[BUG][CPP-QT] HEADER_FILES variable is not defined in generated cpp-qt CMakeLists.txt

Description

The generated CMakeLists.txt for the cpp-qt client uses the variable ${HEADER_FILES} in an install() command, but HEADER_FILES is never defined or populated anywhere in the file. This results in the install command being a no-op or potentially causing errors on some CMake invocations.

Relevant lines:

install(
    FILES ${HEADER_FILES}
    DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/${PROJECT_NAME}
)

No line in the generated file (or the cpp-qt-client/CMakeLists.txt.mustache template) sets or populates HEADER_FILES.

By contrast, other generators (like cpp-restsdk) define this variable using file(GLOB_RECURSE HEADER_FILES ...).

openapi-generator version

7.20.0

OpenAPI declaration file content or url

https://github.com/OpenAPITools/openapi-generator/tree/master/samples/client/petstore/cpp-qt/client

Generation Details

openapi-generator generate --global-property skipFormModel=false -g cpp-qt-client -i myyaml.yml -o generated/

Steps to reproduce

1. Generate a client for CPP-QT (e.g., with the petstore sample or other spec).
2. Inspect the resulting CMakeLists.txt.

Expected vs Actual

Expected: HEADER_FILES should be defined or populated with the headers to be installed.
Actual: HEADER_FILES is undefined.

Suggest a fix

Add a line to globally define HEADER_FILES (for example, using file(GLOB_RECURSE HEADER_FILES "*.h") or enumerating the headers).

---

Code reference for context:

• Caller CMakeLists.txt
• Generator template
• Example where HEADER_FILES is defined (cpp-restsdk sample)

---

Example of correct usage in cpp-restsdk:

file(GLOB_RECURSE HEADER_FILES "include/*.h")
file(GLOB_RECURSE SOURCE_FILES "src/*.cpp")
add_library(${PROJECT_NAME} ${HEADER_FILES} ${SOURCE_FILES})

This ensures all header files are collected and can be installed as needed.

Start with modules/openapi-generator/src/main/resources/cpp-qt-client/CMakeLists.txt.mustache and compare its header handling with the referenced cpp-restsdk sample. Regenerate the petstore cpp-qt client, inspect the resulting CMakeLists.txt, and verify that the install step receives the generated headers.