Revert "bpo-47211: Remove function re.template() and flag re.TEMPLATE (pythonGH-32300)"

This reverts commit b09184b.

Fixes python#92728

Author: hroncok

Lib/re/__init__.py

@@ -129,7 +129,7 @@
 # public symbols
 __all__ = [
     "match", "fullmatch", "search", "sub", "subn", "split",
-    "findall", "finditer", "compile", "purge", "escape",
+    "findall", "finditer", "compile", "purge", "template", "escape",
     "error", "Pattern", "Match", "A", "I", "L", "M", "S", "X", "U",
     "ASCII", "IGNORECASE", "LOCALE", "MULTILINE", "DOTALL", "VERBOSE",
     "UNICODE", "NOFLAG", "RegexFlag",
@@ -148,6 +148,8 @@ class RegexFlag:
     MULTILINE = M = _compiler.SRE_FLAG_MULTILINE # make anchors look for newline
     DOTALL = S = _compiler.SRE_FLAG_DOTALL # make dot match newline
     VERBOSE = X = _compiler.SRE_FLAG_VERBOSE # ignore whitespace and comments
+    # sre extensions (experimental, don't rely on these)
+    TEMPLATE = T = _compiler.SRE_FLAG_TEMPLATE # disable backtracking
     DEBUG = _compiler.SRE_FLAG_DEBUG # dump pattern after compilation
     __str__ = object.__str__
     _numeric_repr_ = hex
@@ -229,6 +231,10 @@ def purge():
     _cache.clear()
     _compile_repl.cache_clear()
 
+def template(pattern, flags=0):
+    "Compile a template pattern, returning a Pattern object"
+    return _compile(pattern, flags|T)
+
 # SPECIAL_CHARS
 # closing ')', '}' and ']'
 # '-' (a range in character set)

Lib/re/_compiler.py

@@ -108,6 +108,8 @@ def _compile(data, pattern, flags):
             else:
                 emit(ANY)
         elif op in REPEATING_CODES:
+            if flags & SRE_FLAG_TEMPLATE:
+                raise error("internal: unsupported template operator %r" % (op,))
             if _simple(av[2]):
                 emit(REPEATING_CODES[op][2])
                 skip = _len(code); emit(0)

Lib/re/_constants.py

@@ -204,6 +204,7 @@ def _makecodes(*names):
 }
 
 # flags
+SRE_FLAG_TEMPLATE = 1 # template mode (disable backtracking)
 SRE_FLAG_IGNORECASE = 2 # case insensitive
 SRE_FLAG_LOCALE = 4 # honour system locale
 SRE_FLAG_MULTILINE = 8 # treat target as multiline string

Lib/re/_parser.py

@@ -61,11 +61,12 @@
     "x": SRE_FLAG_VERBOSE,
     # extensions
     "a": SRE_FLAG_ASCII,
+    "t": SRE_FLAG_TEMPLATE,
     "u": SRE_FLAG_UNICODE,
 }
 
 TYPE_FLAGS = SRE_FLAG_ASCII | SRE_FLAG_LOCALE | SRE_FLAG_UNICODE
-GLOBAL_FLAGS = SRE_FLAG_DEBUG
+GLOBAL_FLAGS = SRE_FLAG_DEBUG | SRE_FLAG_TEMPLATE
 
 class State:
     # keeps track of state for parsing

Lib/test/test_re.py

@@ -2580,11 +2580,11 @@ def test_flags_repr(self):
                          "re.IGNORECASE|re.DOTALL|re.VERBOSE|0x100000")
         self.assertEqual(
                 repr(~re.I),
-                "re.ASCII|re.LOCALE|re.UNICODE|re.MULTILINE|re.DOTALL|re.VERBOSE|re.DEBUG|0x1")
+                "re.ASCII|re.LOCALE|re.UNICODE|re.MULTILINE|re.DOTALL|re.VERBOSE|re.TEMPLATE|re.DEBUG")
         self.assertEqual(repr(~(re.I|re.S|re.X)),
-                         "re.ASCII|re.LOCALE|re.UNICODE|re.MULTILINE|re.DEBUG|0x1")
+                         "re.ASCII|re.LOCALE|re.UNICODE|re.MULTILINE|re.TEMPLATE|re.DEBUG")
         self.assertEqual(repr(~(re.I|re.S|re.X|(1<<20))),
-                         "re.ASCII|re.LOCALE|re.UNICODE|re.MULTILINE|re.DEBUG|0xffe01")
+                         "re.ASCII|re.LOCALE|re.UNICODE|re.MULTILINE|re.TEMPLATE|re.DEBUG|0xffe00")
 
 
 class ImplementationTest(unittest.TestCase):

Modules/_sre/sre.c

@@ -1323,6 +1323,7 @@ pattern_repr(PatternObject *obj)
         const char *name;
         int value;
     } flag_names[] = {
+        {"re.TEMPLATE", SRE_FLAG_TEMPLATE},
         {"re.IGNORECASE", SRE_FLAG_IGNORECASE},
         {"re.LOCALE", SRE_FLAG_LOCALE},
         {"re.MULTILINE", SRE_FLAG_MULTILINE},

Modules/_sre/sre_constants.h

@@ -85,6 +85,7 @@
 #define SRE_CATEGORY_UNI_NOT_WORD 15
 #define SRE_CATEGORY_UNI_LINEBREAK 16
 #define SRE_CATEGORY_UNI_NOT_LINEBREAK 17
+#define SRE_FLAG_TEMPLATE 1
 #define SRE_FLAG_IGNORECASE 2
 #define SRE_FLAG_LOCALE 4
 #define SRE_FLAG_MULTILINE 8