Merge #4903

4903: Add highlighting support for doc comments r=matklad a=Nashenas88

The language server protocol includes a semantic modifier for documentation. This change exports that modifier for doc comments so users can choose to highlight them differently compared to regular comments.

Example:
<img width="375" alt="Screen Shot 2020-06-16 at 10 34 14 AM" src="https://user-images.githubusercontent.com/1673130/84788271-f6599580-afbc-11ea-96e5-7a0215da620b.png">

CC @woody77 

Co-authored-by: Paul Daniel Faria <[email protected]>

4 files changed, 55 insertions, 41 deletions

diff --git a/crates/ra_ide/src/snapshots/highlight_doctest.html b/crates/ra_ide/src/snapshots/highlight_doctest.html
index f92a0aba5..f61c0daa5 100644
--- a/crates/ra_ide/src/snapshots/highlight_doctest.html
+++ b/crates/ra_ide/src/snapshots/highlight_doctest.html
@@ -39,48 +39,48 @@ pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padd
 <span class="keyword">impl</span> <span class="struct">Foo</span> {
     <span class="keyword">pub</span> <span class="keyword">const</span> <span class="constant declaration">bar</span>: <span class="builtin_type">bool</span> = <span class="bool_literal">true</span>;
 
-    <span class="comment">/// Constructs a new `Foo`.</span>
-    <span class="comment">///</span>
-    <span class="comment">/// # Examples</span>
-    <span class="comment">///</span>
-    <span class="comment">/// ```</span>
-    <span class="comment">/// #</span> <span class="attribute">#![</span><span class="function attribute">allow</span><span class="attribute">(unused_mut)]</span>
-    <span class="comment">/// </span><span class="keyword">let</span> <span class="keyword">mut</span> <span class="variable declaration mutable">foo</span>: <span class="struct">Foo</span> = <span class="struct">Foo</span>::<span class="function">new</span>();
-    <span class="comment">/// ```</span>
+    <span class="comment documentation">/// Constructs a new `Foo`.</span>
+    <span class="comment documentation">///</span>
+    <span class="comment documentation">/// # Examples</span>
+    <span class="comment documentation">///</span>
+    <span class="comment documentation">/// ```</span>
+    <span class="comment documentation">/// #</span> <span class="attribute">#![</span><span class="function attribute">allow</span><span class="attribute">(unused_mut)]</span>
+    <span class="comment documentation">/// </span><span class="keyword">let</span> <span class="keyword">mut</span> <span class="variable declaration mutable">foo</span>: <span class="struct">Foo</span> = <span class="struct">Foo</span>::<span class="function">new</span>();
+    <span class="comment documentation">/// ```</span>
     <span class="keyword">pub</span> <span class="keyword">const</span> <span class="keyword">fn</span> <span class="function declaration">new</span>() -&gt; <span class="struct">Foo</span> {
         <span class="struct">Foo</span> { <span class="field">bar</span>: <span class="bool_literal">true</span> }
     }
 
