test: add null-byte escape test cases for '#' handling (#473)

Author: shayannab

test/identifier.test.js

@@ -66,6 +66,43 @@ describe("identifier", () => {
 		run(tests);
 	});
 
+	// Tests for https://github.com/webpack/webpack/issues/16819
+	// To embed a literal '#' in a filesystem path, the caller must use the
+	// '\0#' null-byte escape. Unescaped '#' always starts a fragment.
+	describe("parse identifier. '#' escape with \\0", () => {
+		/** @type {TestSuite[]} */
+		const tests = [
+			// '\0#' in path is unescaped to '#' (part of directory name), no fragment
+			{
+				input: "/home/user/projects/test\0#/webpack/src/file.js",
+				expected: ["/home/user/projects/test#/webpack/src/file.js", "", ""],
+			},
+			// '\0#' dir name, with a real (unescaped) '#' fragment at the end
+			{
+				input: "/projects/test\0#app/src/file.js#fragment",
+				expected: ["/projects/test#app/src/file.js", "", "#fragment"],
+			},
+			// Multiple '\0#' escapes in dir names, then a real fragment
+			{
+				input: "/a\0#b/c\0#d/file.js#hash",
+				expected: ["/a#b/c#d/file.js", "", "#hash"],
+			},
+			// '\0#' dir name with both query and fragment
+			{
+				input: "/projects/test\0#app/file.js?query#fragment",
+				expected: ["/projects/test#app/file.js", "?query", "#fragment"],
+			},
+			// Unescaped '#' mid-segment is still treated as a fragment start
+			// (callers must escape '#' in paths via '\0#' — see webpack#16819)
+			{
+				input: "/home/user/projects/test#/webpack/src/file.js",
+				expected: ["/home/user/projects/test", "", "#/webpack/src/file.js"],
+			},
+		];
+
+		run(tests);
+	});
+
 	describe("parse identifier. Windows-like paths", () => {
 		/** @type {TestSuite[]} */
 		const tests = [
@@ -93,6 +130,17 @@ describe("identifier", () => {
 				input: "path\\#/not/a/hash?not-a-query",
 				expected: ["path\\", "", "#/not/a/hash?not-a-query"],
 			},
+			// Regression (webpack#16819): '\0#' null-byte escape correctly
+			// embeds '#' in a Windows dir name (no fragment produced)
+			{
+				input: "C:\\Users\\test\0#proj\\webpack\\src\\file.js",
+				expected: ["C:\\Users\\test#proj\\webpack\\src\\file.js", "", ""],
+			},
+			// Without escaping, '#' still starts a fragment (caller must escape)
+			{
+				input: "C:\\Users\\test#proj\\webpack\\src\\file.js",
+				expected: ["C:\\Users\\test", "", "#proj\\webpack\\src\\file.js"],
+			},
 		];
 
 		run(tests);