Improve arg_match() message based on context

NEWS.md

@@ -1,5 +1,7 @@
 # rlang (development version)
 
+* `arg_match()` now throws better error messages if `multiple = TRUE` or if a single value is allowed (@olivroy, #1635, #1682).
+
 * `env_browse()` and `env_is_browsed()` are now defunct as they require an API
   that is no longer available to packages (#1727).
 

R/arg.R

@@ -60,7 +60,7 @@ arg_match <- function(arg,
     abort(msg, call = error_call, arg = error_arg)
   }
   if (length(arg) > 1 && !setequal(arg, values)) {
-    msg <- arg_match_invalid_msg(arg, values, error_arg)
+    msg <- arg_match_invalid_msg(arg, values, multiple, error_arg)
     abort(msg, call = error_call, arg = error_arg)
   }
 
@@ -74,6 +74,8 @@ arg_match <- function(arg,
 }
 
 arg_match_multi <- function(arg, values, error_arg, error_call) {
+  # Set an option temporarily to make sure the multiple message shows.
+  local_options("rlang_multiple_error" = TRUE)
   map_chr(arg, ~ arg_match0(.x, values, error_arg, error_call = error_call))
 }
 
@@ -128,7 +130,8 @@ stop_arg_match <- function(arg, values, error_arg, error_call) {
     check_string(arg, arg = error_arg, call = error_call)
   }
 
-  msg <- arg_match_invalid_msg(arg, values, error_arg)
+  multiple <- getOption("rlang_multiple_error", FALSE)
+  msg <- arg_match_invalid_msg(arg, values, multiple, error_arg)
 
   # Try suggest the most probable and helpful candidate value
   candidate <- NULL
@@ -160,14 +163,26 @@ stop_arg_match <- function(arg, values, error_arg, error_call) {
   abort(msg, call = error_call, arg = error_arg)
 }
 
-arg_match_invalid_msg <- function(val, values, error_arg) {
-  msg <- paste0(format_arg(error_arg), " must be one of ")
+arg_match_invalid_msg <- function(val, values, multiple, error_arg) {
+  if (length(values) == 1) {
+    #1635
+    word <- " must be "
+  } else if (multiple) {
+    #1682
+    word <- " must be in "
+  } else {
+    word <- " must be one of "
+  }
+  msg <- paste0(format_arg(error_arg), word)
   msg <- paste0(msg, oxford_comma(chr_quoted(values, "\"")))
 
   if (is_null(val)) {
     msg <- paste0(msg, ".")
   } else {
-    msg <- paste0(msg, sprintf(', not "%s\".', val[[1]]))
+    # only show incorrect values.
+    incorrect_val <- setdiff(val, values)
+    incorrect_val <- oxford_comma(incorrect_val)
+    msg <- paste0(msg, sprintf(', not "%s\".', incorrect_val))
   }
 
   msg

tests/testthat/_snaps/arg.md

@@ -19,6 +19,19 @@
 
     `arg` must be length 1 or a permutation of `c("foo", "bar")`.
 
+# arg_match() works well when multiple = TRUE (#1682)
+
+    Code
+      f("x", values = c("y", "z"))
+    Condition
+      Error in `f()`:
+      ! `x` must be in "y" or "z", not "x".
+    Code
+      f(c("x", "y"), values = c("y", "z"))
+    Condition
+      Error in `f()`:
+      ! `x` must be in "y" or "z", not "x".
+
 # `arg_match()` has informative error messages
 
     Code
@@ -138,14 +151,14 @@
     Output
       <error/rlang_error>
       Error in `my_wrapper()`:
-      ! `my_arg` must be one of "foo", "bar", or "baz", not "ba".
+      ! `my_arg` must be in "foo", "bar", or "baz", not "ba".
       i Did you mean "bar"?
     Code
       (expect_error(my_wrapper(c("foo", "ba"))))
     Output
       <error/rlang_error>
       Error in `my_wrapper()`:
-      ! `my_arg` must be one of "foo", "bar", or "baz", not "ba".
+      ! `my_arg` must be in "foo", "bar", or "baz", not "ba".
       i Did you mean "bar"?
 
 # arg_match0() defuses argument

tests/testthat/_snaps/cnd-abort.md

@@ -1397,21 +1397,21 @@
     Output
       <error/rlang_error>
       Error:
-      ! `"f"` must be one of "foo", not "f".
+      ! `"f"` must be "foo", not "f".
       i Did you mean "foo"?
     Code
       (expect_error(eval_bare(quote(arg_match0("f", "foo")))))
     Output
       <error/rlang_error>
       Error:
-      ! `"f"` must be one of "foo", not "f".
+      ! `"f"` must be "foo", not "f".
       i Did you mean "foo"?
     Code
       (expect_error(eval_bare(quote(arg_match0("f", "foo")), env())))
     Output
       <error/rlang_error>
       Error:
-      ! `"f"` must be one of "foo", not "f".
+      ! `"f"` must be "foo", not "f".
       i Did you mean "foo"?
 
 # error_call() and format_error_call() preserve special syntax ops

tests/testthat/test-arg.R

@@ -50,6 +50,17 @@ test_that("informative error message on partial match", {
   )
 })
 
+test_that("arg_match() works well when multiple = TRUE (#1682)", {
+  f <- function(x, ...) {
+    arg_match(x, ..., multiple = TRUE)
+  }
+  expect_snapshot(error = TRUE, {
+    f("x", values = c("y", "z"))
+    f(c("x", "y"), values = c("y", "z"))
+
+  })
+})
+
 test_that("`arg_match()` has informative error messages", {
   arg_match_wrapper <- function(...) {
     arg_match0_wrapper(...)