3e3a4192d8
`MacArgs` is an enum with three variants: `Empty`, `Delimited`, and `Eq`. It's used in two ways: - For representing attribute macro arguments (e.g. in `AttrItem`), where all three variants are used. - For representing function-like macros (e.g. in `MacCall` and `MacroDef`), where only the `Delimited` variant is used. In other words, `MacArgs` is used in two quite different places due to them having partial overlap. I find this makes the code hard to read. It also leads to various unreachable code paths, and allows invalid values (such as accidentally using `MacArgs::Empty` in a `MacCall`). This commit splits `MacArgs` in two: - `DelimArgs` is a new struct just for the "delimited arguments" case. It is now used in `MacCall` and `MacroDef`. - `AttrArgs` is a renaming of the old `MacArgs` enum for the attribute macro case. Its `Delimited` variant now contains a `DelimArgs`. Various other related things are renamed as well. These changes make the code clearer, avoids several unreachable paths, and disallows the invalid values.
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