-    <span class="comment">/// `bar` method on `Foo`.</span>
-    <span class="comment">///</span>
-    <span class="comment">/// # Examples</span>
-    <span class="comment">///</span>
-    <span class="comment">/// ```</span>
-    <span class="comment">/// </span><span class="keyword">use</span> <span class="module">x</span>::<span class="module">y</span>;
-    <span class="comment">///</span>
-    <span class="comment">/// </span><span class="keyword">let</span> <span class="variable declaration">foo</span> = <span class="struct">Foo</span>::<span class="function">new</span>();
-    <span class="comment">///</span>
-    <span class="comment">/// </span><span class="comment">// calls bar on foo</span>
-    <span class="comment">/// </span><span class="macro">assert!</span>(foo.bar());
-    <span class="comment">///</span>
-    <span class="comment">/// </span><span class="keyword">let</span> <span class="variable declaration">bar</span> = <span class="variable">foo</span>.<span class="field">bar</span> || <span class="struct">Foo</span>::<span class="constant">bar</span>;
-    <span class="comment">///</span>
-    <span class="comment">/// </span><span class="comment">/* multi-line
-    </span><span class="comment">/// </span><span class="comment">       comment */</span>
-    <span class="comment">///</span>
-    <span class="comment">/// </span><span class="keyword">let</span> <span class="variable declaration">multi_line_string</span> = <span class="string_literal">"Foo
-    </span><span class="comment">/// </span><span class="string_literal">  bar
-    </span><span class="comment">/// </span><span class="string_literal">         "</span>;
-    <span class="comment">///</span>
-    <span class="comment">/// ```</span>
-    <span class="comment">///</span>
-    <span class="comment">/// ```rust,no_run</span>
-    <span class="comment">/// </span><span class="keyword">let</span> <span class="variable declaration">foobar</span> = <span class="struct">Foo</span>::<span class="function">new</span>().<span class="function">bar</span>();
-    <span class="comment">/// ```</span>
-    <span class="comment">///</span>
-    <span class="comment">/// ```sh</span>
-    <span class="comment">/// echo 1</span>
-    <span class="comment">/// ```</span>
+    <span class="comment documentation">/// `bar` method on `Foo`.</span>
+    <span class="comment documentation">///</span>
+    <span class="comment documentation">/// # Examples</span>
+    <span class="comment documentation">///</span>
+    <span class="comment documentation">/// ```</span>
+    <span class="comment documentation">/// </span><span class="keyword">use</span> <span class="module">x</span>::<span class="module">y</span>;
+    <span class="comment documentation">///</span>
+    <span class="comment documentation">/// </span><span class="keyword">let</span> <span class="variable declaration">foo</span> = <span class="struct">Foo</span>::<span class="function">new</span>();
+    <span class="comment documentation">///</span>
+    <span class="comment documentation">/// </span><span class="comment">// calls bar on foo</span>
+    <span class="comment documentation">/// </span><span class="macro">assert!</span>(foo.bar());
+    <span class="comment documentation">///</span>
+    <span class="comment documentation">/// </span><span class="keyword">let</span> <span class="variable declaration">bar</span> = <span class="variable">foo</span>.<span class="field">bar</span> || <span class="struct">Foo</span>::<span class="constant">bar</span>;
+    <span class="comment documentation">///</span>
+    <span class="comment documentation">/// </span><span class="comment">/* multi-line
+    </span><span class="comment documentation">/// </span><span class="comment">       comment */</span>
+    <span class="comment documentation">///</span>
+    <span class="comment documentation">/// </span><span class="keyword">let</span> <span class="variable declaration">multi_line_string</span> = <span class="string_literal">"Foo
+    </span><span class="comment documentation">/// </span><span class="string_literal">  bar
+    </span><span class="comment documentation">/// </span><span class="string_literal">         "</span>;
+    <span class="comment documentation">///</span>
+    <span class="comment documentation">/// ```</span>
+    <span class="comment documentation">///</span>
+    <span class="comment documentation">/// ```rust,no_run</span>
+    <span class="comment documentation">/// </span><span class="keyword">let</span> <span class="variable declaration">foobar</span> = <span class="struct">Foo</span>::<span class="function">new</span>().<span class="function">bar</span>();
+    <span class="comment documentation">/// ```</span>
+    <span class="comment documentation">///</span>
+    <span class="comment documentation">/// ```sh</span>
+    <span class="comment documentation">/// echo 1</span>
+    <span class="comment documentation">/// ```</span>
     <span class="keyword">pub</span> <span class="keyword">fn</span> <span class="function declaration">foo</span>(&<span class="self_keyword">self</span>) -&gt; <span class="builtin_type">bool</span> {
         <span class="bool_literal">true</span>
     }
diff --git a/crates/ra_ide/src/syntax_highlighting.rs b/crates/ra_ide/src/syntax_highlighting.rs
index 854b6cc6d..f8f790e59 100644
--- a/crates/ra_ide/src/syntax_highlighting.rs
+++ b/crates/ra_ide/src/syntax_highlighting.rs
@@ -489,7 +489,14 @@ fn highlight_element(
         }
 
