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Revert "types: Remove unfilterable debug output"

Igor Kushnir requested to merge work/prevent-unfilterable-debug-output into master

TypeSystem::registerTypeClassInternal() is called in the constructor and TypeSystem::unregisterTypeClassInternal() - in the destructor of each global-variable object declared via the REGISTER_TYPE macro. registerTypeClassInternal() does not log any messages, therefore these global variables are constructed before the function-local static QLoggingCategory constant LANGUAGE. So the global variables are destroyed after LANGUAGE (in the reverse order of the completion of constructors). unregisterTypeClassInternal() attempts to log a message via qCDebug(LANGUAGE) when the function-local LANGUAGE is already destroyed. This is undefined behavior, which in practice causes the following two issues:

  1. When KDevelop is started normally and kdevplatform.language.debug=true, the "Unregistering type class" messages lack the usual prefix "kdevplatform.language: ".
  2. When KDevelop exits immediately without showing the UI (because of a command-line option such as --help or --list-sessions) and kdevplatform.language.debug=false (the default), the disabled debug messages clutter the program output (curiously, they do start with the "kdevplatform.language: " prefix).

Log a matching "Registering type class" message via qCDebug(LANGUAGE) in registerTypeClassInternal() to complete the constructor of LANGUAGE before the constructors of global variables that use LANGUAGE in their destructors. This eliminates the undefined behavior and its two practical consequences.

The reverted commit's message contains:

This is printed before Qt categorized logging is properly set up and thus may be printed even though it's technically disabled via filters.

I haven't encountered the referenced issue during my testing of this commit. Perhaps the implementation of Qt categorized logging has improved since then (2017) and is now reliably set up in time. If not and the original issue resurfaces, the qCDebug(LANGUAGE) line in registerTypeClassInternal() can be replaced with the line LANGUAGE();, which does not log anything but still initializes the function-local static QLoggingCategory constant.

This reverts commit a5eac48a.

BUG: 442896
FIXED-IN: 5.13.231200

Edited by Igor Kushnir

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