Remove non_exhaustive from Book #2823
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This removes the `non_exhaustive` attribute from the `Book` and its inner types `BookItem` and `Chapter`. These were added in rust-lang#2779. After thinking about it more, I realized that these types cannot be extended in a semver-compatible way, so I am fine with allowing them be exhaustive. The problem is that with CmdPreprocessor, the `Book` will be re-serialized by a preprocessor, which could potentially be on an older version. Attempting to add any new fields/variants means that either the deserialization will fail, or the new fields will be stripped by the preprocessor. These could potentially be structured such that they have a `serde(flatten)` or Other/Unknown variant so that a preprocessor would at least see the extra fields/variants and pass them along back to the output. However, a preprocessor or renderer wouldn't know what to do with those new fields/variants (particularly `BookItem`) which would itself be a problem. It's still possible to do something like this in the future, but for now I think it's fine to restrict these to semver-major changes.
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This removes the
non_exhaustiveattribute from theBookand its inner typesBookItemandChapter. These were added in #2779. After thinking about it more, I realized that these types cannot be extended in a semver-compatible way, so I am fine with allowing them be exhaustive.The problem is that with CmdPreprocessor, the
Bookwill be re-serialized by a preprocessor, which could potentially be on an older version. Attempting to add any new fields/variants means that either the deserialization will fail, or the new fields will be stripped by the preprocessor.These could potentially be structured such that they have a
serde(flatten)or Other/Unknown variant so that a preprocessor would at least see the extra fields/variants and pass them along back to the output. However, a preprocessor or renderer wouldn't know what to do with those new fields/variants (particularlyBookItem) which would itself be a problem. It's still possible to do something like this in the future, but for now I think it's fine to restrict these to semver-major changes.