BUG: Dropping optional fields may give an error on unknown path(s)

[HenrikBengtsson]

It's not possible to drop optional fields. The following is an example with an optional key and value pair:

> dirdf::dirdf_parse(c("foo,tag=100.rds", "bar.rds"), template = "name,key?=value?.ext")
  name  key value ext        pathname
1  foo  tag   100 rds foo,tag=100.rds
2  bar <NA>  <NA> rds         bar.rds

However, it is not safe to drop an optional field because it may result in "unexpected paths". For example, if we try to drop the key fields, we get:

> dirdf::dirdf_parse(c("foo,tag=100.rds", "bar.rds"), template = "name,~key?~=value?.ext")
Error in dirdf::dirdf_parse(c("foo,tag=100.rds", "bar.rds"), template = "name,~key?~=value?.ext") : 
  Unexpected path(s) found:
bar.rds

Ideally we would get:

> dirdf::dirdf_parse(c("foo,tag=100.rds", "bar.rds"), template = "name,~key~?=value?.ext")
  name value ext        pathname
1  foo   100 rds foo,tag=100.rds
2  bar  <NA> rds         bar.rds

[HenrikBengtsson]

Clarification, without non-matching files, it works, e.g.

> dirdf::dirdf_parse("foo,tag=100.rds", template = "name,~key?~=value?.ext")
  name value ext        pathname
1  foo   100 rds foo,tag=100.rds

BTW, this format doesn't give an error but the wrong result:

> dirdf::dirdf_parse("foo,tag=100.rds", template = "name,~key~?=value?.ext")
  name value ext        pathname
1  foo  <NA> rds foo,tag=100.rds

[HenrikBengtsson]

Now ~key~? gives an error:

> dirdf::dirdf_parse("foo,tag=100.rds", template = "name,~key~?=value?.ext")
Error in templateToRegex(template) : 
  Invalid template. ~name~? is invalid whereas ~name?~ is valid: ‘name,~key~?=value?.ext’