Several improvements to textutils.serialise (#920)

- Handle nan and infinity, by emitting them as 0/0 and 0/1.
- Differentiate between repeated and recursive tables in the
  error message.

src/main/resources/data/computercraft/lua/rom/apis/textutils.lua

@@ -268,11 +268,16 @@ local g_tLuaKeywords = {
     ["while"] = true,
 }
 
+local serialize_infinity = math.huge
 local function serialize_impl(t, tracking, indent, opts)
     local sType = type(t)
     if sType == "table" then
         if tracking[t] ~= nil then
-            error("Cannot serialize table with recursive entries", 0)
+            if tracking[t] == false then
+                error("Cannot serialize table with repeated entries", 0)
+            else
+                error("Cannot serialize table with recursive entries", 0)
+            end
         end
         tracking[t] = true
 
@@ -307,13 +312,28 @@ local function serialize_impl(t, tracking, indent, opts)
             result = result .. indent .. "}"
         end
 
-        if opts.allow_repetitions then tracking[t] = nil end
+        if opts.allow_repetitions then
+            tracking[t] = nil
+        else
+            tracking[t] = false
+        end
         return result
 
     elseif sType == "string" then
         return string.format("%q", t)
 
-    elseif sType == "number" or sType == "boolean" or sType == "nil" then
+    elseif sType == "number" then
+        if t ~= t then --nan
+            return "0/0"
+        elseif t == serialize_infinity then
+            return "1/0"
+        elseif t == -serialize_infinity then
+            return "-1/0"
+        else
+            return tostring(t)
+        end
+
+    elseif sType == "boolean" or sType == "nil" then
         return tostring(t)
 
     else

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

@@ -81,14 +81,17 @@ describe("The textutils library", function()
         it("serialises basic tables", function()
             expect(textutils.serialise({ 1, 2, 3, a = 1, b = {} }))
                 :eq("{\n  1,\n  2,\n  3,\n  a = 1,\n  b = {},\n}")
+
+            expect(textutils.serialise({ 0 / 0, 1 / 0, -1 / 0 }))
+                :eq("{\n  0/0,\n  1/0,\n  -1/0,\n}")
         end)
 
-        it("fails on recursive tables", function()
+        it("fails on recursive/repeated tables", function()
             local rep = {}
-            expect.error(textutils.serialise, { rep, rep }):eq("Cannot serialize table with recursive entries")
+            expect.error(textutils.serialise, { rep, rep }):eq("Cannot serialize table with repeated entries")
 
             local rep2 = { 1 }
-            expect.error(textutils.serialise, { rep2, rep2 }):eq("Cannot serialize table with recursive entries")
+            expect.error(textutils.serialise, { rep2, rep2 }):eq("Cannot serialize table with repeated entries")
 
             local recurse = {}
             recurse[1] = recurse