better handle nested bold/italic

based on #307

inline_test.go

@@ -173,6 +173,18 @@ func TestEmphasisMix(t *testing.T) {
 		"***triple emphasis___\n",
 		"<p>***triple emphasis___</p>\n",
 
+		"*italics **and bold** end*\n",
+		"<p><em>italics <strong>and bold</strong> end</em></p>\n",
+
+		"*italics **and bold***\n",
+		"<p><em>italics <strong>and bold</strong></em></p>\n",
+
+		"***bold** and italics*\n",
+		"<p><em><strong>bold</strong> and italics</em></p>\n",
+
+		"*start **bold** and italics*\n",
+		"<p><em>start <strong>bold</strong> and italics</em></p>\n",
+
 		"*__triple emphasis__*\n",
 		"<p><em><strong>triple emphasis</strong></em></p>\n",
 
@@ -183,7 +195,7 @@ func TestEmphasisMix(t *testing.T) {
 		"<p><strong>improper *nesting</strong> is* bad</p>\n",
 
 		"*improper **nesting* is** bad\n",
-		"<p>*improper <strong>nesting* is</strong> bad</p>\n",
+		"<p><em>improper **nesting</em> is** bad</p>\n",
 	}
 	doTestsInline(t, tests)
 }

parser/inline.go

@@ -1185,31 +1185,30 @@ func helperFindEmphChar(data []byte, c byte) int {
 func helperEmphasis(p *Parser, data []byte, c byte) (int, ast.Node) {
 	i := 0
 
-	// skip one symbol if coming from emph3
+	// skip two symbol if coming from emph3, as it detected a double emphasis case
 	if len(data) > 1 && data[0] == c && data[1] == c {
-		i = 1
+		i = 2
 	}
 
 	for i < len(data) {
 		length := helperFindEmphChar(data[i:], c)
-		if length == 0 {
-			return 0, nil
-		}
 		i += length
 		if i >= len(data) {
 			return 0, nil
 		}
 
 		if i+1 < len(data) && data[i+1] == c {
-			i++
+			i += 2
 			continue
 		}
 
 		if data[i] == c && !IsSpace(data[i-1]) {
-
 			if p.extensions&NoIntraEmphasis != 0 {
 				rest := data[i+1:]
 				if !(len(rest) == 0 || IsSpace(rest[0]) || IsPunctuation2(rest)) {
+					if length == 0 {
+						return 0, nil
+					}
 					continue
 				}
 			}
@@ -1218,6 +1217,11 @@ func helperEmphasis(p *Parser, data []byte, c byte) (int, ast.Node) {
 			p.Inline(emph, data[:i])
 			return i + 1, emph
 		}
+
+		// We have to check this at the end, otherwise the scenario where we find repeated c's will get skipped
+		if length == 0 {
+			return 0, nil
+		}
 	}
 
 	return 0, nil

parser/parser.go

@@ -743,7 +743,7 @@ func IsPunctuation2(d []byte) bool {
 	return unicode.IsPunct(r)
 }
 
-// IsSpace returns true if c is a white-space charactr
+// IsSpace returns true if c is a white-space character
 func IsSpace(c byte) bool {
 	return c == ' ' || c == '\t' || c == '\n' || c == '\r' || c == '\f' || c == '\v'
 }