361 cyclocomp linter (#396)

* [WIP] linter works

* adds linting for cyclomatic complexity.

incurs dependency on cyclocomp.
closes #361.

* updates NEWS for cyclocomp_linter

* less verbose message for cyclocomp_linter

* update tests to new message

Author: fabian-s

DESCRIPTION

@@ -16,6 +16,7 @@ Imports:
     rex,
     crayon,
     codetools,
+    cyclocomp,
     stringdist,
     testthat,
     digest,
@@ -47,6 +48,7 @@ Collate:
     'commas_linter.R'
     'comment_linters.R'
     'comments.R'
+    'cyclocomp_linter.R'
     'object_name_linters.R'
     'deprecated.R'
     'equals_na_lintr.R'

NAMESPACE

@@ -20,6 +20,7 @@ export(clear_cache)
 export(closed_curly_linter)
 export(commas_linter)
 export(commented_code_linter)
+export(cyclocomp_linter)
 export(default_linters)
 export(default_settings)
 export(default_undesirable_functions)
@@ -58,6 +59,7 @@ export(undesirable_operator_linter)
 export(unneeded_concatenation_linter)
 export(with_defaults)
 import(rex)
+importFrom(cyclocomp,cyclocomp)
 importFrom(stats,na.omit)
 importFrom(utils,capture.output)
 importFrom(utils,getParseData)

NEWS.md

@@ -1,4 +1,5 @@
 # lintr 1.0.3.9000 # 
+* New cyclocomp_linter() identifies overly complex functions (#361, @fabian-s)
 * Add support for overriding GitHub API Token via `GITHUB_TOKEN` environment
   variable (#63, @mattyb)
 * Changed the default value of the `length` argument to `object_length_linter` to 30 for consistency (#325 @DragosMG) 

R/cyclocomp_linter.R

@@ -0,0 +1,32 @@
+#' @describeIn linters Check for overly complicated expressions. See
+#'   \code{\link[cyclocomp]{cyclocomp}}.
+#' @param complexity_limit expressions with a cyclomatic complexity higher than
+#'   this are linted, defaults to 25. See \code{\link[cyclocomp]{cyclocomp}}.
+#' @importFrom cyclocomp cyclocomp
+#' @export
+cyclocomp_linter <- function(complexity_limit = 25) {
+  function(source_file) {
+    if (!is.null(source_file[["file_lines"]])) {
+      # abort if source_file is entire file, not a top level expression.
+      return(NULL)
+    }
+    complexity <- try_silently(
+      cyclocomp::cyclocomp(parse(text = source_file$content))
+    )
+    if (inherits(complexity, "try-error")) return(NULL)
+    if (complexity <= complexity_limit) return(NULL)
+    Lint(
+      filename = source_file[["filename"]],
+      line_number = source_file[["line"]][1],
+      column_number = source_file[["column"]][1],
+      type = "style",
+      message = paste0(
+        "functions should have cyclomatic complexity of less than ",
+        complexity_limit, ", this has ", complexity,"."
+      ),
+      ranges = list(c(NA, NA)),
+      line = source_file$lines[1],
+      linter = "cyclocomp_linter"
+    )
+  }
+}

R/zzz.R

@@ -89,6 +89,7 @@ default_linters <- with_defaults(default = list(),
   closed_curly_linter(),
   commas_linter,
   commented_code_linter,
+  cyclocomp_linter(15),
   equals_na_linter,
   function_left_parentheses_linter,
   infix_spaces_linter,

inst/example/complexity.R

@@ -0,0 +1,24 @@
+complexity <- function(x) {
+  if (x > 0) {
+    if (x > 10) {
+      if (x > 20) {
+        x <- x / 2
+      } else {
+        return(x)
+      }
+    } else {
+      return(x)
+    }
+  } else {
+    if (x < -10) {
+      if (x < -20) {
+        x <- x * 2
+      } else {
+        return(x)
+      }
+    } else {
+      return(x)
+    }
+  }
+  x
+}

man/default_linters.Rd

@@ -0,0 +1,26 @@
+context("cyclocomp_linter")
+
+test_that("returns the correct linting", {
+  cc_linter_1 <- cyclocomp_linter(1)
+  cc_linter_2 <- cyclocomp_linter(2)
+  msg <- rex("functions should have cyclomatic complexity")
+
+  expect_lint("if(TRUE) 1 else 2", NULL, cc_linter_2)
+  expect_lint("if(TRUE) 1 else 2", msg, cc_linter_1)
+
+  expect_lint(
+    "function(x) {not parsing}",
+    "unexpected symbol", cc_linter_2
+  )
+
+  complexity <- readLines(
+    system.file("example/complexity.R", package = "lintr")
+  )
+  expect_lint(complexity, msg, cc_linter_2)
+  expect_lint(
+    complexity,
+    "should have cyclomatic complexity of less than 2, this has 10",
+    cc_linter_2
+  )
+  expect_lint(complexity, NULL, cyclocomp_linter(10))
+})