Do not error with '<% %>' constructs

Fixes #185

NEWS.md

@@ -1,4 +1,5 @@
 # lintr 1.0.0.9000 #
+* Do not error with '<% %>' constructs (#185).
 * Allow closing parenthesis or comma after closing curly brace (#167, @Enchufa2)
 * Support checkstyle XML output (#156, @joshkgold)
 * seq_linter, finds `1:length(...)` (and similar) expressions (#155, @gaborcsardi)

R/extract.R

@@ -2,7 +2,7 @@
 extract_r_source <- function(filename, lines) {
 
   pattern <- get_knitr_pattern(filename, lines)
-  if (is.null(pattern)) {
+  if (is.null(pattern$chunk.begin) || is.null(pattern$chunk.end)) {
     return(lines)
   }
 

tests/testthat/test-knitr_formats.R

@@ -65,3 +65,12 @@ test_that("it handles asciidoc", {
     default_linters
   )
 })
+
+test_that("it does _not_ handle brew", {
+  expect_lint("'<% a %>'\n",
+    checks = list(
+      rex("Only use double-quotes."),
+      rex("Trailing blank lines are superfluous.")
+    ),
+    default_linters)
+})