Off-by-one error wrapping comments on struct field

% rustfmt --version
rustfmt 1.7.0-nightly (8679004 2024-05-23)

Content of src/lib.rs:

/*
0         1         2         3         4         5         6         7         8         9
0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789
*/

// This line has 100 characters ...................................................................9
pub struct Foo {
    // This line has 100 characters ...............................................................9
    pub foo: u8,
}

pub mod foo {
    // This line has 100 characters ...............................................................9
    pub fn foo() {}
}

Content of rustfmt.toml:

comment_width = 100
wrap_comments = true

Expected formatting is that nothing changes. The file is already correctly formatted.

Actual formatting is the following (the line on the foo field of the Foo struct is wrapped):

/*
0         1         2         3         4         5         6         7         8         9
0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789
*/

// This line has 100 characters ...................................................................9
pub struct Foo {
    // This line has 100 characters
    // ...............................................................9
    pub foo: u8,
}

pub mod foo {
    // This line has 100 characters ...............................................................9
    pub fn foo() {}
}

This is probably a minimum reproduction example of https://github.com/rust-lang/rustfmt/issues/4929, indicating that this is an old issue, and probably not a regression but an off-by-one since the introduction of this feature.

Also I observed that comment_width seems to be capped by max_width although this doesn't seem to be documented. Using comment_width = 200 produces the same off-by-one behavior.

Reproduce the issue with the provided src/lib.rs and rustfmt.toml using rustfmt 1.7.0-nightly, then inspect the comment-wrapping path responsible for struct fields. Done means the 100-character field comment remains unchanged, with coverage for the comment_width and max_width interaction.