error[E0710]: unknown tool name `foo` found in scoped lint: `foo::bar`
  --> $DIR/tool_lints.rs:1:8
   |
LL | #[warn(foo::bar)]
   |        ^^^
   |
   = help: add `#![register_tool(foo)]` to the crate root

error[E0710]: unknown tool name `foo` found in scoped lint: `foo::bar`
  --> $DIR/tool_lints.rs:1:8
   |
LL | #[warn(foo::bar)]
   |        ^^^
   |
   = help: add `#![register_tool(foo)]` to the crate root

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0710`.