union pseudo keyword is no longer accepted in enum variant position as of 2019-11-25

[CAD97]

playground

enum Rule {
    union,
}

Initially reported in arabidopsis/typescript-definitions#4 and then pest-parser/pest#429.

My best guess is #66592; cc @estebank

This issue has been assigned to @kamleshbhalui via this comment.

[CAD97]

Interesting note: this does not apply to async when in edition=2015 mode.

[Centril]

Regression introduced in #66641. My bad... should have remembered that union is contextual!

The fix should be to make changes around here:

rust/src/librustc_parse/parser/item.rs

Line 1742 in 4007d4e

self.token.is_keyword(kw::Union)

You'll want to use look-ahead to ensure that an identifier follows union.

Also, add a regression test for enum A { union }, enum B { union {} }, and enum C { union() }.

[Dylan-DPC-zz]

@rustbot claim @kamleshbhalui

[rustbot]

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[Dylan-DPC-zz]

@rustbot assign @kamleshbhalui

[estebank]

You'll need to change

    fn recover_nested_adt_item(&mut self, keyword: Symbol) -> PResult<'a, bool> {
        if self.token.is_keyword(kw::Enum) ||
            self.token.is_keyword(kw::Struct) ||
            self.token.is_keyword(kw::Union)
        {

to something along the lines of

    fn recover_nested_adt_item(&mut self, keyword: Symbol) -> PResult<'a, bool> {
        if (self.token.is_keyword(kw::Enum) ||
            self.token.is_keyword(kw::Struct) ||
            self.token.is_keyword(kw::Union))
            && self.look_ahead(1, |t| t.is_ident())
        {