Bug with targets being silently overwritten when they differ only in letter case

[markbknudsen]

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Description

Introduction

I have been having a hard-to-identify issue with my pipeline which I have managed to boil down to the following (I presume) bug.

Reproducible example

Consider the following _targets.R script, which defines two targets that have the same name except for lower/upper case.

library(targets)

list(
  tar_target(
    a,
    1
  ),
  
  tar_target(
    A,
    2
  )
)

Running tar_make works completely fine

> tar_make()
▶ dispatched target A
● completed target A [0 seconds, 50 bytes]
▶ dispatched target a
● completed target a [0 seconds, 51 bytes]
▶ ended pipeline [0.14 seconds]

However, when reading the values with tar_read or tar_load they both have the value 1, even though they very clearly should be 1 and 2, respectively

> tar_read(a); tar_read(A)
[1] 1
[1] 1

In the folder _targets/objects there is only a single file a. When running the targets one at a time with tar_make(a) and tar_make(A) it seems that the file from the first target is being overwritten when the later target is built.

Suggestion

While the issue can obviously be circumvented by not using the same names for the targets, it would be preferable to have targets correctly distinguish the case of the names. If that is not possible, targets should at least give an error, as any downstream targets of A will be using an incorrect value without notifying the user.

[wlandau]

Some major file systems are case-insensitive (Mac OS and many Windows machines) and this is not something targets can control. But in recent commits, I did add a warning when there are duplicated target names after converting to lower case, and I added extra documentation to the name argument of tar_target().