docs: source URL can be a list (meta.yaml)

[ytausch]

Description

meta.yaml actually supports a list of URLs in the url field of a single source but this feature is currently undocumented. This is the relevant source code snippet:

conda-build/conda_build/source.py

Lines 63 to 114 in 20b75c1

	source_urls = source_dict["url"]
	if not isinstance(source_urls, list):
	source_urls = [source_urls]
	unhashed_fn = fn = (
	source_dict["fn"] if "fn" in source_dict else basename(source_urls[0])
	)
	hash_added = False
	for hash_type in ("md5", "sha1", "sha256"):
	if hash_type in source_dict:
	if source_dict[hash_type] in (None, ""):
	raise ValueError(f"Empty {hash_type} hash provided for {fn}")
	fn = append_hash_to_fn(fn, source_dict[hash_type])
	hash_added = True
	break
	else:
	log.warn(
	f"No hash (md5, sha1, sha256) provided for {unhashed_fn}. Source download forced. "
	"Add hash to recipe to use source cache."
	)
	path = join(cache_folder, fn)
	if isfile(path):
	if verbose:
	log.info("Found source in cache: %s" % fn)
	else:
	if verbose:
	log.info("Downloading source to cache: %s" % fn)
	for url in source_urls:
	if "://" not in url:
	if url.startswith("~"):
	url = expanduser(url)
	if not os.path.isabs(url):
	url = os.path.normpath(os.path.join(recipe_path, url))
	url = url_path(url)
	else:
	if url.startswith("file:///~"):
	url = "file:///" + expanduser(url[8:]).replace("\\", "/")
	try:
	if verbose:
	log.info("Downloading %s" % url)
	with LoggingContext():
	download(url, path)
	except CondaHTTPError as e:
	log.warn("Error: %s" % str(e).strip())
	rm_rf(path)
	except RuntimeError as e:
	log.warn("Error: %s" % str(e).strip())
	rm_rf(path)
	else:
	if verbose:
	log.info("Success")
	break

Checklist - did you ...

• Add a file to the news directory (using the template) for the next release's release notes?
• Add / update necessary tests?
• Add / update outdated documentation?

[ryanskeith]

As stated in your PR, this isn't a well tested feature. I would suggest adding a warning to the docs about that for now.

[jaimergp]

This is used routinely in the R ecosystem in conda-forge:

https://github.com/search?q=org%3Aconda-forge+%2Furl%3A%5Cn%5Cs%2B-%2F+path%3Ameta.yaml&type=code

[ytausch]

@beeankha thank you for fixing!