Add output-suffix option to customize output filename suffix

src/command/render/output-tex.ts

@@ -15,6 +15,7 @@ import {
   kKeepTex,
   kOutputExt,
   kOutputFile,
+  kOutputSuffix,
   kTargetFormat,
 } from "../../config/constants.ts";
 import { Format } from "../../config/types.ts";
@@ -61,7 +62,8 @@ export function texToPdfOutputRecipe(
     }`;
   }
 
-  const texStem = texSafeFilename(`${inputStem}${fixupInputName}`);
+  const suffix = format.render[kOutputSuffix] || "";
+  const texStem = texSafeFilename(`${inputStem}${suffix}${fixupInputName}`);
 
   // calculate output and args for pandoc (this is an intermediate file
   // which we will then compile to a pdf and rename to .tex)

src/command/render/output-typst.ts

@@ -12,6 +12,7 @@ import {
   kKeepTyp,
   kOutputExt,
   kOutputFile,
+  kOutputSuffix,
   kVariant,
 } from "../../config/constants.ts";
 import { Format } from "../../config/types.ts";
@@ -45,7 +46,8 @@ export function typstPdfOutputRecipe(
   // calculate output and args for pandoc (this is an intermediate file
   // which we will then compile to a pdf and rename to .typ)
   const [inputDir, inputStem] = dirAndStem(input);
-  const output = inputStem + ".typ";
+  const suffix = format.render[kOutputSuffix] || "";
+  const output = inputStem + suffix + ".typ";
   let args = options.pandocArgs || [];
   const pandoc = { ...format.pandoc };
   if (options.flags?.output) {
@@ -62,7 +64,7 @@ export function typstPdfOutputRecipe(
 
     // run typst
     await validateRequiredTypstVersion();
-    const pdfOutput = join(inputDir, inputStem + ".pdf");
+    const pdfOutput = join(inputDir, inputStem + suffix + ".pdf");
     const typstOptions: TypstCompileOptions = {
       quiet: options.flags?.quiet,
       fontPaths: asArray(format.metadata?.[kFontPaths]) as string[],
@@ -111,7 +113,7 @@ export function typstPdfOutputRecipe(
     ? finalOutput === kStdOut
       ? undefined
       : normalizeOutputPath(input, finalOutput)
-    : normalizeOutputPath(input, join(inputDir, inputStem + ".pdf"));
+    : normalizeOutputPath(input, join(inputDir, inputStem + suffix + ".pdf"));
 
   // return recipe
   const recipe: OutputRecipe = {

src/command/render/output.ts

@@ -25,6 +25,7 @@ import {
 import {
   kOutputExt,
   kOutputFile,
+  kOutputSuffix,
   kPreserveYaml,
   kVariant,
 } from "../../config/constants.ts";
@@ -184,18 +185,21 @@ export function outputRecipe(
     const deriveAutoOutput = () => {
       // no output specified: derive an output path from the extension
 
+      // Get the suffix if specified
+      const suffix = format.render[kOutputSuffix] || "";
+
       // derive new output file
-      let output = inputStem + "." + ext;
+      let output = `${inputStem}${suffix}.${ext}`;
       // special case for .md to .md, need to append the writer to create a
       // non-conflicting filename
       if (extname(input) === ".md" && ext === "md") {
-        output = `${inputStem}-${format.identifier["base-format"]}.md`;
+        output = `${inputStem}${suffix}-${format.identifier["base-format"]}.md`;
       }
 
       // special case if the source will overwrite the destination (note: this
       // behavior can be customized with a custom output-ext)
       if (output === basename(context.target.source)) {
-        output = inputStem + `.${kOutExt}.` + ext;
+        output = `${inputStem}${suffix}.${kOutExt}.${ext}`;
       }
 
