Curl module may accidentally reuse URL

[juntuu]

The URL from a previous call can accidentally be reused for later, misconfigured, call.

Reproduction:

local curl = require "plenary.curl"
-- 1. Call any method (even `request`) with the URL string as the first argument
curl.get("localhost", { dry_run = true }) -- { ..., "-X", "GET", "localhost" }
-- 2. Call any method (except `request`) with table as the first argument, with `url` key missing
curl.get({ dry_run = true })              -- { ..., "-X", "GET", "localhost" }

Observed behaviour:

The second call uses the URL from the previous call.

Expected behaviour:

The second call should either:

• raise an error because the url is missing from the options, or
• at least not use the URL from previous call

The error on missing URL could also be better... (Should this be another issue?)

I would expect either an explicit error from the library, or some error from curl itself. (Although I'm not sure if there is any meaningful case where curl could be used without the URL?)

However, now the error happens at

plenary.nvim/lua/plenary/curl.lua

Line 246 in a3e3bc8

table.insert(result, parse.url(opts.url, opts.query))

because parse.url(nil) returns zero values.

$ lua -e 'table.insert({})'
lua: (command line):1: wrong number of arguments to 'insert'

---

Cause:

The spec table is shared between all the methods and calls, but the url field is not always set. This can lead to unintentional reuse of the field.

plenary.nvim/lua/plenary/curl.lua

Lines 325 to 335 in a3e3bc8

	local spec = {}
	local partial = function(method)
	return function(url, opts)
	opts = opts or {}
	if type(url) == "table" then
	opts = url
	spec.method = method
	else
	spec.url = url
	spec.method = method
	end

---

I could see some use case for this behaviour, but I think it should be an explicit API. (The request method is also inconsistent with the others and bit surprising how it may end up ignoring the first argument.)

So, am I correct assuming this is a bug, not a feature?