Auto merge of #106916 - lukas-code:overlapping-substs, r=estebank

Remove overlapping parts of multipart suggestions

This PR adds a debug assertion that the parts of a single substitution cannot overlap, fixes a overlapping substitution from the testsuite, and fixes https://github.com/rust-lang/rust/issues/106870.

Note that a single suggestion can still have multiple overlapping substitutions / possible edits, we just don't suggest overlapping replacements in a single edit anymore.

I've also included a fix for an unrelated bug where rustfix for `explicit_outlives_requirements` would produce multiple trailing commas for a where clause.

2 files changed, 45 insertions, 27 deletions

diff --git a/compiler/rustc_errors/src/diagnostic.rs b/compiler/rustc_errors/src/diagnostic.rs
index 51b2ff6a003..4ad24c1400d 100644
--- a/compiler/rustc_errors/src/diagnostic.rs
+++ b/compiler/rustc_errors/src/diagnostic.rs
@@ -629,19 +629,27 @@ impl Diagnostic {
         applicability: Applicability,
         style: SuggestionStyle,
     ) -> &mut Self {
-        assert!(!suggestion.is_empty());
-        debug_assert!(
-            !(suggestion.iter().any(|(sp, text)| sp.is_empty() && text.is_empty())),
-            "Span must not be empty and have no suggestion"
+        let mut parts = suggestion
+            .into_iter()
+            .map(|(span, snippet)| SubstitutionPart { snippet, span })
+            .collect::<Vec<_>>();
+
+        parts.sort_unstable_by_key(|part| part.span);
+
+        assert!(!parts.is_empty());
+        debug_assert_eq!(
+            parts.iter().find(|part| part.span.is_empty() && part.snippet.is_empty()),
+            None,
+            "Span must not be empty and have no suggestion",
+        );
+        debug_assert_eq!(
+            parts.array_windows().find(|[a, b]| a.span.overlaps(b.span)),
+            None,
+            "suggestion must not have overlapping parts",
         );
 
         self.push_suggestion(CodeSuggestion {
-            substitutions: vec![Substitution {
-                parts: suggestion
-                    .into_iter()
-                    .map(|(span, snippet)| SubstitutionPart { snippet, span })
-                    .collect(),
-            }],
+            substitutions: vec![Substitution { parts }],
             msg: self.subdiagnostic_message_to_diagnostic_message(msg),
             style,
             applicability,
@@ -802,25 +810,34 @@ impl Diagnostic {
         suggestions: impl IntoIterator<Item = Vec<(Span, String)>>,
         applicability: Applicability,
     ) -> &mut Self {
-        let suggestions: Vec<_> = suggestions.into_iter().collect();
-        debug_assert!(
-            !(suggestions
-                .iter()
-                .flatten()
-                .any(|(sp, suggestion)| sp.is_empty() && suggestion.is_empty())),
-            "Span must not be empty and have no suggestion"
-        );
+        let substitutions = suggestions
+            .into_iter()
+            .map(|sugg| {
+                let mut parts = sugg
+                    .into_iter()
+                    .map(|(span, snippet)| SubstitutionPart { snippet, span })
+                    .collect::<Vec<_>>();
+
+                parts.sort_unstable_by_key(|part| part.span);
+
+                assert!(!parts.is_empty());
+                debug_assert_eq!(
+                    parts.iter().find(|part| part.span.is_empty() && part.snippet.is_empty()),
+                    None,
+                    "Span must not be empty and have no suggestion",
+                );
+                debug_assert_eq!(
+                    parts.array_windows().find(|[a, b]| a.span.overlaps(b.span)),
+                    None,
+                    "suggestion must not have overlapping parts",
+                );
+
+                Substitution { parts }
+            })
+            .collect();
 
         self.push_suggestion(CodeSuggestion {
-            substitutions: suggestions
-                .into_iter()
-                .map(|sugg| Substitution {
-                    parts: sugg
-                        .into_iter()
-                        .map(|(span, snippet)| SubstitutionPart { snippet, span })
-                        .collect(),
-                })
-                .collect(),
+            substitutions,
             msg: self.subdiagnostic_message_to_diagnostic_message(msg),
             style: SuggestionStyle::ShowCode,
             applicability,
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index 535812fb0e2..d076fc08b0e 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -3,6 +3,7 @@
 //! This module contains the code for creating and emitting diagnostics.
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
+#![feature(array_windows)]
 #![feature(drain_filter)]
 #![feature(if_let_guard)]
 #![feature(is_terminal)]