rustdoc: use better highlighting for *const, *mut, and &mut

This generates more consistent HTML for these RefKeyWord combinations.

Before:

![image](https://user-images.githubusercontent.com/1593513/138742752-7e00a3f7-4621-4c62-82d1-3e4c2ef503d1.png)

After:

![image](https://user-images.githubusercontent.com/1593513/138743955-90abcdcd-fc88-4e2f-95bb-c1b1635c0001.png)

2 files changed, 23 insertions, 8 deletions

diff --git a/src/librustdoc/html/highlight.rs b/src/librustdoc/html/highlight.rs
index fa8ad2a37e7..de194d5e5d2 100644
--- a/src/librustdoc/html/highlight.rs
+++ b/src/librustdoc/html/highlight.rs
@@ -469,22 +469,37 @@ impl<'a> Classifier<'a> {
             // Assume that '&' or '*' is the reference or dereference operator
             // or a reference or pointer type. Unless, of course, it looks like
             // a logical and or a multiplication operator: `&&` or `* `.
-            TokenKind::Star => match self.peek() {
-                Some(TokenKind::Whitespace) => Class::Op,
+            TokenKind::Star => match self.tokens.peek() {
+                Some((TokenKind::Whitespace, _)) => Class::Op,
+                Some((TokenKind::Ident, "mut")) => {
+                    self.next();
+                    sink(Highlight::Token { text: "*mut", class: Some(Class::RefKeyWord) });
+                    return;
+                }
+                Some((TokenKind::Ident, "const")) => {
+                    self.next();
+                    sink(Highlight::Token { text: "*const", class: Some(Class::RefKeyWord) });
+                    return;
+                }
                 _ => Class::RefKeyWord,
             },
-            TokenKind::And => match lookahead {
-                Some(TokenKind::And) => {
+            TokenKind::And => match self.tokens.peek() {
+                Some((TokenKind::And, _)) => {
                     self.next();
                     sink(Highlight::Token { text: "&&", class: Some(Class::Op) });
                     return;
                 }
-                Some(TokenKind::Eq) => {
+                Some((TokenKind::Eq, _)) => {
                     self.next();
                     sink(Highlight::Token { text: "&=", class: Some(Class::Op) });
                     return;
                 }
-                Some(TokenKind::Whitespace) => Class::Op,
+                Some((TokenKind::Whitespace, _)) => Class::Op,
+                Some((TokenKind::Ident, "mut")) => {
+                    self.next();
+                    sink(Highlight::Token { text: "&mut", class: Some(Class::RefKeyWord) });
+                    return;
+                }
                 _ => Class::RefKeyWord,
             },
 
diff --git a/src/librustdoc/html/highlight/fixtures/sample.html b/src/librustdoc/html/highlight/fixtures/sample.html
index 22e650af7e2..b117a12e39f 100644
--- a/src/librustdoc/html/highlight/fixtures/sample.html
+++ b/src/librustdoc/html/highlight/fixtures/sample.html
@@ -15,11 +15,11 @@
 <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">target_os</span> <span class="op">=</span> <span class="string">&quot;linux&quot;</span>)]</span>
 <span class="kw">fn</span> <span class="ident">main</span>() -&gt; () {
     <span class="kw">let</span> <span class="ident">foo</span> <span class="op">=</span> <span class="bool-val">true</span> <span class="op">&amp;&amp;</span> <span class="bool-val">false</span> <span class="op">|</span><span class="op">|</span> <span class="bool-val">true</span>;
-    <span class="kw">let</span> <span class="kw">_</span>: <span class="kw-2">*</span><span class="kw">const</span> () <span class="op">=</span> <span class="number">0</span>;
+    <span class="kw">let</span> <span class="kw">_</span>: <span class="kw-2">*const</span> () <span class="op">=</span> <span class="number">0</span>;
     <span class="kw">let</span> <span class="kw">_</span> <span class="op">=</span> <span class="kw-2">&amp;</span><span class="ident">foo</span>;
     <span class="kw">let</span> <span class="kw">_</span> <span class="op">=</span> <span class="op">&amp;&amp;</span><span class="ident">foo</span>;
     <span class="kw">let</span> <span class="kw">_</span> <span class="op">=</span> <span class="kw-2">*</span><span class="ident">foo</span>;
-    <span class="macro">mac!</span>(<span class="ident">foo</span>, <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">bar</span>);
+    <span class="macro">mac!</span>(<span class="ident">foo</span>, <span class="kw-2">&amp;mut</span> <span class="ident">bar</span>);
     <span class="macro">assert!</span>(<span class="self">self</span>.<span class="ident">length</span> <span class="op">&lt;</span> <span class="ident">N</span> <span class="op">&amp;&amp;</span> <span class="ident">index</span> <span class="op">&lt;</span><span class="op">=</span> <span class="self">self</span>.<span class="ident">length</span>);
     <span class="ident">::std::env::var</span>(<span class="string">&quot;gateau&quot;</span>).<span class="ident">is_ok</span>();
     <span class="attribute">#[<span class="ident">rustfmt::skip</span>]</span>