Fix YamlConverter adding extra quotes to string values

Co-authored-by: baywet <[email protected]>

Author: Copilot

src/Microsoft.OpenApi.YamlReader/YamlConverter.cs

@@ -133,7 +133,30 @@ ScalarStyle.Plain when YamlNullRepresentations.Contains(yaml.Value) => null,
 
         private static YamlScalarNode ToYamlScalar(this JsonValue val)
         {
-            return new YamlScalarNode(val.ToJsonString());
+            // Try to get the underlying value based on its actual type
+            // First try to get it as a string
+            if (val.TryGetValue(out string? stringValue))
+            {
+                // For string values, we need to determine if they should be quoted in YAML
+                // Strings that look like numbers, booleans, or null need to be quoted
+                // to preserve their string type when round-tripping
+                var needsQuoting = decimal.TryParse(stringValue, NumberStyles.Float, CultureInfo.InvariantCulture, out _) ||
+                                   bool.TryParse(stringValue, out _) ||
+                                   YamlNullRepresentations.Contains(stringValue);
+                
+                return new YamlScalarNode(stringValue)
+                {
+                    Style = needsQuoting ? ScalarStyle.DoubleQuoted : ScalarStyle.Plain
+                };
+            }
+            
+            // For non-string values (numbers, booleans, null), use their string representation
+            // These should remain unquoted in YAML
+            var valueString = val.ToString();
+            return new YamlScalarNode(valueString)
+            {
+                Style = ScalarStyle.Plain
+            };
         }
     }
 }

test/Microsoft.OpenApi.Readers.Tests/YamlConverterTests.cs

@@ -2,6 +2,8 @@
 using SharpYaml.Serialization;
 using Xunit;
 using Microsoft.OpenApi.YamlReader;
+using System.IO;
+using System.Text.Json.Nodes;
 
 namespace Microsoft.OpenApi.Readers.Tests;
 
