Qt Creator Clang Code Model

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Documentation: http://doc.qt.io/qtcreator/creator-clang-codemodel.html


With the following invocation debugging output will be generated:


export QT_LOGGING_RULES=qtc.clang*=true

Windows (start DebugView in advance to see the output):

set QT_LOGGING_RULES=qtc.clang*=true

The debugging output contains among others:

  • The IPC messages send/received
  • Output of libclang while parsing

Internal command line

The debugging output from above will contain all the command line options that are passed on to libclang, which is enough for most cases.

However, to see also the resulting internal command line of libclang run:

  1. Restart Qt Creator with QTC_CLANG_NO_DIAGNOSTIC_CHECK=1 (>= Qt Creator 4.5)
  2. Switch to projects mode and there to the "Clang Code Model"
  3. Copy some warning configuration by clicking on "Copy...", give it a name like "Debug"
  4. Replace all the options from the copied configuration with "-###"
  5. Close and re-open the editor document - the new debugging output will contain also the internal command line

Note that libclang/clangbackend will crash afterwards, so do not forget to switch back to a sane warning configuration.

Related Environment Variables

Build related

  • QTC_NO_CLANG_LIBTOOLING - Do not build against Clang's C++ libs; the ClangRefactoring plugin won't be build.

Run time related

  • LIBCLANG_TIMING - Timings from libclang for parse / reparse / preamble generation / completion.
  • QTC_CLANG_NO_DIAGNOSTIC_CHECK - Avoid validation of warning configuration (>= Qt Creator 4.5)
  • QTC_CLANG_NO_SUPPORTIVE_TRANSLATIONUNIT - Use only one translation unit per document.
  • QTC_CLANG_NO_ALIVE_TIMER - Simplifies debugging in certain cases.
  • QTC_CLANG_FORCE_VERBOSE_ALIVE - Simplifies debugging in certain cases.


libclang is used inside clangbackend to provide code model features


Linux and Mac:

libclang is built with the same compilers as Qt Creator ("Clang 7.0 (Apple)" for macOS, and GCC 5.3 from RHEL (which turns on old ABI compatibility with _GLIBCXX_USE_CXX11_ABI=0 by default) on Linux)


Currently libclang is built with optimized MinGW compiler for all Qt Creator versions. More information about Windows builds: Build libclang on Windows

Minimal libclang installation that Qt Creator can use

The following targets are sufficient for this:

install-libclang install-libclang-headers install-clang-headers install-llvm-config

Clang Plugins

Clang plugins support is not yet in QtCreator but it's definitely on the way. There are already private builds that support Tidy and Clazy.

Plugins usage significantly reduces libclang performance:


with default settings (level1) adds 50% to the parse/re-parse time, level0 adds only 25%

Clang Tidy

with -checks='-*,clang-diagnostic-*,llvm-*,misc-*,-misc-unused-parameters,readability-identifier-naming' adds 200% to the original libclang parse/re-parse times

Because of that we want to make plugins options configurable when they appear in Qt Creator to give user the control over the amount of warnings/performance balance that one requires.