Improve error handling for typos and odd calls

R/join-by.R

@@ -436,7 +436,17 @@ parse_join_by_expr <- function(expr, i, error_call) {
     expr[[1]] <- sym(call_name(expr))
   }
 
-  op <- as_string(expr[[1]])
+  op <- expr[[1]]
+
+  if (!is_symbol(op)) {
+    if (is_call(op, name = "::")) {
+      stop_invalid_namespaced_expression(expr, i, error_call)
+    } else {
+      stop_invalid_top_expression(expr, i, error_call)
+    }
+  }
+
+  op <- as_string(op)
 
   switch(
     op,
@@ -481,6 +491,15 @@ stop_invalid_top_expression <- function(expr, i, call) {
   abort(message, call = call)
 }
 
+stop_invalid_namespaced_expression <- function(expr, i, call) {
+  message <- c(
+    glue("Expressions can only be namespace prefixed with `dplyr::`."),
+    i = glue("Expression {i} is {err_expr(expr)}.")
+  )
+
+  abort(message, call = call)
+}
+
 parse_join_by_name <- function(expr,
                                i,
                                default_side,

tests/testthat/_snaps/join-by.md

@@ -157,6 +157,24 @@
       ! Each element of `...` must be a single column name or a join by expression.
       x Element 1 is not a name and not an expression.
 
+---
+
+    Code
+      join_by(1())
+    Condition
+      Error in `join_by()`:
+      ! Expressions must use one of: `==`, `>=`, `>`, `<=`, `<`, `closest()`, `between()`, `overlaps()`, or `within()`.
+      i Expression 1 is `1()`.
+
+---
+
+    Code
+      join_by(dplyrr::between(x, left, right))
+    Condition
+      Error in `join_by()`:
+      ! Expressions can only be namespace prefixed with `dplyr::`.
+      i Expression 1 is `dplyrr::between(x, left, right)`.
+
 ---
 
     Code

tests/testthat/test-join-by.R

@@ -283,6 +283,13 @@ test_that("has informative error messages", {
   # Garbage input
   expect_snapshot(error = TRUE, join_by(1))
 
+  # Call with non-symbol first element
+  expect_snapshot(error = TRUE, join_by(1()))
+
+  # Namespace prefixed helper with non-dplyr namespace
+  # (typo or re-export, which currently isn't allowed)
+  expect_snapshot(error = TRUE, join_by(dplyrr::between(x, left, right)))
+
   # Top level usage of `$`
   expect_snapshot(error = TRUE, join_by(x$a))