From 7ba56c24800f56643d406448e1551c575cae1e58 Mon Sep 17 00:00:00 2001
From: Claire-ovo <132752951+Claire-ovo@users.noreply.github.com>
Date: Tue, 27 Oct 2026 18:48:26 +0800
Subject: [PATCH] fix: isolate processor caches by plugin function identity

---
 .changeset/quiet-plugins-render.md            |  5 ++
 .../__tests__/plugin-cache.test.tsx           | 89 +++++++++++++++++++
 packages/streamdown/lib/markdown.ts           | 32 +++----
 3 files changed, 111 insertions(+), 15 deletions(-)
 create mode 100644 .changeset/quiet-plugins-render.md
 create mode 100644 packages/streamdown/__tests__/plugin-cache.test.tsx

diff --git a/.changeset/quiet-plugins-render.md b/.changeset/quiet-plugins-render.md
new file mode 100644
index 000000000..5ada25f2f
--- /dev/null
+++ b/.changeset/quiet-plugins-render.md
@@ -0,0 +1,5 @@
+---
+"streamdown": patch
+---
+
+Distinguish remark and rehype plugins by function identity when caching processors, so same-name plugins with different closures do not reuse each other's behavior.
diff --git a/packages/streamdown/__tests__/plugin-cache.test.tsx b/packages/streamdown/__tests__/plugin-cache.test.tsx
new file mode 100644
index 000000000..ccaf70244
--- /dev/null
+++ b/packages/streamdown/__tests__/plugin-cache.test.tsx
@@ -0,0 +1,89 @@
+import { render } from "@testing-library/react";
+import type { Root } from "hast";
+import type { PluggableList, Plugin } from "unified";
+import { visit } from "unist-util-visit";
+import { describe, expect, it } from "vitest";
+import { Streamdown } from "../index";
+import { Markdown } from "../lib/markdown";
+
+const createPlugin = (value: string): Plugin<[{ suffix?: string }?], Root> =>
+  function replaceText(options) {
+    return (tree) => {
+      visit(tree, "text", (node) => {
+        node.value = value + (options?.suffix ?? "");
+      });
+    };
+  };
+
+describe("processor plugin identity", () => {
+  for (const stage of ["remarkPlugins", "rehypePlugins"] as const) {
+    for (const tuple of [false, true]) {
+      it(`isolates same-name ${stage} with tuple=${tuple}`, () => {
+        const first = createPlugin("first");
+        const second = createPlugin("second");
+        expect(first.name).toBe(second.name);
+        const plugins = (plugin: typeof first): PluggableList =>
+          tuple ? [[plugin, { suffix: "!" }]] : [plugin];
+        const { container, rerender } = render(
+          <Markdown {...{ [stage]: plugins(first) }}>input</Markdown>
+        );
+        expect(container.textContent).toBe(tuple ? "first!" : "first");
+        rerender(<Markdown {...{ [stage]: plugins(second) }}>input</Markdown>);
+        expect(container.textContent).toBe(tuple ? "second!" : "second");
+        rerender(<Markdown {...{ [stage]: plugins(first) }}>input</Markdown>);
+        expect(container.textContent).toBe(tuple ? "first!" : "first");
+      });
+    }
+  }
+
+  it("reuses the same function across new plugin arrays", () => {
+    let setups = 0;
+    const plugin: Plugin = () => {
+      setups += 1;
+    };
+    const { rerender } = render(
+      <Markdown remarkPlugins={[plugin]}>first</Markdown>
+    );
+    rerender(<Markdown remarkPlugins={[plugin]}>second</Markdown>);
+    expect(setups).toBe(1);
+  });
+
+  it("keeps options distinct for the same function", () => {
+    const plugin = createPlugin("text");
+    const { container, rerender } = render(
+      <Markdown remarkPlugins={[[plugin, { suffix: "1" }]]}>input</Markdown>
+    );
+    expect(container.textContent).toBe("text1");
+    rerender(
+      <Markdown remarkPlugins={[[plugin, { suffix: "2" }]]}>input</Markdown>
+    );
+    expect(container.textContent).toBe("text2");
+  });
+
+  for (const mode of ["static", "streaming"] as const) {
+    it(`isolates simultaneous Streamdown instances in ${mode} mode`, () => {
+      const first = createPlugin("left");
+      const second = createPlugin("right");
+      const { container } = render(
+        <>
+          <section data-testid="left">
+            <Streamdown mode={mode} remarkPlugins={[first]}>
+              input
+            </Streamdown>
+          </section>
+          <section data-testid="right">
+            <Streamdown mode={mode} remarkPlugins={[second]}>
+              input
+            </Streamdown>
+          </section>
+        </>
+      );
+      expect(container.querySelector('[data-testid="left"]')?.textContent).toBe(
+        "left"
+      );
+      expect(
+        container.querySelector('[data-testid="right"]')?.textContent
+      ).toBe("right");
+    });
+  }
+});
diff --git a/packages/streamdown/lib/markdown.ts b/packages/streamdown/lib/markdown.ts
index a6d4a610f..f15843ce4 100644
--- a/packages/streamdown/lib/markdown.ts
+++ b/packages/streamdown/lib/markdown.ts
@@ -58,9 +58,22 @@ export interface Options {
 const EMPTY_PLUGINS: PluggableList = [];
 const DEFAULT_REMARK_REHYPE_OPTIONS = { allowDangerousHtml: true };
 
-// Plugin name cache for faster serialization
+// Function names do not distinguish closures or minified plugins.
 // biome-ignore lint/complexity/noBannedTypes: "Need Function type for plugin caching"
-const pluginNameCache = new WeakMap<Function, string>();
+const pluginIds = new WeakMap<Function, number>();
+let nextPluginId = 0;
+
+// biome-ignore lint/complexity/noBannedTypes: "Need Function type for plugin caching"
+const getPluginId = (plugin: Function): number => {
+  const cached = pluginIds.get(plugin);
+  if (cached !== undefined) {
+    return cached;
+  }
+  const id = nextPluginId;
+  nextPluginId += 1;
+  pluginIds.set(plugin, id);
+  return id;
+};
 
 // LRU Cache for unified processors
 class ProcessorCache {
@@ -88,7 +101,6 @@ class ProcessorCache {
     }
 
     // Optimize serialization for plugins
-    // biome-ignore lint/complexity/noExcessiveCognitiveComplexity: "Plugin serialization requires checking multiple plugin formats"
     const serializePlugins = (plugins: PluggableList | undefined): string => {
       if (!plugins || plugins.length === 0) {
         return "";
@@ -105,12 +117,7 @@ class ProcessorCache {
           // Plugin with options: [plugin, options]
           const [pluginFn, pluginOptions] = plugin;
           if (typeof pluginFn === "function") {
-            let name = pluginNameCache.get(pluginFn);
-            if (!name) {
-              name = pluginFn.name;
-              pluginNameCache.set(pluginFn, name);
-            }
-            result += name;
+            result += getPluginId(pluginFn);
           } else {
             result += String(pluginFn);
           }
@@ -118,12 +125,7 @@ class ProcessorCache {
           result += JSON.stringify(pluginOptions);
         } else if (typeof plugin === "function") {
           // Plugin without options
-          let name = pluginNameCache.get(plugin);
-          if (!name) {
-            name = plugin.name;
-            pluginNameCache.set(plugin, name);
-          }
-          result += name;
+          result += getPluginId(plugin);
         } else {
           result += String(plugin);
         }