Improvements to the various file system programs (rm, mv, rename) (#440)

This enforces several sanity checks before actually attempting
the move, allowing us to produce friendlier error messages.

src/test/resources/test-rom/spec/programs/move_spec.lua

@@ -1,11 +1,13 @@
 local capture = require "test_helpers".capture_program
 
 describe("The move program", function()
+    local function cleanup() fs.delete("/test-files/move") end
     local function touch(file)
         io.open(file, "w"):close()
     end
 
     it("move a file", function()
+        cleanup()
         touch("/test-files/move/a.txt")
 
         shell.run("move /test-files/move/a.txt /test-files/move/b.txt")
@@ -14,11 +16,57 @@ describe("The move program", function()
         expect(fs.exists("/test-files/move/b.txt")):eq(true)
     end)
 
-    it("try to move a not existing file", function()
+    it("moves a file to a directory", function()
+        cleanup()
+        touch("/test-files/move/a.txt")
+        fs.makeDir("/test-files/move/a")
+
+        expect(capture(stub, "move /test-files/move/a.txt /test-files/move/a"))
+            :matches { ok = true }
+
+        expect(fs.exists("/test-files/move/a.txt")):eq(false)
+        expect(fs.exists("/test-files/move/a/a.txt")):eq(true)
+    end)
+
+    it("fails when moving a file which doesn't exist", function()
         expect(capture(stub, "move nothing destination"))
             :matches { ok = true, output = "", error = "No matching files\n" }
     end)
 
+    it("fails when overwriting an existing file", function()
+        cleanup()
+        touch("/test-files/move/a.txt")
+
+        expect(capture(stub, "move /test-files/move/a.txt /test-files/move/a.txt"))
+            :matches { ok = true, output = "", error = "Destination exists\n" }
+    end)
+
+    it("fails when moving to read-only locations", function()
+        cleanup()
+        touch("/test-files/move/a.txt")
+
+        expect(capture(stub, "move /test-files/move/a.txt /rom/test.txt"))
+            :matches { ok = true, output = "", error = "Destination is read-only\n" }
+    end)
+
+    it("fails when moving from read-only locations", function()
+        expect(capture(stub, "move /rom/startup.lua /test-files/move/not-exist.txt"))
+            :matches { ok = true, output = "", error = "Cannot move read-only file /rom/startup.lua\n" }
+    end)
+
+    it("fails when moving mounts", function()
+        expect(capture(stub, "move /rom /test-files/move/rom"))
+            :matches { ok = true, output = "", error = "Cannot move mount /rom\n" }
+    end)
+
+    it("fails when moving a file multiple times", function()
+        cleanup()
+        touch("/test-files/move/a.txt")
+        touch("/test-files/move/b.txt")
+        expect(capture(stub, "move /test-files/move/*.txt /test-files/move/c.txt"))
+            :matches { ok = true, output = "", error = "Cannot overwrite file multiple times\n" }
+    end)
+
     it("displays the usage with no arguments", function()
         expect(capture(stub, "move"))
             :matches { ok = true, output = "Usage: mv <source> <destination>\n", error = "" }