Backport fix and test for typecasting bug in Tcl_GetUniChar().

2 files changed, 9 insertions, 2 deletions

diff --git a/generic/tclStringObj.c b/generic/tclStringObj.c
index d1e709c..4afd12a 100644
--- a/generic/tclStringObj.c
+++ b/generic/tclStringObj.c
@@ -576,7 +576,7 @@ Tcl_GetUniChar(
 	    TclNumUtfChars(stringPtr->numChars, objPtr->bytes, objPtr->length);
 	}
 	if (stringPtr->numChars == objPtr->length) {
-	    return (Tcl_UniChar) objPtr->bytes[index];
+	    return (unsigned char) objPtr->bytes[index];
 	}
 	FillUnicodeRep(objPtr);
 	stringPtr = GET_STRING(objPtr);
@@ -632,7 +632,7 @@ TclGetUCS4(
 	    TclNumUtfChars(stringPtr->numChars, objPtr->bytes, objPtr->length);
 	}
 	if (stringPtr->numChars == objPtr->length) {
-	    return (Tcl_UniChar) objPtr->bytes[index];
+	    return (unsigned char) objPtr->bytes[index];
 	}
 	FillUnicodeRep(objPtr);
 	stringPtr = GET_STRING(objPtr);
diff --git a/tests/string.test b/tests/string.test
index 66eb6ad..977e875 100644
--- a/tests/string.test
+++ b/tests/string.test
@@ -323,6 +323,13 @@ test string-5.20 {string index, bytearray object out of bounds} {
     string index [binary format I* {0x50515253 0x52}] 20
 } {}
 
+test string-5.22 {string index} -constraints testbytestring -setup {
+    set string string
+} -body {
+    list [scan [$string index [testbytestring \xFF] 0] %c var] $var
+} -cleanup {
+    unset string
+} -result {1 255}
 
 proc largest_int {} {
     # This will give us what the largest valid int on this machine is,