Check normalized and not normalized versions of parent and link

The "toRealPath()" of the child should with "realParentPath" to avoid
silent NoSuchFileException's if the constructed link does not match
actual (fully resolved) file system state of the local file we are
checking.

Fixes #2220

Author: iloveeclipse

resources/bundles/org.eclipse.core.resources/src/org/eclipse/core/internal/localstore/UnifiedTree.java

@@ -523,19 +523,12 @@ private boolean isRecursiveLink(IFileStore parentStore, IFileInfo localInfo) {
 			if (disable_advanced_recursive_link_checks) {
 				// Multiple ../ backwards links can go outside the project tree
 				if (linkTarget != null && PatternHolder.REPEATING_BACKWARDS_PATTERN.matcher(linkTarget).matches()) {
-					Path targetPath = parent.resolve(linkTarget).normalize();
-
-					// Recursive if literal target points to the literal parent of this tree
-					if (parent.normalize().startsWith(targetPath)) {
+					if (isRecursiveBackwardsLink(parent, linkTarget, false)) {
 						return true;
 					}
-
-					// Recursive if resolved target points to the resolved parent of this tree
-					Path realTargetPath = targetPath.toRealPath();
-					if (realParentPath.startsWith(realTargetPath)) {
+					if (isRecursiveBackwardsLink(realParentPath, linkTarget, true)) {
 						return true;
 					}
-
 					// If link is outside the project tree, consider as non recursive
 					// The link still can create recursion in the tree, but we can't detect it here.
 				}
@@ -573,6 +566,29 @@ private boolean isRecursiveLink(IFileStore parentStore, IFileInfo localInfo) {
 		return false;
 	}
 
+	private static boolean isRecursiveBackwardsLink(Path parent, String linkTarget, boolean resolveRealTarget)
+			throws IOException {
+		// Cheap tests first
+		// Recursive if literal target points to the literal parent of this tree
+		Path notNormalizedLink = parent.resolve(linkTarget);
+		if (parent.startsWith(notNormalizedLink)) {
+			return true;
+		}
+		// Same as above but using normalized variants
+		Path normalizedLink = notNormalizedLink.normalize();
+		if (parent.normalize().startsWith(normalizedLink)) {
+			return true;
+		}
+		// Next check costs more time because it does real IO when resolving paths
+		if (resolveRealTarget) {
+			Path realTarget = normalizedLink.toRealPath();
+			if (parent.startsWith(realTarget)) {
+				return true;
+			}
+		}
+		return false;
+	}
+
 	protected boolean isValidLevel(int currentLevel, int depth) {
 		return switch (depth) {
 		case IResource.DEPTH_INFINITE -> true;