Make fs.combine accept multiple arguments

Means we can now do fs.combine("a", "b", "c"). Of course, one may just
write "a/b/c" in this case, but it's definitely useful elsewhere.

This is /technically/ a breaking change as fs.combine(a, b:gsub(...))
will no longer function (as gsub returns multiple arguments). However,
I've done a quick search through GH and my Pastebin archives and can't
find any programs which would break. Fingers crossed.

src/main/java/dan200/computercraft/core/apis/FSAPI.java

@@ -5,6 +5,7 @@
  */
 package dan200.computercraft.core.apis;
 
+import dan200.computercraft.api.lua.IArguments;
 import dan200.computercraft.api.lua.ILuaAPI;
 import dan200.computercraft.api.lua.LuaException;
 import dan200.computercraft.api.lua.LuaFunction;
@@ -83,17 +84,28 @@ public class FSAPI implements ILuaAPI
     }
 
     /**
-     * Combines two parts of a path into one full path, adding separators as
+     * Combines several parts of a path into one full path, adding separators as
      * needed.
      *
-     * @param pathA The first part of the path. For example, a parent directory path.
+     * @param arguments The paths to combine.
-     * @param pathB The second part of the path. For example, a file name.
      * @return The new path, with separators added between parts as needed.
+     * @cc.tparam string path The first part of the path. For example, a parent directory path.
+     * @cc.tparam string ... Additional parts of the path to combine.
      */
     @LuaFunction
-    public final String combine( String pathA, String pathB )
+    public final String combine( IArguments arguments ) throws LuaException
     {
-        return fileSystem.combine( pathA, pathB );
+        StringBuilder result = new StringBuilder();
+        result.append( FileSystem.sanitizePath( arguments.getString( 0 ), true ) );
+
+        for( int i = 1, n = arguments.count(); i < n; i++ )
+        {
+            String part = FileSystem.sanitizePath( arguments.getString( i ), true );
+            if( result.length() != 0 && !part.isEmpty() ) result.append( '/' );
+            result.append( part );
+        }
+
+        return FileSystem.sanitizePath( result.toString(), true );
     }
 
     /**
@@ -385,8 +397,8 @@ public class FSAPI implements ILuaAPI
      *
      * @param path The path to check the free space for.
      * @return The amount of free space available, in bytes.
-     * @cc.treturn number|"unlimited" The amount of free space available, in bytes, or "unlimited".
      * @throws LuaException If the path doesn't exist.
+     * @cc.treturn number|"unlimited" The amount of free space available, in bytes, or "unlimited".
      */
     @LuaFunction
     public final Object getFreeSpace( String path ) throws LuaException

src/main/java/dan200/computercraft/core/filesystem/FileSystem.java

@@ -98,7 +98,7 @@ public class FileSystem
         mounts.remove( sanitizePath( path ) );
     }
 
-    public synchronized String combine( String path, String childPath )
+    public String combine( String path, String childPath )
     {
         path = sanitizePath( path, true );
         childPath = sanitizePath( childPath, true );
@@ -479,7 +479,7 @@ public class FileSystem
 
     private static final Pattern threeDotsPattern = Pattern.compile( "^\\.{3,}$" );
 
-    private static String sanitizePath( String path, boolean allowWildcards )
+    public static String sanitizePath( String path, boolean allowWildcards )
     {
         // Allow windowsy slashes
         path = path.replace( '\\', '/' );

src/test/resources/test-rom/spec/apis/fs_spec.lua

@@ -39,15 +39,19 @@ describe("The fs library", function()
         end)
     end)
 
-    describe("fs.list", function()
+    describe("fs.combine", function()
-        it("fails on files", function()
+        it("removes . and ..", function()
-            expect.error(fs.list, "rom/startup.lua"):eq("/rom/startup.lua: Not a directory")
+            expect(fs.combine("./a/b")):eq("a/b")
-            expect.error(fs.list, "startup.lua"):eq("/startup.lua: Not a directory")
+            expect(fs.combine("a/b", "../c")):eq("a/c")
+            expect(fs.combine("a", "../c")):eq("c")
+            expect(fs.combine("a", "../../c")):eq("../c")
         end)
 
-        it("fails on non-existent nodes", function()
+        it("combines empty paths", function()
-            expect.error(fs.list, "rom/x"):eq("/rom/x: Not a directory")
+            expect(fs.combine("a")):eq("a")
-            expect.error(fs.list, "x"):eq("/x: Not a directory")
+            expect(fs.combine("a", "")):eq("a")
+            expect(fs.combine("", "a")):eq("a")
+            expect(fs.combine("a", "", "b", "c")):eq("a/b/c")
         end)
     end)