From de70321f608b47c7847b8df69a4f5310df1257a8 Mon Sep 17 00:00:00 2001
From: Romain Francois <romain@rstudio.com>
Date: Mon, 20 May 2019 11:30:44 -0400
Subject: [PATCH] colwise functions support constants in formulas;

closes #4374.
---
 NEWS.md                                |  2 ++
 inst/include/dplyr/hybrid/Expression.h |  3 +++
 tests/testthat/test-colwise-mutate.R   | 12 ++++++++++++
 3 files changed, 17 insertions(+)

diff --git a/NEWS.md b/NEWS.md
index d33a896faa..66f92436df 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -2,6 +2,8 @@
 
 * `rename_at()` handles empty selection (#4324). 
 
+* colwise functions support constants in formulas (#4374). 
+
 # dplyr 0.8.1
 
 ## Breaking changes
diff --git a/inst/include/dplyr/hybrid/Expression.h b/inst/include/dplyr/hybrid/Expression.h
index f9383ea705..c0555a05e5 100644
--- a/inst/include/dplyr/hybrid/Expression.h
+++ b/inst/include/dplyr/hybrid/Expression.h
@@ -139,6 +139,9 @@ class Expression {
     if (TYPEOF(head) == CLOSXP && Rf_inherits(head, "inline_colwise_function")) {
       dot_alias = CADR(expr);
       expr = CADR(Rf_getAttrib(head, symbols::formula));
+      if (TYPEOF(expr) != LANGSXP) {
+        return;
+      }
       head = CAR(expr);
     }
 
diff --git a/tests/testthat/test-colwise-mutate.R b/tests/testthat/test-colwise-mutate.R
index 57702408f0..e7be7c89be 100644
--- a/tests/testthat/test-colwise-mutate.R
+++ b/tests/testthat/test-colwise-mutate.R
@@ -405,3 +405,15 @@ test_that("summarise_at() can refer to local variables and columns (#4304)", {
   })
 
 })
+
+test_that("colwise mutate handles formulas with constants (#4374)", {
+  expect_identical(
+    tibble(x = 12) %>% mutate_all(~ 42),
+    tibble(x = 42)
+  )
+  expect_identical(
+    tibble(x = 12) %>% mutate_at("x", ~ 42),
+    tibble(x = 42)
+  )
+})
+