From 6b4059a5fd13a5f30391524991868040df2a85f0 Mon Sep 17 00:00:00 2001
From: Hugo Gruson <10783929+Bisaloo@users.noreply.github.com>
Date: Mon, 4 Aug 2025 15:13:56 +0200
Subject: [PATCH 1/4] Add tests for is.unsorted() recommendation on identical()

---
 tests/testthat/test-sort_linter.R | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tests/testthat/test-sort_linter.R b/tests/testthat/test-sort_linter.R
index 15d8ab209e..c054cc3db3 100644
--- a/tests/testthat/test-sort_linter.R
+++ b/tests/testthat/test-sort_linter.R
@@ -108,15 +108,19 @@ test_that("sort_linter blocks simple disallowed usages", {
   sorted_msg <- rex::rex("Use !is.unsorted(x) to test the sortedness of a vector.")
 
   expect_lint("sort(x) == x", sorted_msg, linter)
+  expect_lint("identical(x, sort(x))", sorted_msg, linter)
 
   # argument order doesn't matter
   expect_lint("x == sort(x)", sorted_msg, linter)
+  expect_lint("identical(sort(x), x)", sorted_msg, linter)
 
   # inverted version
   expect_lint("sort(x) != x", unsorted_msg, linter)
+  expect_lint("!identical(x, sort(x))", unsorted_msg, linter)
 
   # expression matching
   expect_lint("sort(foo(x)) == foo(x)", sorted_msg, linter)
+  expect_lint("identical(foo(x), sort(foo(x))", sorted_msg, linter)
 })
 
 test_that("lints vectorize", {

From 7fdade77c5db0e9283d4d51b06760165d8a86245 Mon Sep 17 00:00:00 2001
From: Hugo Gruson <10783929+Bisaloo@users.noreply.github.com>
Date: Mon, 4 Aug 2025 15:14:14 +0200
Subject: [PATCH 2/4] Add new XPath components for identical()

---
 R/sort_linter.R | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/R/sort_linter.R b/R/sort_linter.R
index aa66ece89a..15ac789d13 100644
--- a/R/sort_linter.R
+++ b/R/sort_linter.R
@@ -85,12 +85,11 @@ sort_linter <- function() {
   sorted_xpath <- "
   parent::expr[not(SYMBOL_SUB)]
     /parent::expr[
-      (EQ or NE)
+      (EQ or NE or expr/SYMBOL_FUNCTION_CALL/text() = 'identical')
       and expr/expr = expr
     ]
   "
 
-
   arguments_xpath <-
     ".//SYMBOL_SUB[text() = 'method' or text() = 'decreasing' or text() = 'na.last']"
 

From fe8d654507066277b70bac253d19ba8e566c24e0 Mon Sep 17 00:00:00 2001
From: Hugo Gruson <10783929+Bisaloo@users.noreply.github.com>
Date: Tue, 5 Aug 2025 17:24:42 +0200
Subject: [PATCH 3/4] Split XPaths for idential() and ==

---
 R/sort_linter.R                   | 25 +++++++++++++++++++++++--
 tests/testthat/test-sort_linter.R |  2 +-
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/R/sort_linter.R b/R/sort_linter.R
index 15ac789d13..abff5d8dec 100644
--- a/R/sort_linter.R
+++ b/R/sort_linter.R
@@ -85,7 +85,14 @@ sort_linter <- function() {
   sorted_xpath <- "
   parent::expr[not(SYMBOL_SUB)]
     /parent::expr[
-      (EQ or NE or expr/SYMBOL_FUNCTION_CALL/text() = 'identical')
+      (EQ or NE)
+      and expr/expr = expr
+    ]
+  "
+  sorted_identical_xpath <- "
+  parent::expr[not(SYMBOL_SUB)]
+    /parent::expr[
+      expr/SYMBOL_FUNCTION_CALL[text() = 'identical']
       and expr/expr = expr
     ]
   "
@@ -141,8 +148,22 @@ sort_linter <- function() {
       "Use is.unsorted(x) to test the unsortedness of a vector."
     )
 
+    sorted_identical_expr <- xml_find_all(xml_calls, sorted_identical_xpath)
+    is_negated <- !is.na(
+      xml_find_first(sorted_identical_expr, "preceding-sibling::*[not(self::COMMENT)][1][self::OP-EXCLAMATION]")
+    )
+
+    lint_message <- c(
+      lint_message,
+      ifelse(
+        is_negated,
+        "Use is.unsorted(x) to test the unsortedness of a vector.",
+        "Use !is.unsorted(x) to test the sortedness of a vector."
+      )
+    )
+
     sorted_lints <- xml_nodes_to_lints(
-      sorted_expr,
+      combine_nodesets(sorted_expr, sorted_identical_expr),
       source_expression = source_expression,
       lint_message = lint_message,
       type = "warning"
diff --git a/tests/testthat/test-sort_linter.R b/tests/testthat/test-sort_linter.R
index c054cc3db3..02dd9bda77 100644
--- a/tests/testthat/test-sort_linter.R
+++ b/tests/testthat/test-sort_linter.R
@@ -120,7 +120,7 @@ test_that("sort_linter blocks simple disallowed usages", {
 
   # expression matching
   expect_lint("sort(foo(x)) == foo(x)", sorted_msg, linter)
-  expect_lint("identical(foo(x), sort(foo(x))", sorted_msg, linter)
+  expect_lint("identical(foo(x), sort(foo(x)))", sorted_msg, linter)
 })
 
 test_that("lints vectorize", {

From 9be67fe4bfaa7acb6318aae3bbf0112258e92ee8 Mon Sep 17 00:00:00 2001
From: Hugo Gruson <10783929+Bisaloo@users.noreply.github.com>
Date: Tue, 5 Aug 2025 17:38:56 +0200
Subject: [PATCH 4/4] Add NEWS item

---
 NEWS.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/NEWS.md b/NEWS.md
index d7e38ccabc..b92a8ca3d2 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -48,6 +48,7 @@
 * `object_usage_linter()` lints missing packages that may cause false positives (#2872, @AshesITR)
 * New argument `include_s4_slots` for the `xml_find_function_calls()` entry in the `get_source_expressions()` to govern whether calls of the form `s4Obj@fun()` are included in the result (#2820, @MichaelChirico).
 * `sprintf_linter()` lints `sprintf()` and `gettextf()` calls when a constant string is passed to `fmt` (#2894, @Bisaloo).
+* `sort_linter()` recommends usage of `!is.unsorted(x)` over `identical(x, sort(x))` (#2921, @Bisaloo).
 
 ### New linters