setCallbackContext error occurs in pattern-matching callbacks with one or more input IDs as strings

[rpkyle]

In translating a Python demo app for pattern-matching callbacks with the following signature

app$callback(
 output(id = list("index" = MATCH, "type" = "dynamic-output"), property = "figure"),
 params = list(
 input(id = list("index" = MATCH, "type" = "dynamic-dropdown-x"), property = "value"),
 input(id = list("index" = MATCH, "type" = "dynamic-dropdown-y"), property = "value"),
 input(id = "country", property = "value")

I encountered the error:

values must be length 1,
 but FUN(X[[1]]) result is length 2

I was able to trace this error to setCallbackContext, and the following statement:

dashR/R/utils.R

Line 1065 in add8dd3

id_match <- vapply(callback_elements$inputs, function(x) x$id %in% input_id, logical(1))

I suspect that the issue is that we convert the IDs to JSON-like syntax later in the function, and so the length of the IDs is not uniformly 1:

> input_id 
[1] "country"

> callback_elements$inputs 
[[1]]
[[1]]$id
[[1]]$id$index
[1] 0

[[1]]$id$type
[1] "dynamic-dropdown-x"


[[1]]$property
[1] "value"

[[1]]$value
[1] "year"


[[2]]
[[2]]$id
[[2]]$id$index
[1] 0

[[2]]$id$type
[1] "dynamic-dropdown-y"


[[2]]$property
[1] "value"

[[2]]$value
[1] "gdpPercap"


[[3]]
[[3]]$id
[1] "country"

[[3]]$property
[1] "value"

[[3]]$value
[1] "Bulgaria"

One option is to unlist the IDs when matching on their value. Alternatively, we could consider whether the ordering of the if/else logic within setCallbackContext is ultimately what we want.

Whatever solution we identify, we should ensure that a heterogeneous mix of IDs that are lists and vectors (i.e. using selectors or not) is allowed when describing callbacks so that this error does not occur.

[rpkyle]

Resolved via #237, closing.