Extract text from STR_CONST nodes

Convert STR_CONST text() values into R strings. This is useful to account for arbitrary character literals, e.g. R"------[hello]------", which is parsed in R as "hello". It is quite cumbersome to write XPaths allowing for strings like this, so whenever your linter logic requires testing a STR_CONST node's value, use this function. NB: this is also properly vectorized on s, and accepts a variety of inputs. Empty inputs will become NA outputs, which helps ensure that length(get_r_string(s)) == length(s).

Usage

get_r_string(s, xpath = NULL)

Arguments

s

An input string or strings. If s is an xml_node or xml_nodeset and xpath is NULL, extract its string value with xml2::xml_text(). If s is an xml_node or xml_nodeset and xpath is specified, it is extracted with xml2::xml_find_chr().

xpath

An XPath, passed on to xml2::xml_find_chr() after wrapping with string().

Examples

tmp <- tempfile()
writeLines("c('a', 'b')", tmp)
expr_as_xml <- get_source_expressions(tmp)$expressions[[1L]]$xml_parsed_content
writeLines(as.character(expr_as_xml))
#> 
#> 
#>   
#>     
#>       c
#>     
#>     (
#>     
#>       'a'
#>     
#>     ,
#>     
#>       'b'
#>     
#>     )
#>   
#> 
#> 
get_r_string(expr_as_xml, "expr[2]")
#> [1] "a"
get_r_string(expr_as_xml, "expr[3]")
#> [1] "b"
unlink(tmp)

# more importantly, extract raw strings correctly
tmp_raw <- tempfile()
writeLines("c(R'(a\\b)', R'--[a\\\"\'\"\\b]--')", tmp_raw)
expr_as_xml_raw <- get_source_expressions(tmp_raw)$expressions[[1L]]$xml_parsed_content
writeLines(as.character(expr_as_xml_raw))
#> 
#> 
#>   
#>     
#>       c
#>     
#>     (
#>     
#>       R'(a\b)'
#>     
#>     ,
#>     
#>       R'--[a\"'"\b]--'
#>     
#>     )
#>   
#> 
#> 
get_r_string(expr_as_xml_raw, "expr[2]")
#> [1] "a\\b"
get_r_string(expr_as_xml_raw, "expr[3]")
#> [1] "a\\\"'\"\\b"
unlink(tmp_raw)