Allow using englue() for simple glue interpolation

Closes #1601

Author: lionel-

NEWS.md

@@ -1,5 +1,9 @@
 # rlang (development version)
 
+* `englue()` now allows omitting `{{`. This is to make it easier to
+  embed in external functions that need to support either `{` and `{{`
+  (#1601).
+
 * Fix for CRAN checks.
 
 * `stop_input_type()` now handles `I()` input literally in `arg`

R/nse-inject.R

@@ -449,18 +449,6 @@ englue <- function(x,
                    error_call = current_env(),
                    error_arg = "x") {
   check_string(x, arg = error_arg, call = error_call)
-
-  if (!grepl("{{", x, fixed = TRUE)) {
-    abort(
-      c(
-        "Must use `{{`.",
-        i = "Use `glue::glue()` for interpolation with `{`."
-      ),
-      arg = error_arg,
-      call = error_call
-    )
-  }
-
   glue_embrace(x, env = env)
 }
 

tests/testthat/_snaps/nse-inject.md

@@ -50,30 +50,13 @@
       <error/rlang_error>
       Error in `my_englue()`:
       ! `text` must be a single string, not an environment.
-    Code
-      (expect_error(my_englue("{'foo'}")))
-    Output
-      <error/rlang_error>
-      Error in `my_englue()`:
-      ! Must use `{{`.
-      i Use `glue::glue()` for interpolation with `{`.
     Code
       (expect_error(fn()))
     Output
       <error/rlang_error>
       Error in `fn()`:
       ! `x` is absent but must be supplied.
 
-# englue() works
-
-    Code
-      err(englue("{'foo'}"), "Must use")
-    Output
-      <error/rlang_error>
-      Error in `englue()`:
-      ! Must use `{{`.
-      i Use `glue::glue()` for interpolation with `{`.
-
 # englue() checks for the size of its result (#1492)
 
     Code

tests/testthat/test-nse-inject.R

@@ -681,11 +681,11 @@ test_that("can wrap englue() (#1565)", {
   }
 
   expect_equal(fn(bar), "bar_QUX_FOO")
+  expect_equal(my_englue("{'foo'}"), "foo")
 
   expect_snapshot({
     (expect_error(my_englue(c("a", "b"))))
     (expect_error(my_englue(env())))
-    (expect_error(my_englue("{'foo'}")))
     (expect_error(fn()))
   })
 })
@@ -820,8 +820,7 @@ test_that("englue() works", {
 
   g <- function(var) englue("prefix_{{ var }}_suffix")
   expect_equal(g(cyl), "prefix_cyl_suffix")
-
-  expect_snapshot(err(englue("{'foo'}"), "Must use"))
+  expect_equal(englue("{'foo'}"), "foo")
 })
 
 test_that("englue() checks for the size of its result (#1492)", {