From 83026fe621ddc1f80e8f2ff0a8850d1ec3416d46 Mon Sep 17 00:00:00 2001
From: Linus Rath <139418639+rathlinus@users.noreply.github.com>
Date: Sun, 16 Aug 2026 22:20:49 +0200
Subject: [PATCH] fix: keep already written text when applying a template in
 compose #540

---
 components/email/email-composer.tsx   | 40 ++++++++++++++++++++++-----
 lib/__tests__/signature-utils.test.ts | 31 +++++++++++++++++++++
 lib/__tests__/template-utils.test.ts  | 37 +++++++++++++++++++++++++
 lib/signature-utils.ts                | 23 +++++++++++++++
 lib/template-utils.ts                 | 38 +++++++++++++++++++++++--
 5 files changed, 160 insertions(+), 9 deletions(-)

diff --git a/components/email/email-composer.tsx b/components/email/email-composer.tsx
index 3396e106e..d808aff6d 100644
--- a/components/email/email-composer.tsx
+++ b/components/email/email-composer.tsx
@@ -31,11 +31,11 @@ import { useContactStore, getContactDisplayName, getContactPrimaryEmail } from "
 import { useTemplateStore } from "@/stores/template-store";
 import { SubAddressHelper } from "@/components/identity/sub-address-helper";
 import { generateSubAddress } from "@/lib/sub-addressing";
-import { substitutePlaceholders, spliceTemplateAboveSignature } from "@/lib/template-utils";
+import { substitutePlaceholders, spliceTemplateAboveSignature, composeBodyHasUserContent } from "@/lib/template-utils";
 import { TemplatePicker } from "@/components/templates/template-picker";
 import { TemplateForm } from "@/components/templates/template-form";
 import type { EmailTemplate } from "@/lib/template-types";
-import { appendPlainTextSignature, getPlainTextSignature, plainTextBodyHasSignature } from "@/lib/signature-utils";
+import { appendPlainTextSignature, getPlainTextSignature, plainTextBodyHasSignature, plainTextBodyWithoutSignature } from "@/lib/signature-utils";
 import { findComposeIdentityId, findDraftIdentityId, resolveReplyFrom } from "@/lib/reply-identity";
 import { buildReplyRecipients, isSelfSent } from "@/lib/reply-recipients";
 import { computeReplyThreadingHeaders } from "@/lib/email-threading";
@@ -1199,18 +1199,44 @@ export function EmailComposer({
       : `<p>${filledBody.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;').replace(/\n/g, '<br>')}</p>`;
 
     if (mode === 'compose') {
-      setSubject(filledSubject);
+      // An empty template subject must not wipe one the user typed (#540).
+      if (filledSubject) {
+        setSubject(filledSubject);
+      }
       // Compose bodies carry the embedded signature (see
       // shouldEmbedSignatureInNewMail) and the send path assumes it stays
       // there, so replace only the message content, not the signature block.
       // Keyed on the previous body rather than the mode: a re-opened draft is
       // in compose mode too but carries its own signature (#823).
+      // Once the user has written something, the template is inserted at the
+      // caret instead of replacing that text, as in reply/forward mode (#540).
       if (plainTextMode) {
-        setBody((prev) => plainTextBodyHasSignature(prev, signatureIdentity)
-          ? appendPlainTextSignature(bodyContent, signatureIdentity, { separator: signatureSeparatorEnabled })
-          : bodyContent);
+        const textarea = bodyRef.current;
+        const hasUserText = !!textarea
+          && plainTextBodyWithoutSignature(textarea.value, signatureIdentity).trim().length > 0;
+        if (hasUserText && textarea) {
+          const start = textarea.selectionStart ?? textarea.value.length;
+          const end = textarea.selectionEnd ?? start;
+          setBody((prev) => prev.slice(0, start) + bodyContent + prev.slice(end));
+          requestAnimationFrame(() => {
+            const caret = start + bodyContent.length;
+            textarea.focus();
+            textarea.setSelectionRange(caret, caret);
+          });
+        } else {
+          setBody((prev) => plainTextBodyHasSignature(prev, signatureIdentity)
+            ? appendPlainTextSignature(bodyContent, signatureIdentity, { separator: signatureSeparatorEnabled })
+            : bodyContent);
+        }
       } else {
-        setBody((prev) => spliceTemplateAboveSignature(prev, bodyContent));
+        const editor = editorRef.current;
+        // serializeEditorContent (not getHTML) so the check sees the same
+        // markup the body state holds.
+        if (editor && composeBodyHasUserContent(serializeEditorContent(editor))) {
+          editor.chain().focus().insertContent(bodyContent).run();
+        } else {
+          setBody((prev) => spliceTemplateAboveSignature(prev, bodyContent));
+        }
       }
       if (template.defaultRecipients?.to?.length) {
         setTo(template.defaultRecipients.to.map(parseRecipient));
diff --git a/lib/__tests__/signature-utils.test.ts b/lib/__tests__/signature-utils.test.ts
index 878d6c0ad..795e57419 100644
--- a/lib/__tests__/signature-utils.test.ts
+++ b/lib/__tests__/signature-utils.test.ts
@@ -6,6 +6,7 @@ import {
   getPlainTextSignature,
   hasMeaningfulHtmlBody,
   plainTextBodyHasSignature,
+  plainTextBodyWithoutSignature,
 } from '../signature-utils';
 
