Description of problem:
Code parsing in KDevelop seems to have completely stopped working recently.

Version-Release number of selected component (if applicable):
bash-4.4.23-6.fc29.x86_64
cmake-3.12.1-1.fc29.x86_64
cppcheck-1.86-1.fc29.x86_64
git-2.20.1-1.fc29.x86_64
glibc-2.28-26.fc29.x86_64
grantlee-qt5-5.1.0-10.fc29.x86_64
kdevelop-5.3.1-1.fc29.x86_64
kdevelop-libs-5.3.1-1.fc29.x86_64
kf5-kauth-5.54.0-1.fc29.x86_64
kf5-kcodecs-5.54.0-1.fc29.x86_64
kf5-kcompletion-5.54.0-1.fc29.x86_64
kf5-kconfig-core-5.54.0-1.fc29.x86_64
kf5-kconfig-gui-5.54.0-1.fc29.x86_64
kf5-kconfigwidgets-5.54.0-1.fc29.x86_64
kf5-kcoreaddons-5.54.0-1.fc29.x86_64
kf5-kcrash-5.54.0-1.fc29.x86_64
kf5-kdeclarative-5.54.0-1.fc29.x86_64
kf5-ki18n-5.54.0-1.fc29.x86_64
kf5-kiconthemes-5.54.0-1.fc29.x86_64
kf5-kio-core-libs-5.54.1-1.fc29.x86_64
kf5-kio-widgets-libs-5.54.1-1.fc29.x86_64
kf5-kjobwidgets-5.54.0-1.fc29.x86_64
kf5-kpackage-5.54.0-1.fc29.x86_64
kf5-kparts-5.54.0-1.fc29.x86_64
kf5-kservice-5.54.0-1.fc29.x86_64
kf5-ktexteditor-5.54.0-1.fc29.x86_64
kf5-ktextwidgets-5.54.0-1.fc29.x86_64
kf5-kwidgetsaddons-5.54.0-1.fc29.x86_64
kf5-kxmlgui-5.54.0-1.fc29.x86_64
kf5-sonnet-ui-5.54.0-1.fc29.x86_64
kf5-threadweaver-5.54.0-1.fc29.x86_64
libgcc-8.2.1-6.fc29.x86_64
libstdc++-8.2.1-6.fc29.x86_64
qt5-qtbase-5.11.3-1.fc29.x86_64
qt5-qtbase-gui-5.11.3-1.fc29.x86_64
qt5-qtdeclarative-5.11.3-1.fc29.x86_64

How reproducible:
Always

Steps to Reproduce:
1. Load any CMake-based (C++) project.

Actual results:
Source files are not parsed. No features that depend on code parsing (e.g. supplemental highlighting, 'go to definition', quick-open) work.

Expected results:
Code parsing works.

Additional info:
This seems to have stopped working "recently" (within the last few weeks, I believe). KDevelop built from master (kdevelop and kdevelop-pg-qt built against system packages) works.

Some possibly-relevant log messages:

  (on startup)
  kdevplatform.language: Failed to load enviromment-information for
    "/home/src/matthew/foo/bar/MainWindow.cxx"
  kdevelop.plugins.contextbrowser: found no language for document
    QUrl("file:///home/src/matthew/foo/bar/MainWindow.cxx")

  (upon reloading project)
  kdevelop.plugins.cmake: registering... QVector(
    ...files...
    "/usr/local/src/matthew/foo/bar/MainWindow.cxx" ,
    ...more files and other stuff...
  (...)
  kdevelop.plugins.cmake: adding target "bar" with sources QVector(
    ...files...
    "/home/src/matthew/foo/bar/MainWindow.cxx" ,
    ...more files and other stuff...
  (...)
  kdevplatform.shell: showing done progress "Loading Project foo"
  kdevplatform.language: starting project parse job
  kdevplatform.language: BackgroundParser::addDocument
    "/home/src/matthew/foo/bar/MainWindow.cxx"
    QUrl("file:///home/src/matthew/foo/bar/MainWindow.cxx")