From de85abf54863c9d2b54ea4ec7feda6cd78766fbf Mon Sep 17 00:00:00 2001
From: Mats Bosson <mats.bosson@gmail.com>
Date: Sun, 29 Mar 2026 05:28:35 +0700
Subject: [PATCH] Fix Presence reactivity

---
 .../core/src/utilities/presence/presence.tsx  | 79 ++++++++++++-------
 .../core/tests/utilities/presence.test.tsx    | 58 +++++++++++++-
 2 files changed, 104 insertions(+), 33 deletions(-)

diff --git a/packages/core/src/utilities/presence/presence.tsx b/packages/core/src/utilities/presence/presence.tsx
index f062b80..169bb78 100644
--- a/packages/core/src/utilities/presence/presence.tsx
+++ b/packages/core/src/utilities/presence/presence.tsx
@@ -1,8 +1,11 @@
-import { type Accessor, type JSX, Show, children, createEffect, createSignal } from "solid-js";
+import { type Accessor, type JSX, Show, createEffect, createSignal, on } from "solid-js";
 
 export interface PresenceChildProps {
+  /** Whether the content is currently present (tracks props.present directly). */
   present: Accessor<boolean>;
+  /** True briefly after present transitions from false→true. For enter animations. */
   opening: Accessor<boolean>;
+  /** True briefly after present transitions from true→false. For exit animations. */
   closing: Accessor<boolean>;
 }
 
@@ -11,54 +14,72 @@ export interface PresenceProps {
   present: boolean;
   /**
    * When true, keeps children mounted even when present is false.
-   * Useful for controlling exit animations with external libraries.
+   * Use this when an external animation library controls unmounting.
    */
   forceMount?: boolean;
   children: JSX.Element | ((props: PresenceChildProps) => JSX.Element);
 }
 
 /**
- * Keeps exiting elements mounted during CSS/JS animations.
- * Emits data-opening and data-closing attributes for CSS-driven transitions.
+ * Controls mount/unmount of children with enter/exit animation support.
+ * Exposes opening and closing signals via the children-as-function API.
  *
- * Usage with CSS:
- *   .content[data-opening] { animation: fadeIn 200ms; }
- *   .content[data-closing] { animation: fadeOut 150ms; }
+ * Usage with children-as-function:
+ *   <Presence present={open()}>
+ *     {({ opening, closing }) => (
+ *       <div classList={{ opening: opening(), closing: closing() }}>…</div>
+ *     )}
+ *   </Presence>
  */
 export function Presence(props: PresenceProps): JSX.Element {
   const [mounted, setMounted] = createSignal(props.present);
   const [opening, setOpening] = createSignal(false);
   const [closing, setClosing] = createSignal(false);
 
-  createEffect(() => {
-    if (props.present) {
-      setMounted(true);
-      setClosing(false);
-      setOpening(true);
-      // Clear opening flag after a microtask so CSS can pick it up
-      queueMicrotask(() => setOpening(false));
-    } else {
-      setOpening(false);
-      setClosing(true);
-      // Keep mounted while closing — consumers use forceMount for animation control
-      setClosing(false);
-      setMounted(false);
-    }
-  });
+  // defer: true skips the initial run — only react to changes after mount.
+  createEffect(
+    on(
+      () => props.present,
+      (isPresent) => {
+        if (isPresent) {
+          setMounted(true);
+          setClosing(false);
+          setOpening(true);
+          // Clear opening after a microtask — gives consumers one reactive tick
+          // to read the opening state before it resets.
+          queueMicrotask(() => setOpening(false));
+        } else {
+          setOpening(false);
+          setClosing(true);
+          // In the baseline, unmount immediately (no animation duration known).
+          // With forceMount, the consumer controls the lifecycle externally.
+          if (!props.forceMount) {
+            setMounted(false);
+          }
+          queueMicrotask(() => setClosing(false));
+        }
+      },
+      { defer: true },
+    ),
+  );
 
   const shouldMount = () => props.forceMount || mounted();
 
   const childProps: PresenceChildProps = {
-    present: mounted,
+    // Reflect props.present directly — no reactive lag from the mounted signal.
+    present: () => props.present,
     opening,
     closing,
   };
 
-  const resolved = children(() =>
-    typeof props.children === "function"
-      ? (props.children as (p: PresenceChildProps) => JSX.Element)(childProps)
-      : props.children,
+  // Wrap in a function so Show evaluates children lazily (only when mounted).
+  return (
+    <Show when={shouldMount()}>
+      {() =>
+        typeof props.children === "function"
+          ? (props.children as (p: PresenceChildProps) => JSX.Element)(childProps)
+          : props.children
+      }
+    </Show>
   );
-
-  return <Show when={shouldMount()}>{resolved()}</Show>;
 }
diff --git a/packages/core/tests/utilities/presence.test.tsx b/packages/core/tests/utilities/presence.test.tsx
index b4377ed..d096cf0 100644
--- a/packages/core/tests/utilities/presence.test.tsx
+++ b/packages/core/tests/utilities/presence.test.tsx
@@ -22,20 +22,33 @@ describe("Presence", () => {
     expect(queryByTestId("content")).toBeNull();
   });
 
-  it("adds data-opening attribute when transitioning in", async () => {
+  it("mounts children when present transitions false→true", async () => {
     const [present, setPresent] = createSignal(false);
     const { queryByTestId } = render(() => (
       <Presence present={present()}>
         <div data-testid="content">hello</div>
       </Presence>
     ));
+    expect(queryByTestId("content")).toBeNull();
     setPresent(true);
     await Promise.resolve();
-    const el = queryByTestId("content");
-    expect(el).toBeTruthy();
+    expect(queryByTestId("content")).toBeTruthy();
   });
 
-  it("keeps children mounted with forceMount", () => {
+  it("unmounts children when present transitions true→false", async () => {
+    const [present, setPresent] = createSignal(true);
+    const { queryByTestId } = render(() => (
+      <Presence present={present()}>
+        <div data-testid="content">hello</div>
+      </Presence>
+    ));
+    expect(queryByTestId("content")).toBeTruthy();
+    setPresent(false);
+    await Promise.resolve();
+    expect(queryByTestId("content")).toBeNull();
+  });
+
+  it("keeps children mounted with forceMount when present is false", () => {
     const { getByTestId } = render(() => (
       <Presence present={false} forceMount>
         <div data-testid="content">hello</div>
@@ -43,4 +56,41 @@ describe("Presence", () => {
     ));
     expect(getByTestId("content")).toBeTruthy();
   });
+
+  it("exposes opening signal via children-as-function", async () => {
+    const [present, setPresent] = createSignal(false);
+    let capturedOpening = false;
+
+    render(() => (
+      <Presence present={present()}>
+        {({ opening }) => {
+          if (opening()) capturedOpening = true;
+          return <div data-testid="content">hello</div>;
+        }}
+      </Presence>
+    ));
+
+    setPresent(true);
+    // opening is true for one microtask after transitioning in
+    await Promise.resolve();
+    expect(capturedOpening).toBe(true);
+  });
+
+  it("exposes closing signal via children-as-function", async () => {
+    const [present, setPresent] = createSignal(true);
+    let capturedClosing = false;
+
+    render(() => (
+      <Presence present={present()} forceMount>
+        {({ closing }) => {
+          if (closing()) capturedClosing = true;
+          return <div data-testid="content">hello</div>;
+        }}
+      </Presence>
+    ));
+
+    setPresent(false);
+    await Promise.resolve();
+    expect(capturedClosing).toBe(true);
+  });
 });