fix: improve missing attribute value error (#134)

Author: DylanPiercey

.changeset/moody-donuts-enjoy.md

@@ -0,0 +1,5 @@
+---
+"htmljs-parser": patch
+---
+
+Improve missing attribute error when the tag is immediately closed without the attribute value.

src/__tests__/fixtures/attr-value-missing/__snapshots__/attr-value-missing.expected.txt

@@ -0,0 +1,6 @@
+1╭─ <span class=>
+ │  ││    │     ╰─ error(INVALID_ATTRIBUTE_VALUE:Missing value for attribute)
+ │  ││    ╰─ attrName "class"
+ │  │╰─ tagName "span"
+ ╰─ ╰─ openTagStart
+2╰─ 

src/__tests__/fixtures/attr-value-missing/input.marko

@@ -0,0 +1 @@
+<span class=>

src/states/ATTRIBUTE.ts

@@ -266,15 +266,22 @@ function shouldTerminateHtmlAttrName(code: number, data: string, pos: number) {
   }
 }
 
-function shouldTerminateHtmlAttrValue(code: number, data: string, pos: number) {
+function shouldTerminateHtmlAttrValue(
+  this: STATE.ExpressionMeta,
+  code: number,
+  data: string,
+  pos: number
+) {
   switch (code) {
     case CODE.COMMA:
       return true;
     case CODE.FORWARD_SLASH:
       return data.charCodeAt(pos + 1) === CODE.CLOSE_ANGLE_BRACKET;
-    // Add special case for =>
     case CODE.CLOSE_ANGLE_BRACKET:
-      return data.charCodeAt(pos - 1) !== CODE.EQUAL;
+      // Add special case for =>
+      // We only look behind to match => if we're not at the start of the expression
+      // otherwise this would match something like "<span class=>".
+      return pos === this.start || data.charCodeAt(pos - 1) !== CODE.EQUAL;
     default:
       return false;
   }