The following code yields "error[internal]: left behind trailing whitespace" error on rustfmt:

fn foo(
    a: <u16 as intercom::type_system::ExternType<
        intercom::type_system::AutomationTypeSystem,
    >>::ForeignType,
) {}

(Playground)

As far as I know, this has worked in the past, but has regressed somewhere within this year (unfortunately can't pinpoint the timeframe more accurately than that). Also I believe rustfmt does manage to format that properly, but adds an extra newline before the parameter.

From what I can tell, the output from rustfmt is:

fn foo(
    
    a: <u16 as intercom::type_system::ExternType<
        intercom::type_system::AutomationTypeSystem,
    >>::ForeignType,
) {}

(The second line has indent, but no other content.)

Unfortunately the lines are output from a proc macro and end up as top-level functions in the module. I'm using full mod paths to avoid polluting the caller scope by introducing elements with use statements. Although in my case I'm using rustfmt just to get nicer test output for macro expansion tests so it's not like this is breaking crate usage, just tests.

Meta

• rustfmt version: rustfmt 1.4.38-nightly (532d2b1 2021-12-03) and whatever playground has.
• Running with: cargo fmt or playground