From e3598c6e9fa1a9088038a0ff4cb95a391d6821ae Mon Sep 17 00:00:00 2001
From: djrenren <john@jrenner.net>
Date: Thu, 18 Jul 2019 11:54:24 -0700
Subject: [PATCH] Fix lexing of attributes and doc comments in Rust lexer
 (#957)

A bug was causing files starting with attributes and doc comments to
produce incorrect error nodes. This commit fixes that bug while also
allowing attributes to occur in positions other than the start of a
line, bringing it in line with Rust's grammar.
---
 lib/rouge/lexers/rust.rb | 19 +++++++++++--------
 spec/visual/samples/rust |  1 +
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/lib/rouge/lexers/rust.rb b/lib/rouge/lexers/rust.rb
index 4ecff63bc1..c80c3086ca 100644
--- a/lib/rouge/lexers/rust.rb
+++ b/lib/rouge/lexers/rust.rb
@@ -49,6 +49,7 @@ def macro_closed?
 
       start {
         @macro_delims = { ']' => 0, ')' => 0, '}' => 0 }
+        push :bol
       }
 
       delim_map = { '[' => ']', '(' => ')', '{' => '}' }
@@ -60,20 +61,21 @@ def macro_closed?
       )x
       size = /8|16|32|64/
 
-      state :start_line do
+      # Although not officially part of Rust, the rustdoc tool allows code in
+      # comments to begin with `#`. Code like this will be evaluated but not
+      # included in the HTML output produced by rustdoc. So that code intended
+      # for these comments can be higlighted with Rouge, the  Rust lexer needs
+      # to check if the beginning of the line begins with a `# `.
+      state :bol do
         mixin :whitespace
-        rule %r/\s+/, Text
-        rule %r/#\[/ do
-          token Name::Decorator; push :attribute
-        end
+        rule %r/#\s[^\n]*/, Comment::Special
         rule(//) { pop! }
-        rule %r/#\s[^\n]*/, Comment::Preproc
       end
 
       state :attribute do
         mixin :whitespace
         mixin :has_literals
-        rule %r/[(,)=]/, Name::Decorator
+        rule %r/[(,)=:]/, Name::Decorator
         rule %r/\]/, Name::Decorator, :pop!
         rule id, Name::Decorator
       end
@@ -85,8 +87,9 @@ def macro_closed?
       end
 
       state :root do
-        rule %r/\n/, Text, :start_line
+        rule %r/\n/, Text, :bol
         mixin :whitespace
+        rule %r/#!?\[/, Name::Decorator, :attribute
         rule %r/\b(?:#{Rust.keywords.join('|')})\b/, Keyword
         mixin :has_literals
 
diff --git a/spec/visual/samples/rust b/spec/visual/samples/rust
index 7f57c304e6..5b8c33cbeb 100644
--- a/spec/visual/samples/rust
+++ b/spec/visual/samples/rust
@@ -1,3 +1,4 @@
+#![test(a::b)]
 fn f() {
     let a = String::new("hello");
     let b: &str = a;