Behavioral difference: dofile() script-dir tracking on WASM vs native

[cderv]

Reporting a behavioral difference between the WASM and native Lua paths for dofile() and quarto.utils.resolve_path(). This came up during the WASM testing cleanup in #109 — sharing for discussion.

Observation

On WASM, register_wasm_dofile overrides Lua's built-in dofile and adds push/pop of the script-dir stack around each call. On native, Lua's C dofile is used and doesn't interact with the stack.

This means the same Lua filter produces different results:

-- filter.lua (in /ext/)
local resolved = dofile("helpers/ui.lua")

-- helpers/ui.lua
return quarto.utils.resolve_path("style.css")
-- WASM result: /ext/helpers/style.css
-- Native result: /ext/style.css

How this was discovered

While removing the #[cfg(any(target_arch = "wasm32", test))] proxy in #109, the test_dofile_script_dir_stack test started failing on native. The proxy had been routing native tests through register_wasm_dofile, masking the difference. In #109 we resolved this by marking the test as #[ignore] on non-wasm32 targets.

Context

The original design (commit f87b11b) intentionally limited the dofile override to WASM because native C fopen works fine. The script-dir push/pop was bundled with the file I/O override since both were needed on WASM.

Neither Pandoc nor Quarto CLI provides script-dir tracking for raw dofile():

• Pandoc: dofile resolves relative to CWD. PANDOC_SCRIPT_FILE is set once for the top-level filter.
• Quarto CLI: has a scriptFile stack via _quarto.withScriptFile, but only for shortcodes and wrapped filters. Raw dofile() uses standard Lua CWD-relative behavior.

Open question

Should these behave the same? Two directions are possible:

1. Native gains the push/pop behavior (wrap C dofile to add stack tracking without replacing file I/O). This would be an improvement over both Pandoc and Quarto CLI.
2. WASM drops the push/pop behavior (only override file I/O via SystemRuntime, don't add stack tracking). This would align WASM with native and with Pandoc/Quarto CLI behavior.

Relevant code

q2/crates/pampa/src/lua/dofile_wasm.rs

Lines 47 to 106 in dd1cdd4

	/// Register `dofile` and `loadfile` overrides for the restricted Lua environment.
	pub fn register_wasm_dofile(lua: &Lua, runtime: Arc<dyn SystemRuntime>) -> Result<()> {
	// dofile(path) — read, compile, push script dir, execute, pop, return results
	let rt = runtime.clone();
	lua.globals().set(
	"dofile",
	lua.create_function(move |lua, path: String| {
	let resolved = resolve_dofile_path(lua, &path)?;
	let content = rt.file_read_string(Path::new(&resolved)).map_err(|e| {
	mlua::Error::runtime(format!("dofile: cannot read '{}': {}", path, e))
	})?;
	let chunk = lua.load(&content).set_name(&path);
	// Push the loaded file's directory onto the script-dir stack
	let file_dir = Path::new(&resolved)
	.parent()
	.unwrap_or(Path::new(""))
	.to_string_lossy()
	.to_string();
	push_script_dir(lua, &file_dir)?;
	let result = chunk.eval::<MultiValue>();
	pop_script_dir(lua)?;
	result
	})?,
	)?;
	// loadfile(path) — read and compile only, return chunk (or nil + error)
	lua.globals().set(
	"loadfile",
	lua.create_function(move |lua, path: String| {
	let resolved = resolve_dofile_path(lua, &path)?;
	let content = match runtime.file_read_string(Path::new(&resolved)) {
	Ok(c) => c,
	Err(e) => {
	// Lua semantics: loadfile returns (nil, error_message) on failure
	return Ok(MultiValue::from_iter([
	Value::Nil,
	Value::String(lua.create_string(format!("cannot read '{}': {}", path, e))?),
	]));
	}
	};
	match lua.load(&content).set_name(&path).into_function() {
	Ok(func) => Ok(MultiValue::from_iter([Value::Function(func)])),
	Err(e) => Ok(MultiValue::from_iter([
	Value::Nil,
	Value::String(lua.create_string(e.to_string())?),
	])),
	}
	})?,
	)?;
	Ok(())
	}

q2/crates/pampa/src/lua/filter.rs

Lines 135 to 147 in dd1cdd4

	#[cfg(any(target_arch = "wasm32", test))]
	let lua = {
	use mlua::StdLib;
	let libs = StdLib::COROUTINE | StdLib::TABLE | StdLib::STRING | StdLib::UTF8 | StdLib::MATH;
	let lua = Lua::new_with(libs, mlua::LuaOptions::default())
	.map_err(|e| LuaFilterError::LuaError(e))?;
	super::os_wasm::register_wasm_os(&lua, runtime.clone())?;
	super::io_wasm::register_wasm_io(&lua, runtime.clone())?;
	super::dofile_wasm::register_wasm_dofile(&lua, runtime.clone())?;
	lua
	};
	#[cfg(not(any(target_arch = "wasm32", test)))]
	let lua = Lua::new();