From d027ef50c486abae5cdf3b3f0566d80cdf643263 Mon Sep 17 00:00:00 2001
From: DavisVaughan <davis@rstudio.com>
Date: Fri, 6 Dec 2019 11:25:44 -0500
Subject: [PATCH 1/3] Use `is_unspecified()` in `vec_cast.list.default()`

---
 R/type-bare.R                   | 2 +-
 tests/testthat/test-type-bare.R | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/R/type-bare.R b/R/type-bare.R
index 48a511708..7524562e4 100644
--- a/R/type-bare.R
+++ b/R/type-bare.R
@@ -413,7 +413,7 @@ vec_cast.list.list <- function(x, to, ...) {
 #' @export
 #' @method vec_cast.list default
 vec_cast.list.default <- function(x, to, ...) {
-  if (inherits(x, "vctrs_unspecified")) {
+  if (is_unspecified(x)) {
     return(vec_init(to, length(x)))
   }
 
diff --git a/tests/testthat/test-type-bare.R b/tests/testthat/test-type-bare.R
index 7fe3251e9..ef28c71a9 100644
--- a/tests/testthat/test-type-bare.R
+++ b/tests/testthat/test-type-bare.R
@@ -302,7 +302,7 @@ test_that("can sort raw", {
 
 test_that("safe casts work as expected", {
   expect_equal(vec_cast(NULL, list()), NULL)
-  expect_equal(vec_cast(NA, list()), list(NA))
+  expect_equal(vec_cast(NA, list()), list(NULL))
   expect_equal(vec_cast(1:2, list()), list(1L, 2L))
   expect_equal(vec_cast(list(1L, 2L), list()), list(1L, 2L))
 })

From b675847b06e3b72614abfe9fa169f70ae4097690 Mon Sep 17 00:00:00 2001
From: DavisVaughan <davis@rstudio.com>
Date: Thu, 2 Jan 2020 10:27:52 -0500
Subject: [PATCH 2/3] Replace `NA` values with `NULL` when casting to list

---
 R/type-bare.R                   |  5 +++++
 tests/testthat/test-type-bare.R | 12 ++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/R/type-bare.R b/R/type-bare.R
index 7524562e4..5bff9e287 100644
--- a/R/type-bare.R
+++ b/R/type-bare.R
@@ -419,6 +419,8 @@ vec_cast.list.default <- function(x, to, ...) {
 
   out <- lapply(seq_along(x), function(i) x[[i]])
 
+  vec_slice(out, vec_equal_na(x)) <- list(NULL)
+
   if (!is.object(to)) {
     out <- shape_broadcast(out, to)
   }
@@ -433,6 +435,9 @@ vec_cast.list.data.frame <- function(x, to, ...) {
   # equivalent for `vec_get()`
   row.names(x) <- NULL
   out <- vec_chop(x)
+
+  vec_slice(out, vec_equal_na(x)) <- list(NULL)
+
   out
 }
 
diff --git a/tests/testthat/test-type-bare.R b/tests/testthat/test-type-bare.R
index ef28c71a9..50393e1bb 100644
--- a/tests/testthat/test-type-bare.R
+++ b/tests/testthat/test-type-bare.R
@@ -320,6 +320,18 @@ test_that("data frames are cast to list row wise (#639)", {
   expect_equal(vec_cast(x, list()), expect)
 })
 
+test_that("Casting atomic `NA` values to list results in a `NULL`", {
+  x <- c(NA, 1)
+  expect <- list(NULL, 1)
+  expect_equal(vec_cast(x, list()), expect)
+})
+
+test_that("Casting data frame `NA` rows to list results in a `NULL`", {
+  x <- data.frame(x = c(NA, NA, 1), y = c(NA, 1, 2))
+  expect <- list(NULL, vec_slice(x, 2), vec_slice(x, 3))
+  expect_equal(vec_cast(x, list()), expect)
+})
+
 # Unspecified
 
 test_that("unspecified can be cast to bare methods", {

From b25174d60bb07f62a9ab05ac33195848a71c1ac5 Mon Sep 17 00:00:00 2001
From: DavisVaughan <davis@rstudio.com>
Date: Thu, 2 Jan 2020 10:36:20 -0500
Subject: [PATCH 3/3] Ensure that data frames can be cast to shaped lists

---
 R/type-bare.R                   |  4 ++++
 tests/testthat/test-type-bare.R | 10 ++++++++++
 2 files changed, 14 insertions(+)

diff --git a/R/type-bare.R b/R/type-bare.R
index 5bff9e287..e8261b125 100644
--- a/R/type-bare.R
+++ b/R/type-bare.R
@@ -438,6 +438,10 @@ vec_cast.list.data.frame <- function(x, to, ...) {
 
   vec_slice(out, vec_equal_na(x)) <- list(NULL)
 
+  if (!is.object(to)) {
+    out <- shape_broadcast(out, to)
+  }
+
   out
 }
 
diff --git a/tests/testthat/test-type-bare.R b/tests/testthat/test-type-bare.R
index 50393e1bb..4ab6e7aa5 100644
--- a/tests/testthat/test-type-bare.R
+++ b/tests/testthat/test-type-bare.R
@@ -320,6 +320,16 @@ test_that("data frames are cast to list row wise (#639)", {
   expect_equal(vec_cast(x, list()), expect)
 })
 
+test_that("data frames can be cast to shaped lists", {
+  to <- array(list(), dim = c(0, 2, 1))
+  x <- data.frame(x = 1:2, y = 3:4)
+
+  expect <- list(vec_slice(x, 1), vec_slice(x, 2))
+  expect <- array(expect, dim = c(2, 2, 1))
+
+  expect_equal(vec_cast(x, to), expect)
+})
+
 test_that("Casting atomic `NA` values to list results in a `NULL`", {
   x <- c(NA, 1)
   expect <- list(NULL, 1)