Omit anchor-esque pattern in string_boundary_linter() (#2757)

NEWS.md

@@ -18,6 +18,7 @@
 ### Lint accuracy fixes: removing false positives
 
 * `unnecessary_nesting_linter()` treats function bodies under the shorthand lambda (`\()`) the same as normal function bodies (#2748, @MichaelChirico).
+* `string_boundary_linter()` omits lints of patterns like `\\^` which have an anchor but are not regular expressions (#2636, @MichaelChirico).
 * `implicit_integer_linter(allow_colon = TRUE)` is OK with negative literals, e.g. `-1:1` or `1:-1` (#2673, @MichaelChirico).
 
 ## Notes

R/string_boundary_linter.R

@@ -103,16 +103,17 @@ string_boundary_linter <- function(allow_grepl = FALSE) {
     terminal_anchor <- endsWith(patterns, "$")
     search_start <- 1L + initial_anchor
     search_end <- nchar(patterns) - terminal_anchor
-    can_replace <- is_not_regex(substr(patterns, search_start, search_end))
-    initial_anchor <- initial_anchor[can_replace]
-    terminal_anchor <- terminal_anchor[can_replace]
+    should_lint <- (initial_anchor | terminal_anchor) &
+      is_not_regex(substr(patterns, search_start, search_end))
+    initial_anchor <- initial_anchor[should_lint]
+    terminal_anchor <- terminal_anchor[should_lint]
 
     lint_type <- character(length(initial_anchor))
 
     lint_type[initial_anchor & terminal_anchor] <- "both"
     lint_type[initial_anchor & !terminal_anchor] <- "initial"
     lint_type[!initial_anchor & terminal_anchor] <- "terminal"
-    list(lint_expr = expr[can_replace], lint_type = lint_type)
+    list(lint_expr = expr[should_lint], lint_type = lint_type)
   }
 
   substr_xpath <- glue("

tests/testthat/test-string_boundary_linter.R

@@ -8,6 +8,10 @@ test_that("string_boundary_linter skips allowed grepl() usages", {
   # regex pattern --> no lint
   expect_no_lint("grepl('^[a-z]', x)", linter)
   expect_no_lint("grepl('[a-z]$', x)", linter)
+  # anchor-ish but not a regex --> no lint (#2636)
+  expect_no_lint(R"[grepl("\\^", x)]", linter)
+  expect_no_lint(R"[grepl("\\\\^", x)]", linter)
+  expect_no_lint(R"[grepl("$\\\\", x)]", linter)
 
   # ignore.case --> no lint
   expect_no_lint("grepl('^abc', x, ignore.case = TRUE)", linter)
@@ -151,6 +155,8 @@ test_that("whole-string regex recommends ==, not {starts,ends}With()", {
 })
 
 test_that("vectorization + metadata work as intended", {
+  linter <- string_boundary_linter()
+
   expect_lint(
     trim_some("{
       substring(a, 1, 3) == 'abc'
@@ -176,6 +182,16 @@ test_that("vectorization + metadata work as intended", {
       list("endsWith", line_number = 10L),
       list("==", line_number = 11L)
     ),
-    string_boundary_linter()
+    linter
+  )
+
+  # some but not all anchor-esque as in #2636
+  expect_lint(
+    trim_some(R"[{
+      grepl("\\^", x)
+      grepl("^abc", x)
+    }]"),
+    list("startsWith", line_number = 3L),
+    linter
   )
 })