Fix crash when HOME env variable is not set

[lolgab]

Steps to reproduce:

• Link any Scala Native binary using the java.lang.System object
• unset the HOME environment variable
• run the binary:

$ unset HOME
$ target/scala-2.11/hello-out

And it crashes with:

java.lang.NullPointerException
        at java.lang.Throwable.fillInStackTrace(Unknown Source)
        at java.util.Hashtable.put(Unknown Source)
        at java.util.Properties.setProperty(Unknown Source)
        at java.lang.System$.loadProperties(Unknown Source)
        at java.lang.System$.<init>(Unknown Source)
        at <none>._SM17java.lang.System$G4load(Unknown Source)
        at scala.sys.package$.env(Unknown Source)
        at JsonAction$class.main(Unknown Source)
        at Main$.main(Unknown Source)
        at <none>.main(Unknown Source)

[lolgab]

On Mac Os X and Linux (tried with alpine on docker) it is set correctly regardless of the HOME environment variable. So this PR doesn't solve the problem. I faced the crash on a docker environment.. I don't know if we want to have a proper solution with platform dependent code, for sure I don't want my applications to suddenly crash in some environments.
As a workaround you can call:

import scala.scalanative.posix.stdlib.setenv
setenv(c"HOME", c"", 0)

as first instruction in the main.

[ekrich]

Here is a discussion I found on SOF - https://stackoverflow.com/questions/2910377/get-home-directory-in-linux
Not sure without playing with this if it could be an option.

[ekrich]

@lolgab Maybe some code like this? Not sure if you need to look at HOME at all.
Tested in Xcode on macOS. The only question here is POSIX ok for the core system if we are trying to get more modular?

#include <unistd.h>
#include <pwd.h> // POSIX only

char* home = getenv("HOME"); // STD C
printf("HOME: %s\n", home);    
unsetenv("HOME");
const char *homedir;

if ((homedir = getenv("HOME")) == NULL) {
    printf("HOME NULL\n");
    uid_t uid = getuid();
    struct passwd *pw = getpwuid(uid);
    homedir = pw->pw_dir;
}
printf("HOME2: %s\n", homedir);

Output:

HOME: /Users/eric
HOME NULL
HOME2: /Users/eric

[lolgab]

Nice! I'll try it on Linux and update the PR if it works!

[lolgab]

@ekrich I applied your suggestion! Thank you 🙏

[ekrich]

Based on your JVM test, I was thinking that is what they might be doing.

[ekrich]

The function you are calling (5fc1189#diff-9f67b7df156c5096453ed90792be0ad2R69) is a Scala Native wrapper function that you are proposing to remove in #1743

This is the reason I was confused. We are not using error number at all after calling struct passwd *getpwuid(uid_t); , just some logic from the wrapper. https://github.com/scala-native/scala-native/blob/master/nativelib/src/main/resources/pwd.c#L25-L30

I am unclear what should be done as the POSIX pwd needs updating too. These wrappers and struct copying perhaps were created earlier because we didn't have UInt and ULong support.

If you add the real getpwuid function in this PR and just check whether the Ptr returned is NULL or not that might be good for this PR and then the other PR can also stand as well.

[ekrich]

@lolgab Looks good to me.

[sjrd]

Would you mind rebasing on top of the latest master to make sure that changes to scalafmt do not affect this?

Thank you.

[sjrd]

Consider using

Suggested change

	{
	locally {

to make this more readable.

Also, consider wrapping the following code for user.dir in a similar locally {} block, since it also has a val buf.

[lolgab]

Did not know about locally existence! Thank you :-) I'll implement the suggested changes!

[lolgab]

@sjrd Ready for another review round.