Fix show() edge case

src/show.luau

@@ -1,28 +1,33 @@
+local source = require "./source"
 local derive = require "./derive"
+local effect = require "./effect"
 local untrack = require "./untrack"
 
-local function show<T, U>(source: () -> T?, component: (() -> T) -> U, fallback: (() -> U)?): () -> U?
+local function show<T, U>(input: () -> T?, component: (() -> T) -> U, fallback: (() -> U)?): () -> U?
-    local truthy = derive(function()
+    local filtered_input = source()
-        return not not source()
+
+    effect(function()
+        local v = input() 
+        if v then
+            filtered_input(v)
+        end
     end)
 
-    -- seemingly redundant derivation to extend the reactive graph so that
+    local input_is_truthy = derive(function()
-    -- the propogation of the source's update is delayed, giving time for
+        return not not input()
-    -- the show() scope to be destroyed before potential effects registered
-    -- by the component can run when they should not run
-    -- todo: are there cases this method does not cover?
-    local derived = derive(function()
-        return source()
     end)
 
+    -- todo: is this needed?
+    -- local filtered_input_is_truthy = derive(function()
+    --     return not not filtered_input()
+    -- end)
+
     return derive(function()
         return
-            if truthy() then untrack(function() return component(derived :: () -> T) end)
+            if input_is_truthy() then untrack(function() return component(filtered_input :: () -> T) end)
             elseif fallback then untrack(fallback)
             else nil
     end)
 end
 
-return show :: (
+return show
-    ( <T, U>(source: () -> T?, component: (() -> T) -> U) -> () -> U? )
-)

test/tests.luau

@@ -1153,6 +1153,80 @@ TEST("show()", wrap_root(function()
         CHECK(count == 3)
     end
 
+    do CASE "special strict case"
+        type Weapon = {
+            id: string,
+            enchant: string?
+        }
+
+        vide.strict = true
+
+        local count = 0
+        local branch = 0
+
+        local weapon = source(nil :: Weapon?)
+
+        effect(function()
+            weapon()
+        end)
+
+        effect(function()
+            weapon()
+        end)
+
+        show(weapon, function(weapon: () -> Weapon)
+            local enchant = function() return weapon().enchant end
+    
+            show(enchant, function(enchant: () -> string)
+                effect(function()
+                    local e = enchant()
+                    count += 1
+                    CHECK(e ~= nil)
+                    if branch == 1 then
+                        CHECK(e == "fire")
+                    elseif branch == 2 then
+                        CHECK(e == "poison")
+                    end
+                end)
+
+                return {}
+            end)
+
+            return {}
+        end)
+
+        effect(function()
+            weapon()
+        end)
+
+        effect(function()
+            weapon()
+        end)
+
+        branch = 1
+        weapon { id = "1", enchant = "fire" }
+        CHECK(count == 8)
+
+        branch = 2
+        weapon { id = "1", enchant = "poison" }
+        CHECK(count == 10)
+
+        weapon { id = "1", enchant = nil }
+        CHECK(count == 10)
+
+        branch = 1
+        weapon { id = "1", enchant = "fire" }
+        CHECK(count == 14)
+
+        weapon(nil)
+
+        branch = 2
+        weapon { id = "1", enchant = "poison" }
+        CHECK(count == 22)
+
+        vide.strict = false
+    end
+
     do CASE "alt" -- todo: move test
         local visible = vide.source(true)
         local count = vide.source(0)