The regex pattern is not validated prior to executing the MatchString function

[agmanchon]

If the regex pattern specified for a field in the JSON schema is invalid, the MatchString function fails. To prevent this, the pattern should be validated in advance, and MatchString code should only be generated for valid patterns. For example, the pattern "^(?!\s*$)[a-zA-Z0-9\.]*$" causes MatchString to fail because the Go regexp package does not support lookaheads. Implementing a validation step to check for such unsupported patterns before code generation is a suggested improvement.Attached is a potential solution implemented in the code:

if len(v.pattern) != 0 {
      if v.isNillable {
	      out.Printlnf("if %s != nil {", value)
	      out.Indent(1)
      }
      if _, err := regexp.Compile(v.pattern); err != nil {
	      fmt.Println("WARNING: regex pattern not compatible with go regexp library, ignoring ...")
      } else {
	      out.Printlnf(
		      `if matched, _ := regexp.MatchString(`+"`%s`"+`, string(%s%s)); !matched {`,
		      v.pattern, pointerPrefix, value,
	      )
	      out.Indent(1)
	      out.Printlnf(
		      `return fmt.Errorf("field %%s pattern match: must match %%s", `+"`%s`"+`, "%s")`,
		      v.pattern, v.fieldName,
	      )
	      out.Indent(-1)
	      out.Printlnf("}")
      
	      if v.isNillable {
		      out.Indent(-1)
		      out.Printlnf("}")
	      }
      }
}