Don't ignore {1}+ when it is applied to a parenthesized item.

ChangeLog

@@ -61,6 +61,11 @@ addition (a) the default limit for groups requested by -o<n> has been raised to
 50, (b) the new --om-capture option changes the limit, (c) an error is raised 
 if -o asks for a group that is above the limit.
 
+12. The quantifier {1} was always being ignored, but this is incorrect when it
+is made possessive and applied to an item in parentheses, because a
+parenthesized item may contain multiple branches or other backtracking points,
+for example /(a|ab){1}+c/ or /(a+){1}+a/.
+
 
 Version 10.33 16-April-2019
 ---------------------------

src/pcre2_compile.c

@@ -6758,10 +6758,6 @@ for (;; pptr++)
     reqvary = (repeat_min == repeat_max)? 0 : REQ_VARY;
     op_type = 0;
 
-    /* If the repeat is {1} we can ignore it. */
-
-    if (repeat_max == 1 && repeat_min == 1) goto END_REPEAT;
-
     /* Adjust first and required code units for a zero repeat. */
 
     if (repeat_min == 0)
@@ -6804,7 +6800,10 @@ for (;; pptr++)
     tempcode = previous;
     op_previous = *previous;
 
-    /* Now handle repetition for the different types of item. */
+    /* Now handle repetition for the different types of item. If the repeat
+    minimum and the repeat maximum are both 1, we can ignore the quantifier for
+    non-parenthesized items, as they have only one alternative. For anything in
+    parentheses, we must not ignore if {1} is possessive. */
 
     switch (op_previous)
       {
@@ -6818,6 +6817,7 @@ for (;; pptr++)
       case OP_CHARI:
       case OP_NOT:
       case OP_NOTI:
+      if (repeat_max == 1 && repeat_min == 1) goto END_REPEAT;
       op_type = chartypeoffset[op_previous - OP_CHAR];
 
       /* Deal with UTF characters that take up more than one code unit. */
@@ -6864,6 +6864,7 @@ for (;; pptr++)
         code = previous;
         goto END_REPEAT;
         }
+      if (repeat_max == 1 && repeat_min == 1) goto END_REPEAT;
 
       if (repeat_min == 0 && repeat_max == REPEAT_UNLIMITED)
         *code++ = OP_CRSTAR + repeat_type;
@@ -6898,6 +6899,8 @@ for (;; pptr++)
       repetition. */
 
       case OP_RECURSE:
+      if (repeat_max == 1 && repeat_min == 1 && !possessive_quantifier)
+        goto END_REPEAT;
 
       /* Generate unwrapped repeats for a non-zero minimum, except when the
       minimum is 1 and the maximum unlimited, because that can be handled with
@@ -6980,6 +6983,9 @@ for (;; pptr++)
         PCRE2_UCHAR *bralink = NULL;
         PCRE2_UCHAR *brazeroptr = NULL;
 
+        if (repeat_max == 1 && repeat_min == 1 && !possessive_quantifier)
+          goto END_REPEAT;
+
         /* Repeating a DEFINE group (or any group where the condition is always
         FALSE and there is only one branch) is pointless, but Perl allows the
         syntax, so we just ignore the repeat. */
@@ -7196,11 +7202,12 @@ for (;; pptr++)
         and SCRIPT_RUN groups at runtime, but in a different way.]
 
         Then, if the quantifier was possessive and the bracket is not a
-        conditional, we convert the BRA code to the POS form, and the KET code to
+        conditional, we convert the BRA code to the POS form, and the KET code
-        KETRPOS. (It turns out to be convenient at runtime to detect this kind of
+        to KETRPOS. (It turns out to be convenient at runtime to detect this
-        subpattern at both the start and at the end.) The use of special opcodes
+        kind of subpattern at both the start and at the end.) The use of
-        makes it possible to reduce greatly the stack usage in pcre2_match(). If
+        special opcodes makes it possible to reduce greatly the stack usage in
-        the group is preceded by OP_BRAZERO, convert this to OP_BRAPOSZERO.
+        pcre2_match(). If the group is preceded by OP_BRAZERO, convert this to
+        OP_BRAPOSZERO.
 
         Then, if the minimum number of matches is 1 or 0, cancel the possessive
         flag so that the default action below, of wrapping everything inside
@@ -7301,6 +7308,8 @@ for (;; pptr++)
         int prop_type, prop_value;
         PCRE2_UCHAR *oldcode;
 
+        if (repeat_max == 1 && repeat_min == 1) goto END_REPEAT;
+
         op_type = OP_TYPESTAR - OP_STAR;      /* Use type opcodes */
         mclength = 0;                         /* Not a character */
 

testdata/testinput1

@@ -6351,4 +6351,18 @@ ef) x/x,mark
     acb
     abc     
 
+/(?:a|ab){1}+c/
+\= Expect no match
+    abc
+
+/(a|ab){1}+c/
+    abc
+    
+/(a+){1}+a/
+\= Expect no match
+    aaaa
+
+/(?(DEFINE)(a|ab))(?1){1}+c/
+    abc    
+
 # End of testinput1 

testdata/testoutput1

@@ -10063,4 +10063,22 @@ MK: 2
  0: a
 MK: 2
 
+/(?:a|ab){1}+c/
+\= Expect no match
+    abc
+No match
+
+/(a|ab){1}+c/
+    abc
+No match
+    
+/(a+){1}+a/
+\= Expect no match
+    aaaa
+No match
+
+/(?(DEFINE)(a|ab))(?1){1}+c/
+    abc    
+No match
+
 # End of testinput1