Strange behavior from `similar_names` in most recent clippy version

[sgrif]

I'm updating Diesel to the most recent nightly for our tests. This issue occurred with rustup component add clippy-preview on the most recent nightly (rustc 1.29.0-nightly (1ecf6929d 2018-07-16)).

When running cargo clippy on our code base, I receive the following error:

error: binding's name is too similar to existing binding
  |
note: existing binding defined here
 --> diesel_cli/src/main.rs:121:27
  |
12|         ("generate", Some(args)) => {
  |                           ^^^^
help: separate the discriminating character by an underscore like: `arg_1`
  = help: for further information visit https://rust-lang-nursery.github.io/rust-clippy/v0.0.212/index.html#similar_names

error: binding's name is too similar to existing binding
  |
note: existing binding defined here
 --> diesel_cli/src/main.rs:121:27
  |
12|         ("generate", Some(args)) => {
  |                           ^^^^
help: separate the discriminating character by an underscore like: `arg_0`
  = help: for further information visit https://rust-lang-nursery.github.io/rust-clippy/v0.0.212/index.html#similar_names

The first point of note is that it doesn't seem to be pointing to the line that is causing the error, the only span it's showing is in the note section for the existing binding. The second problem is that it's just pointing to the same line multiple times. There is no binding in scope at all close to args other than that one, so it seems to think that the name is too similar to itself.

[phansch]

I think this is similar to #2651. The span is wrong and the suggestion makes it look like it tries to match on some macro expansion somewhere. This might be fixed by rust-lang/rust#52467, and I will try to reproduce it once that's merged.

[H2CO3]

I am also encountering strange error messages. Here's one:

error: binding's name is too similar to existing binding
   --> redacted/src/lib.rs:111:5
    |
111 |     pub tls_identity_pwd: String,
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
note: existing binding defined here
   --> redacted/src/lib.rs:89:5
    |
89  |     pub host: String,
    |     ^^^^^^^^^^^^^^^^
    = help: for further information visit https://rust-lang-nursery.github.io/rust-clippy/v0.0.212/index.html#similar_names

error: aborting due to 2 previous errors

error: Could not compile `redacted`.

Clearly, it's either thinking host and tls_identity_pwd are too similar, or the span is wrong.

[flip1995]

Still happening with the newest nightly: #3050

[H2CO3]

🎉