refactor: since we are showing regexes, make them a bit simpler

The old code would always wrap the regex in a needless `(?s:...)`
parenthesis.  Path aliases are always single regexes, so they don't need
that extra wrapping.  This makes logged path maps easier to understand.

Author: nedbat

coverage/misc.py

@@ -182,7 +182,11 @@ def bool_or_none(b):
 
 def join_regex(regexes):
     """Combine a series of regexes into one that matches any of them."""
-    return "|".join(f"(?:{r})" for r in regexes)
+    regexes = list(regexes)
+    if len(regexes) == 1:
+        return regexes[0]
+    else:
+        return "|".join(f"(?:{r})" for r in regexes)
 
 
 def file_be_gone(path):

tests/test_files.py

@@ -309,9 +309,9 @@ def test_multiple_patterns(self, rel_yn):
             assert msgs == [
                 "Aliases (relative=True):",
                 " Rule: '/home/*/src' -> './mysrc/' using regex " +
-                    "'(?:(?s:[\\\\\\\\/]home[\\\\\\\\/].*[\\\\\\\\/]src[\\\\\\\\/]))'",
+                    "'(?s:[\\\\\\\\/]home[\\\\\\\\/].*[\\\\\\\\/]src[\\\\\\\\/])'",
                 " Rule: '/lib/*/libsrc' -> './mylib/' using regex " +
-                    "'(?:(?s:[\\\\\\\\/]lib[\\\\\\\\/].*[\\\\\\\\/]libsrc[\\\\\\\\/]))'",
+                    "'(?s:[\\\\\\\\/]lib[\\\\\\\\/].*[\\\\\\\\/]libsrc[\\\\\\\\/])'",
                 "Matched path '/home/foo/src/a.py' to rule '/home/*/src' -> './mysrc/', " +
                     "producing './mysrc/a.py'",
                 "Matched path '/lib/foo/libsrc/a.py' to rule '/lib/*/libsrc' -> './mylib/', " +
@@ -321,9 +321,9 @@ def test_multiple_patterns(self, rel_yn):
             assert msgs == [
                 "Aliases (relative=False):",
                 " Rule: '/home/*/src' -> './mysrc/' using regex " +
-                    "'(?:(?s:[\\\\\\\\/]home[\\\\\\\\/].*[\\\\\\\\/]src[\\\\\\\\/]))'",
+                    "'(?s:[\\\\\\\\/]home[\\\\\\\\/].*[\\\\\\\\/]src[\\\\\\\\/])'",
                 " Rule: '/lib/*/libsrc' -> './mylib/' using regex " +
-                    "'(?:(?s:[\\\\\\\\/]lib[\\\\\\\\/].*[\\\\\\\\/]libsrc[\\\\\\\\/]))'",
+                    "'(?s:[\\\\\\\\/]lib[\\\\\\\\/].*[\\\\\\\\/]libsrc[\\\\\\\\/])'",
                 "Matched path '/home/foo/src/a.py' to rule '/home/*/src' -> './mysrc/', " +
                     f"producing {files.canonical_filename('./mysrc/a.py')!r}",
                 "Matched path '/lib/foo/libsrc/a.py' to rule '/lib/*/libsrc' -> './mylib/', " +