       // assign output

src/command/render/render-contexts.ts

@@ -49,6 +49,7 @@ import {
   kMetadataFormat,
   kOutputExt,
   kOutputFile,
+  kOutputSuffix,
   kServer,
   kTargetFormat,
   kWarning,
@@ -330,7 +331,8 @@ export async function renderFormats(
     // resolve output-file
     if (!format.pandoc[kOutputFile]) {
       const [_dir, stem] = dirAndStem(file);
-      format.pandoc[kOutputFile] = `${stem}.${format.render[kOutputExt]}`;
+      const suffix = format.render[kOutputSuffix] || "";
+      format.pandoc[kOutputFile] = `${stem}${suffix}.${format.render[kOutputExt]}`;
     }
     // provide engine
     format.execute[kEngine] = context.engine.name;

src/config/constants.ts

@@ -90,6 +90,7 @@ export const kKeepIpynb = "keep-ipynb";
 export const kKeepSource = "keep-source";
 export const kVariant = "variant";
 export const kOutputExt = "output-ext";
+export const kOutputSuffix = "output-suffix";
 export const kOutputDivs = "output-divs";
 export const kPageWidth = "page-width";
 export const kFigAlign = "fig-align";
@@ -191,6 +192,7 @@ export const kRenderDefaultsKeys = [
   kClearHiddenClasses,
   kVariant,
   kOutputExt,
+  kOutputSuffix,
   kOutputDivs,
   kPreferHtml,
   kPageWidth,

src/config/types.ts

@@ -172,6 +172,7 @@ import {
   kOutputDivs,
   kOutputExt,
   kOutputFile,
+  kOutputSuffix,
   kPageWidth,
   kPdfEngine,
   kPdfEngineOpt,
@@ -469,6 +470,7 @@ export interface FormatRender {
   [kOutputDivs]?: boolean;
   [kVariant]?: string;
   [kOutputExt]?: string;
+  [kOutputSuffix]?: string;
   [kPageWidth]?: number;
   [kFigAlign]?: "left" | "right" | "center" | "default";
   [kFigPos]?: string | null;

src/core/render.ts

@@ -4,7 +4,7 @@
  * Copyright (C) 2020-2022 Posit Software, PBC
  */
 
-import { kOutputExt, kOutputFile, kServer } from "../config/constants.ts";
+import { kOutputExt, kOutputFile, kOutputSuffix, kServer } from "../config/constants.ts";
 import { Format, Metadata } from "../config/types.ts";
 import { kJupyterEngine, kKnitrEngine } from "../execute/types.ts";
 import { dirAndStem } from "./path.ts";
@@ -47,6 +47,19 @@ export function isServerShinyKnitr(
 export function formatOutputFile(format: Format) {
   let outputFile = format.pandoc[kOutputFile];
   if (outputFile) {
+    // Apply output-suffix if specified (insert before extension)
+    const suffix = format.render[kOutputSuffix];
+    if (suffix) {
+      const ext = extname(outputFile);
+      if (ext) {
+        const stem = outputFile.slice(0, -ext.length);
+        outputFile = `${stem}${suffix}${ext}`;
+      } else {
+        // No extension, just append suffix
+        outputFile = `${outputFile}${suffix}`;
+      }
+    }
+
     if (format.render[kOutputExt]) {
       // Don't append the output extension if the same output
       // extension is already present. If you update this logic,

src/resources/schema/document-render.yml

@@ -18,6 +18,13 @@
   description: |
     Extension to use for generated output file
 
+- name: output-suffix
+  schema: string
+  description: |
+    Suffix to append to the output filename stem (before the extension).
+    For example, with `output-suffix: "-slides"`, `presentation.qmd` 
+    becomes `presentation-slides.html`.
+
 - name: template
   disabled: [$office-all, ipynb]
   schema: path

tests/docs/smoke-all/2026/01/10/13111-output-suffix.qmd

@@ -0,0 +1,21 @@
+---
+title: "Output Suffix Test"
+format:
+  html:
+    output-suffix: "-readable"
+  revealjs:
+    output-suffix: "-slides"
+---
+
+# Test Document
+
+This document tests the `output-suffix` feature.
+
+## Purpose
+
+When rendered with `output-suffix: "-readable"`, this file should produce:
+- `13111-output-suffix-readable.html` (from HTML format)
+- `13111-output-suffix-slides.html` (from RevealJS format)
+
+This addresses GitHub issue #13111 where using compound extensions like
+`.onepage.html` in `output-ext` caused double-extension bugs.