From 8ce8c42e0bf66d32504659cbbe91ad2a0c315891 Mon Sep 17 00:00:00 2001
From: Esteban Küber <esteban@kuber.com.ar>
Date: Sat, 22 Jun 2024 04:32:49 +0000
Subject: Do not underline suggestions for code that is already there

When a suggestion part is for already present code, do not highlight it. If after that there are no highlights left, do not show the suggestion at all.

Fix clippy lint suggestion incorrectly treated as `span_help`.
---
 compiler/rustc_errors/src/emitter.rs | 21 +++++++++++++++++++--
 compiler/rustc_errors/src/lib.rs     | 22 ++++++++++++++++------
 2 files changed, 35 insertions(+), 8 deletions(-)

(limited to 'compiler/rustc_errors')

diff --git a/compiler/rustc_errors/src/emitter.rs b/compiler/rustc_errors/src/emitter.rs
index 73908e58085..8963b009c31 100644
--- a/compiler/rustc_errors/src/emitter.rs
+++ b/compiler/rustc_errors/src/emitter.rs
@@ -1767,7 +1767,10 @@ impl HumanEmitter {
         debug!(?suggestions);
 
         if suggestions.is_empty() {
-            // Suggestions coming from macros can have malformed spans. This is a heavy handed
+            // Here we check if there are suggestions that have actual code changes. We sometimes
+            // suggest the same code that is already there, instead of changing how we produce the
+            // suggestions and filtering there, we just don't emit the suggestion.
+            // Suggestions coming from macros can also have malformed spans. This is a heavy handed
             // approach to avoid ICEs by ignoring the suggestion outright.
             return Ok(());
         }
@@ -2046,7 +2049,9 @@ impl HumanEmitter {
                     assert!(underline_start >= 0 && underline_end >= 0);
                     let padding: usize = max_line_num_len + 3;
                     for p in underline_start..underline_end {
-                        if let DisplaySuggestion::Underline = show_code_change {
+                        if let DisplaySuggestion::Underline = show_code_change
+                            && is_different(sm, &part.snippet, part.span)
+                        {
                             // If this is a replacement, underline with `~`, if this is an addition
                             // underline with `+`.
                             buffer.putc(
@@ -2824,6 +2829,18 @@ impl Style {
     }
 }
 
+/// Whether the original and suggested code are the same.
+pub fn is_different(sm: &SourceMap, suggested: &str, sp: Span) -> bool {
+    let found = match sm.span_to_snippet(sp) {
+        Ok(snippet) => snippet,
+        Err(e) => {
+            warn!(error = ?e, "Invalid span {:?}", sp);
+            return true;
+        }
+    };
+    found != suggested
+}
+
 /// Whether the original and suggested code are visually similar enough to warrant extra wording.
 pub fn is_case_difference(sm: &SourceMap, suggested: &str, sp: Span) -> bool {
     // FIXME: this should probably be extended to also account for `FO0` → `FOO` and unicode.
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index 09855394cdb..ceebcd46a6f 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -50,7 +50,7 @@ pub use diagnostic_impls::{
     IndicateAnonymousLifetime, SingleLabelManySpans,
 };
 pub use emitter::ColorConfig;
-use emitter::{is_case_difference, DynEmitter, Emitter};
+use emitter::{is_case_difference, is_different, DynEmitter, Emitter};
 use registry::Registry;
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
 use rustc_data_structures::stable_hasher::{Hash128, StableHasher};
@@ -357,10 +357,16 @@ impl CodeSuggestion {
                             _ => 1,
                         })
                         .sum();
-                    line_highlight.push(SubstitutionHighlight {
-                        start: (cur_lo.col.0 as isize + acc) as usize,
-                        end: (cur_lo.col.0 as isize + acc + len) as usize,
-                    });
+                    if !is_different(sm, &part.snippet, part.span) {
+                        // Account for cases where we are suggesting the same code that's already
+                        // there. This shouldn't happen often, but in some cases for multipart
+                        // suggestions it's much easier to handle it here than in the origin.
+                    } else {
+                        line_highlight.push(SubstitutionHighlight {
+                            start: (cur_lo.col.0 as isize + acc) as usize,
+                            end: (cur_lo.col.0 as isize + acc + len) as usize,
+                        });
+                    }
                     buf.push_str(&part.snippet);
                     let cur_hi = sm.lookup_char_pos(part.span.hi());
                     // Account for the difference between the width of the current code and the
@@ -392,7 +398,11 @@ impl CodeSuggestion {
                 while buf.ends_with('\n') {
                     buf.pop();
                 }
-                Some((buf, substitution.parts, highlights, only_capitalization))
+                if highlights.iter().all(|parts| parts.is_empty()) {
+                    None
+                } else {
+                    Some((buf, substitution.parts, highlights, only_capitalization))
+                }
             })
             .collect()
     }
-- 
cgit 1.4.1-3-g733a5