Idea: settings hierarchy / categorization

Something to consider for 2.0

Right now settings are all over the place in terms of how they are named (e.g. wrap_comments, comment_width, format_code_in_comments, doc_comment_code_block_width) because they inhabit a single namespace. This makes finding formatting options related to various topics require a lexical search through a long document of semi-related items rather than a categorical search through a shorter list.

It might be useful to categorize the settings into groups.

E.g.:

rustfmt.edition
rustfmt.color

comments.wrap
comments.width
comments.doc_comment.format_code
comments.doc_comment.code_block_width

imports.granularity
imports.group

The toml files would have a similar structure to Cargo.toml files, with sections for each table:

[comments]
wrap = true
width = 100

[comments.doc_comments]
# ...

This would make documentation easier to navigate, and make it possible to providing tooling that modifies the config while showing docs and the allowable settings in a GUI (e.g. similar to how vscode displays rust-analyzer settings).

No files or tests are named. Start by locating rustfmt's settings definitions, configuration parsing, and documentation, then determine the scope of introducing categorized settings and the compatibility implications; done would require an agreed hierarchy and documented behavior.