Unnamed argument in type alias parsed incorrectly

[hanmertens]

The following type alias with an unnamed argument (_)

pub type test = unsafe extern "C" fn(_: *const gchar) -> ();

gives some errors when parsed by rust-analyzer (commit 29f5e7e):

 test.rs     1  39 error           rust-analyzer: Syntax Error: expected type (lsp-ui)
 test.rs     1  39 error           rust-analyzer: Syntax Error: expected COMMA (lsp-ui)
 test.rs     1  40 error           rust-analyzer: Syntax Error: expected COMMA (lsp-ui)

When the variable is named or the unnamed variable is in a function declaration no syntax errors are generated:

pub type test = unsafe extern "C" fn(test: *const gchar) -> ();
unsafe extern "C" fn test(_: *const gchar) -> ();