tar_assign() informative error

R/tar_assign.R

@@ -59,7 +59,7 @@ tar_assign <- function(targets) {
     as.list(expr[-1L]),
     list(expr)
   )
-  check_assign <- function(x){
+  check_assign <- function(x) {
     identical(x[[1L]], quote(`<-`)) || identical(x[[1L]], quote(`=`))
   }
   targets::tar_assert_true(
@@ -76,6 +76,14 @@ tar_assign <- function(targets) {
 }
 
 tar_assign_parse <- function(statement, envir) {
+  targets::tar_assert_true(
+    length(statement) > 2L && is.call(statement[[3L]]),
+    msg = paste0(
+      "tar_assign() failed to parse statement `",
+      tar_deparse_language(statement),
+      "` because the right-hand side is not a function call."
+    )
+  )
   call <- statement[[3L]]
   call$name <- statement[[2L]]
   eval(call, envir = envir)

tests/testthat/test-tar_assign.R

@@ -5,8 +5,7 @@ targets::tar_test("tar_assign() single statement", {
   expect_equal(out$command, "c(1L, 2L)")
   targets::tar_make(callr_function = NULL)
   expect_equal(targets::tar_read(x), c(1L, 2L))
-
-  targets::tar_script(tar_assign({x = tar_target(c(1L, 2L))}))
+  targets::tar_script(tar_assign({x = tar_target(c(1L, 2L))})) # nolint
   out <- targets::tar_manifest(callr_function = NULL)
   expect_equal(out$name, "x")
   expect_equal(out$command, "c(1L, 2L)")
@@ -17,7 +16,7 @@ targets::tar_test("tar_assign() single statement", {
 targets::tar_test("tar_assign()", {
   targets::tar_script({
     tar_assign({
-      x = tar_target(c(1L, 2L))
+      x = tar_target(c(1L, 2L)) # nolint
       y <- tar_target(x + 1L, pattern = map(x))
       z <- tar_rep(TRUE, batches = 2L)
     })
@@ -44,3 +43,14 @@ targets::tar_test("tar_assign()", {
   expect_equal(targets::tar_read(z_batch), c(1L, 2L))
   expect_equal(unname(targets::tar_read(z)), rep(TRUE, 2L))
 })
+
+targets::tar_test("tar_assign() non-calls", {
+  expect_error(
+    tar_assign({
+      x <- targets::tar_target(1)
+      y <- 3
+      z <- tar_target(x + y)
+    }),
+    class = "tar_condition_validate"
+  )
+})