fix: ensure ATX headings follow spec for space after hash characters (#421)

* fix: ensure ATX headings follow spec for space after hash characters

* test: use \u00A0 for non-breaking spaces

Author: TKDev7

src/rules/no-missing-atx-heading-space.js

@@ -16,7 +16,7 @@
 // Helpers
 //-----------------------------------------------------------------------------
 
-const headingPattern = /^(#{1,6})(?:[^#\s]|$)/u;
+const headingPattern = /^(#{1,6})(?:[^# \t]|$)/u;
 const newLinePattern = /\r?\n/u;
 
 //-----------------------------------------------------------------------------

tests/rules/no-missing-atx-heading-space.test.js

@@ -106,6 +106,14 @@ const validHeadings = [
 
 	// 12. Content starting with more than 4 spaces(turn to codeblock)
 	"    #Heading 1",
+
+	// 13. Valid Spaces
+	"## \u00A0Normal outer non-breaking inner space",
+	"## Normal space (both) ##",
+	"## \u00A0Normal outer non-breaking inner space (both)\u00A0 ##",
+	"##\tTab",
+	"##\tTab (left) ##",
+	"## Tab (right)\t##",
 ];
 
 //------------------------------------------------------------------------------
@@ -475,6 +483,34 @@ const invalidTests = [
 			},
 		],
 	},
+
+	// 8. Invalid Spaces
+	{
+		code: "##\u00A0Non-breaking space",
+		output: "## \u00A0Non-breaking space",
+		errors: [
+			{
+				messageId: "missingSpace",
+				column: 1,
+				line: 1,
+				endLine: 1,
+				endColumn: 4,
+			},
+		],
+	},
+	{
+		code: "##\u00A0\u00A0Extra non-breaking space",
+		output: "## \u00A0\u00A0Extra non-breaking space",
+		errors: [
+			{
+				messageId: "missingSpace",
+				column: 1,
+				line: 1,
+				endLine: 1,
+				endColumn: 4,
+			},
+		],
+	},
 ];
 
 ruleTester.run("no-missing-atx-heading-space", rule, {