More useful error message if no writeable cache path

[brprice]

kpathsea has some perhaps-surprising rules around "safe filenames". We attempt to make this information more discoverable by linking from the error message.

I have spent a bunch of time debugging why upgrading texlive-2023 to texlive-2025 meant I couldn't build my document via nix. The error message was rather unhelpful (yes there is a writeable cache directory, it is right there) as I was unaware of the "no hidden directories" rule. Hopefully this patch will save some time for the next person to trip across this (i.e. me in a few months time!)

Probably there is better phrasing of the additions to the message.

[gucci-on-fleek]

(Not a luaotfload developer, so feel free to ignore any of my comments here)

I don't think that logs.report wraps its output (assuming that it behaves like the version from ConTeXt), so it might be better to add the hint to a separate line:

Suggested change

	logs.report("system","no writeable cache path, quiting. Try setting TEXMFCACHE or TEXMFVAR and reading https://www.tug.org/texinfohtml/kpathsea.html#Safe-filenames")
	logs.report("system","no writeable cache path, quiting")
	logs.report("system","Try setting TEXMFCACHE or TEXMFVAR and reading https://www.tug.org/texinfohtml/kpathsea.html#Safe-filenames")

In general though, adding a hint to this error message seems like a really good idea to me.

[brprice]

I would like to be able to do this, but because of

luaotfload/src/luaotfload-init.lua

Lines 293 to 306 in ecfe7d0

	do
	local saved_reporter = texio.reporter
	local saved_exit = os.exit
	local errmsg
	function texio.reporter(msg, ...)
	errmsg = msg
	end
	function os.exit()
	error(errmsg)
	end
	load_fontloader_module "basics-gen"
	texio.reporter = saved_reporter
	os.exit = saved_exit
	end

only the last log is reported.

(I'm not a lua dev, so could easily be missing something here)

Trying to embed a newline in the string also makes the reporting a bit odd wrt indentation.

luaotfload | load : FATAL ERROR
luaotfload | load :   × Failed to load "fontloader" module "basics-gen".
luaotfload | load :   × Error message:
luaotfload | load :     × "./luaotfload-init.lua:301: system : no writeable cache path, quiting.\
Try setting TEXMFCACHE or TEXMFVAR and reading https://www.tug.org/texinfohtml/kpathsea.html#Safe-filenames".

...

./luaotfload-init.lua:301: system : no writeable cach
e path, quiting.
Try setting TEXMFCACHE or TEXMFVAR and reading https://www.tug.org/texinfohtml/
kpathsea.html#Safe-filenames

whereas just one long string gives

luaotfload | load : FATAL ERROR
luaotfload | load :   × Failed to load "fontloader" module "basics-gen".
luaotfload | load :   × Error message:
luaotfload | load :     × "./luaotfload-init.lua:301: system : no writeable cache path, quiting. Try setting TEXMFCACHE or TEXMFVAR and reading https://www.tug.org/texinfohtml/kpathsea.html#Safe-filenames".

...

./luaotfload-init.lua:301: system : no writeable cach
e path, quiting. Try setting TEXMFCACHE or TEXMFVAR and reading https://www.tug
.org/texinfohtml/kpathsea.html#Safe-filenames

I'm not particularly happy with either option here. Hopefully a maintainer can suggest a non-invasive change with nicer output.

[zauguin]

Either option is fine really. Currently the output looks weird but that shouldn't be worked around here but fixed in the output printer.

I think doing multiple calls to texio.reporter is the cleanest option for now.