New consecutive_mutate_linter

DESCRIPTION

@@ -81,6 +81,7 @@ Collate:
     'condition_message_linter.R'
     'conjunct_test_linter.R'
     'consecutive_assertion_linter.R'
+    'consecutive_mutate_linter.R'
     'cyclocomp_linter.R'
     'declared_functions.R'
     'deprecated.R'

NAMESPACE

@@ -40,6 +40,7 @@ export(comparison_negation_linter)
 export(condition_message_linter)
 export(conjunct_test_linter)
 export(consecutive_assertion_linter)
+export(consecutive_mutate_linter)
 export(consecutive_stopifnot_linter)
 export(cyclocomp_linter)
 export(default_linters)

NEWS.md

@@ -33,6 +33,7 @@
 * `which_grepl_linter()` for discouraging `which(grepl(ptn, x))` in favor of directly using `grep(ptn, x)` (part of #884, @MichaelChirico).
 * `list_comparison_linter()` for discouraging comparisons on the output of `lapply()`, e.g. `lapply(x, sum) > 10` (part of #884, @MichaelChirico).
 * `print_linter()` for discouraging usage of `print()` on string literals like `print("Reached here")` or `print(paste("Found", nrow(DF), "rows."))` (#1894, @MichaelChirico).
+* `consecutive_mutate_linter()` for encouraging consecutive calls to `dplyr::mutate()` to be combined (part of #884, @MichaelChirico).
 * `if_switch_linter()` for encouraging `switch()` over repeated `if`/`else` tests (part of #884, @MichaelChirico).
 * `nested_pipe_linter()` for discouraging pipes within pipes, e.g. `df1 %>% inner_join(df2 %>% select(a, b))` (part of #884, @MichaelChirico).
 * `nrow_subset_linter()` for discouraging usage like `nrow(subset(x, conditions))` in favor of something like `with(x, sum(conditions))` which doesn't require a full subset of `x` (part of #884, @MichaelChirico).

R/consecutive_mutate_linter.R

@@ -0,0 +1,101 @@
+#' Require consecutive calls to mutate() to be combined when possible
+#'
+#' `dplyr::mutate()` accepts any number of columns, so sequences like
+#'   `DF %>% dplyr::mutate(..1) %>% dplyr::mutate(..2)` are redundant --
+#'   they can always be expressed with a single call to `dplyr::mutate()`.
+#'
+#' An exception is for some SQL back-ends, where the translation logic may not be
+#'   as sophisticated as that in the default `dplyr`, for example in
+#'   `DF %>% mutate(a = a + 1) %>% mutate(b = a - 2)`.
+#'
+#' @param invalid_backends Character vector of packages providing dplyr backends
+#'   which may not be compatible with combining `mutate()` calls in all cases.
+#'   Defaults to `"dbplyr"` since not all SQL backends can handle re-using
+#'   a variable defined in the same `mutate()` expression.
+#'
+#' @examples
+#' # will produce lints
+#' lint(
+#'   text = "x %>% mutate(a = 1) %>% mutate(b = 2)",
+#'   linters = consecutive_mutate_linter()
+#' )
+#'
+#' # okay
+#' lint(
+#'   text = "x %>% mutate(a = 1, b = 2)",
+#'   linters = consecutive_mutate_linter()
+#' )
+#'
+#' code <- "library(dbplyr)\nx %>% mutate(a = 1) %>% mutate(a = a + 1)"
+#' writeLines(code)
+#' lint(
+#'   text = code,
+#'   linters = consecutive_mutate_linter()
+#' )
+#'
+#' @evalRd rd_tags("consecutive_mutate_linter")
+#' @seealso [linters] for a complete list of linters available in lintr.
+#' @export
+consecutive_mutate_linter <- function(invalid_backends = "dbplyr") {
+  attach_pkg_xpath <- glue("
+  //SYMBOL_FUNCTION_CALL[text() = 'library' or text() = 'require']
+    /parent::expr
+    /following-sibling::expr
+    /*[self::SYMBOL or self::STR_CONST]
+  ")
+
+  namespace_xpath <- glue("
+  //SYMBOL_PACKAGE[{ xp_text_in_table(invalid_backends) }]
+  |
+  //COMMENT[
+    contains(text(), '@import')
+    and (
+      {xp_or(sprintf(\"contains(text(), '%s')\", invalid_backends))}
+    )
+  ]
+  ")
+
+  # match on the expr, not the SYMBOL_FUNCTION_CALL, to ensure
+  #   namespace-qualified calls only match if the namespaces do.
+  # expr[2] needed in expr[1][expr[2]] to skip matches on pipelines
+  #   starting like mutate(DF, ...) %>% foo() %>% mutate().
+  # similarly, expr[1][expr[call='mutate']] covers pipelines
+  #   starting like mutate(DF, ...) %>% mutate(...)
+  mutate_cond <- xp_and(
+    "expr/SYMBOL_FUNCTION_CALL[text() = 'mutate']",
+    "not(SYMBOL_SUB[text() = '.keep' or text() = '.by'])"
+  )
+  xpath <- glue("
+  (//PIPE | //SPECIAL[{ xp_text_in_table(magrittr_pipes) }])
+    /preceding-sibling::expr[expr[2][{ mutate_cond }] or ({ mutate_cond })]
+    /following-sibling::expr[{ mutate_cond }]
+  ")
+
+  Linter(function(source_expression) {
+    # need the full file to also catch usages at the top level
+    if (!is_lint_level(source_expression, "file")) {
+      return(list())
+    }
+
+    xml <- source_expression$full_xml_parsed_content
+
+    attach_str <- get_r_string(xml_find_all(xml, attach_pkg_xpath))
+    if (any(invalid_backends %in% attach_str)) {
+      return(list())
+    }
+
+    namespace_expr <- xml_find_first(xml, namespace_xpath)
+    if (!is.na(namespace_expr)) {
+      return(list())
+    }
+
+    bad_expr <- xml_find_all(xml, xpath)
+
+    xml_nodes_to_lints(
+      bad_expr,
+      source_expression = source_expression,
+      lint_message = "Unify consecutive calls to mutate().",
+      type = "warning"
+    )
+  })
+}

inst/lintr/linters.csv

@@ -14,6 +14,7 @@ comparison_negation_linter,readability consistency
 condition_message_linter,best_practices consistency
 conjunct_test_linter,package_development best_practices readability configurable pkg_testthat
 consecutive_assertion_linter,style readability consistency
+consecutive_mutate_linter,consistency readability configurable efficiency
 consecutive_stopifnot_linter,style readability consistency deprecated
 cyclocomp_linter,style readability best_practices default configurable
 duplicate_argument_linter,correctness common_mistakes configurable