Add regression test

Author: JonathanBrouwer

tests/incremental/hashes/delayed_lints.rs

@@ -0,0 +1,27 @@
+// Some lints are emitted in `rustc_attr_parsing`, during ast lowering.
+// Emitting these lints is delayed until after ast lowering.
+// This test tests that the delayed hints are correctly hashed for incremental.
+
+//@ check-pass
+//@ revisions: cfail1 cfail2 cfail3
+//@ compile-flags: -Z query-dep-graph -O -Zincremental-ignore-spans
+//@ ignore-backends: gcc
+#![feature(rustc_attrs)]
+
+// This attribute is here so the `has_delayed_lints` will be true on all revisions
+#[doc(test = 1)]
+//~^ WARN `#[doc(test(...)]` takes a list of attributes [invalid_doc_attributes]
+
+// Between revision 1 and 2, the only thing we change is that we add "test = 2"
+// This will emit an extra delayed lint, but it will not change the HIR hash.
+// We check that even tho the HIR hash didn't change, the extra lint is emitted
+#[cfg_attr(cfail1, doc(hidden))]
+#[cfg_attr(not(cfail1), doc(hidden, test = 2))]
+//[cfail2,cfail3]~^ WARN `#[doc(test(...)]` takes a list of attributes [invalid_doc_attributes]
+
+// The HIR hash should not change between revisions, for this test to be representative
+#[rustc_clean(cfg="cfail2")]
+#[rustc_clean(cfg="cfail3")]
+trait Test {}
+
+fn main() {}