From fa3eebb26e103a8f0fa81b378e8c8525a80baf32 Mon Sep 17 00:00:00 2001
From: Esteban Kuber <esteban@kuber.com.ar>
Date: Wed, 17 Nov 2021 23:35:38 +0000
Subject: [PATCH] Modify `bounds_span` to ignore bounds coming from a `derive`
 macro

---
 compiler/rustc_hir/src/hir.rs                 | 15 +++++++++---
 .../derive-macro-missing-bounds.stderr        | 24 +++++++++----------
 2 files changed, 24 insertions(+), 15 deletions(-)

diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index 69f770265dda..d5132ad5bdf2 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -17,7 +17,7 @@ use rustc_index::vec::IndexVec;
 use rustc_macros::HashStable_Generic;
 use rustc_span::source_map::Spanned;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
-use rustc_span::{def_id::LocalDefId, BytePos, MultiSpan, Span, DUMMY_SP};
+use rustc_span::{def_id::LocalDefId, BytePos, ExpnKind, MacroKind, MultiSpan, Span, DUMMY_SP};
 use rustc_target::asm::InlineAsmRegOrRegClass;
 use rustc_target::spec::abi::Abi;
 
@@ -527,8 +527,17 @@ pub struct GenericParam<'hir> {
 impl GenericParam<'hir> {
     pub fn bounds_span(&self) -> Option<Span> {
         self.bounds.iter().fold(None, |span, bound| {
-            let span = span.map(|s| s.to(bound.span())).unwrap_or_else(|| bound.span());
-            Some(span)
+            if let ExpnKind::Macro(MacroKind::Derive, _) =
+                bound.span().ctxt().outer_expn_data().kind
+            {
+                // We ignore bounds that come from exclusively from a `#[derive(_)]`, because we
+                // can't really point at them, and we sometimes use this method to get a span
+                // appropriate for suggestions.
+                span
+            } else {
+                let span = span.map(|s| s.to(bound.span())).unwrap_or_else(|| bound.span());
+                Some(span)
+            }
         })
     }
 }
diff --git a/src/test/ui/suggestions/derive-macro-missing-bounds.stderr b/src/test/ui/suggestions/derive-macro-missing-bounds.stderr
index 396781059309..7a4f7e209c19 100644
--- a/src/test/ui/suggestions/derive-macro-missing-bounds.stderr
+++ b/src/test/ui/suggestions/derive-macro-missing-bounds.stderr
@@ -31,10 +31,10 @@ LL |     impl<T: Debug + Trait> Debug for Inner<T> {
    = note: required because of the requirements on the impl of `Debug` for `&c::Inner<T>`
    = note: required for the cast to the object type `dyn Debug`
    = note: this error originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info)
-help: consider further restricting this bound
+help: consider restricting type parameter `T`
    |
-LL |     #[derive(Debug + c::Trait)]
-   |                    ++++++++++
+LL |     struct Outer<T: c::Trait>(Inner<T>);
+   |                   ++++++++++
 
 error[E0277]: the trait bound `T: d::Trait` is not satisfied
   --> $DIR/derive-macro-missing-bounds.rs:56:21
@@ -53,10 +53,10 @@ LL |     impl<T> Debug for Inner<T> where T: Debug, T: Trait {
    = note: required because of the requirements on the impl of `Debug` for `&d::Inner<T>`
    = note: required for the cast to the object type `dyn Debug`
    = note: this error originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info)
-help: consider further restricting this bound
+help: consider restricting type parameter `T`
    |
-LL |     #[derive(Debug + d::Trait)]
-   |                    ++++++++++
+LL |     struct Outer<T: d::Trait>(Inner<T>);
+   |                   ++++++++++
 
 error[E0277]: the trait bound `T: e::Trait` is not satisfied
   --> $DIR/derive-macro-missing-bounds.rs:71:21
@@ -75,10 +75,10 @@ LL |     impl<T> Debug for Inner<T> where T: Debug + Trait {
    = note: required because of the requirements on the impl of `Debug` for `&e::Inner<T>`
    = note: required for the cast to the object type `dyn Debug`
    = note: this error originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info)
-help: consider further restricting this bound
+help: consider restricting type parameter `T`
    |
-LL |     #[derive(Debug + e::Trait)]
-   |                    ++++++++++
+LL |     struct Outer<T: e::Trait>(Inner<T>);
+   |                   ++++++++++
 
 error[E0277]: the trait bound `T: f::Trait` is not satisfied
   --> $DIR/derive-macro-missing-bounds.rs:86:21
@@ -97,10 +97,10 @@ LL |     impl<T: Debug> Debug for Inner<T> where T: Trait {
    = note: required because of the requirements on the impl of `Debug` for `&f::Inner<T>`
    = note: required for the cast to the object type `dyn Debug`
    = note: this error originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info)
-help: consider further restricting this bound
+help: consider restricting type parameter `T`
    |
-LL |     #[derive(Debug + f::Trait)]
-   |                    ++++++++++
+LL |     struct Outer<T: f::Trait>(Inner<T>);
+   |                   ++++++++++
 
 error: aborting due to 5 previous errors