Fill placeholders when a template is inserted

Templates were a fixed subject and body, so anything that changed per
message -- who it is going to, today's date -- had to be typed over
afterwards.

Eight names are recognised: recipientName, recipientFirstName,
recipientEmail, myName, myEmail, subject, date and time. Dates and times
go through datetime.ts rather than toLocaleDateString, so a template
follows the date order and clock the app was already told to use.

Filling happens on insert rather than on send. What a placeholder came to
is then visible in the composer and can be edited, instead of the message
changing between writing it and sending it.

Two things are deliberately left alone. A placeholder that cannot be
answered yet -- a recipient's name on a draft nobody has addressed -- stays
in the body as written, because substituting an empty string produces
"Hi ,", which is wrong rather than visibly unfinished; leaving the name
says which word is still missing and can be typed over. And a name that is
not a placeholder is left as written too, since a body that quietly ate an
unrecognised token would be worse than one that shows it.

Values are escaped on the way into HTML: a display name comes from a
contact card or a typed address and is not trusted markup.

web/src/lib/__tests__/templatePlaceholders.test.ts

@@ -0,0 +1,80 @@
+import { describe, expect, it } from "vitest";
+import { fillPlaceholders, PLACEHOLDER_NAMES, type PlaceholderContext } from "@/lib/templatePlaceholders";
+
+const AT = new Date("2026-03-04T15:07:00Z");
+
+function ctx(over: Partial<PlaceholderContext> = {}): PlaceholderContext {
+  return {
+    to: [{ name: "Ada Lovelace", email: "[email protected]" }],
+    from: { name: "Grace Hopper", email: "[email protected]" },
+    subject: "Quarterly report",
+    now: AT,
+    ...over,
+  };
+}
+
+describe("fillPlaceholders", () => {
+  it("fills the names it knows", () => {
+    expect(fillPlaceholders("Hi {{recipientFirstName}},", ctx(), { html: true })).toBe("Hi Ada,");
+    expect(fillPlaceholders("{{recipientName}} <{{recipientEmail}}>", ctx(), { html: false })).toBe("Ada Lovelace <[email protected]>");
+    expect(fillPlaceholders("-- {{myName}}", ctx(), { html: true })).toBe("-- Grace Hopper");
+    expect(fillPlaceholders("Re: {{subject}}", ctx(), { html: false })).toBe("Re: Quarterly report");
+  });
+
+  it("tolerates spaces inside the braces but not a different case", () => {
+    expect(fillPlaceholders("{{ myEmail }}", ctx(), { html: false })).toBe("[email protected]");
+    expect(fillPlaceholders("{{MyEmail}}", ctx(), { html: false })).toBe("{{MyEmail}}");
+  });
+
+  it("leaves a placeholder it cannot answer exactly as written", () => {
+    // The case the design is about: a template inserted before the message is
+    // addressed. "Hi ," would be wrong; "Hi {{recipientFirstName}}," is unfinished.
+    const unaddressed = ctx({ to: [] });
+    expect(fillPlaceholders("Hi {{recipientFirstName}},", unaddressed, { html: true })).toBe("Hi {{recipientFirstName}},");
+    expect(fillPlaceholders("{{recipientEmail}}", unaddressed, { html: false })).toBe("{{recipientEmail}}");
+    expect(fillPlaceholders("{{myName}}", ctx({ from: null }), { html: false })).toBe("{{myName}}");
+  });
+
+  it("leaves a name it does not know alone rather than eating it", () => {
+    expect(fillPlaceholders("{{nonsense}} {{}} {{ }}", ctx(), { html: true })).toBe("{{nonsense}} {{}} {{ }}");
+  });
+
+  it("falls back to the local part when a recipient has no name", () => {
+    const c = ctx({ to: [{ name: null, email: "[email protected]" }] });
+    expect(fillPlaceholders("{{recipientName}}", c, { html: false })).toBe("ada.lovelace");
+    expect(fillPlaceholders("{{recipientFirstName}}", c, { html: false })).toBe("ada.lovelace");
+  });
+
+  it("escapes a substituted value on the way into HTML, and not into a subject", () => {
+    const c = ctx({ to: [{ name: 'Ada <script>alert("x")</script>', email: "[email protected]" }] });
+    expect(fillPlaceholders("{{recipientName}}", c, { html: true })).not.toContain("<script>");
+    expect(fillPlaceholders("{{recipientName}}", c, { html: true })).toContain("&lt;script&gt;");
+    expect(fillPlaceholders("{{recipientName}}", c, { html: false })).toContain("<script>");
+  });
+
+  it("repeats a placeholder as many times as it appears", () => {
+    expect(fillPlaceholders("{{recipientFirstName}} {{recipientFirstName}}", ctx(), { html: true })).toBe("Ada Ada");
+  });
+
+  it("answers date and time from the injected clock", () => {
+    const date = fillPlaceholders("{{date}}", ctx(), { html: false });
+    const time = fillPlaceholders("{{time}}", ctx(), { html: false });
+    expect(date).not.toBe("{{date}}");
+    expect(date).toMatch(/2026/);
+    expect(time).not.toBe("{{time}}");
+    expect(time).toMatch(/\d/);
+  });
+
+  it("names every resolver in the list Settings shows", () => {
+    expect(PLACEHOLDER_NAMES).toEqual([
+      "recipientName",
+      "recipientFirstName",
+      "recipientEmail",
+      "myName",
+      "myEmail",
+      "subject",
+      "date",
+      "time",
+    ]);
+  });
+});

