Use hidden suggestions for unused imports lint

3 files changed, 49 insertions, 3 deletions

diff --git a/src/librustc_errors/diagnostic.rs b/src/librustc_errors/diagnostic.rs
index 588cdfcb1af..f0083949396 100644
--- a/src/librustc_errors/diagnostic.rs
+++ b/src/librustc_errors/diagnostic.rs
@@ -250,6 +250,32 @@ impl Diagnostic {
         self
     }
 
+    /// Prints out a message with for a multipart suggestion without showing the suggested code.
+    ///
+    /// This is intended to be used for suggestions that are obvious in what the changes need to
+    /// be from the message, showing the span label inline would be visually unpleasant
+    /// (marginally overlapping spans or multiline spans) and showing the snippet window wouldn't
+    /// improve understandability.
+    pub fn tool_only_multipart_suggestion(
+        &mut self,
+        msg: &str,
+        suggestion: Vec<(Span, String)>,
+        applicability: Applicability,
+    ) -> &mut Self {
+        self.suggestions.push(CodeSuggestion {
+            substitutions: vec![Substitution {
+                parts: suggestion
+                    .into_iter()
+                    .map(|(span, snippet)| SubstitutionPart { snippet, span })
+                    .collect(),
+            }],
+            msg: msg.to_owned(),
+            style: SuggestionStyle::CompletelyHidden,
+            applicability,
+        });
+        self
+    }
+
     /// Prints out a message with a suggested edit of the code.
     ///
     /// In case of short messages and a simple suggestion, rustc displays it as a label:
@@ -318,7 +344,7 @@ impl Diagnostic {
             }],
             msg: msg.to_owned(),
             style: SuggestionStyle::HideCodeInline,
-            applicability: applicability,
+            applicability,
         });
         self
     }
@@ -341,7 +367,7 @@ impl Diagnostic {
             }],
             msg: msg.to_owned(),
             style: SuggestionStyle::HideCodeInline,
-            applicability: applicability,
+            applicability,
         });
         self
     }
diff --git a/src/librustc_errors/diagnostic_builder.rs b/src/librustc_errors/diagnostic_builder.rs
index 9f838987f0c..4ed7b0a2456 100644
--- a/src/librustc_errors/diagnostic_builder.rs
+++ b/src/librustc_errors/diagnostic_builder.rs
@@ -205,6 +205,24 @@ impl<'a> DiagnosticBuilder<'a> {
         self
     }
 
+    pub fn tool_only_multipart_suggestion(
+        &mut self,
+        msg: &str,
+        suggestion: Vec<(Span, String)>,
+        applicability: Applicability,
+    ) -> &mut Self {
+        if !self.allow_suggestions {
+            return self
+        }
+        self.diagnostic.tool_only_multipart_suggestion(
+            msg,
+            suggestion,
+            applicability,
+        );
+        self
+    }
+
+
     pub fn span_suggestion(
         &mut self,
         sp: Span,
diff --git a/src/librustc_errors/emitter.rs b/src/librustc_errors/emitter.rs
index 5e7c5315d68..eaae1e9e848 100644
--- a/src/librustc_errors/emitter.rs
+++ b/src/librustc_errors/emitter.rs
@@ -48,7 +48,9 @@ impl Emitter for EmitterWriter {
                // don't display multiline suggestions as labels
                !sugg.substitutions[0].parts[0].snippet.contains('\n') &&
                // when this style is set we want the suggestion to be a message, not inline
-               sugg.style != SuggestionStyle::HideCodeAlways
+               sugg.style != SuggestionStyle::HideCodeAlways &&
+               // trivial suggestion for tooling's sake, never shown
+               sugg.style != SuggestionStyle::CompletelyHidden
             {
                 let substitution = &sugg.substitutions[0].parts[0].snippet.trim();
                 let msg = if substitution.len() == 0 || sugg.style.hide_inline() {