Add library call linter

DESCRIPTION

@@ -114,6 +114,7 @@ Collate:
     'is_lint_level.R'
     'is_numeric_linter.R'
     'lengths_linter.R'
+    'library_call_linter.R'
     'line_length_linter.R'
     'lint.R'
     'linter_tag_docs.R'

NAMESPACE

@@ -78,6 +78,7 @@ export(inner_combine_linter)
 export(is_lint_level)
 export(is_numeric_linter)
 export(lengths_linter)
+export(library_call_linter)
 export(line_length_linter)
 export(lint)
 export(lint_dir)

R/library_call_linter.R

@@ -0,0 +1,60 @@
+#' Library call linter
+#'
+#' Force library calls to all be at the top of the script.
+#'
+#' @examples
+#'  # will produce lints
+#'  lint(
+#'    text = c("library(dplyr)", "print('test')", "library(tidyr)"),
+#'    linters = library_call_linter()
+#'  )
+#'
+#'  lint(
+#'    text = c("library(dplyr)", "print('test')", "library(tidyr)", "library(purrr)"),
+#'    linters = library_call_linter()
+#'  )
+#'
+#'  # okay
+#'  lint(
+#'    text = c("library(dplyr)", "print('test')"),
+#'    linters = library_call_linter()
+#'  )
+#'
+#'  lint(
+#'    text = c("# comment", "library(dplyr)"),
+#'    linters = library_call_linter()
+#'  )
+#'
+#' @evalRd rd_tags("library_call_linter")
+#' @seealso [linters] for a complete list of linters available in lintr.
+#' @export
+library_call_linter <- function() {
+
+  xpath <- "
+  (//SYMBOL_FUNCTION_CALL[text() = 'library'])[last()]
+  //preceding::expr
+  //SYMBOL_FUNCTION_CALL[text() != 'library'][last()]
+  //following::expr[SYMBOL_FUNCTION_CALL[text() = 'library']]
+  "
+
+  Linter(function(source_expression) {
+    if (!is_lint_level(source_expression, "file")) {
+      return(list())
+    }
+
+    xml <- source_expression$full_xml_parsed_content
+
+    bad_expr <- xml2::xml_find_all(xml, xpath)
+
+    if (length(bad_expr) == 0L) {
+      return(list())
+    }
+
+    xml_nodes_to_lints(
+      bad_expr,
+      source_expression = source_expression,
+      lint_message = "Move all library calls to the top of the script.",
+      type = "warning"
+    )
+  })
+}

inst/lintr/linters.csv

@@ -42,6 +42,7 @@ infix_spaces_linter,style readability default configurable
 inner_combine_linter,efficiency consistency readability
 is_numeric_linter,readability best_practices consistency
 lengths_linter,efficiency readability best_practices
+library_call_linter,style best_practices
 line_length_linter,style readability default configurable
 literal_coercion_linter,best_practices consistency efficiency
 matrix_apply_linter,readability efficiency

tests/testthat/test-library_call_linter.R

@@ -0,0 +1,51 @@
+test_that("library_call_linter skips allowed usages", {
+
+  expect_lint(c("library(dplyr)", "print('test')"),
+    NULL,
+    library_call_linter()
+  )
+
+  expect_lint("print('test')",
+    NULL,
+    library_call_linter()
+  )
+
+  expect_lint(c("# comment", "library(dplyr)"),
+    NULL,
+    library_call_linter()
+  )
+
+  expect_lint(c("print('test')", "# library(dplyr)"),
+    NULL,
+    library_call_linter()
+  )
+})
+
+test_that("library_call_linter warns on disallowed usages", {
+  lint_message <- rex::rex("Move all library calls to the top of the script.")
+
+  expect_lint(c("library(dplyr)", "print('test')", "library(tidyr)"),
+    lint_message,
+    library_call_linter()
+  )
+
+  expect_lint(c("library(dplyr)", "print('test')", "library(tidyr)", "library(purrr)"),
+    list(lint_message, lint_message),
+    library_call_linter()
+  )
+
+  expect_lint(c("library(dplyr)", "print('test')", "print('test')", "library(tidyr)"),
+    rex("Move all library calls to the top of the script."),
+    library_call_linter()
+  )
+
+  expect_lint(c("library(dplyr)", "print('test')", "library(tidyr)", "print('test')"),
+    lint_message,
+    library_call_linter()
+  )
+
+  expect_lint(c("library(dplyr)", "print('test')", "library(tidyr)", "print('test')", "library(tidyr)"),
+    list(lint_message, lint_message),
+    library_call_linter()
+  )
+})