Bug or feature? Strings accepted instead of numbers in Types/*ProductPrototype

[Pi-C]

I've got a crash report for one of my mods:

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7.436 Error ModManager.cpp:1623: Failed to load mod "GCKI": __GCKI__/libs/recipe-functions.lua:1111: attempt to compare number with string

The crash happened when the last of the following results:

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   7.443 Script @__GCKI__/libs/debugging.lua:159: results: {
  {
    amount = 1,
    name = "nullius-box-phosphorus",
    type = "item"
  },
  {
    amount = 12,
    name = "nullius-box-gravel",
    type = "item"
  },
  {
    amount = "120",	-- String instead of number!
    name = "nullius-carbon-monoxide",
    type = "fluid"
  }
}

was passed on to my function:

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  for r, result in ipairs(results or {}) do
      amount = result[2] or result.amount
      if amount and amount > 0 then	-- CRASHING 
    	…

According to the description of the property amount of Types/FluidProductType, there's nothing wrong with me assuming that amount will always be a number, so I've forwarded the crash report to the author of the mod that created the faulty recipe. But then I started wondering why nobody has noticed before that there was something wrong with that recipe.

I removed my mod, restarted the game -- and sure enough, the recipe was there, and it also created the expected fluid result! So, if Types/FluidProductPrototype.amount is a string that can be converted to a number, the game will accept it.

I've dug around some more and found that this also applies to the properties amount_min, amount_max, and catalyst_amount (both Types/ItemProductType and Types/FluidProductType) as well as the property temperature (only Types/FluidProductType).
Changing recipe.results to

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    results = {
      {"nullius-box-phosphorus", 1},
      -- {"nullius-box-gravel", 12},
      {type = "item", name = "nullius-box-gravel", amount_min = "12", amount_max = "15", catalyst_amount = "7"},
      -- {type="fluid", name="nullius-carbon-monoxide", amount = "120"}
      {type="fluid", name="nullius-carbon-monoxide", amount_min = "120", amount_max = "123", temperature = "66.6", catalyst_amount = "5"}
    },

will show this in the game:

recipe.png (1.3 MiB) Viewed 983 times

For both product types, this also applies to the property probability if the string starts with a number. For example, changing the last result to

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      {type="fluid", name="nullius-carbon-monoxide", amount_min = "120", amount_max = "123", temperature = "66.6", catalyst_amount = "5", probability = "0.5"}

will give you this:

recipe_in_game.png (55.36 KiB) Viewed 983 times

However, changing probability to

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-- probability = "0.5"
probability = ".5"

will result in

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Error ModManager.cpp:1623: Error while loading recipe prototype "lambent-nil-boxed-phosphorus-1" (recipe): Difficulty normal: Value must be a number in property tree at ROOT.recipe.lambent-nil-boxed-phosphorus-1.results[2].probability

I'd consider the current behavior rather a bug than a feature because it will only work for strings formatted in a particular way (leading zeros are not optional) and because this behavior isn't documented (so mods which don't take into account that strings translating to numbers are valid may crash). But I must admit that the game trying to convert strings to numbers automatically is convenient and could be a feature.

My recommendation: Keep the current behavior (but fix that the first character of a number-strings may not be a decimal point) and update the documentation.

[Rseding91]

The behavior is legacy from long ago. In 1.2 it will be removed and require all of the values be numbers.

[Pi-C]

Thanks for the info!