Special-case item attributes in the suggestion output

Author: estebank

compiler/rustc_errors/src/emitter.rs

@@ -1886,6 +1886,7 @@ impl EmitterWriter {
             }
             let mut unhighlighted_lines = Vec::new();
             let mut last_pos = 0;
+            let mut is_item_attribute = false;
             for (line_pos, (line, highlight_parts)) in lines.by_ref().zip(highlights).enumerate() {
                 last_pos = line_pos;
                 debug!(%line_pos, %line, ?highlight_parts);
@@ -1895,6 +1896,12 @@ impl EmitterWriter {
                     unhighlighted_lines.push((line_pos, line));
                     continue;
                 }
+                if highlight_parts.len() == 1
+                    && line.trim().starts_with("#[")
+                    && line.trim().ends_with(']')
+                {
+                    is_item_attribute = true;
+                }
 
                 match unhighlighted_lines.len() {
                     0 => (),
@@ -1971,11 +1978,13 @@ impl EmitterWriter {
                     is_multiline,
                 )
             }
-            if let DisplaySuggestion::Add = show_code_change {
+            if let DisplaySuggestion::Add = show_code_change && is_item_attribute {
                 // The suggestion adds an entire line of code, ending on a newline, so we'll also
                 // print the *following* line, to provide context of what we're advicing people to
                 // do. Otherwise you would only see contextless code that can be confused for
                 // already existing code, despite the colors and UI elements.
+                // We special case `#[derive(_)]\n` and other attribute suggestions, because those
+                // are the ones where context is most useful.
                 let file_lines = sm
                     .span_to_lines(span.primary_span().unwrap().shrink_to_hi())
                     .expect("span_to_lines failed when emitting suggestion");

src/tools/clippy/tests/ui/crashes/ice-6252.stderr

@@ -7,13 +7,10 @@ LL |     _n: PhantomData,
 help: consider importing one of these items
    |
 LL + use core::marker::PhantomData;
-LL | trait TypeVal<T> {
    |
 LL + use serde::__private::PhantomData;
-LL | trait TypeVal<T> {
    |
 LL + use std::marker::PhantomData;
-LL | trait TypeVal<T> {
    |
 
 error[E0412]: cannot find type `VAL` in this scope

src/tools/clippy/tests/ui/new_without_default.stderr

@@ -14,7 +14,6 @@ LL +     fn default() -> Self {
 LL +         Self::new()
 LL +     }
 LL + }
-LL | impl Foo {
    |
 
 error: you should consider adding a `Default` implementation for `Bar`
@@ -32,7 +31,6 @@ LL +     fn default() -> Self {
 LL +         Self::new()
 LL +     }
 LL + }
-LL | impl Bar {
    |
 
 error: you should consider adding a `Default` implementation for `LtKo<'c>`
@@ -50,7 +48,6 @@ LL +     fn default() -> Self {
 LL +         Self::new()
 LL +     }
 LL + }
-LL | impl<'c> LtKo<'c> {
    |
 
 error: you should consider adding a `Default` implementation for `NewNotEqualToDerive`
@@ -68,7 +65,6 @@ LL +     fn default() -> Self {
 LL +         Self::new()
 LL +     }
 LL + }
-LL | impl NewNotEqualToDerive {
    |
 
 error: you should consider adding a `Default` implementation for `FooGenerics<T>`
@@ -86,7 +82,6 @@ LL +     fn default() -> Self {
 LL +         Self::new()
 LL +     }
 LL + }
-LL | impl<T> FooGenerics<T> {
    |
 
 error: you should consider adding a `Default` implementation for `BarGenerics<T>`
@@ -104,7 +99,6 @@ LL +     fn default() -> Self {
 LL +         Self::new()
 LL +     }
 LL + }
-LL | impl<T: Copy> BarGenerics<T> {
    |
 
 error: you should consider adding a `Default` implementation for `Foo<T>`

tests/ui/coherence/coherence_inherent.stderr

@@ -8,7 +8,6 @@ LL |         s.the_fn();
 help: the following trait is implemented but not in scope; perhaps add a `use` for it:
    |
 LL +     use Lib::TheTrait;
-LL |     use Lib::TheStruct;
    |
 
 error: aborting due to previous error

tests/ui/coherence/coherence_inherent_cc.stderr

@@ -8,7 +8,6 @@ LL |         s.the_fn();
 help: the following trait is implemented but not in scope; perhaps add a `use` for it:
    |
 LL +     use coherence_inherent_cc_lib::TheTrait;
-LL |     use coherence_inherent_cc_lib::TheStruct;
    |
 
 error: aborting due to previous error

tests/ui/const-generics/generic_const_exprs/issue-94287.stderr

@@ -9,7 +9,6 @@ help: consider enabling this feature
   --> $DIR/issue-94287.rs:1:1
    |
 LL + #![feature(generic_const_exprs)]
-LL | #![feature(generic_const_exprs)]
    |
 
 error: aborting due to previous error

tests/ui/const-generics/issues/issue-82956.stderr

@@ -7,16 +7,12 @@ LL |         let mut iter = IntoIter::new(self);
 help: consider importing one of these items
    |
 LL + use std::array::IntoIter;
-LL | pub struct ConstCheck<const CHECK: bool>;
    |
 LL + use std::collections::binary_heap::IntoIter;
-LL | pub struct ConstCheck<const CHECK: bool>;
    |
 LL + use std::collections::btree_map::IntoIter;
-LL | pub struct ConstCheck<const CHECK: bool>;
    |
 LL + use std::collections::btree_set::IntoIter;
-LL | pub struct ConstCheck<const CHECK: bool>;
    |
      and 8 other candidates
 

tests/ui/derived-errors/issue-31997-1.stderr

@@ -7,7 +7,6 @@ LL |     let mut map = HashMap::new();
 help: consider importing this struct
    |
 LL + use std::collections::HashMap;
-LL | use std::io::prelude::*;
    |
 
 error: aborting due to previous error

tests/ui/did_you_mean/issue-56028-there-is-an-enum-variant.stderr

@@ -25,16 +25,12 @@ LL | fn setup() -> Set { Set }
 help: consider importing one of these items
    |
 LL + use AffixHeart::Set;
-LL | enum PutDown { Set }
    |
 LL + use CauseToBe::Set;
-LL | enum PutDown { Set }
    |
 LL + use Determine::Set;
-LL | enum PutDown { Set }
    |
 LL + use PutDown::Set;
-LL | enum PutDown { Set }
    |
      and 3 other candidates
 

tests/ui/hygiene/globs.stderr

@@ -14,7 +14,6 @@ LL |         g();
 help: consider importing this function
    |
 LL + use foo::f;
-LL | mod foo {
    |
 
 error[E0425]: cannot find function `g` in this scope
@@ -41,7 +40,6 @@ LL |     f();
 help: consider importing this function
    |
 LL + use bar::g;
-LL | mod foo {
    |
 
 error[E0425]: cannot find function `f` in this scope