web/src/lib/templatePlaceholders.ts

@@ -0,0 +1,91 @@
+/**
+ * Placeholders in templates, filled at the moment one is inserted.
+ *
+ * Two rules decide the whole design:
+ *
+ *  - **An unresolved placeholder is left exactly as written.** A template
+ *    inserted before the message is addressed cannot know who it is going to,
+ *    and substituting an empty string there produces "Hi ," -- a greeting that
+ *    is wrong rather than unfinished. Leaving `{{recipientName}}` in the body
+ *    says which word is still missing, and it can be typed over. It is also
+ *    what makes inserting a template early a valid thing to do rather than a
+ *    mistake to undo.
+ *  - **A name that is not a placeholder is left alone too.** Templates are
+ *    written by hand and `{{` is not reserved anywhere else, but a body that
+ *    silently ate an unrecognised token would be worse than one that shows it.
+ *
+ * Dates and times go through `datetime.ts` rather than `toLocaleDateString`,
+ * so a template follows the same date order and clock the rest of the app was
+ * told to use.
+ */
+import { escapeHtml } from "./text";
+import { formatDate, formatClock } from "./datetime";
+import type { EmailAddress } from "@/jmap/types";
+
+export interface PlaceholderContext {
+  /** Where the message is addressed, in order; the first is what the singular names refer to. */
+  to: EmailAddress[];
+  /** The identity the draft is sending as. */
+  from: { name?: string | null; email?: string | null } | null;
+  subject: string;
+  /** Injectable so tests do not depend on the clock. */
+  now?: Date;
+}
+
+/**
+ * What each name resolves to, in the order they are shown in Settings.
+ * `null` from a resolver means "cannot be answered yet", which is the case
+ * the rule above is about -- distinct from an empty string, which is an answer.
+ */
+const RESOLVERS: Record<string, (c: PlaceholderContext) => string | null> = {
+  recipientName: (c) => personalName(c.to[0]),
+  recipientFirstName: (c) => {
+    const n = personalName(c.to[0]);
+    return n ? (n.split(/\s+/)[0] ?? null) : null;
+  },
+  recipientEmail: (c) => c.to[0]?.email || null,
+  myName: (c) => c.from?.name?.trim() || null,
+  myEmail: (c) => c.from?.email || null,
+  subject: (c) => c.subject || null,
+  date: (c) => formatDate(c.now ?? new Date()),
+  time: (c) => formatClock(c.now ?? new Date()),
+};
+
+/** The names, for the list shown under the template editor. */
+export const PLACEHOLDER_NAMES = Object.keys(RESOLVERS);
+
+/**
+ * A recipient's human name: what they are called if we know it, otherwise the
+ * local part, which for `firstname.lastname@` is still better than the whole
+ * address in the middle of a sentence. Never the domain.
+ */
+function personalName(a: EmailAddress | undefined): string | null {
+  if (!a) return null;
+  const name = a.name?.trim();
+  if (name) return name;
+  const local = (a.email ?? "").split("@")[0] ?? "";
+  return local || null;
+}
+
+/**
+ * `{{ name }}` tolerates the spaces; the name itself is matched exactly,
+ * because `{{Date}}` meaning `{{date}}` would make the list in Settings a
+ * suggestion rather than the set.
+ */
+const TOKEN = /\{\{\s*([A-Za-z][A-Za-z0-9]*)\s*\}\}/g;
+
+/**
+ * Fill `input`, escaping substituted values when the destination is HTML.
+ * Escaping happens here rather than at the call site because the values come
+ * from contact cards and typed addresses -- a display name is not trusted
+ * markup, and the body it lands in is inserted as HTML.
+ */
+export function fillPlaceholders(input: string, ctx: PlaceholderContext, opts: { html: boolean }): string {
+  return input.replace(TOKEN, (whole, name: string) => {
+    const resolver = RESOLVERS[name];
+    if (!resolver) return whole;
+    const value = resolver(ctx);
+    if (value === null) return whole;
+    return opts.html ? escapeHtml(value) : value;
+  });
+}

web/src/store/compose.ts

@@ -11,6 +11,7 @@ import { ensureScheduledMailbox, useScheduled } from "./scheduled";
 import { formatScheduleTime, holdUntil } from "@/lib/schedule";
 import { t as translate } from "@/lib/i18n";
 import { settings } from "./settings";
+import { fillPlaceholders, type PlaceholderContext } from "@/lib/templatePlaceholders";
 
