"insert [...] on conflict" hangs on conflict on an unmentioned gist index

Hi,

The last insert of the following statements causes a busy loop that does not complete:

create table gist_test (
bar text,
foo text,
constraint gist_test_bar_unique unique (bar),
constraint gist_test_foo_gist_unique exclude using gist (foo with =)
);
insert into gist_test (bar, foo) values ('bar', 'foo');
insert into gist_test (bar, foo) values ('baz', 'foo’) on conflict on constraint gist_test_bar_unique do nothing;

Expected behaviour is a conflict on the gist_test_foo_gist_unique -index.

The issue is present at least in the following PostgreSQL versions:

PostgreSQL 9.5.3 on x86_64-apple-darwin15.4.0, compiled by Apple LLVM version 7.3.0 (clang-703.0.31), 64-bit
PostgreSQL 9.5.3 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-16), 64-bit

Best regards,

- Heikki Rauhala.