core: fix evaluation of ${raw_hl:...} with escaped prefix inside

Now `${raw_hl:\${` returns `\${` instead of `${`.

src/core/wee-eval.c

@@ -2033,6 +2033,7 @@ eval_replace_vars (const char *expr, struct t_eval_context *eval_context)
             expr,
             eval_context->prefix,
             eval_context->suffix,
+            (eval_context->syntax_highlight) ? 0 : 1,
             (eval_context->syntax_highlight) ?
             no_replace_prefix_list_col : no_replace_prefix_list_std,
             &eval_replace_vars_cb,

src/core/wee-string.c

@@ -4122,6 +4122,11 @@ string_levenshtein (const char *string1, const char *string2,
  *
  * Nested variables are supported, for example: "${var1:${var2}}".
  *
+ * If allow_escape == 1, the prefix/suffix can be escaped with a backslash
+ * (which is then omitted in the result).
+ * If allow_escape == 0, the backslash is kept as-is and can not be
+ * used to escape the prefix/suffix.
+ *
  * Argument "list_prefix_no_replace" is a list to prevent replacements in
  * string if beginning with one of the prefixes. For example if the list is
  * { "if:", NULL } and string is: "${if:cond?true:false}${test${abc}}"
@@ -4138,6 +4143,7 @@ char *
 string_replace_with_callback (const char *string,
                               const char *prefix,
                               const char *suffix,
+                              int allow_escape,
                               const char **list_prefix_no_replace,
                               char *(*callback)(void *data,
                                                 const char *prefix,
@@ -4171,8 +4177,16 @@ string_replace_with_callback (const char *string,
             if ((string[index_string] == '\\')
                 && (string[index_string + 1] == prefix[0]))
             {
-                index_string++;
-                result[index_result++] = string[index_string++];
+                if (allow_escape)
+                {
+                    index_string++;
+                    result[index_result++] = string[index_string++];
+                }
+                else
+                {
+                    result[index_result++] = string[index_string++];
+                    result[index_result++] = string[index_string++];
+                }
             }
             else if (strncmp (string + index_string, prefix, length_prefix) == 0)
             {
@@ -4187,7 +4201,8 @@ string_replace_with_callback (const char *string,
                             break;
                         sub_level--;
                     }
-                    if ((pos_end_name[0] == '\\')
+                    if (allow_escape
+                        && (pos_end_name[0] == '\\')
                         && (pos_end_name[1] == prefix[0]))
                     {
                         pos_end_name++;
@@ -4226,6 +4241,7 @@ string_replace_with_callback (const char *string,
                                 key,
                                 prefix,
                                 suffix,
+                                1,
                                 list_prefix_no_replace,
                                 callback,
                                 callback_data,

src/core/wee-string.h

@@ -146,6 +146,7 @@ extern int string_levenshtein (const char *string1, const char *string2,
 extern char *string_replace_with_callback (const char *string,
                                            const char *prefix,
                                            const char *suffix,
+                                           int allow_escpae,
                                            const char **list_prefix_no_replace,
                                            char *(*callback)(void *data,
                                                              const char *prefix,