[mojo-nightly] struct lifetime issue

[dorjeduck]

Bug description

In the following test demo. It seems the destructor is called on the filehandle instead of move.
The demo runs without problems with stable but i get the following with nightly:

file handle address: 0x0
error reading: invalid file handle

struct FileManager:
    var fh:FileHandle

    fn __init__(inout self):
        self.fh = FileHandle()

    fn open(inout self,file_name:String):
        try:
            self.fh = open(file_name,"r")^
            print("file handle address:",self.fh.handle.address)
        except e:
            print("error opening:",e)
        
    fn read(self)  -> String:
        try:
            return self.fh.read()
        except e:
            print("error reading:",e)
            return ""
    
    fn close(inout self):
        try:
            self.fh.close()
        except e:
            print("error closing:",e)

fn main() raises:

    var file_name="./my_file.txt"
    var fh = FileManager()
    fh.open(file_name)
    print(fh.read())
    fh.close()

Changing the open command line to

self.fh = open(…)^

results in the following warning

.../demo.mojo:9:42: warning: transfer from an owned value has no effect and can be removed

and the programs reads the file content as expected

System information

MacOS 14.4.1 (23E224)
modular 0.7.2 (d0adc668)
mojo-nightly 2024.4.2621 (6dff3016)

[dorjeduck]

This is now in the stable mojo 24.3.0 (9882e19d).

Is there any workaround (without a warning) for now?

[stumpOS]

A fix is currently in review; for now there is not a work around the warning

[lattner]

I verified this, it still happens, I haven't dug in all the way though. @stumpOS do you have a patch, if so can you ping me?

[stumpOS]

yea I have a patch open