From aa82fd6d1dd2f2ac6a44dbfa99e1de779b58428a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Esteban=20K=C3=BCber?= <esteban@kuber.com.ar>
Date: Thu, 24 Oct 2024 00:20:04 +0000
Subject: [PATCH] Tweak highlighting when trait is available for different type

When printing

```
  = help: the trait `chumsky::private::ParserSealed<'_, &'a str, ((), ()), chumsky::extra::Full<EmptyErr, (), ()>>` is implemented for `Then<Ignored<chumsky::combinator::Filter<chumsky::primitive::Any<&str, chumsky::extra::Full<EmptyErr, (), ()>>, {closure@src/main.rs:9:17: 9:27}>, char>, chumsky::combinator::Map<impl CSTParser<'a, O>, O, {closure@src/main.rs:11:24: 11:27}>, (), (), chumsky::extra::Full<EmptyErr, (), ()>>`
  = help: for that trait implementation, expected `((), ())`, found `()`
```

Highlight only the `expected` and `found` types, instead of the full type in the first `help`.
---
 .../traits/fulfillment_errors.rs              | 19 ++++++++++++++-----
 ...between-expected-trait-and-found-trait.svg |  4 ++--
 2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
index b7e2ed391cd..1852837d5c7 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
@@ -1835,6 +1835,7 @@ pub(super) fn report_similar_impl_candidates(
                     if impl_trait_ref.references_error() {
                         return false;
                     }
+                    let self_ty = impl_trait_ref.self_ty().to_string();
                     err.highlighted_help(vec![
                         StringPart::normal(format!(
                             "the trait `{}` ",
@@ -1842,16 +1843,24 @@ pub(super) fn report_similar_impl_candidates(
                         )),
                         StringPart::highlighted("is"),
                         StringPart::normal(" implemented for `"),
-                        StringPart::highlighted(impl_trait_ref.self_ty().to_string()),
+                        if let [TypeError::Sorts(_)] = &terrs[..] {
+                            StringPart::normal(self_ty)
+                        } else {
+                            StringPart::highlighted(self_ty)
+                        },
                         StringPart::normal("`"),
                     ]);
 
                     if let [TypeError::Sorts(exp_found)] = &terrs[..] {
                         let exp_found = self.resolve_vars_if_possible(*exp_found);
-                        err.help(format!(
-                            "for that trait implementation, expected `{}`, found `{}`",
-                            exp_found.expected, exp_found.found
-                        ));
+                        err.highlighted_help(vec![
+                            StringPart::normal("for that trait implementation, "),
+                            StringPart::normal("expected `"),
+                            StringPart::highlighted(exp_found.expected.to_string()),
+                            StringPart::normal("`, found `"),
+                            StringPart::highlighted(exp_found.found.to_string()),
+                            StringPart::normal("`"),
+                        ]);
                     }
 
                     true
diff --git a/tests/ui/impl-trait/diagnostics/highlight-difference-between-expected-trait-and-found-trait.svg b/tests/ui/impl-trait/diagnostics/highlight-difference-between-expected-trait-and-found-trait.svg
index aaf08b9a246..e09b96e5ff2 100644
--- a/tests/ui/impl-trait/diagnostics/highlight-difference-between-expected-trait-and-found-trait.svg
+++ b/tests/ui/impl-trait/diagnostics/highlight-difference-between-expected-trait-and-found-trait.svg
@@ -33,9 +33,9 @@
 </tspan>
     <tspan x="10px" y="118px"><tspan>   </tspan><tspan class="fg-ansi256-012 bold">|</tspan>
 </tspan>
-    <tspan x="10px" y="136px"><tspan>   </tspan><tspan class="fg-ansi256-012 bold">= </tspan><tspan class="bold">help</tspan><tspan>: the trait `Bar&lt;()&gt;` </tspan><tspan class="fg-magenta bold">is</tspan><tspan> implemented for `</tspan><tspan class="fg-magenta bold">Struct</tspan><tspan>`</tspan>
+    <tspan x="10px" y="136px"><tspan>   </tspan><tspan class="fg-ansi256-012 bold">= </tspan><tspan class="bold">help</tspan><tspan>: the trait `Bar&lt;()&gt;` </tspan><tspan class="fg-magenta bold">is</tspan><tspan> implemented for `Struct`</tspan>
 </tspan>
-    <tspan x="10px" y="154px"><tspan>   </tspan><tspan class="fg-ansi256-012 bold">= </tspan><tspan class="bold">help</tspan><tspan>: for that trait implementation, expected `()`, found `i32`</tspan>
+    <tspan x="10px" y="154px"><tspan>   </tspan><tspan class="fg-ansi256-012 bold">= </tspan><tspan class="bold">help</tspan><tspan>: for that trait implementation, expected `</tspan><tspan class="fg-magenta bold">()</tspan><tspan>`, found `</tspan><tspan class="fg-magenta bold">i32</tspan><tspan>`</tspan>
 </tspan>
     <tspan x="10px" y="172px"><tspan class="fg-ansi256-010 bold">note</tspan><tspan>: required for `Struct` to implement `Foo&lt;i32&gt;`</tspan>
 </tspan>