fix: inline math blocks can't be preceeded/followed by alphanumerical characters

Fixes issue go-gitea#27605, changed tests to account for these changes. This bug happened because of the changes introduced in PR go-gitea#21171.

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

@@ -55,12 +55,6 @@ 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 +69,15 @@ 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 '\' && char before ender -2 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)
 	}