Fix fs.isDriveRoot for missing files

fs.getDrive returns nil for missing files, rather than the mount of the
parent file. This is a bit confusing — other mount-related functions
(e.g. getFreeSpace) find the nearest mount — but I think it's too late
to change this. Instead, we check if the file exists first.

projects/core/src/main/resources/data/computercraft/lua/rom/apis/fs.lua

@@ -223,16 +223,21 @@ end
 --- Returns true if a path is mounted to the parent filesystem.
 --
 -- The root filesystem "/" is considered a mount, along with disk folders and
--- the rom folder. Other programs (such as network shares) can exstend this to
--- make other mount types by correctly assigning their return value for getDrive.
+-- the rom folder.
 --
 -- @tparam string path The path to check.
 -- @treturn boolean If the path is mounted, rather than a normal file/folder.
 -- @throws If the path does not exist.
 -- @see getDrive
 -- @since 1.87.0
-function fs.isDriveRoot(sPath)
-    expect(1, sPath, "string")
+function fs.isDriveRoot(path)
+    expect(1, path, "string")
+
+    local parent = fs.getDir(path)
+
     -- Force the root directory to be a mount.
-    return fs.getDir(sPath) == ".." or fs.getDrive(sPath) ~= fs.getDrive(fs.getDir(sPath))
+    if parent == ".." then return true end
+
+    local drive = fs.getDrive(path)
+    return drive ~= nil and drive ~= fs.getDrive(parent)
 end

projects/core/src/main/resources/data/computercraft/lua/rom/programs/lua.lua

@@ -104,7 +104,7 @@ while running do
             end
         else
             printError(results[2])
-            require "cc.internal.exception".report(results[2], results[3], chunk_map)
+            exception.report(results[2], results[3], chunk_map)
         end
     else
         local parser = require "cc.internal.syntax"

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

@@ -83,6 +83,10 @@ describe("The fs library", function()
             expect(fs.isDriveRoot("/rom/startup.lua")):eq(false)
             expect(fs.isDriveRoot("/rom/programs/delete.lua")):eq(false)
         end)
+
+        it("returns false for missing files", function()
+            expect(fs.isDriveRoot("does_not_exist")):eq(false)
+        end)
     end)
 
     describe("fs.list", function()
@@ -555,6 +559,22 @@ describe("The fs library", function()
         end)
     end)
 
+    describe("fs.getDrive", function()
+        it("returns the drive for the mount roots", function()
+            expect(fs.getDrive("")):eq("hdd")
+            expect(fs.getDrive("rom")):eq("rom")
+        end)
+
+        it("returns the drive for subdirectories", function()
+            expect(fs.getDrive("rom/startup.lua")):eq("rom")
+        end)
+
+        it("returns nothing for missing files", function()
+            -- Peculiar, but we return no values, rather than nil!
+            expect(table.pack(fs.getDrive("no_such_file"))):same { n = 0 }
+        end)
+    end)
+
     describe("fs.attributes", function()
         it("errors on non-existent files", function()
             expect.error(fs.attributes, "xuxu_nao_existe"):eq("/xuxu_nao_existe: No such file")