Support modifying output files names in post render script

[cderv]

Post render script is ran as part of renderProject

quarto-cli/src/command/render/project.ts

Lines 857 to 858 in 7483c62

	// run post-render if this isn't incremental
	if (postRenderScripts.length) {

post render does allow access to output files

quarto-cli/src/command/render/project.ts

Lines 876 to 878 in 7483c62

	env.QUARTO_PROJECT_OUTPUT_FILES = outputFiles
	.map((outputFile) => relative(projDir, outputFile.file))
	.join("\n");

This post render step is done before other steps that use the output files

quarto-cli/src/command/preview/cmd.ts

Lines 360 to 371 in 7483c62

	const renderResult = await renderProject(project, {
	services,
	progress: false,
	useFreezer: false,
	flags,
	pandocArgs: args,
	previewServer: true,
	}, [file]);
	if (renderResult.error) {
	throw renderResult.error;
	}
	handleRenderResult(file, renderResult);

This is specifically the compute of finalOutput that fails

quarto-cli/src/command/preview/preview.ts

Lines 394 to 398 in 7483c62

	// print output created
	const finalOutput = renderResultFinalOutput(
	renderResult,
	dirname(file),
	);

It could happen that the output file's name is modified by the post render step. However, there is no mechanism to pass back this information for the rest of the process.

I see to choice here:

• Either supporting passing back information of modification

  • For example, QUARTO_PROJECT_OUTPUT_FILES or QUARTO_USE_FILE_FOR_PROJECT_OUTPUT_FILES with a modified by post render script, and read that for new output files

• Either document that this should not happen in post render script or quarto preview won't work.

For render, the final output is also computed, but if no found based on input name, it will just show nothing and not error like in preview

quarto-cli/src/command/render/cmd.ts

Lines 269 to 286 in 7483c62

	if (renderResult && renderResultInput) {
	// report output created
	if (!options.flags?.quiet && options.flags?.output !== kStdOut) {
	const finalOutput = renderResultFinalOutput(
	renderResult,
	Deno.statSync(renderResultInput).isDirectory
	? renderResultInput
	: dirname(renderResultInput),
	);
	if (finalOutput) {
	info("Output created: " + finalOutput + "\n");
	}
	if (renderResult) {
	renderResult.context.cleanup();
	}
	}

The real issue is the error at

quarto-cli/src/command/preview/preview.ts

Lines 399 to 401 in 7483c62

	if (!finalOutput) {
	throw new Error("No output created by quarto render " + basename(file));
	}

leading to

ERROR: No output created by quarto render 02_filtering.qmd

Stack trace:
    at handleRenderResult (file:///Applications/RStudio.app/Contents/Resources/app/quarto/bin/quarto.js:91527:15)
    at renderForPreview (file:///Applications/RStudio.app/Contents/Resources/app/quarto/bin/quarto.js:91543:25)
    at eventLoopTick (ext:core/01_core.js:175:7)
    at async render (file:///Applications/RStudio.app/Contents/Resources/app/quarto/bin/quarto.js:91416:29)
GET: /Analysis/02_filtering.html (404: Not Found)

when post render modify the name of 02_filtering.html

Maybe not erroring and just previewing the base url (for index.html as a fallback) is better 🤷‍♂

Use case: Using post render script to rename output file was given as workaround to support adding date to output file name. See

• How can I make append the current date to the PDF's file name? #10732
• quarto preview does not work but quarto render works fine. #13052

[cderv]

Reprex about the use case by @AlbertoFabbri93 is from #10732 (reply in thread)

---

Sorry for the lack of details, here is the repro:

_quarto.yml:

project:
  title: "test_datastamp"
  post-render: ./datestamp_output_file.R

test_datastamp.qmd:

---
title: "test_datastamp"
---

## Quarto

To learn more about Quarto see <https://quarto.org>.

```{r}
1 + 1
```

datestamp_output_file.R:

output_file <- Sys.getenv("QUARTO_PROJECT_OUTPUT_FILES")

file.rename(
  output_file,
  paste0(
    tools::file_path_sans_ext(output_file),
    format(Sys.time(), '-%Y-%m-%d'),
    '.',
    tools::file_ext(output_file)
  )
)

And yes, the error happens when running quarto preview test_datastamp.qmd.

[cderv]

I have just seen that we do not allow modification of the output dir. From our doc:

Note that pre-render scripts cannot modify the project directory, the output directory, or the project type. If a pre-render script modifies any of these values, an error will be returned and the render will fail.

We don't say anything for output file name