Add support for generating .editorconfig from rustfmt configs #2999

[LoKolbasz]

Generate editorconfig based on the current/selected rustfmt config, that sets the rules for all rust source files.
Available only as a nightly option.

Usage

1. Output editorconfig to stdout

rustfmt --editorconfig
# Generated by rustfmt version: 1.8.0-nightly (0332da0148 2025-06-21)

[*.rs]
indent_style = space
indent_size = tab
tab_width = 4
charset = utf-8
trim_trailing_whitespace = true
insert_final_newline = true
max_line_length = 100

2. Append to the specified file

rustfmt --editorconfig=.editorconfig
cat .editorconfig
# Generated by rustfmt version: 1.8.0-nightly (0332da0148 2025-06-21)

[*.rs]
indent_style = space
indent_size = tab
tab_width = 4
charset = utf-8
trim_trailing_whitespace = true
insert_final_newline = true
max_line_length = 100

3. Append to the .editorconfig file in a specified directory

rustfmt --editorconfig=./
cat .editorconfig
# Generated by rustfmt version: 1.8.0-nightly (0332da0148 2025-06-21)

[*.rs]
indent_style = space
indent_size = tab
tab_width = 4
charset = utf-8
trim_trailing_whitespace = true
insert_final_newline = true
max_line_length = 100

4. Specify rustfmt.toml path for the generator to use

rustfmt --editorconfig --config-path=/path/to/rustfmt/config/
# Generated by rustfmt version: 1.8.0-nightly (0332da0148 2025-06-21)

[*.rs]
indent_style = space
indent_size = tab
tab_width = 4
charset = utf-8
trim_trailing_whitespace = true
insert_final_newline = true
max_line_length = 100

Value mapping:

Rustfmt	EditorConfig
indentstyle	indent_style(left unset when auto)
X	indent_size=tab
tab_spaces	tab_width
new_line_style	end_of_line
X	charset=utf-8 (AFAIK all rust files are utf-8)
X	trim_trailing_whitespace=true
X	insert_final_newline=true
max_width	max_line_length

• I'm unsure about indent_size and tab_spaces. It might be better to switch them up, and only set indent_size
• trim_trailing_whitespace and insert_final_newline are set to true, as that is what rustfmt does without any explicit configuration needed (AFAIK).

Important

This option does not check wether the generated config will be placed in the root editorconfig. root=true must be set in the preamble of the .editorcofig file by the user if it is the root editorconfig.

[ytmimi]

I don't think we're going to support this at this time

[LoKolbasz]

In #2999 they said, that we could submit a PR 😞 .
But I understand.