         // Simple token-based highlighting
-        COMMENT => HighlightTag::Comment.into(),
+        COMMENT => {
+            let comment = element.into_token().and_then(ast::Comment::cast)?;
+            let h = HighlightTag::Comment;
+            match comment.kind().doc {
+                Some(_) => h | HighlightModifier::Documentation,
+                None => h.into(),
+            }
+        }
         STRING | RAW_STRING | RAW_BYTE_STRING | BYTE_STRING => HighlightTag::StringLiteral.into(),
         ATTR => HighlightTag::Attribute.into(),
         INT_NUMBER | FLOAT_NUMBER => HighlightTag::NumericLiteral.into(),
diff --git a/crates/ra_ide/src/syntax_highlighting/injection.rs b/crates/ra_ide/src/syntax_highlighting/injection.rs
index 929a5cc5c..415f24a6d 100644
--- a/crates/ra_ide/src/syntax_highlighting/injection.rs
+++ b/crates/ra_ide/src/syntax_highlighting/injection.rs
@@ -7,7 +7,10 @@ use hir::Semantics;
 use ra_syntax::{ast, AstToken, SyntaxNode, SyntaxToken, TextRange, TextSize};
 use stdx::SepBy;
 
-use crate::{call_info::ActiveParameter, Analysis, HighlightTag, HighlightedRange, RootDatabase};
+use crate::{
+    call_info::ActiveParameter, Analysis, HighlightModifier, HighlightTag, HighlightedRange,
+    RootDatabase,
+};
 
 use super::HighlightedRangeStack;
 
@@ -118,7 +121,7 @@ pub(super) fn extract_doc_comments(
                     range.start(),
                     range.start() + TextSize::try_from(pos).unwrap(),
                 ),
-                highlight: HighlightTag::Comment.into(),
+                highlight: HighlightTag::Comment | HighlightModifier::Documentation,
                 binding_hash: None,
             });
             line_start += range.len() - TextSize::try_from(pos).unwrap();
@@ -164,6 +167,7 @@ pub(super) fn highlight_doc_comment(
                 h.range.start() + start_offset,
                 h.range.end() + end_offset.unwrap_or(start_offset),
             );
+
             stack.add(h);
         }
     }
diff --git a/crates/ra_ide/src/syntax_highlighting/tags.rs b/crates/ra_ide/src/syntax_highlighting/tags.rs
index 400d22fb6..93bbb4b4d 100644
--- a/crates/ra_ide/src/syntax_highlighting/tags.rs
+++ b/crates/ra_ide/src/syntax_highlighting/tags.rs
@@ -56,6 +56,7 @@ pub enum HighlightModifier {
     /// `foo` in `fn foo(x: i32)` is a definition, `foo` in `foo(90 + 2)` is
     /// not.
     Definition,
+    Documentation,
     Mutable,
     Unsafe,
 }
@@ -108,6 +109,7 @@ impl HighlightModifier {
         HighlightModifier::Attribute,
         HighlightModifier::ControlFlow,
         HighlightModifier::Definition,
+        HighlightModifier::Documentation,
         HighlightModifier::Mutable,
         HighlightModifier::Unsafe,
     ];
@@ -117,6 +119,7 @@ impl HighlightModifier {
             HighlightModifier::Attribute => "attribute",
             HighlightModifier::ControlFlow => "control",
             HighlightModifier::Definition => "declaration",
+            HighlightModifier::Documentation => "documentation",
             HighlightModifier::Mutable => "mutable",
             HighlightModifier::Unsafe => "unsafe",
         }