@@ -26,4 +28,181 @@ public void YamlNullValuesReturnNullJsonNode(string value)
         // Then
         Assert.Null(jsonNode);
     }
+
+    [Fact]
+    public void ToYamlNode_StringValue_NotQuotedInYaml()
+    {
+        // Arrange
+        var json = JsonNode.Parse(@"{""fooString"": ""fooStringValue""}");
+
+        // Act
+        var yamlNode = json!.ToYamlNode();
+        var yamlOutput = ConvertYamlNodeToString(yamlNode);
+
+        // Assert
+        Assert.Contains("fooString: fooStringValue", yamlOutput);
+        Assert.DoesNotContain("\"fooStringValue\"", yamlOutput);
+        Assert.DoesNotContain("'fooStringValue'", yamlOutput);
+    }
+
+    [Fact]
+    public void ToYamlNode_StringThatLooksLikeNumber_QuotedInYaml()
+    {
+        // Arrange
+        var json = JsonNode.Parse(@"{""fooStringOfNumber"": ""200""}");
+
+        // Act
+        var yamlNode = json!.ToYamlNode();
+        var yamlOutput = ConvertYamlNodeToString(yamlNode);
+
+        // Assert
+        Assert.Contains("fooStringOfNumber: \"200\"", yamlOutput);
+    }
+
+    [Fact]
+    public void ToYamlNode_ActualNumber_NotQuotedInYaml()
+    {
+        // Arrange
+        var json = JsonNode.Parse(@"{""actualNumber"": 200}");
+
+        // Act
+        var yamlNode = json!.ToYamlNode();
+        var yamlOutput = ConvertYamlNodeToString(yamlNode);
+
+        // Assert
+        Assert.Contains("actualNumber: 200", yamlOutput);
+        Assert.DoesNotContain("\"200\"", yamlOutput);
+    }
+
+    [Fact]
+    public void ToYamlNode_StringThatLooksLikeDecimal_QuotedInYaml()
+    {
+        // Arrange
+        var json = JsonNode.Parse(@"{""decimalString"": ""123.45""}");
+
+        // Act
+        var yamlNode = json!.ToYamlNode();
+        var yamlOutput = ConvertYamlNodeToString(yamlNode);
+
+        // Assert
+        Assert.Contains("decimalString: \"123.45\"", yamlOutput);
+    }
+
+    [Fact]
+    public void ToYamlNode_ActualDecimal_NotQuotedInYaml()
+    {
+        // Arrange
+        var json = JsonNode.Parse(@"{""actualDecimal"": 123.45}");
+
+        // Act
+        var yamlNode = json!.ToYamlNode();
+        var yamlOutput = ConvertYamlNodeToString(yamlNode);
+
+        // Assert
+        Assert.Contains("actualDecimal: 123.45", yamlOutput);
+        Assert.DoesNotContain("\"123.45\"", yamlOutput);
+    }
+
+    [Fact]
+    public void ToYamlNode_StringThatLooksLikeBoolean_QuotedInYaml()
+    {
+        // Arrange
+        var json = JsonNode.Parse(@"{""boolString"": ""true""}");
+
+        // Act
+        var yamlNode = json!.ToYamlNode();
+        var yamlOutput = ConvertYamlNodeToString(yamlNode);
+
+        // Assert
+        Assert.Contains("boolString: \"true\"", yamlOutput);
+    }
+
+    [Fact]
+    public void ToYamlNode_ActualBoolean_NotQuotedInYaml()
+    {
+        // Arrange
+        var json = JsonNode.Parse(@"{""actualBool"": true}");
+
+        // Act
+        var yamlNode = json!.ToYamlNode();
+        var yamlOutput = ConvertYamlNodeToString(yamlNode);
+
+        // Assert
+        Assert.Contains("actualBool: true", yamlOutput);
+        Assert.DoesNotContain("\"true\"", yamlOutput);
+    }
+
+    [Fact]
+    public void ToYamlNode_StringThatLooksLikeNull_QuotedInYaml()
+    {
+        // Arrange
+        var json = JsonNode.Parse(@"{""nullString"": ""null""}");
+
+        // Act
+        var yamlNode = json!.ToYamlNode();
+        var yamlOutput = ConvertYamlNodeToString(yamlNode);
+
+        // Assert
+        Assert.Contains("nullString: \"null\"", yamlOutput);
+    }
+
+    [Fact]
+    public void ToYamlNode_MixedTypes_CorrectQuoting()
+    {
+        // Arrange
+        var json = JsonNode.Parse(@"{
+            ""str"": ""hello"",
+            ""numStr"": ""42"",
+            ""num"": 42,
+            ""boolStr"": ""false"",
+            ""bool"": false
+        }");
+
+        // Act
+        var yamlNode = json!.ToYamlNode();
+        var yamlOutput = ConvertYamlNodeToString(yamlNode);
+
+        // Assert
+        Assert.Contains("str: hello", yamlOutput);
+        Assert.Contains("numStr: \"42\"", yamlOutput);
+        Assert.Contains("num: 42", yamlOutput);
+        Assert.DoesNotContain("num: \"42\"", yamlOutput);
+        Assert.Contains("boolStr: \"false\"", yamlOutput);
+        Assert.Contains("bool: false", yamlOutput);
+        Assert.DoesNotContain("bool: \"false\"", yamlOutput);
+    }
+
+    [Fact]
+    public void ToYamlNode_FromIssueExample_CorrectOutput()
+    {
+        // Arrange - Example from issue #1951
+        var json = JsonNode.Parse(@"{
+            ""fooString"": ""fooStringValue"",
+            ""fooStringOfNumber"": ""200""
+        }");
+
+        // Act
+        var yamlNode = json!.ToYamlNode();
+        var yamlOutput = ConvertYamlNodeToString(yamlNode);
+
+        // Assert
+        Assert.Contains("fooString: fooStringValue", yamlOutput);
+        Assert.Contains("fooStringOfNumber: \"200\"", yamlOutput);
+        
+        // Ensure no extra quotes on regular strings
+        Assert.DoesNotContain("\"fooStringValue\"", yamlOutput);
+        Assert.DoesNotContain("'fooStringValue'", yamlOutput);
+    }
+
+    private static string ConvertYamlNodeToString(YamlNode yamlNode)
+    {
+        using var ms = new MemoryStream();
+        var yamlStream = new YamlStream(new YamlDocument(yamlNode));
+        var writer = new StreamWriter(ms);
+        yamlStream.Save(writer);
+        writer.Flush();
+        ms.Seek(0, SeekOrigin.Begin);
+        var reader = new StreamReader(ms);
+        return reader.ReadToEnd();
+    }
 }