Allow math expressions to be preceeded but not suceeded by alphanumerical characters

Signed-off-by: João Tiago <joao.leal.tintas@tecnico.ulisboa.pt>

Author: jmlt2002

modules/markup/markdown/markdown_test.go

@@ -509,23 +509,23 @@ func TestMathBlock(t *testing.T) {
 		},
 		{
 			`$a a$b b$`,
-			`<p><code class="language-math is-loading">a a</code>b b$</p>` + nl,
+			`<p>$a a<code class="language-math is-loading">b b</code></p>` + nl,
 		},
 		{
 			`a a$b b`,
 			`<p>a a$b b</p>` + nl,
 		},
 		{
 			`a$b $a a$b b$`,
-			`<p>a<code class="language-math is-loading">b </code>a a<code class="language-math is-loading">b b</code></p>` + nl,
+			`<p>a$b $a a<code class="language-math is-loading">b b</code></p>` + nl,
 		},
 		{
 			"a$x$",
 			`<p>a<code class="language-math is-loading">x</code></p>` + nl,
 		},
 		{
 			"$x$a",
-			`<p><code class="language-math is-loading">x</code>a</p>` + nl,
+			`<p>$x$a</p>` + nl,
 		},
 		{
 			"$$a$$",

modules/markup/markdown/math/inline_parser.go

@@ -41,6 +41,11 @@ 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()
@@ -69,6 +74,9 @@ func (parser *inlineParser) Parse(parent ast.Node, block text.Reader, pc parser.
 		if len(line) <= pos {
 			break
 		}
+		if isAlphanumeric(line[pos]) {
+			return nil
+		}
 		if line[ender-1] != '\\' {
 			break
 		}