Fix #27605: inline math blocks can't be preceeded/followed by alphanumerical characters

Inline math blocks couldn't be preceeded or succeeded by alphanumerical characters due to changes introduced in PR #21171. Removed the condition that caused this (precedingCharacter) and added a new if statement that checks if a specific '$' was escaped using '\'.
Signed-off-by: João Tiago <[email protected]>

Author: jmlt2002

modules/markup/markdown/markdown_test.go

@@ -509,15 +509,15 @@ func TestMathBlock(t *testing.T) {
 		},
 		{
 			`$a a$b b$`,
-			`<p><code class="language-math is-loading">a a$b b</code></p>` + nl,
+			`<p><code class="language-math is-loading">a a</code>b b$</p>` + nl,
 		},
 		{
 			`a a$b b`,
 			`<p>a a$b b</p>` + nl,
 		},
 		{
 			`a$b $a a$b b$`,
-			`<p>a$b <code class="language-math is-loading">a a$b b</code></p>` + nl,
+			`<p>a<code class="language-math is-loading">b </code>a a<code class="language-math is-loading">b b</code></p>` + nl,
 		},
 		{
 			"$$a$$",

modules/markup/markdown/math/inline_parser.go

@@ -41,11 +41,6 @@ func (parser *inlineParser) Trigger() []byte {
 	return parser.start[0:1]
 }
 
-func isAlphanumeric(b byte) bool {
-	// Github only cares about 0-9A-Za-z
-	return (b >= '0' && b <= '9') || (b >= 'A' && b <= 'Z') || (b >= 'a' && b <= 'z')
-}
-
 // Parse parses the current line and returns a result of parsing.
 func (parser *inlineParser) Parse(parent ast.Node, block text.Reader, pc parser.Context) ast.Node {
 	line, _ := block.PeekLine()
@@ -55,12 +50,6 @@ func (parser *inlineParser) Parse(parent ast.Node, block text.Reader, pc parser.
 		return nil
 	}
 
-	precedingCharacter := block.PrecendingCharacter()
-	if precedingCharacter < 256 && isAlphanumeric(byte(precedingCharacter)) {
-		// need to exclude things like `a$` from being considered a start
-		return nil
-	}
-
 	// move the opener marker point at the start of the text
 	opener := len(parser.start)
 
@@ -75,14 +64,15 @@ func (parser *inlineParser) Parse(parent ast.Node, block text.Reader, pc parser.
 		ender += pos
 
 		// Now we want to check the character at the end of our parser section
-		// that is ender + len(parser.end)
+		// that is ender + len(parser.end) and check if char before ender is '\'
 		pos = ender + len(parser.end)
 		if len(line) <= pos {
 			break
 		}
-		if !isAlphanumeric(line[pos]) {
+		if line[ender-1] != '\\' {
 			break
 		}
+
 		// move the pointer onwards
 		ender += len(parser.end)
 	}