[BUG][C#] IllegalArgumentException if string enum value ends with backslash

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

If a string enum value ends with a backslash, openapi-generator fails to generate code for csharp due to java.lang.IllegalArgumentException.

openapi-generator version

Tested with 4.2.2 and current master (2d24d42e65).

OpenAPI declaration file content or url

{
  "swagger": "2.0",
  "info": {
    "title": "Problematic enum strings example",
    "version": "1.0.0"
  },
  "definitions": {
    "ErrorMessage": {
      "type": "string",
      "enum": [
        "Error: Invalid character: \\",
        "RangeError: Too many items."
      ]
    }
  },
  "paths": {
    "/count": {
      "get": {
        "operationId": "getCount",
        "responses": {
          "200": {
            "description": "Success",
            "schema": {
              "type": "integer"
            }
          },
          "default": {
            "description": "Error",
            "schema": {
              "$ref": "#/definitions/ErrorMessage"
            }
          }
        }
      }
    }
  }
}

Command line used for generation

openapi-generator generate -g csharp -i openapi.json -o generated

Steps to reproduce

1. Copy example OpenAPI document into openapi.json.

2. Run above command.

3. Observe output similar to the following:

    [main] INFO  o.o.codegen.DefaultGenerator - OpenAPI Generator: csharp (client)
    [main] INFO  o.o.codegen.DefaultGenerator - Generator 'csharp' is considered stable.
    [main] INFO  o.o.c.l.AbstractCSharpCodegen - Environment variable CSHARP_POST_PROCESS_FILE not defined so the C# code may not be properly formatted by uncrustify (0.66 or later) or other code formatter. To define it, try `export CSHARP_POST_PROCESS_FILE="/usr/local/bin/uncrustify --no-backup" && export UNCRUSTIFY_CONFIG=/path/to/uncrustify-rules.cfg` (Linux/Mac). Note: replace /path/to with the location of uncrustify-rules.cfg
    [main] INFO  o.o.c.l.AbstractCSharpCodegen - NOTE: To enable file post-processing, 'enablePostProcessFile' must be set to `true` (--enable-post-process-file for CLI).
    [main] INFO  o.o.c.languages.CSharpClientCodegen - Generating code for .NET Framework v4.5
    [main] WARN  o.o.codegen.utils.URLPathUtils - 'host' (OAS 2.0) or 'servers' (OAS 3.0) not defined in the spec. Default to [http://localhost] for server URL [http://localhost/]
    [main] WARN  o.o.codegen.utils.URLPathUtils - 'host' (OAS 2.0) or 'servers' (OAS 3.0) not defined in the spec. Default to [http://localhost] for server URL [http://localhost/]
    Exception in thread "main" java.lang.RuntimeException: Could not process model 'ErrorMessage'.Please make sure that your schema is correct!
    	at org.openapitools.codegen.DefaultGenerator.generateModels(DefaultGenerator.java:472)
    	at org.openapitools.codegen.DefaultGenerator.generate(DefaultGenerator.java:923)
    	at org.openapitools.codegen.cmd.Generate.run(Generate.java:416)
    	at org.openapitools.codegen.OpenAPIGenerator.main(OpenAPIGenerator.java:61)
    Caused by: java.lang.IllegalArgumentException: character to be escaped is missing
    	at java.base/java.util.regex.Matcher.appendExpandedReplacement(Matcher.java:1020)
    	at java.base/java.util.regex.Matcher.appendReplacement(Matcher.java:998)
    	at java.base/java.util.regex.Matcher.replaceAll(Matcher.java:1182)
    	at org.openapitools.codegen.utils.StringUtils.camelize(StringUtils.java:96)
    	at org.openapitools.codegen.utils.StringUtils.camelize(StringUtils.java:55)
    	at org.openapitools.codegen.languages.CSharpClientCodegen.toEnumVarName(CSharpClientCodegen.java:757)
    	at org.openapitools.codegen.DefaultCodegen.postProcessModelsEnum(DefaultCodegen.java:438)
    	at org.openapitools.codegen.languages.AbstractCSharpCodegen.postProcessModels(AbstractCSharpCodegen.java:405)
    	at org.openapitools.codegen.DefaultGenerator.processModels(DefaultGenerator.java:1199)
    	at org.openapitools.codegen.DefaultGenerator.generateModels(DefaultGenerator.java:467)
    	... 3 more
   

Related issues/PRs

None that I could find.

Suggest a fix

StringUtils.camelize could use Matcher.quoteReplacement on the replacement string.

Thanks for considering,
Kevin

Start with modules/openapi-generator/src/main/java/org/openapitools/codegen/utils/StringUtils.java and the StringUtils.camelize stack-trace location, then reproduce with the supplied OpenAPI document and csharp generation command. Check CSharpClientCodegen.toEnumVarName as the caller; done means generation handles an enum value ending in a backslash without the reported IllegalArgumentException.