From 319437d4bd7c97ab18275d3eaf1bc190554f9df7 Mon Sep 17 00:00:00 2001
From: Andrew Leech <andrew.leech@planetinnovation.com.au>
Date: Fri, 25 Sep 2020 12:27:02 +1000
Subject: [PATCH] extmod/modure: Allow \\ in re.sub replacements.

---
 extmod/modure.c         | 3 +++
 tests/extmod/ure_sub.py | 6 ++++++
 2 files changed, 9 insertions(+)

diff --git a/extmod/modure.c b/extmod/modure.c
index 328c897d88..220587b42f 100644
--- a/extmod/modure.c
+++ b/extmod/modure.c
@@ -343,6 +343,9 @@ STATIC mp_obj_t re_sub_helper(size_t n_args, const mp_obj_t *args) {
                         const char *end_match = match->caps[match_no * 2 + 1];
                         vstr_add_strn(&vstr_return, start_match, end_match - start_match);
                     }
+                } else if (*repl == '\\') {
+                    // Add the \ character
+                    vstr_add_byte(&vstr_return, *repl++);
                 }
             } else {
                 // Just add the current byte from the replacement string
diff --git a/tests/extmod/ure_sub.py b/tests/extmod/ure_sub.py
index 953e7bf62a..ae6ad28d62 100644
--- a/tests/extmod/ure_sub.py
+++ b/tests/extmod/ure_sub.py
@@ -43,6 +43,9 @@ print(
     )
 )
 
+# \g immediately followed by another \g
+print(re.sub("(abc)", r"\g<1>\g<1>", "abc"))
+
 # no matches at all
 print(re.sub("a", "b", "c"))
 
@@ -69,3 +72,6 @@ try:
     re.sub(123, "a", "a")
 except TypeError:
     print("TypeError")
+
+# Include \ in the sub replacement
+print(re.sub("b", "\\\\b", "abc"))