False positive on 'useless_let_if_seq'

When I ran cargo clippy against rustfmt repository, I got the following suggestion, which is incorrect:

warning: `if _ { .. } else { .. }` is an expression
   --> src/visitor.rs:189:9
    |
189 | /         let mut unindent_comment = self.is_if_else_block && !b.stmts.is_empty();
190 | |         if unindent_comment {
191 | |             let end_pos = source!(self, b.span).hi() - brace_compensation - remove_len;
192 | |             let snippet = self.snippet(mk_sp(self.last_pos, end_pos));
193 | |             unindent_comment = snippet.contains("//") || snippet.contains("/*");
194 | |         }
    | |_________^ help: it is more idiomatic to write: `let <mut> unindent_comment = if unindent_comment { ..; snippet.contains("//") || snippet.contains("/*") } else { self.is_if_else_block && !b.stmts.is_empty() };`
    |
    = note: #[warn(useless_let_if_seq)] on by default
    = note: you might not need `mut` at all
    = help: for further information visit https://rust-lang-nursery.github.io/rust-clippy/v0.0.166/index.html#useless_let_if_seq

This looks similar to #975.
I am using 0.0.166.

Reproduce the report by running cargo clippy against the rustfmt repository, then inspect src/visitor.rs around line 189 and the useless_let_if_seq lint. Compare the behavior with issue #975; done means the shown conditional reassignment no longer produces an incorrect suggestion.