(WIP) Allows the use of = instead of <-

R/assignment_linter.R

@@ -7,6 +7,8 @@
 #' @param allow_right_assign Logical, default `FALSE`. If `TRUE`, `->` and `->>` are allowed.
 #' @param allow_trailing Logical, default `TRUE`. If `FALSE` then assignments aren't allowed at end of lines.
 #' @param allow_pipe_assign Logical, default `FALSE`. If `TRUE`, magrittr's `%<>%` assignment is allowed.
+#' @param allow_equal_assign Logical, default `FALSE`.
+#'   If `TRUE`, `=` instead of `<-` is used for assignment.
 #'
 #' @examples
 #' # will produce lints
@@ -73,7 +75,8 @@
 assignment_linter <- function(allow_cascading_assign = TRUE,
                               allow_right_assign = FALSE,
                               allow_trailing = TRUE,
-                              allow_pipe_assign = FALSE) {
+                              allow_pipe_assign = FALSE,
+                              allow_equal_assign = FALSE) {
   trailing_assign_xpath <- paste(
     collapse = " | ",
     c(
@@ -88,7 +91,7 @@ assignment_linter <- function(allow_cascading_assign = TRUE,
 
   xpath <- paste(collapse = " | ", c(
     # always block = (NB: the parser differentiates EQ_ASSIGN, EQ_SUB, and EQ_FORMALS)
-    "//EQ_ASSIGN",
+    if (allow_equal_assign) "//LEFT_ASSIGN[text() = '<-']" else "//EQ_ASSIGN",
     # -> and ->> are both 'RIGHT_ASSIGN'
     if (!allow_right_assign) "//RIGHT_ASSIGN" else if (!allow_cascading_assign) "//RIGHT_ASSIGN[text() = '->>']",
     # <-, :=, and <<- are all 'LEFT_ASSIGN'; check the text if blocking <<-.
@@ -108,7 +111,12 @@ assignment_linter <- function(allow_cascading_assign = TRUE,
     }
 
     operator <- xml_text(bad_expr)
-    lint_message_fmt <- rep("Use <-, not %s, for assignment.", length(operator))
+    lint_message_fmt <- rep(
+      paste0("Use ",
+             if (allow_equal_assign) "=" else "<-",
+             ", not %s, for assignment."),
+      length(operator)
+    )
     lint_message_fmt[operator %in% c("<<-", "->>")] <-
       "Replace %s by assigning to a specific environment (with assign() or <-) to avoid hard-to-predict behavior."
     lint_message_fmt[operator == "%<>%"] <-

tests/testthat/test-assignment_linter.R

@@ -192,3 +192,80 @@ test_that("multiple lints throw correct messages", {
     assignment_linter(allow_cascading_assign = FALSE)
   )
 })
+
+# TODO
+# test multiple lints (as in above)
+test_that("= can be used for top-level assignment in addition to <-", {
+  linter <- assignment_linter(allow_explicit_equal_assign = "allowed")
+
+  expect_lint("blah = 1", NULL, linter)
+  expect_lint("blah <- 1", NULL, linter)
+
+  # implicit <- assignmnet is unaffected
+  expect_lint("if (x <- 1L) TRUE", NULL, linter)
+  expect_lint("while (x <- 0L) FALSE", NULL, linter)
+  expect_lint("for (x in y <- 1:10) print(x)", NULL, linter)
+
+  # data.table's left assign := needs to be silent
+  expect_lint("dt[, x := 42]", NULL, linter)
+})
+
+
+test_that("multiple lints throw correct messages when both = and <- is allowed", {
+  expect_lint(
+    trim_some("{
+      x <<- 1
+      y ->> 2
+      z -> 3
+      x %<>% as.character()
+      foo <- 1
+      bar = 2
+    }"),
+    list(
+      list(message = "Replace <<- by assigning to a specific environment", line_number = 2L),
+      list(message = "Replace ->> by assigning to a specific environment", line_number = 3L),
+      list(message = "Use <-, not ->", line_number = 4L),
+      list(message = "Avoid the assignment pipe %<>%", line_number = 5L)
+    ),
+    assignment_linter(allow_cascading_assign = FALSE, allow_explicit_equal_assign = "allowed")
+  )
+})
+
+
+test_that("= must be used for top-level assignment instead of <-", {
+  linter <- assignment_linter(allow_explicit_equal_assign = "required")
+  lint_msg <- rex::rex("Use =, not <-, for top-level assignment.")
+
+  expect_lint("blah = 1", NULL, linter)
+  expect_lint("blah <- 1", lint_msg, linter)
+
+  # implicit <- assignmnet is unaffected
+  expect_lint("if (x <- 1L) TRUE", NULL, linter)
+  expect_lint("while (x <- 0L) FALSE", NULL, linter)
+  expect_lint("for (x in y <- 1:10) print(x)", NULL, linter)
+
+  # data.table's left assign := needs to be silent
+  expect_lint("dt[, x := 42]", NULL, linter)
+})
+
+
+test_that("multiple lints throw correct messages when = is required", {
+  expect_lint(
+    trim_some("{
+      x <<- 1
+      y ->> 2
+      z -> 3
+      x %<>% as.character()
+      foo <- 1
+      bar = 2
+    }"),
+    list(
+      list(message = "Replace <<- by assigning to a specific environment", line_number = 2L),
+      list(message = "Replace ->> by assigning to a specific environment", line_number = 3L),
+      list(message = "Use <-, not ->", line_number = 4L),
+      list(message = "Avoid the assignment pipe %<>%", line_number = 5L),
+      list(message = "Use =, not <-, for top-level assignment.", line_number = 6L)
+    ),
+    assignment_linter(allow_cascading_assign = FALSE, allow_explicit_equal_assign = "required")
+  )
+})