[BUG] Generated Kotlin compilation error `Identifier expected` when comments include certain strings or characters in brackets

Description

When the OpenAPI yaml from which a (multiplatform) Kotlin project is generated contains any descriptions that have certain strings and/or symbols in brackets, the compilation of the Kotlin code fails with the error Identifier expected, since the code ends up containing invalid KDoc.

openapi-generator version

7.3.0

OpenAPI declaration file content or url

This public OpenAPI definition (YAML) reproduces the problem, when the openapi-generator Gradle plugin is used to generate Kotlin (Multiplatform) client code from it.

A specific problematic snippet from the YAML file:

        totalCost:
          type: number
          description: "Total cost of the charging session in Euro [€]."
          format: double

Generation Details

Generate a Kotlin Multiplatform client library with a build.gradle.kts file configured as in this example on GitHub.

Steps to reproduce

Then try to build the generated code with ./gradlew clean build test (you probably have to specify the subdirectory containing the generated code under build, using the -p parameter as well)

You should see errors like this:

> Task :compileCommonMainKotlinMetadata FAILED
e: file:///[path omitted]/generated/model/ChargingSession.kt:36:65 Identifier expected
e: file:///[path omitted]/generated/model/GetChargingSession.kt:36:65 Identifier expected
e: file:///[path omitted]/generated/model/GetChargingSessionResponseChargingSession.kt:35:65 Identifier expected
e: file:///[path omitted]/generated/model/PatchChargingSessionDto.kt:32:65 Identifier expected
e: file:///[path omitted]/generated/model/ReplaceChargingSessionDto.kt:32:65 Identifier expected
e: file:///[path omitted]/generated/model/ReportChargingSession.kt:33:65 Identifier expected

Related issues/PRs

This issue appears to be very similar to this one that was reported in the protobuf project earlier, and has since been fixed in that project.

Suggest a fix

Perhaps the relevant parts of this merged PR in the protobuf project could be ported to the openapi-generator project to fix it here as well.

But without even having looked at that fix in detail yet, one solution that comes to mind would be a filter or encoder for API descriptions that could for instance escape brackets and other KDoc-sensitive symbols such as brackets. Alternatively, brackets could be replaced by parentheses or other appropriate alternative symbols that KDoc wouldn't choke on.

This probably fits in the more general security best practice to always encode and escape received data context-specifically before outputting it.

Start by generating Kotlin Multiplatform code from the linked OpenAPI YAML using the Gradle plugin, then inspect the generated model files around the descriptions containing bracketed symbols. Run ./gradlew clean build test in the generated project; done means those descriptions produce valid KDoc and the generated code compiles without Identifier expected errors.