findGlobals() chooses to be conservative when a variable is a global conditionally

[HenrikBengtsson]

Issue

findGlobals() choose to be conservative when a variable is a global conditionally on a run-time variable/value:

> findGlobals({ if (runif(1) < 1/2) y <- 0; y }, substitute = TRUE)
[1] "{"     "if"    "<"     "runif" "/"     "<-"

Here we probably want to pick up y as a global variable too.

I'm acknowledging that such ambiguous expression should be avoid, but we still might want to support them, and there might be cases where it could be argued for. Maybe the following is an example:

foo <- function(x, resample = FALSE) {
  idxs <- slow_creation_of_indices(x)  ## Make only once
  future_lapply(x, FUN = function(z) {
     if (resample) idxs <- sample(idxs)
     z[c(1,length(z))]
  })
}

Though it could be argued that what is really used here is:

foo <- function(x, resample = FALSE) {
  idxs0 <- slow_creation_of_indices(x)  ## Make only once
  future_lapply(x, FUN = function(z) {
     if (resample) idxs <- sample(idxs0) else idxs <- idxs0
     z[c(1,length(z))]
  })
}

[HenrikBengtsson]

Here's a miminal reproducible example that illustrates the problem and that can be used as a test case (in the future package).

library("future")
plan(multisession, workers = 2L)

reset <- TRUE
x <- 1
y %<-% { if (reset) x <- 0; x + 1 }
y
## [1] 1

reset <- FALSE
x <- 1
y %<-% { if (reset) x <- 0; x + 1 }
y
## Error: object 'x' not found

[HenrikBengtsson]

And for the record:

## Default
> globals::findGlobals({ if (reset) x <- 0; x + 1 }, method = "ordered", substitute = TRUE)
[1] "{"     "if"    "reset" "<-"    "+"    

> globals::findGlobals({ if (reset) x <- 0; x + 1 }, method = "conservative", substitute = TRUE)
[1] "{"     "if"    "reset" "<-"    "+"    

> globals::findGlobals({ if (reset) x <- 0; x + 1 }, method = "liberal", substitute = TRUE)
[1] "{"     "if"    "reset" "<-"    "+"     "x"    

[HenrikBengtsson]

Branch feature/if-ambiguity now has an initial prototype for handling this, e.g.

> globals::findGlobals({ if (reset) x <- 0; x + 1 }, method = "ordered", substitute = TRUE)
[1] "{"     "if"    "x"     "reset" "<-"    "+"

However, this does not appear to work when inside a function, e.g.

> globals::findGlobals(function() { if (reset) x <- 0; x + 1 }, method = "ordered", substitute = TRUE)
[1] "{"     "if"    "reset" "<-"    "+"

so more work is needed.

[HenrikBengtsson]

Previously, I've found one example of this in the caret package, and just now another example in the phylolm package (variable MLEsigma2_error).