From ed3d8a5c300d7029bc85bc0c012386ae933e230f Mon Sep 17 00:00:00 2001
From: dgp <dgp@users.sourceforge.net>
Date: Thu, 10 Aug 2017 17:03:53 +0000
Subject: Backport [array names -regexp] should support backrefs

---
 generic/tclRegexp.c | 15 +++++++++++----
 tests/set-old.test  |  7 +++++++
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/generic/tclRegexp.c b/generic/tclRegexp.c
index ea25d4b..cfe6388 100644
--- a/generic/tclRegexp.c
+++ b/generic/tclRegexp.c
@@ -502,10 +502,17 @@ Tcl_RegExpMatchObj(
 {
     Tcl_RegExp re;
 
-    re = Tcl_GetRegExpFromObj(interp, patternObj,
-	    TCL_REG_ADVANCED | TCL_REG_NOSUB);
-    if (re == NULL) {
-	return -1;
+    /*
+     * For performance reasons, first try compiling the RE without support for
+     * subexpressions. On failure, try again without TCL_REG_NOSUB in case the
+     * RE has backreferences in it. Closely related to [Bug 1366683]. If this
+     * still fails, an error message will be left in the interpreter.
+     */
+
+    if (!(re = Tcl_GetRegExpFromObj(interp, patternObj,
+            TCL_REG_ADVANCED | TCL_REG_NOSUB))
+     && !(re = Tcl_GetRegExpFromObj(interp, patternObj, TCL_REG_ADVANCED))) {
+        return -1;
     }
     return Tcl_RegExpExecObj(interp, re, textObj, 0 /* offset */,
 	    0 /* nmatches */, 0 /* flags */);
diff --git a/tests/set-old.test b/tests/set-old.test
index 1c68f91..6138ed8 100644
--- a/tests/set-old.test
+++ b/tests/set-old.test
@@ -652,6 +652,13 @@ test set-old-8.52 {array command, array names -regexp on regexp pattern} {
     set a(11) 1
     list [catch {lsort [array names a -regexp ^1]} msg] $msg
 } {0 {1*2 11 12}}
+test set-old-8.52.1 {array command, array names -regexp, backrefs} {
+    catch {unset a}
+    set a(1*2) 1
+    set a(12) 1
+    set a(11) 1
+    list [catch {lsort [array names a -regexp {^(.)\1}]} msg] $msg
+} {0 11}
 test set-old-8.53 {array command, array names -regexp} {
     catch {unset a}
     set a(-glob) 1
-- 
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