From f31d8febbfe62b35d4f259bc1c731cfcd15e70f7 Mon Sep 17 00:00:00 2001
From: Jonathan Coates <git@squiddev.cc>
Date: Mon, 15 Dec 2025 23:46:18 +0000
Subject: [PATCH] Handle more of Windows's weird paths

AFAICT, any sequence of ".[ .]*" (except from "") is equivalent to "."
on Windows. Let's handle that in our path sanitisation code.

Fixes #2151.
---
 .../core/filesystem/FileSystem.java           | 26 +++++++------------
 .../core/filesystem/FileSystemTest.java       |  1 +
 .../resources/test-rom/spec/apis/fs_spec.lua  |  5 ++++
 3 files changed, 15 insertions(+), 17 deletions(-)

diff --git a/projects/core/src/main/java/dan200/computercraft/core/filesystem/FileSystem.java b/projects/core/src/main/java/dan200/computercraft/core/filesystem/FileSystem.java
index 509ee63f8..6fb31162f 100644
--- a/projects/core/src/main/java/dan200/computercraft/core/filesystem/FileSystem.java
+++ b/projects/core/src/main/java/dan200/computercraft/core/filesystem/FileSystem.java
@@ -352,7 +352,7 @@ public class FileSystem {
         return sanitizePath(path, false);
     }
 
-    private static final Pattern threeDotsPattern = Pattern.compile("^\\.{3,}$");
+    private static final Pattern manyDotsPattern = Pattern.compile("^[. ]+$");
 
     // IMPORTANT: Both arrays are sorted by ASCII value.
     private static final char[] specialChars = new char[]{ '"', '*', ':', '<', '>', '?', '|' };
@@ -376,27 +376,19 @@ public class FileSystem {
         for (var fullPart : Splitter.on('/').split(path)) {
             var part = fullPart.strip();
 
-            if (part.isEmpty() || part.equals(".") || threeDotsPattern.matcher(part).matches()) {
-                // . is redundant
-                // ... and more are treated as .
-                continue;
-            }
+            // Limit part length to 255.
+            if (part.length() > 255) part = part.substring(0, 255).strip();
 
             if (part.equals("..")) {
                 // .. can cancel out the last folder entered
-                if (!outputParts.isEmpty()) {
-                    var top = outputParts.peekLast();
-                    if (!top.equals("..")) {
-                        outputParts.removeLast();
-                    } else {
-                        outputParts.addLast("..");
-                    }
-                } else {
+                if (outputParts.isEmpty() || outputParts.peekLast().equals("..")) {
                     outputParts.addLast("..");
+                } else {
+                    outputParts.removeLast();
                 }
-            } else if (part.length() >= 255) {
-                // If part length > 255 and it is the last part
-                outputParts.addLast(part.substring(0, 255).strip());
+            } else if (part.isEmpty() || (part.startsWith(".") && manyDotsPattern.matcher(part).matches())) {
+                // Skip empty paths, ".", or any other sequence of "[. ]+" (as this is also treated as "." on Windows).
+                continue;
             } else {
                 // Anything else we add to the stack
                 outputParts.addLast(part);
diff --git a/projects/core/src/test/java/dan200/computercraft/core/filesystem/FileSystemTest.java b/projects/core/src/test/java/dan200/computercraft/core/filesystem/FileSystemTest.java
index 90f67a9b5..56284f60a 100644
--- a/projects/core/src/test/java/dan200/computercraft/core/filesystem/FileSystemTest.java
+++ b/projects/core/src/test/java/dan200/computercraft/core/filesystem/FileSystemTest.java
@@ -89,6 +89,7 @@ public class FileSystemTest {
             new String[]{ "a/./b", "a/b" },
             new String[]{ "a/../b", "b" },
             new String[]{ "a/.../b", "a/b" },
+            new String[]{ "a/. ./b", "a/b" },
             new String[]{ " a ", "a" },
             new String[]{ "a b c", "a b c" },
         };
diff --git a/projects/core/src/test/resources/test-rom/spec/apis/fs_spec.lua b/projects/core/src/test/resources/test-rom/spec/apis/fs_spec.lua
index 05fc9c849..b5e256084 100644
--- a/projects/core/src/test/resources/test-rom/spec/apis/fs_spec.lua
+++ b/projects/core/src/test/resources/test-rom/spec/apis/fs_spec.lua
@@ -156,6 +156,11 @@ describe("The fs library", function()
             expect(fs.combine("a", "../../c")):eq("../c")
         end)
 
+        it("handles weird Windows paths", function()
+            expect(fs.combine("a", "...")):eq("a")
+            expect(fs.combine("a", ". .")):eq("a")
+        end)
+
         it("combines empty paths", function()
             expect(fs.combine("a")):eq("a")
             expect(fs.combine("a", "")):eq("a")