
     assert index == expected
 
 
 @pytest.mark.parametrize(
-    ("egg_info", "canonical_name"),
+    ("fragment", "canonical_name"),
     [
         # A dash must follow the package name.
         ("zope.interface4.5.0", "zope-interface"),
@@ -554,15 +554,15 @@ def test_find_name_version_sep(egg_info, canonical_name, expected):
         ("zope.interface", "zope-interface"),
     ],
 )
-def test_find_name_version_sep_failure(egg_info, canonical_name):
+def test_find_name_version_sep_failure(fragment, canonical_name):
     with pytest.raises(ValueError) as ctx:
-        _find_name_version_sep(egg_info, canonical_name)
-    message = "{} does not match {}".format(egg_info, canonical_name)
+        _find_name_version_sep(fragment, canonical_name)
+    message = "{} does not match {}".format(fragment, canonical_name)
     assert str(ctx.value) == message
 
 
 @pytest.mark.parametrize(
-    ("egg_info", "canonical_name", "expected"),
+    ("fragment", "canonical_name", "expected"),
     [
         # Trivial.
         ("pip-18.0", "pip", "18.0"),
@@ -594,8 +594,8 @@ def test_find_name_version_sep_failure(egg_info, canonical_name):
         ("zope.interface", "zope-interface", None),
     ],
 )
-def test_egg_info_matches(egg_info, canonical_name, expected):
-    version = _egg_info_matches(egg_info, canonical_name)
+def test_extract_version_from_fragment(fragment, canonical_name, expected):
+    version = _extract_version_from_fragment(fragment, canonical_name)
     assert version == expected