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The release work continues apace, with just 3 open issues left! I worked on documentation a bit and then when it seemed like there was nothing blocking the release that I could easily finish, went back to one of the bugs that got deferred, #4850. I had done some work on this last week but got over-ambitious in trying to restructure trans, when the urgent thing was to fix the bug.
Once I started over, with the knowledge I gleaned from last week's debugging, it was pretty obvious that the issue was that trans code was assuming that the self argument to a trait reference is always passed by reference. But Rust allows traits to be declared with their self argument passed by value; depending on what type self actually is (and this is usually, but not always, known at compile time, since Rust compiles polymorphism by monomorphization), that means either moving it into the callee, or copying it. So there was some code assuming self was passed by reference, other code assuming it was passed by value, so in some cases with by-value self, the result was generated code that segfaulted.
It seems like the trans code could be better structured as far as how many pieces of code know things about self. But I'm trying to make minimal changes right now, and am just patching up those places as they appear to take into account that the self argument to a method might not always be a pointer. However, I'm worried that the fact that the size of the self argument depends on the monomorphized code for the method is going to cause problems. It hasn't yet, but I'm afraid it will, and that this will mean bigger restructuring is needed for trans.
I'm setting this aside in any case once we tag the release, though, and moving on to focus on rustpkg for a while, so I don't get totally lost in bug-fixing.
Once I started over, with the knowledge I gleaned from last week's debugging, it was pretty obvious that the issue was that trans code was assuming that the self argument to a trait reference is always passed by reference. But Rust allows traits to be declared with their self argument passed by value; depending on what type self actually is (and this is usually, but not always, known at compile time, since Rust compiles polymorphism by monomorphization), that means either moving it into the callee, or copying it. So there was some code assuming self was passed by reference, other code assuming it was passed by value, so in some cases with by-value self, the result was generated code that segfaulted.
It seems like the trans code could be better structured as far as how many pieces of code know things about self. But I'm trying to make minimal changes right now, and am just patching up those places as they appear to take into account that the self argument to a method might not always be a pointer. However, I'm worried that the fact that the size of the self argument depends on the monomorphized code for the method is going to cause problems. It hasn't yet, but I'm afraid it will, and that this will mean bigger restructuring is needed for trans.
I'm setting this aside in any case once we tag the release, though, and moving on to focus on rustpkg for a while, so I don't get totally lost in bug-fixing.