Thanks all for looking into this. Unfortunately I don't know my way around Bugzilla and I'm a bit occupied for the next few days - it would be great if a bug report could be opened on my behalf.
Best, June On Fri, Apr 5, 2024 at 10:12 AM <luke-tier...@uiowa.edu> wrote: > On Fri, 5 Apr 2024, Ivan Krylov via R-devel wrote: > > > On Fri, 5 Apr 2024 08:15:20 -0400 > > June Choe <jchoe...@gmail.com> wrote: > > > >> When assigning a list to an out of bounds index (ex: the next, n+1 > >> index), it errors the same but now changes the values of the vector > >> to NULL: > >> > >> ``` > >> x <- expression(a,b,c) > >> x[[4]] <- list() # Error > >> x > >> #> expression(NULL, NULL, NULL) > >> ``` > >> > >> Curiously, this behavior disappears if a prior attempt is made at > >> assigning to the same index, using a different incompatible object > >> that does not share this bug (like a function) > > > > Here's how the problem happens: > > > > 1. The call lands in src/main/subassign.c, do_subassign2_dflt(). > > > > 2. do_subassign2_dflt() calls SubassignTypeFix() to prepare the operand > > for the assignment. > > > > 3. Since the assignment is "stretching", SubassignTypeFix() calls > > EnlargeVector() to provide the space for the assignment. > > > > The bug relies on `x` not being IS_GROWABLE(), which may explain > > why a plain x[[4]] <- list() sometimes doesn't fail. > > > > The future assignment result `x` is now expression(a, b, c, NULL), and > > the old `x` set to expression(NULL, NULL, NULL) by SET_VECTOR_ELT(newx, > > i, VECTOR_ELT(x, i)); CLEAR_VECTOR_ELT(x, i); during EnlargeVector(). > > > > 4. But then the assignment fails, raising the error back in > > do_subassign2_dflt(), because the assignment kind is invalid: there is > > no way to put data.frames into an expression vector. The new resized > > `x` is lost, and the old overwritten `x` stays there. > > > > Not sure what the right way to fix this is. It's desirable to avoid > > shallow_duplicate(x) for the overwriting assignments, but then the > > sub-assignment must either succeed or leave the operand untouched. > > Is there a way to perform the type check before overwriting the operand? > > Yes. There are two places where there are some checks, one early and > the other late. The early one is explicitly letting this one through > and shouldn't. So a one line change would address this particular > problem. But it would be a good idea to review why we the late checks > are needed at all and maybe change that. I'll look into it. > > Best, > > luke > > -- > Luke Tierney > Ralph E. Wareham Professor of Mathematical Sciences > University of Iowa Phone: 319-335-3386 > Department of Statistics and Fax: 319-335-3017 > Actuarial Science > 241 Schaeffer Hall email: luke-tier...@uiowa.edu > Iowa City, IA 52242 WWW: http://www.stat.uiowa.edu > -- June Choe (최용준 / Yong June Choe) He/Him/His [[alternative HTML version deleted]] ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