 export interface ComposeAttachment {
   id: string;
@@ -575,8 +576,17 @@ export const useCompose = create<ComposeState>((set, get) => ({
   insertTemplate(key, html, subject) {
     const d = get().drafts.find((x) => x.key === key);
     if (!d) return;
-    const patch: Partial<Draft> = { html: `<div>${sanitizeEditorHtml(html)}</div>${d.html}`, text: `${htmlToText(html)}\n${d.text}` };
-    if (subject && !d.subject) patch.subject = subject;
+    // Placeholders are filled against the draft as it stands right now, which
+    // is why this happens on insert rather than on send: what the template is
+    // filled with is visible and editable afterwards, instead of changing
+    // under the message between writing it and sending it.
+    const ident = d.identityId ? useMail.getState().identities.find((i) => i.id === d.identityId) : undefined;
+    const ctx: PlaceholderContext = { to: d.to, from: ident ? { name: ident.name, email: ident.email } : null, subject: d.subject };
+    // The body is filled once as HTML and the plain-text side derived from the
+    // result, so the two cannot disagree about what a placeholder came to.
+    const filled = fillPlaceholders(html, ctx, { html: true });
+    const patch: Partial<Draft> = { html: `<div>${sanitizeEditorHtml(filled)}</div>${d.html}`, text: `${htmlToText(filled)}\n${d.text}` };
+    if (subject && !d.subject) patch.subject = fillPlaceholders(subject, ctx, { html: false });
     get().update(key, patch);
   },
 }));

web/src/styles/app.css

@@ -1376,3 +1376,8 @@ button.dp-open:disabled { cursor: default; opacity: .5; }
 .composer-field label .link-btn { background: none; border: 0; padding: 0; font: inherit; color: inherit; cursor: pointer; text-decoration: underline; text-decoration-style: dotted; text-underline-offset: 3px; }
 .composer-field label .link-btn:hover { color: var(--accent); }
 .composer-field label .link-btn:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; border-radius: 3px; }
+
+/* The placeholder reference under a template's body. */
+.placeholder-list { display: grid; grid-template-columns: auto 1fr; gap: 4px 12px; align-items: baseline; }
+.placeholder-row { display: contents; }
+.placeholder-list code { font-family: var(--font-mono); font-size: 12.5px; background: var(--bg-sunken); border: 1px solid var(--border); border-radius: 4px; padding: .1em .4em; white-space: nowrap; }

web/src/views/settings/TemplatesSettings.tsx

@@ -5,6 +5,7 @@ import { Dialog } from "@/ui/dialog";
 import { RichEditor } from "../compose/RichEditor";
 import { htmlToText } from "@/lib/text";
 import { t as translate } from "@/lib/i18n";
+import { PLACEHOLDER_NAMES } from "@/lib/templatePlaceholders";
 
 export function TemplatesSettings() {
   const templates = useSettings((s) => s.settings.templates);
@@ -37,8 +38,48 @@ export function TemplatesSettings() {
               <RichEditor html={editing.html} onChange={(html) => setEditing({ ...editing, html })} showToolbar placeholder={translate("Template text…")} />
             </div>
           </div>
+          <PlaceholderReference />
         </Dialog>
       )}
     </div>
   );
 }
+
+/**
+ * What each placeholder answers, shown under the body so the names are
+ * discoverable without documentation. Rendered from `PLACEHOLDER_NAMES` rather
+ * than from this map, so a name added to the lib and forgotten here appears
+ * with no description instead of quietly not appearing at all.
+ */
+function placeholderHint(name: string): string {
+  switch (name) {
+    case "recipientName": return translate("Who the message is addressed to");
+    case "recipientFirstName": return translate("Their first name alone");
+    case "recipientEmail": return translate("Their address");
+    case "myName": return translate("The name on the identity you are sending as");
+    case "myEmail": return translate("That identity's address");
+    case "subject": return translate("The subject already on the message");
+    case "date": return translate("Today, in your date format");
+    case "time": return translate("Now, on your clock");
+    default: return "";
+  }
+}
+
+function PlaceholderReference() {
+  return (
+    <div className="field">
+      <label>{translate("Placeholders")}</label>
+      <div className="placeholder-list">
+        {PLACEHOLDER_NAMES.map((name) => (
+          <div key={name} className="placeholder-row">
+            <code>{`{{${name}}}`}</code>
+            <span className="hint">{placeholderHint(name)}</span>
+          </div>
+        ))}
+      </div>
+      <p className="hint">
+        {translate("Filled in when the template is inserted, so you can edit the result before sending. One that cannot be answered yet — a recipient's name on a message you have not addressed — is left in the body as written, rather than becoming a blank.")}
+      </p>
+    </div>
+  );
+}