pyrediff: unescaping \\ is version specific

python's re.escape() escapes different character sets
from version 3.3 and then from version 3.7.
Adjust the escaping mechanism (originally written
for python2) to cope.

Reverts the unescaping at EOL workaround from commit ce5f932.

Author: lukem

src/ax_at_check_pyrediff.m4

@@ -60,9 +60,16 @@ __version__ = "17"
 class Pyrediff:
     _add_del_re = re.compile(r"^(\d+a\d+(,\d+)?|\d+(,\d+)?d\d+)@S|@")
     _change_re = re.compile(r"^\d+(,\d+)?c\d+(,\d+)?@S|@")
-    _ws_eol_re = re.compile(r"\\(\s)$")
-    _escape_re = re.compile(r"(?<!\\)\\(@<:@-\s!\"#&%,/:;<=>@_`'~@:>@)")
     _group_re = re.compile(r"\\g<(@<:@^>@:>@+)>")
+    if sys.version_info < (3,3):
+        _escape_re = re.compile(r"\\(@<:@-\s!\"#&%,/:;<=>@_`'~@:>@)")
+    elif sys.version_info < (3,7):
+        # 3.3 .. 3.6 doesn't escape "_"
+        _escape_re = re.compile(r"\\(@<:@-\s!\"#&%,/:;<=>@`'~@:>@)")
+    else:
+        # 3.7+ doesn't escape '!', '"', '%', "'", ',', '/', ':', ';',
+        # '<', '=', '>', '@', and "`"
+        _escape_re = re.compile(r"\\(@<:@-\s#&%,~@:>@)")
 
     def __init__(self):
         self.fail = False
@@ -79,7 +86,6 @@ class Pyrediff:
         with io.open(input_name, "r", encoding="utf-8") as output_fp:
             for line in output_fp:
                 esc = re.escape(line)
-                esc = self._ws_eol_re.sub(r"\1", esc)
                 esc = self._escape_re.sub(r"\1", esc)
                 sys.stdout.write(esc)
 

src/pyrediff

@@ -37,9 +37,16 @@ __version__ = "17"
 class Pyrediff:
     _add_del_re = re.compile(r"^(\d+a\d+(,\d+)?|\d+(,\d+)?d\d+)$")
     _change_re = re.compile(r"^\d+(,\d+)?c\d+(,\d+)?$")
-    _ws_eol_re = re.compile(r"\\(\s)$")
-    _escape_re = re.compile(r"(?<!\\)\\([-\s!\"#&%,/:;<=>@_`'~])")
     _group_re = re.compile(r"\\g<([^>]+)>")
+    if sys.version_info < (3,3):
+        _escape_re = re.compile(r"\\([-\s!\"#&%,/:;<=>@_`'~])")
+    elif sys.version_info < (3,7):
+        # 3.3 .. 3.6 doesn't escape "_"
+        _escape_re = re.compile(r"\\([-\s!\"#&%,/:;<=>@`'~])")
+    else:
+        # 3.7+ doesn't escape '!', '"', '%', "'", ',', '/', ':', ';',
+        # '<', '=', '>', '@', and "`"
+        _escape_re = re.compile(r"\\([-\s#&%,~])")
 
     def __init__(self):
         self.fail = False
@@ -56,7 +63,6 @@ class Pyrediff:
         with io.open(input_name, "r", encoding="utf-8") as output_fp:
             for line in output_fp:
                 esc = re.escape(line)
-                esc = self._ws_eol_re.sub(r"\1", esc)
                 esc = self._escape_re.sub(r"\1", esc)
                 sys.stdout.write(esc)