How to change variable from within qmake replace function

Question

I am trying to create a custom qmake "replace function" that basically appends some stuff to the INCLUDEPATH variables like so:

defineReplace(myFunc) {
    lo=$$lower($$1)
    INCLUDEPATH += /someDir/libs/lib$${lo}
    message("| INCLUDEPATH A: " $${INCLUDEPATH})
    return (true)
}

However when I run this function with a parameter and then print out INCLUDEPATH variables like this:

$$myFunc(whatever)
message("| INCLUDEPATH B: " $${INCLUDEPATH})

I get the following in the log:

Project MESSAGE: | INCLUDEPATH A: /someDir/libs/libwhatever
Project MESSAGE: | INCLUDEPATH B: 

This indicates that the function works, but somehow the changes made to the INCLUDEPATH variable are not preserved.

I want to know how I can get the behavior I expected (INCLUDEPATH maintains the changes made to it after I run my function). How can I do that?

Answer 1

You need to add a call to export. From the qmake manual:

export(variablename)

Exports the current value of variablename from the local context of a function > to the global context

So your code should be

defineReplace(myFunc) {
    lo=$$lower($$1)
    INCLUDEPATH += /someDir/libs/lib$${lo}
    message("| INCLUDEPATH A: " $${INCLUDEPATH})

    export(INCLUDEPATH)                            # <-- This is new

    return (true)
}