🔀 Add support for element fragments. (#99)

* #16 add fragment POC

* WIP

* 16 add fragment support to morph

* add keys for fragments

* ensure proper fragment order, refactor to handle fragment/element more similarly

* fix comment typo, incorrect child typo, simplify key check

* fix comment typo

* add snapshot tests

* flatten fragment using fold right, appending elements

* doc update

---------

Co-authored-by: Hayleigh Thompson <me@hayleigh.dev>

2 files changed, 96 insertions, 0 deletions

diff --git a/test/apps/fragment.gleam b/test/apps/fragment.gleam
new file mode 100644
index 0000000..d20400e
--- /dev/null
+++ b/test/apps/fragment.gleam
@@ -0,0 +1,45 @@
+// Similar to count app, with fragments and edge cases
+
+// IMPORTS ---------------------------------------------------------------------
+
+import gleam/int
+import lustre/element.{text}
+import lustre/element/html.{button, p}
+import lustre/event
+
+// MODEL -----------------------------------------------------------------------
+
+pub type Model =
+  Int
+
+pub fn init(count) {
+  count
+}
+
+// UPDATE ----------------------------------------------------------------------
+
+pub type Msg {
+  Increment
+  Decrement
+}
+
+pub fn update(model, msg) {
+  case msg {
+    Increment -> model + 1
+    Decrement -> model - 1
+  }
+}
+
+// VIEW ------------------------------------------------------------------------
+
+pub fn view(model) {
+  let count = int.to_string(model)
+  element.fragment([
+    element.fragment([p([], [element.text("start fragment")])]),
+    element.fragment([p([], [element.text("middle fragment")])]),
+    element.fragment([p([], [element.text(count)])]),
+    button([event.on_click(Decrement)], [text("-")]),
+    button([event.on_click(Increment)], [text("+")]),
+    p([], [element.text("order check, last element")]),
+  ])
+}
diff --git a/test/lustre_test.gleam b/test/lustre_test.gleam
index 9e47a01..f3a2993 100644
--- a/test/lustre_test.gleam
+++ b/test/lustre_test.gleam
@@ -1,6 +1,7 @@
 // IMPORTS ---------------------------------------------------------------------
 
 import apps/counter
+import apps/fragment
 import apps/static
 import birdie
 import gleam/erlang/process
@@ -98,3 +99,53 @@ pub fn counter_diff_test() {
   birdie.snap(json.to_string(patch.element_diff_to_json(diff)), title)
   process.send(runtime, Shutdown)
 }
+
+pub fn fragment_init_test() {
+  let title = "Can render an application's initial state when using fragments"
+  let app = lustre.simple(fragment.init, fragment.update, fragment.view)
+  let assert Ok(runtime) = lustre.start_actor(app, 0)
+  let el =
+    process.call(
+      runtime,
+      function.curry2(process.send)
+        |> function.compose(View)
+        |> function.compose(Debug),
+      100,
+    )
+
+  birdie.snap(element.to_string(el), title)
+  process.send(runtime, Shutdown)
+}
+
+pub fn fragment_counter_diff_test() {
+  let title = "Can compute a diff from one render to the next with fragments"
+  let app = lustre.simple(fragment.init, fragment.update, fragment.view)
+  let assert Ok(runtime) = lustre.start_actor(app, 0)
+
+  let prev =
+    process.call(
+      runtime,
+      function.curry2(process.send)
+        |> function.compose(View)
+        |> function.compose(Debug),
+      100,
+    )
+
+  process.send(runtime, Dispatch(fragment.Increment))
+  process.send(runtime, Dispatch(fragment.Increment))
+  process.send(runtime, Dispatch(fragment.Increment))
+
+  let next =
+    process.call(
+      runtime,
+      function.curry2(process.send)
+        |> function.compose(View)
+        |> function.compose(Debug),
+      100,
+    )
+
+  let diff = patch.elements(prev, next)
+
+  birdie.snap(json.to_string(patch.element_diff_to_json(diff)), title)
+  process.send(runtime, Shutdown)
+}