Support manual callout with string argument at start of condition.

src/pcre2_compile.c

@@ -5218,11 +5218,41 @@ for (;; ptr++)
         used to check for an assertion condition. That's all that is needed! */
 
         if (ptr[1] == CHAR_QUESTION_MARK && ptr[2] == CHAR_C)
+          {
+          if (IS_DIGIT(ptr[3]) || ptr[3] == CHAR_RIGHT_PARENTHESIS)
             {
             for (i = 3;; i++) if (!IS_DIGIT(ptr[i])) break;
             if (ptr[i] == CHAR_RIGHT_PARENTHESIS)
               tempptr += i + 1;
             }
+          else
+            {
+            uint32_t delimiter = 0;
+            for (i = 0; PRIV(callout_start_delims)[i] != 0; i++)
+              {
+              if (ptr[3] == PRIV(callout_start_delims)[i])
+                {
+                delimiter = PRIV(callout_end_delims)[i];
+                break;
+                }
+              }
+            if (delimiter != 0)
+              {
+              for (i = 4; ptr + i < cb->end_pattern; i++)
+                {
+                if (ptr[i] == delimiter)
+                  {
+                  if (ptr[i+1] == delimiter) i++;
+                  else
+                    {
+                    if (ptr[i+1] == CHAR_RIGHT_PARENTHESIS) tempptr += i + 2;
+                    break;
+                    }
+                  }   
+                }
+              }
+            }
+          }
 
         /* For conditions that are assertions, check the syntax, and then exit
         the switch. This will take control down to where bracketed groups

testdata/testinput2

@@ -4210,4 +4210,12 @@ a random value. /Ix
 
 /(?:a(?C`code`)){3}/B
 
+/^(?(?C25)(?=abc)abcd|xyz)/B
+    abcdefg
+    xyz123 
+
+/^(?(?C$abc$)(?=abc)abcd|xyz)/B
+    abcdefg
+    xyz123 
+
 # End of testinput2 

testdata/testinput6

@@ -4827,4 +4827,12 @@
 /^a(b)c(?C{AB})def/B
       abcdef\=callout_capture
 
+/^(?(?C25)(?=abc)abcd|xyz)/B
+    abcdefg
+    xyz123 
+
+/^(?(?C$abc$)(?=abc)abcd|xyz)/B
+    abcdefg
+    xyz123 
+
 # End of testinput6

testdata/testoutput2

@@ -14094,4 +14094,56 @@ Callout: {AB} last capture = 1
         End
 ------------------------------------------------------------------
 
+/^(?(?C25)(?=abc)abcd|xyz)/B
+------------------------------------------------------------------
+        Bra
+        ^
+        Cond
+        Callout 25 9 7
+        Assert
+        abc
+        Ket
+        abcd
+        Alt
+        xyz
+        Ket
+        Ket
+        End
+------------------------------------------------------------------
+    abcdefg
+--->abcdefg
+ 25 ^           (?=abc)
+ 0: abcd
+    xyz123 
+--->xyz123
+ 25 ^          (?=abc)
+ 0: xyz
+
+/^(?(?C$abc$)(?=abc)abcd|xyz)/B
+------------------------------------------------------------------
+        Bra
+        ^
+        Cond
+        CalloutStr $abc$ 12 7
+        Assert
+        abc
+        Ket
+        abcd
+        Alt
+        xyz
+        Ket
+        Ket
+        End
+------------------------------------------------------------------
+    abcdefg
+Callout: $abc$
+--->abcdefg
+    ^           (?=abc)
+ 0: abcd
+    xyz123 
+Callout: $abc$
+--->xyz123
+    ^          (?=abc)
+ 0: xyz
+
 # End of testinput2 

testdata/testoutput6

@@ -7835,4 +7835,56 @@ Callout: {AB} last capture = 0
     ^  ^       d
  0: abcdef
 
+/^(?(?C25)(?=abc)abcd|xyz)/B
+------------------------------------------------------------------
+        Bra
+        ^
+        Cond
+        Callout 25 9 7
+        Assert
+        abc
+        Ket
+        abcd
+        Alt
+        xyz
+        Ket
+        Ket
+        End
+------------------------------------------------------------------
+    abcdefg
+--->abcdefg
+ 25 ^           (?=abc)
+ 0: abcd
+    xyz123 
+--->xyz123
+ 25 ^          (?=abc)
+ 0: xyz
+
+/^(?(?C$abc$)(?=abc)abcd|xyz)/B
+------------------------------------------------------------------
+        Bra
+        ^
+        Cond
+        CalloutStr $abc$ 12 7
+        Assert
+        abc
+        Ket
+        abcd
+        Alt
+        xyz
+        Ket
+        Ket
+        End
+------------------------------------------------------------------
+    abcdefg
+Callout: $abc$
+--->abcdefg
+    ^           (?=abc)
+ 0: abcd
+    xyz123 
+Callout: $abc$
+--->xyz123
+    ^          (?=abc)
+ 0: xyz
+
 # End of testinput6