fix: an issue where numeric property names would be missing quotes in yaml conversion

src/Microsoft.OpenApi.YamlReader/YamlConverter.cs

@@ -87,7 +87,10 @@ public static JsonObject ToJsonObject(this YamlMappingNode yaml)
 
         private static YamlMappingNode ToYamlMapping(this JsonObject obj)
         {
-            return new YamlMappingNode(obj.ToDictionary(x => (YamlNode)new YamlScalarNode(x.Key), x => x.Value!.ToYamlNode()));
+            return new YamlMappingNode(obj.ToDictionary(x => (YamlNode)new YamlScalarNode(x.Key)
+            {
+                Style = NeedsQuoting(x.Key) ? ScalarStyle.DoubleQuoted : ScalarStyle.Plain
+            }, x => x.Value!.ToYamlNode()));
         }
 
         /// <summary>
@@ -132,6 +135,11 @@ ScalarStyle.Plain when YamlNullRepresentations.Contains(yaml.Value) => (JsonValu
             };
         }
 
+        private static bool NeedsQuoting(string value) =>
+        decimal.TryParse(value, NumberStyles.Float, CultureInfo.InvariantCulture, out _) ||
+                                   bool.TryParse(value, out _) ||
+                                   YamlNullRepresentations.Contains(value);
+
         private static YamlScalarNode ToYamlScalar(this JsonValue val)
         {
             // Try to get the underlying value based on its actual type
@@ -142,9 +150,7 @@ private static YamlScalarNode ToYamlScalar(this JsonValue val)
                 // 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);
+                var needsQuoting = NeedsQuoting(stringValue);
 
                 return new YamlScalarNode(stringValue)
                 {

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

@@ -1,4 +1,5 @@
-using Microsoft.OpenApi.YamlReader;
+using Microsoft.OpenApi.Tests;
+using Microsoft.OpenApi.YamlReader;
 using SharpYaml;
 using SharpYaml.Serialization;
 using System.IO;
@@ -208,10 +209,7 @@ public void ToYamlNode_StringWithLineBreaks_PreservesLineBreaks()
         var yamlOutput = ConvertYamlNodeToString(yamlNode);
 
         // Convert back to JSON to verify round-tripping
-        var yamlStream = new YamlStream();
-        using var sr = new StringReader(yamlOutput);
-        yamlStream.Load(sr);
-        var jsonBack = yamlStream.Documents[0].ToJsonNode();
+        var jsonBack = ConvertYamlStringToJsonNode(yamlOutput);
 
         // Assert - line breaks should be preserved during round-trip
         var originalMultiline = json["multiline"]?.GetValue<string>();
@@ -225,12 +223,80 @@ public void ToYamlNode_StringWithLineBreaks_PreservesLineBreaks()
         Assert.Contains("\n", roundTripDescription);
     }
 
+    [Fact]
+    public void NumericPropertyNamesShouldRemainStringsFromJson()
+    {
+        // Given
+        var yamlInput =
+        """
+        "123": value1
+        "456": value2
+        """;
+
+        // Given
+        var jsonNode = Assert.IsType<JsonObject>(JsonNode.Parse(@"{
+            ""123"": ""value1"",
+            ""456"": ""value2""
+        }"));
+
+        // When
+        var convertedBack = jsonNode.ToYamlNode();
+        var convertedBackOutput = ConvertYamlNodeToString(convertedBack);
+
+        // Then
+        Assert.Equal(yamlInput.MakeLineBreaksEnvironmentNeutral(), convertedBackOutput.MakeLineBreaksEnvironmentNeutral());
+    }
+
+    [Fact]
+    public void NumericPropertyNamesShouldRemainStringsFromYaml()
+    {
+        // Given
+        var yamlInput =
+        """
+        "123": value1
+        "456": value2
+        """;
+
+        var jsonNode = ConvertYamlStringToJsonNode(yamlInput);
+
+        var convertedBack = jsonNode.ToYamlNode();
+        var convertedBackOutput = ConvertYamlNodeToString(convertedBack);
+        // Then
+        Assert.Equal(yamlInput.MakeLineBreaksEnvironmentNeutral(), convertedBackOutput.MakeLineBreaksEnvironmentNeutral());
+    }
+
+    [Fact]
+    public void BooleanPropertyNamesShouldRemainStringsFromYaml()
+    {
+        // Given
+        var yamlInput =
+        """
+        "true": value1
+        "false": value2
+        """;
+
+        var jsonNode = ConvertYamlStringToJsonNode(yamlInput);
+
+        var convertedBack = jsonNode.ToYamlNode();
+        var convertedBackOutput = ConvertYamlNodeToString(convertedBack);
+        // Then
+        Assert.Equal(yamlInput.MakeLineBreaksEnvironmentNeutral(), convertedBackOutput.MakeLineBreaksEnvironmentNeutral());
+    }
+    private static JsonNode ConvertYamlStringToJsonNode(string yamlInput)
+    {
+        var yamlDocument = new YamlStream();
+        using var sr = new StringReader(yamlInput);
+        yamlDocument.Load(sr);
+        var yamlRoot = yamlDocument.Documents[0].RootNode;
+        return yamlRoot.ToJsonNode();
+    }
+
     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);
+        yamlStream.Save(writer, isLastDocumentEndImplicit: true);
         writer.Flush();
         ms.Seek(0, SeekOrigin.Begin);
         var reader = new StreamReader(ms);