# Create two directories to serve as mime search paths.
# `a` corresponds to the `~/local/share/mime/` and `b` to `/usr/share/mime/`.
mkdir -p {a,b}/mime/packages/

# Write an XML file installed by a user application (wine)
cat > a/mime/packages/x-wine-extension-jfif.xml <<EOF
<?xml version="1.0" encoding="UTF-8"?>
<mime-info xmlns="http://www.freedesktop.org/standards/shared-mime-info">
  <mime-type type="image/jpeg">
    <glob pattern="*.jfif"/>
    <comment>JPEG Image</comment>
  </mime-type>
</mime-info>
EOF

# And the part of the system file with the same mime type
cat > b/mime/packages/freedesktop.org.xml <<EOF
<?xml version="1.0" encoding="UTF-8"?>
<mime-info xmlns="http://www.freedesktop.org/standards/shared-mime-info">
  <mime-type type="image/jpeg">
    <comment>JPEG image</comment>
    <acronym>JPEG</acronym>
    <expanded-acronym>Joint Photographic Experts Group</expanded-acronym>
    <magic>
      <match type="string" value="\377\330\377" offset="0"/>
      <match type="big16" value="0xffd8" offset="0"/>
    </magic>
    <glob pattern="*.jpg"/>
    <glob pattern="*.jpeg"/>
    <glob pattern="*.jpe"/>
    <alias type="image/pjpeg"/>
  </mime-type>
</mime-info>
EOF

# Create a mime database in each directory
for d in a b; do update-mime-database $d/mime/ ;done


# Write a simple test applications using `QMimeType.globPatterns()`
# (`.suffixes()` has the same behaviour.)
cat > main.cpp <<EOF
#include <iostream>
#include <QMimeDatabase>

int main(int argc, char *argv[])
{
    QMimeDatabase db;
    for (auto p : db.mimeTypeForFile("foo.jpg").globPatterns()) {
        std::cout << p.toStdString() << std::endl;
    }
    return 0;
}
EOF
g++ -o main-qt5 main.cpp `pkgconf --libs --cflags Qt5Core` -fPIC
g++ -o main-qt6 main.cpp `pkgconf --libs --cflags Qt6Core` -fPIC

# And run them
# XDG_DATA_DIRS is set to the directories created above, in a specific order.
# XDG_DATA_HOME is set to a non-existent directory to stop it from looking in
# your real home dir.
printf "\nFound by Qt5:\n" && XDG_DATA_DIRS="$PWD/a:$PWD/b" XDG_DATA_HOME='/tmp/nope' ./main-qt5
printf "\nFound by Qt6:\n" && XDG_DATA_DIRS="$PWD/a:$PWD/b" XDG_DATA_HOME='/tmp/nope' ./main-qt6

Found by Qt5:
*.jpg
*.jpeg
*.jpe
*.jfif

Found by Qt6:
*.jfif

Found by Qt5:
*.jfif
*.jpg
*.jpeg
*.jpe

Found by Qt6:
*.jpg
*.jpeg
*.jpe