QtCS2017 Before Runtime discussion

Presentation / starting Subjects

Make the API easy?

• Copy on Write to avoid copies at runtime
• Can we do it at compile time?
• Let tools get const and references right
• Warn about unnecessary copies
• Clang can help here

Make changes easy

• API changes are expensive
• API looks outdated if not adapted to current paradigms (legacy code)
• How can we make them easy
• How can Clang help here

Clang Query

• Think about it as SQL for the AST
• Makes big changes much cheaper and secure

Immediate feedback vs overnight refactoring

• Both are important
• Immediate feedback reduces refactorings and reviews
• Run refactorings overnight for expansive refactorings
• Integration with the CI

Notes

• need real examples
• QtCreator supports only very basic refactoring tools
  • having tools outside of QtCreator and use these tools maybe inside
• API changes need to be available by Clangtidy scripts (?)
• what about templates?
  • concept
• the tools cannot fit to all cases
• this kind of tools can help to move to Qt 6(or other future versions)
• renaming methods would be easier with this kind of tools
• mental work to remember this new name is still there
• can a tool do exchange deprecate things with the new "right" thing
  • using clang "Fixit" maybe possible
  • clang is here a tool and not the only compiler
  • these "Fixit" information should be inside the code
    • if it is not there it will lose sync to the code
    • maybe inside the code there can be a link to something?
• how far can we get with transformation with tools?
• Clangtidy is alreadys there
  • can have plugins
  • how can it be a part of our workflow
• these tools are not available on all desktop platforms
  • so this can not the only way to do these transformations
• example: new Qt connections -> running transformation -> slightly different behavior
• problem with #ifdef sections
• kind of cross compilation with clangtidy with necessary defines
  • possibility to skip some of the problematic headers
• warn about section where we can not do our work
• the tool only helps when changes are there, but it should not decrease the border to have these changes
• good example: QRegEx -> QRegularExpression

Conclusion

• we need and want this
• this should not only happen in the Berlin office
• can QtCreator show Clazy warnings?
  • was not working in the past
  • but this would be the first step to go further