New numeric_leading_zero_linter

DESCRIPTION

@@ -93,6 +93,7 @@ Collate:
     'namespace.R'
     'namespace_linter.R'
     'no_tab_linter.R'
+    'numeric_leading_zero_linter.R'
     'object_name_linters.R'
     'object_usage_linter.R'
     'open_curly_linter.R'

NAMESPACE

@@ -58,6 +58,7 @@ export(missing_package_linter)
 export(namespace_linter)
 export(no_tab_linter)
 export(nonportable_path_linter)
+export(numeric_leading_zero_linter)
 export(object_length_linter)
 export(object_name_linter)
 export(object_usage_linter)

NEWS.md

@@ -101,6 +101,7 @@ function calls. (#850, #851, @renkun-ken)
    * `vector_logic_linter()` Require use of scalar logical operators (`&&` and `||`) inside `if()` conditions and similar
    * `any_is_na_linter()` Require usage of `anyNA(x)` over `any(is.na(x))`
    * `outer_negation_linter()` Require usage of `!any(x)` over `all(!x)` and `!all(x)` over `any(!x)`
+   * `numeric_leading_zero_linter()` Require a leading `0` in fractional numeric constants, e.g. `0.1` instead of `.1`
 * `assignment_linter()` now lints right assignment (`->` and `->>`) and gains two arguments. `allow_cascading_assign` (`TRUE` by default) toggles whether to lint `<<-` and `->>`; `allow_right_assign` toggles whether to lint `->` and `->>` (#915, @michaelchirico)
 * `infix_spaces_linter()` gains argument `exclude_operators` to disable lints on selected infix operators. By default, all "low-precedence" operators throw lints; see `?infix_spaces_linter` for an enumeration of these. (#914 @michaelchirico)
 * `infix_spaces_linter()` now throws a lint on `a~b` and `function(a=1) {}` (#930, @michaelchirico)

R/numeric_leading_zero_linter.R

@@ -0,0 +1,34 @@
+#' Require usage of a leading zero in all fractional numerics
+#'
+#' While .1 and 0.1 mean the same thing, the latter is easier to read due
+#' to the small size of the '.' glyph.
+#'
+#' @evalRd rd_tags("numeric_leading_zero_linter")
+#' @seealso [linters] for a complete list of linters available in lintr.
+#' @export
+numeric_leading_zero_linter <- function() {
+  Linter(function(source_file) {
+    if (length(source_file$parsed_content) == 0L) {
+      return(list())
+    }
+
+    xml <- source_file$xml_parsed_content
+
+    # NB:
+    #  1. negative constants are split to two components:
+    #    OP-MINUS, NUM_CONST
+    #  2. complex constants are split to three components:
+    #    NUM_CONST, OP-PLUS/OP-MINUS, NUM_CONST
+    xpath <- "//NUM_CONST[starts-with(text(), '.')]"
+
+    bad_expr <- xml2::xml_find_all(xml, xpath)
+
+    return(lapply(
+      bad_expr,
+      xml_nodes_to_lint,
+      source_file = source_file,
+      lint_message = "Include the leading zero for fractional numeric constants.",
+      type = "warning"
+    ))
+  })
+}

inst/lintr/linters.csv

@@ -31,6 +31,7 @@ missing_package_linter,robustness common_mistakes
 namespace_linter,correctness robustness configurable
 no_tab_linter,style consistency default
 nonportable_path_linter,robustness best_practices configurable
+numeric_leading_zero_linter,style consistency readability
 object_length_linter,style readability default configurable
 object_name_linter,style consistency default configurable
 object_usage_linter,style readability correctness default

tests/testthat/test-numeric_leading_zero_linter.R

@@ -0,0 +1,25 @@
+test_that("numeric_leading_zero_linter skips allowed usages", {
+  expect_lint("a <- 0.1", NULL, numeric_leading_zero_linter())
+  expect_lint("b <- -0.2", NULL, numeric_leading_zero_linter())
+  expect_lint("c <- 3.0", NULL, numeric_leading_zero_linter())
+  expect_lint("d <- 4L", NULL, numeric_leading_zero_linter())
+  expect_lint("e <- TRUE", NULL, numeric_leading_zero_linter())
+  expect_lint("f <- 0.5e6", NULL, numeric_leading_zero_linter())
+  expect_lint("g <- 0x78", NULL, numeric_leading_zero_linter())
+  expect_lint("h <- 0.9 + 0.1i", NULL, numeric_leading_zero_linter())
+  expect_lint("h <- 0.9+0.1i", NULL, numeric_leading_zero_linter())
+  expect_lint("h <- 0.9 - 0.1i", NULL, numeric_leading_zero_linter())
+  expect_lint("i <- 2L + 3.4i", NULL, numeric_leading_zero_linter())
+})
+
+test_that("numeric_leading_zero_linter blocks simple disallowed usages", {
+  linter <- numeric_leading_zero_linter()
+  lint_message <- rex::rex("Include the leading zero for fractional numeric constants.")
+
+  expect_lint("a <- .1", lint_message, linter)
+  expect_lint("b <- -.2", lint_message, linter)
+  expect_lint("c <- .3 + 4.5i", lint_message, linter)
+  expect_lint("d <- 6.7 + .8i", lint_message, linter)
+  expect_lint("d <- 6.7+.8i", lint_message, linter)
+  expect_lint("e <- .9e10", lint_message, linter)
+})