Bad indent for anonymous field types with trailing comma

[yohannd1]

Before anything, a minimal vimrc:

set nocompatible
" set runtimepath^=/path/to/zig.vim
syntax on
filetype plugin indent on

And my neovim version:

$ nvim --version
NVIM v0.4.4
Build type: Release
LuaJIT 2.0.5
Compilation: /usr/bin/cc -D_FORTIFY_SOURCE=2 -march=x86-64 -mtune=generic -O2 -pipe -fno-plt -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=1 -O2 -DNDEBUG -DMIN_LOG_LEVEL=3 -Wall -Wextra -pedantic -Wno-unused-parameter -Wstrict-prototypes -std=gnu99 -Wshadow -Wconversion -Wmissing-prototypes -Wimplicit-fallthrough -Wvla -fstack-protector-strong -fno-common -fdiagnostics-color=always -DINCLUDE_GENERATED_DECLARATIONS -D_GNU_SOURCE -DNVIM_MSGPACK_HAS_FLOAT32 -DNVIM_UNIBI_HAS_VAR_FROM -I/build/neovim/src/build/config -I/build/neovim/src/neovim-0.4.4/src -I/usr/include -I/build/neovim/src/build/src/nvim/auto -I/build/neovim/src/build/include
Compiled by builduser

Features: +acl +iconv +tui
See ":help feature-compile"

   system vimrc file: "$VIM/sysinit.vim"
  fall-back for $VIM: "/usr/share/nvim"

Run :checkhealth for more info

Here we have a struct declaration, with one of the fields being of type <anonymous enum>.

pub const St = struct {
    anon_field: enum {
    },
};

For some strange reason, this specific example doesn't indent properly. If indenting the line with the }, in it (using ==), it becomes:

pub const St = struct {
    anon_field: enum {
},
};

That doesn't happen, though, if there is any non-empty line between the opening and closing brackets of the enum declaration:

pub const St = struct {
    anon_field: enum {
        some_field
    }, // indents properly
};

Some other situations:

// if there is no trailing comma, it indents properly
pub const St = struct {
    anon_field: enum {
        some_field
    }
};

// if there is any character other than a comma after the line, it also indents properly
pub const St = struct {
    anon_field: enum {
    }, // this comment prevents the indent problem
};
pub const St = struct {
    anon_field: enum {
    }, 
    // (there's a trailing whitespace on the line above)
};

// empty lines do not solve the problem
pub const St = struct {
    anon_field: enum {

},
};

// identifiers that are on the same line as the opening bracket do not solve the issue either.
pub const St = struct {
    anon_field: enum { foo, bar
},
};
pub const St = struct {
    anon_field: enum { foo, bar,
        a // it solved with this one here, though
    },
};

// it also happens with `struct` and any other type. The problem seems to be on the brackets themselves.
pub const St = struct {
    anon_field: struct {
},
};
pub const St = struct {
    anon_field: union(enum) {
},
};
pub const St = struct {
    anon_field: {
},
};