fix: Empty urls are not rewritten to relative requests

Prior to this commit, `urlToRequest` rewrote an empty URL `''` to `'./'` which is correct from a theoretical point of view since CSS files do not distinguish between relative paths starting with ./ or not (like CommonJS does). However, an empty URL is most likely an error which webpack should warn about. If we rewrite the empty string to ./, webpack won't warn against this anymore because requiring ./ is valid.

Related discussion: #80

Author: darrenscerri

lib/urlToRequest.js

@@ -4,6 +4,11 @@
 const matchNativeWin32Path = /^[A-Z]:[/\\]|^\\\\/i;
 
 function urlToRequest(url, root) {
+	// Do not rewrite an empty url
+	if(url === "") {
+		return "";
+	}
+
 	const moduleRequestRegex = /^[^?]*~/;
 	let request;
 

test/urlToRequest.test.js

@@ -35,7 +35,9 @@ describe("urlToRequest()", () => {
 		// error cases
 		[["/path/to/thing", 1], new ExpectedError(/unexpected parameters/i), "should throw an error on invalid root"],
 		// difficult cases
-		[["a:b-not-\\window-path"], "./a:b-not-\\window-path", "should not incorrectly detect windows paths"]
+		[["a:b-not-\\window-path"], "./a:b-not-\\window-path", "should not incorrectly detect windows paths"],
+		// empty url
+		[[""], "", "should do nothing if url is empty"]
 	].forEach((test) => {
 		it(test[2], () => {
 			const expected = test[1];