From b87f5bc55a4dd4210c0d8bcd1ea68d26c75c75d0 Mon Sep 17 00:00:00 2001
From: Philipp Hansch <dev@phansch.net>
Date: Mon, 4 Mar 2019 22:56:33 +0100
Subject: [PATCH] Don't trigger missing_const_for_fn in external macros

As reported in #3841. Only fixes the part where it triggers on the
`derive`.
---
 clippy_lints/src/missing_const_for_fn.rs       | 4 ++--
 tests/ui/missing_const_for_fn/cant_be_const.rs | 4 ++++
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/clippy_lints/src/missing_const_for_fn.rs b/clippy_lints/src/missing_const_for_fn.rs
index 00a3de0632f8..bd9e8ce8b8df 100644
--- a/clippy_lints/src/missing_const_for_fn.rs
+++ b/clippy_lints/src/missing_const_for_fn.rs
@@ -2,7 +2,7 @@ use crate::utils::{is_entrypoint_fn, span_lint};
 use rustc::hir;
 use rustc::hir::intravisit::FnKind;
 use rustc::hir::{Body, Constness, FnDecl, HirId};
-use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
+use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintPass};
 use rustc::{declare_tool_lint, lint_array};
 use rustc_mir::transform::qualify_min_const_fn::is_min_const_fn;
 use syntax_pos::Span;
@@ -82,7 +82,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MissingConstForFn {
     ) {
         let def_id = cx.tcx.hir().local_def_id_from_hir_id(hir_id);
 
-        if is_entrypoint_fn(cx, def_id) {
+        if in_external_macro(cx.tcx.sess, span) || is_entrypoint_fn(cx, def_id) {
             return;
         }
 
diff --git a/tests/ui/missing_const_for_fn/cant_be_const.rs b/tests/ui/missing_const_for_fn/cant_be_const.rs
index 36efe16b84f0..4a2e6adb8f06 100644
--- a/tests/ui/missing_const_for_fn/cant_be_const.rs
+++ b/tests/ui/missing_const_for_fn/cant_be_const.rs
@@ -55,3 +55,7 @@ trait Foo {
         33
     }
 }
+
+// Don't lint in external macros (derive)
+#[derive(PartialEq, Eq)]
+struct Point(isize, isize);