Allow Colon : in HTML Attribute Names (#496)

This pull request updates the parser to allow HTML Attributes to start
with a colon, which is typical in the Vue.js style:

```html
<div :class="classes"></div>
```

Previously, this caused a syntax error: 
```js
@ UnexpectedError (location: (1:5)-(1:6))
├── message: "Unexpected Token. Expected: `TOKEN_IDENTIFIER, TOKEN_AT, TOKEN_ERB_START,TOKEN_WHITESPACE, or TOKEN_NEWLINE`, found: `TOKEN_COLON`."
├── description: "Unexpected Token"
├── expected: "TOKEN_IDENTIFIER, TOKEN_AT, TOKEN_ERB_START,TOKEN_WHITESPACE, or TOKEN_NEWLINE"
└── found: "TOKEN_COLON"
```

Now this parses as:

```js
@ HTMLAttributeNode (location: (1:5)-(1:21))
├── errors: []
├── name: 
│   └── @ HTMLAttributeNameNode (location: (1:5)-(1:11))
│       ├── errors: []
│       └── children: (1 item)
│           └── @ LiteralNode (location: (1:5)-(1:11))
│               ├── errors: []
│               └── content: ":class"
│                      
├── equals: "=" (location: (1:11)-(1:12))
└── value: 
    └── @ HTMLAttributeValueNode (location: (1:12)-(1:21))
        ├── errors: []
        ├── open_quote: """ (location: (1:12)-(1:13))
        ├── children: (1 item)
        │   └── @ LiteralNode (location: (1:13)-(1:20))
        │       ├── errors: []
        │       └── content: "classes"
        │       
        │   
        ├── close_quote: """ (location: (1:20)-(1:21))
        └── quoted: true
```

Author: marcoroth

src/parser.c

@@ -805,6 +805,20 @@ static AST_HTML_OPEN_TAG_NODE_T* parser_parse_html_open_tag(parser_T* parser) {
       continue;
     }
 
+    if (parser->current_token->type == TOKEN_COLON) {
+      lexer_T lexer_copy = *parser->lexer;
+      token_T* next_token = lexer_next_token(&lexer_copy);
+
+      if (next_token && next_token->type == TOKEN_IDENTIFIER) {
+        token_free(next_token);
+        array_append(children, parser_parse_html_attribute(parser));
+
+        continue;
+      }
+
+      token_free(next_token);
+    }
+
     parser_append_unexpected_error(
       parser,
       "Unexpected Token",

test/parser/attributes_test.rb

@@ -159,5 +159,37 @@ class AttributesTest < Minitest::Spec
     test "attribute with backtick containing HTML (invalid)" do
       assert_parsed_snapshot(%(<div data-template=`<span>Hello</span>`></div>))
     end
+
+    test "Vue-style directive attribute with value" do
+      assert_parsed_snapshot(%(<div :value="something"></div>))
+    end
+
+    test "Vue-style directive attributes multiple" do
+      assert_parsed_snapshot(%(<input :model="user" :disabled="isDisabled" :class="className"></input>))
+    end
+
+    test "Vue-style directive attribute without value" do
+      assert_parsed_snapshot(%(<div :disabled></div>))
+    end
+
+    test "Mixed Vue directives and regular attributes" do
+      assert_parsed_snapshot(%(<div id="app" :class="dynamicClass" data-test="static"></div>))
+    end
+
+    test "Standalone colon with space is invalid" do
+      assert_parsed_snapshot(%(<div : class="hello"></div>))
+    end
+
+    test "Colon immediately followed by attribute name is valid" do
+      assert_parsed_snapshot(%(<div :class="hello"></div>))
+    end
+
+    test "Double colon is invalid" do
+      assert_parsed_snapshot(%(<div ::value="hello"></div>))
+    end
+
+    test "Vue directive with namespace-like syntax" do
+      assert_parsed_snapshot(%(<div :v-model="user"></div>))
+    end
   end
 end