 describe('signature-utils', () => {
@@ -55,6 +56,36 @@ describe('signature-utils', () => {
     });
   });
 
+  describe('plainTextBodyWithoutSignature', () => {
+    const identity = { textSignature: 'Regards,\nAlice' };
+
+    it('returns nothing for a body that is only the signature (#540)', () => {
+      expect(plainTextBodyWithoutSignature(appendPlainTextSignature('', identity), identity)).toBe('');
+    });
+
+    it('returns the text the user typed above the signature', () => {
+      expect(plainTextBodyWithoutSignature(appendPlainTextSignature('Hello Mr.', identity), identity)).toBe('Hello Mr.');
+    });
+
+    it('strips the signature after a CRLF round-trip', () => {
+      const saved = appendPlainTextSignature('Hello Mr.', identity).replace(/\n/g, '\r\n');
+      expect(plainTextBodyWithoutSignature(saved, identity)).toBe('Hello Mr.');
+    });
+
+    it('handles a body written without the "-- " separator', () => {
+      const saved = appendPlainTextSignature('Hello Mr.', identity, { separator: false });
+      expect(plainTextBodyWithoutSignature(saved, identity)).toBe('Hello Mr.');
+    });
+
+    it('leaves a body that does not end with the signature untouched', () => {
+      expect(plainTextBodyWithoutSignature('Hello Mr.', identity)).toBe('Hello Mr.');
+    });
+
+    it('leaves the body untouched when the identity has no signature', () => {
+      expect(plainTextBodyWithoutSignature('Hello Mr.', {})).toBe('Hello Mr.');
+    });
+  });
+
   describe('appendHtmlSignature', () => {
     it('appends a sanitized html signature, preserving formatting', () => {
       expect(appendHtmlSignature('<div>Hello</div>', { htmlSignature: '<strong>Alice</strong>' }))
diff --git a/lib/__tests__/template-utils.test.ts b/lib/__tests__/template-utils.test.ts
index 32162a182..16404ade4 100644
--- a/lib/__tests__/template-utils.test.ts
+++ b/lib/__tests__/template-utils.test.ts
@@ -11,6 +11,7 @@ import {
   exportTemplates,
   importTemplates,
   spliceTemplateAboveSignature,
+  composeBodyHasUserContent,
 } from '../template-utils';
 import type { EmailTemplate } from '../template-types';
 
@@ -371,3 +372,39 @@ describe('spliceTemplateAboveSignature', () => {
     expect(result).toContain('Sig');
   });
 });
+
+describe('composeBodyHasUserContent', () => {
+  const signature = '<p data-signature-block="separator">-- </p><div>My signature</div><p data-signature-block="end"></p>';
+
+  it('is false for a fresh compose body (empty paragraph + signature)', () => {
+    expect(composeBodyHasUserContent(`<p></p>${signature}`)).toBe(false);
+  });
+
+  it('is false for an empty body', () => {
+    expect(composeBodyHasUserContent('')).toBe(false);
+    expect(composeBodyHasUserContent('<p></p>')).toBe(false);
+  });
+
+  it('is true once the user typed above the signature (#540)', () => {
+    expect(composeBodyHasUserContent(`<p>Hello Mr.</p>${signature}`)).toBe(true);
+  });
+
+  it('is true for a body without a signature block', () => {
+    expect(composeBodyHasUserContent('<p>Hello Mr.</p>')).toBe(true);
+  });
+
+  it('ignores signature text so a signature-only body stays untouched', () => {
+    expect(composeBodyHasUserContent(`<p></p>${signature}`)).toBe(false);
+    expect(composeBodyHasUserContent(`<p><br></p>${signature}`)).toBe(false);
+  });
+
+  it('counts text-free content such as a pasted image', () => {
+    expect(composeBodyHasUserContent(`<p><img src="cid:1"></p>${signature}`)).toBe(true);
+  });
+
+  it('handles a signature range without an end marker', () => {
+    const openEnded = '<p data-signature-block="start"></p><div>My signature</div>';
+    expect(composeBodyHasUserContent(`<p></p>${openEnded}`)).toBe(false);
+    expect(composeBodyHasUserContent(`<p>Hello Mr.</p>${openEnded}`)).toBe(true);
+  });
+});
diff --git a/lib/signature-utils.ts b/lib/signature-utils.ts
index 330fe45f7..180ae7854 100644
--- a/lib/signature-utils.ts
+++ b/lib/signature-utils.ts
@@ -61,6 +61,29 @@ export function plainTextBodyHasSignature(
   return normalizeSignatureLineBreaks(body).endsWith(plainTextSignature);
 }
 
