From 25639101ddd18f5bcc47e924015d9a3143840397 Mon Sep 17 00:00:00 2001
From: Mara Bos <m-ou.se@m-ou.se>
Date: Fri, 4 Jun 2021 10:43:25 +0200
Subject: [PATCH 1/2] Don't treat `cfg!()` as a constant.

---
 clippy_utils/src/consts.rs | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/clippy_utils/src/consts.rs b/clippy_utils/src/consts.rs
index 0d7fdeeb920..15c27d1a996 100644
--- a/clippy_utils/src/consts.rs
+++ b/clippy_utils/src/consts.rs
@@ -1,6 +1,6 @@
 #![allow(clippy::float_cmp)]
 
-use crate::{clip, sext, unsext};
+use crate::{clip, is_direct_expn_of, sext, unsext};
 use if_chain::if_chain;
 use rustc_ast::ast::{self, LitFloatType, LitKind};
 use rustc_data_structures::sync::Lrc;
@@ -230,7 +230,13 @@ impl<'a, 'tcx> ConstEvalLateContext<'a, 'tcx> {
         match e.kind {
             ExprKind::Path(ref qpath) => self.fetch_path(qpath, e.hir_id, self.typeck_results.expr_ty(e)),
             ExprKind::Block(block, _) => self.block(block),
-            ExprKind::Lit(ref lit) => Some(lit_to_constant(&lit.node, self.typeck_results.expr_ty_opt(e))),
+            ExprKind::Lit(ref lit) => {
+                if is_direct_expn_of(e.span, "cfg").is_some() {
+                    None
+                } else {
+                    Some(lit_to_constant(&lit.node, self.typeck_results.expr_ty_opt(e)))
+                }
+            },
             ExprKind::Array(vec) => self.multi(vec).map(Constant::Vec),
             ExprKind::Tup(tup) => self.multi(tup).map(Constant::Tuple),
             ExprKind::Repeat(value, _) => {

From 38ab1a616631944e8cef21c9441e2ef2ffa3a594 Mon Sep 17 00:00:00 2001
From: Mara Bos <m-ou.se@m-ou.se>
Date: Fri, 4 Jun 2021 10:43:39 +0200
Subject: [PATCH 2/2] Add test for not linting on assert!(cfg!(..)).

---
 tests/ui/assertions_on_constants.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tests/ui/assertions_on_constants.rs b/tests/ui/assertions_on_constants.rs
index e989de65404..6617ca183a8 100644
--- a/tests/ui/assertions_on_constants.rs
+++ b/tests/ui/assertions_on_constants.rs
@@ -28,4 +28,7 @@ fn main() {
     debug_assert!(false); // #3948
     assert_const!(3);
     assert_const!(-1);
+
+    // Don't lint on this:
+    assert!(cfg!(feature = "hey") || cfg!(not(feature = "asdf")));
 }