Simplify YAML WriteValue by not preserving newlines

The YAML 1.2 spec says
> Line breaks inside scalar content must be normalized by the YAML processor. Each such line break must be parsed into a single line feed character. The original line break format is a presentation detail and must not be used to convey content information.
https://yaml.org/spec/1.2/spec.html#id2774608

Not preserving newlines simplifies the `OpenApiYamlWriter.WriteValue`
and reduces number of test cases.

Author: foriequal0

src/Microsoft.OpenApi/Writers/OpenApiYamlWriter.cs

@@ -198,39 +198,24 @@ public override void WriteValue(string value)
 
                 IncreaseIndentation();
 
-                var start = 0;
-                while (start < value.Length && value.IndexOfAny(new [] {'\n', '\r'}, start) is var lineBreak)
+                using (var reader = new StringReader(value))
                 {
-                    if (lineBreak == -1)
+                    bool firstLine = true;
+                    while (reader.ReadLine() is var line && line != null)
                     {
-                        break;
+                        if (firstLine)
+                            firstLine = false;
+                        else
+                            Writer.WriteLine();
+                        
+                        // Indentations for empty lines aren't needed.
+                        if (line.Length > 0)
+                        {
+                            WriteIndentation();
+                        }
+
+                        Writer.Write(line);
                     }
-
-                    // To preserves line break characters.
-                    var end = lineBreak;
-                    if (lineBreak + 1 < value.Length && value[lineBreak] == '\r' && value[lineBreak + 1] == '\n')
-                    { 
-                        // The line ends with "\r\n". YAML 1.2 specifies only three line breaks. "\r\n" | "\r" | "\n"
-                        end++;
-                    }
-                    
-                    if (lineBreak - start != 0)
-                    {
-                        // Indentation for empty lines aren't needed.
-                        WriteIndentation();
-                    }
-
-                    var line = value.Substring(start, end - start + 1);
-                    Writer.Write(line);
-
-                    start = end + 1;
-                }
-
-                // Last line
-                if (start < value.Length)
-                {
-                    WriteIndentation(); 
-                    Writer.Write(value.Substring(start));
                 }
 
                 DecreaseIndentation();

test/Microsoft.OpenApi.Tests/Writers/OpenApiWriterSpecialCharacterTests.cs

@@ -77,16 +77,10 @@ public void WriteStringWithSpecialCharactersAsYamlWorks(string input, string exp
         }
 
         [Theory]
-        [InlineData("multiline\r\nstring", "test: |\n  multiline\r\n  string")]
-        [InlineData("multiline\nstring", "test: |\n  multiline\n  string")]
-        [InlineData("multiline\rstring", "test: |\n  multiline\r  string")]
-        [InlineData("multiline\n\rstring", "test: |\n  multiline\n\r  string")]
-        [InlineData("ends with\r\nline break\r\n", "test: |+\n  ends with\r\n  line break\r\n")]
-        [InlineData("ends with\nline break\n", "test: |+\n  ends with\n  line break\n")]
-        [InlineData("ends with\rline break\r", "test: |+\n  ends with\r  line break\r")]
-        [InlineData("ends with\n\rline break\n\r", "test: |+\n  ends with\n\r  line break\n\r")]
+        [InlineData("multiline\r\nstring", "test: |\n  multiline\n  string")]
+        [InlineData("ends with\r\nline break\r\n", "test: |+\n  ends with\n  line break")]
         [InlineData("  starts with\nspaces", "test: |2\n    starts with\n  spaces")]
-        [InlineData("  starts with\nspaces, and ends with line break\n", "test: |+2\n    starts with\n  spaces, and ends with line break\n")]
+        [InlineData("  starts with\nspaces, and ends with line break\n", "test: |+2\n    starts with\n  spaces, and ends with line break")]
         [InlineData("contains\n\n\nempty lines", "test: |\n  contains\n\n\n  empty lines")]
         [InlineData("no line breaks fallback ", "test: 'no line breaks fallback '")]
         public void WriteStringWithNewlineCharactersInObjectAsYamlWorks(string input, string expected)
@@ -100,23 +94,19 @@ public void WriteStringWithNewlineCharactersInObjectAsYamlWorks(string input, st
             writer.WritePropertyName("test");
             writer.WriteValue(input);
             writer.WriteEndObject();
-            var actual = outputStringWriter.GetStringBuilder().ToString();
+            var actual = outputStringWriter.GetStringBuilder().ToString()
+                // Normalize newline for cross platform
+                .Replace("\r", "");
 
             // Assert
             actual.Should().Be(expected);
         }
 
         [Theory]
-        [InlineData("multiline\r\nstring", "- |\n  multiline\r\n  string")]
-        [InlineData("multiline\nstring", "- |\n  multiline\n  string")]
-        [InlineData("multiline\rstring", "- |\n  multiline\r  string")]
-        [InlineData("multiline\n\rstring", "- |\n  multiline\n\r  string")]
-        [InlineData("ends with\r\nline break\r\n", "- |+\n  ends with\r\n  line break\r\n")]
-        [InlineData("ends with\nline break\n", "- |+\n  ends with\n  line break\n")]
-        [InlineData("ends with\rline break\r", "- |+\n  ends with\r  line break\r")]
-        [InlineData("ends with\n\rline break\n\r", "- |+\n  ends with\n\r  line break\n\r")]
+        [InlineData("multiline\r\nstring", "- |\n  multiline\n  string")]
+        [InlineData("ends with\r\nline break\r\n", "- |+\n  ends with\n  line break")]
         [InlineData("  starts with\nspaces", "- |2\n    starts with\n  spaces")]
-        [InlineData("  starts with\nspaces, and ends with line break\n", "- |+2\n    starts with\n  spaces, and ends with line break\n")]
+        [InlineData("  starts with\nspaces, and ends with line break\n", "- |+2\n    starts with\n  spaces, and ends with line break")]
         [InlineData("contains\n\n\nempty lines", "- |\n  contains\n\n\n  empty lines")]
         [InlineData("no line breaks fallback ", "- 'no line breaks fallback '")]
         public void WriteStringWithNewlineCharactersInArrayAsYamlWorks(string input, string expected)
@@ -128,7 +118,9 @@ public void WriteStringWithNewlineCharactersInArrayAsYamlWorks(string input, str
             // Act
             writer.WriteStartArray();
             writer.WriteValue(input);
-            var actual = outputStringWriter.GetStringBuilder().ToString();
+            var actual = outputStringWriter.GetStringBuilder().ToString()
+                // Normalize newline for cross platform
+                .Replace("\r", "");
 
             // Assert
             actual.Should().Be(expected);