+/**
+ * The plain-text body with a trailing signature - and the `-- ` separator
+ * line in front of it - removed. Returns the body unchanged when it does not
+ * end with the identity's signature. Used to tell an untouched compose body
+ * (signature only) from one the user has already written into (#540).
+ */
+export function plainTextBodyWithoutSignature(
+  body: string,
+  signature?: SignatureSource | null,
+): string {
+  const plainTextSignature = getPlainTextSignature(signature);
+  if (!plainTextSignature) {
+    return body;
+  }
+  const normalized = normalizeSignatureLineBreaks(body);
+  if (!normalized.endsWith(plainTextSignature)) {
+    return body;
+  }
+  return normalized
+    .slice(0, normalized.length - plainTextSignature.length)
+    .replace(/\n*(?:-- ?)?\n*$/, '');
+}
+
 /**
  * Append a signature to an HTML body, preserving rich formatting. Used by the
  * quick-reply path so an HTML signature keeps its markup instead of being
diff --git a/lib/template-utils.ts b/lib/template-utils.ts
index a4ca6f32d..114fa84b2 100644
--- a/lib/template-utils.ts
+++ b/lib/template-utils.ts
@@ -80,6 +80,9 @@ export function filterTemplates(templates: EmailTemplate[], query: string): Emai
   );
 }
 
+const SIGNATURE_START_SELECTOR = '[data-signature-block="separator"], [data-signature-block="start"]';
+const SIGNATURE_END_SELECTOR = '[data-signature-block="end"]';
+
 // Compose bodies carry the embedded signature bracketed by
 // data-signature-block markers (see email-composer's
 // buildEmbeddedSignatureHtml). Applying a template must replace only the
@@ -87,9 +90,9 @@ export function filterTemplates(templates: EmailTemplate[], query: string): Emai
 // of overwriting the whole body.
 export function spliceTemplateAboveSignature(prevHtml: string, templateHtml: string): string {
   const doc = new DOMParser().parseFromString(prevHtml, 'text/html');
-  const startEl = doc.querySelector('[data-signature-block="separator"], [data-signature-block="start"]');
+  const startEl = doc.querySelector(SIGNATURE_START_SELECTOR);
   if (!startEl) return templateHtml;
-  const endEl = doc.querySelector('[data-signature-block="end"]');
+  const endEl = doc.querySelector(SIGNATURE_END_SELECTOR);
   const host = doc.createElement('div');
   let cursor: Node | null = startEl;
   while (cursor) {
@@ -100,6 +103,37 @@ export function spliceTemplateAboveSignature(prevHtml: string, templateHtml: str
   return templateHtml + host.innerHTML;
 }
 
+/**
+ * Whether a compose body holds anything the user wrote above the embedded
+ * signature. A fresh compose body is just an empty paragraph plus the
+ * signature range, so this stays false until the user types something -
+ * the composer then inserts the template at the caret rather than splicing
+ * it over the draft (#540).
+ */
+export function composeBodyHasUserContent(prevHtml: string): boolean {
+  if (!prevHtml.trim()) return false;
+
+  const doc = new DOMParser().parseFromString(prevHtml, 'text/html');
+  const startEl = doc.querySelector(SIGNATURE_START_SELECTOR);
+  if (startEl) {
+    // Drop the signature range [start … end] inclusive, mirroring the
+    // traversal spliceTemplateAboveSignature uses to keep it.
+    const endEl = doc.querySelector(SIGNATURE_END_SELECTOR);
+    let cursor: Node | null = startEl;
+    while (cursor) {
+      const next: Node | null = cursor.nextSibling;
+      const isEnd = cursor === endEl;
+      cursor.parentNode?.removeChild(cursor);
+      if (isEnd) break;
+      cursor = next;
+    }
+  }
+
+  if (doc.body.textContent?.trim()) return true;
+  // Text-free content still counts as a draft worth keeping.
+  return doc.body.querySelector('img, table, hr, [data-quoted-html]') !== null;
+}
+
 function sanitizeText(value: unknown): string {
   return DOMPurify.sanitize(String(value || ''), STRIP_HTML_CONFIG);
 }