LibMarkdown: Handle CRLF line endings

Previously, MDDocument only split on Unix-style line endings. This adds
a new function to StringView which handles LF, CR and CRLF.

AK/StringView.cpp

@@ -40,6 +40,46 @@ Vector<StringView> StringView::split_view(const char separator, bool keep_empty)
     return v;
 }
 
+Vector<StringView> StringView::lines(bool consider_cr) const
+{
+    if (is_empty())
+        return {};
+
+    if (!consider_cr)
+        return split_view('\n', true);
+
+    Vector<StringView> v;
+    ssize_t substart = 0;
+    bool last_ch_was_cr = false;
+    bool split_view = false;
+    for (ssize_t i = 0; i < length(); ++i) {
+        char ch = characters_without_null_termination()[i];
+        if (ch == '\n') {
+            split_view = true;
+            if (last_ch_was_cr) {
+                substart = i + 1;
+                split_view = false;
+                last_ch_was_cr = false;
+            }
+        }
+        if (ch == '\r') {
+            split_view = true;
+            last_ch_was_cr = true;
+        }
+        if (split_view) {
+            ssize_t sublen = i - substart;
+            if (sublen != 0)
+                v.append(substring_view(substart, sublen));
+            substart = i + 1;
+        }
+        split_view = false;
+    }
+    ssize_t taillen = length() - substart;
+    if (taillen != 0)
+        v.append(substring_view(substart, taillen));
+    return v;
+}
+
 bool StringView::starts_with(const StringView& str) const
 {
     if (str.is_empty())

AK/StringView.h

@@ -46,6 +46,12 @@ public:
     StringView substring_view(int start, int length) const;
     Vector<StringView> split_view(char, bool keep_empty = false) const;
 
+    // Create a Vector of StringViews split by line endings. As of CommonMark
+    // 0.29, the spec defines a line ending as "a newline (U+000A), a carriage
+    // return (U+000D) not followed by a newline, or a carriage return and a
+    // following newline.".
+    Vector<StringView> lines(bool consider_cr = true) const;
+
     // FIXME: These should be shared between String and StringView somehow!
     unsigned to_uint(bool& ok) const;
     int to_int(bool& ok) const;

AK/Tests/TestStringView.cpp

@@ -42,4 +42,25 @@ TEST_CASE(starts_with)
     EXPECT(!test_string_view.starts_with("DEF"));
 }
 
+TEST_CASE(lines)
+{
+    String test_string = "a\nb\r\nc\rd";
+    StringView test_string_view = test_string.view();
+    Vector<StringView> test_string_vector = test_string_view.lines();
+    EXPECT_EQ(test_string_vector.size(), 4);
+    EXPECT(test_string_vector.at(0) == String("a"));
+    EXPECT(test_string_vector.at(1) == String("b"));
+    EXPECT(test_string_vector.at(2) == String("c"));
+    EXPECT(test_string_vector.at(3) == String("d"));
+
+    test_string = "```\nHello there\r\nHello there\n```";
+    test_string_view = test_string.view();
+    test_string_vector = test_string_view.lines();
+    EXPECT_EQ(test_string_vector.size(), 4);
+    EXPECT(test_string_vector.at(0) == String("```"));
+    EXPECT(test_string_vector.at(1) == String("Hello there"));
+    EXPECT(test_string_vector.at(2) == String("Hello there"));
+    EXPECT(test_string_vector.at(3) == String("```"));
+}
+
 TEST_MAIN(StringView)

Libraries/LibMarkdown/MDDocument.cpp

@@ -49,7 +49,7 @@ static bool helper(Vector<StringView>::ConstIterator& lines, NonnullOwnPtrVector
 
 bool MDDocument::parse(const StringView& str)
 {
-    const Vector<StringView> lines_vec = str.split_view('\n', true);
+    const Vector<StringView> lines_vec = str.lines();
     auto lines = lines_vec.begin();
 
     while (true) {