Implement support for package lazy data

Fixes klmr#219.

DESCRIPTION

@@ -34,6 +34,7 @@ Suggests:
     rlang,
     roxygen2 (>= 7.0.2),
     shiny,
+    stringr,
     testthat (>= 3.0.3)
 Enhances:
     rstudioapi

NEWS.md

@@ -1,5 +1,6 @@
 # box (development version)
 
+* Feature: Support lazy data loading for packages (#219)
 * Enhancement: Improve error messages for invalid `use` declarations (#253)
 * Feature: Add `purge_cache` function (@kamilzyla, #236)
 

R/env.r

@@ -201,11 +201,28 @@ import_into_env = function (to_env, to_names, from_env, from_names) {
         ) {
             makeActiveBinding(to_names[i], fun, to_env)
         } else {
-            assign(to_names[i], get(from_names[i], from_env), envir = to_env)
+            assign(to_names[i], env_get(from_env, from_names[i]), envir = to_env)
         }
     }
 }
 
+env_get = function (env, name) {
+    UseMethod('env_get')
+}
+
+# Method for package namespace environments. This distinction is necessary since
+# lazydata in packages can’t be loaded via `get`.
+env_get.environment = function (env, name) {
+    getExportedValue(env, name)
+}
+
+`env_get.box$mod` =
+`env_get.box$ns` = function (env, name) {
+    # Explicitly allow inherited values, which is used to support re-exporting
+    # imports in modules.
+    get(name, envir = env)
+}
+
 active_binding_function = if (as.integer(version$major) >= 4L) {
     function (sym, env) activeBindingFunction(sym, env)
 } else {

R/use.r

@@ -445,7 +445,7 @@ mod_export_names = function (info, mod_ns) {
 }
 
 `mod_export_names.box$pkg_info` = function (info, mod_ns) {
-    getNamespaceExports(mod_ns)
+    c(getNamespaceExports(mod_ns), ls(getNamespaceInfo(mod_ns, 'lazydata')))
 }
 
 #' @rdname importing

tests/testthat/test-pkg.r

@@ -167,3 +167,20 @@ test_that('S3 lookup works for partial exports', {
     expected = roxygen2::roxy_tag_parse(x)
     expect_equal(actual, expected)
 })
+
+test_that('packages with lazydata can be loaded', {
+    # Data inside ‘datasets’ is available via `get`.
+    expect_error(box::use(datasets), NA)
+    expect_error(get('mtcars', asNamespace('datasets')), NA)
+
+    # ‘stringr’ uses lazydata; `get` doesn’t work.
+    expect_error(box::use(stringr), NA)
+    expect_error(get('fruit', asNamespace('stringr')))
+    expect_in('fruit', ls(stringr))
+    expect_type(stringr$fruit, 'character')
+
+    # Test that attach lists work
+    expect_error(box::use(stringr[ff = fruit, ...]), NA)
+    expect_equal(ff, stringr$fruit)
+    expect_equal(words, stringr$words)
+})