QQmlEngine::addImportPath(...) vs QML2_IMPORT_PATH difference?

[viktoria.nemkin]

I'm trying to install a qml module that I have created into my project.

Try 1: When I register it like this:

QQmlApplicationEngine engine;
engine.addImportPath("<path>");
engine.load(...);

QQmlApplicationEngine engine;
engine.addImportPath("<path>");
engine.load(...);

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in my main.cpp it builds and runs.

Try 2: When I add the same path like this:

QML_IMPORT_PATH += <path>
QML2_IMPORT_PATH += <path>

QML_IMPORT_PATH += <path>
QML2_IMPORT_PATH += <path>

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to my .pro file, it builds and then I get an error:

QQmlApplicationEngine failed to load component
qrc:/main.qml:4 module "mymodule" is not installed

Here is a minimal example:

C:/Users/vnemkin/Documents/example/example.pro

TEMPLATE = app
 
QT += qml quick widgets
 
CONFIG += c++11
 
SOURCES += main.cpp
 
RESOURCES += qml.qrc
 
# Additional import path used to resolve QML modules in Qt Creator's code model
# Try 2 : Uncomment these two, and it does not work.
#QML_IMPORT_PATH += C:/Users/vnemkin/Documents/
#QML2_IMPORT_PATH += C:/Users/vnemkin/Documents/
 
# Default rules for deployment.
include(deployment.pri)

TEMPLATE = app

QT += qml quick widgets

CONFIG += c++11

SOURCES += main.cpp

RESOURCES += qml.qrc

# Additional import path used to resolve QML modules in Qt Creator's code model
# Try 2 : Uncomment these two, and it does not work.
#QML_IMPORT_PATH += C:/Users/vnemkin/Documents/
#QML2_IMPORT_PATH += C:/Users/vnemkin/Documents/

# Default rules for deployment.
include(deployment.pri)

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C:/Users/vnemkin/Documents/example/main.cpp

#include <QApplication>
#include <QQmlApplicationEngine>
#include <QtDebug>
 
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
 
    QQmlApplicationEngine engine;
    //Try 1 : Uncomment this, it works.
    //engine.addImportPath("C:/Users/vnemkin/Documents");
 
    for(QString path : engine.importPathList())
    {
        qDebug(path.toStdString().c_str());
    }
 
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
 
    return app.exec();
}

#include <QApplication>
#include <QQmlApplicationEngine>
#include <QtDebug>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    QQmlApplicationEngine engine;
    //Try 1 : Uncomment this, it works.
    //engine.addImportPath("C:/Users/vnemkin/Documents");

    for(QString path : engine.importPathList())
    {
        qDebug(path.toStdString().c_str());
    }

    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

    return app.exec();
}

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C:/Users/vnemkin/Documents/example/main.qml

import QtQuick 2.4
import QtQuick.Controls 1.3
import QtQuick.Dialogs 1.2
import mymodule 1.0
 
ApplicationWindow {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")
}

import QtQuick 2.4
import QtQuick.Controls 1.3
import QtQuick.Dialogs 1.2
import mymodule 1.0

ApplicationWindow {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")
}

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C:/Users/vnemkin/Documents/mymodule/qmldir

module mymodule
 
Example 1.0 Example.qml

module mymodule

Example 1.0 Example.qml

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C:/Users/vnemkin/Documents/mymodule/Example.qml

import QtQuick 2.4
import QtQuick.Controls 1.3
import QtQuick.Dialogs 1.2
 
Button {
 
}

import QtQuick 2.4
import QtQuick.Controls 1.3
import QtQuick.Dialogs 1.2

Button {

}

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To me the Qt Documentation here seems to say both ways mentioned do the same thing:

"Additional import paths can be added through QQmlEngine::addImportPath() or the QML2_IMPORT_PATH environment variable."

http://doc.qt.io/qt-5/qtqml-syntax-imports.html

In my main.cpp I write to the debug console what engine.importPathList() contains. When I do Try 1, it contains the path, when I do Try 2, it does not.

The reason why I want to include my module in the .pro file is because there I have the $$PWD variable, and I can use that to specify the relative path from the .pro file to the module. In the .cpp code the only thing I know is where the exe is located, which depends on where we build our project.

Why is QML2_IMPORT_PATH not working for me?

I'm using:
QtCreator 3.6.1
Qt 5.6.0 (MSVC 2013, 32 bit)

Edit:

In project settings, if I go to "Run" and there "Run Environment", I have Use Build Environment specified, but it does not contain my variable.

If I add the variable:

QML2_IMPORT_PATH = C:/Users/vnemkin/Documents/

it builds and runs.

So essentially my question is: why does the build environment not contain the variables specified in my .pro file?