Add support for OpenAPI schema generation for POCOs

src/Microsoft.OpenApi/Extensions/OpenApiTypeMapper.cs

@@ -0,0 +1,85 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license. 
+
+using System;
+using System.Collections.Generic;
+using Microsoft.OpenApi.Models;
+
+namespace Microsoft.OpenApi.Extensions
+{
+    /// <summary>
+    /// Extension methods for <see cref="Type"/>.
+    /// </summary>
+    public static class OpenApiTypeMapper
+    {
+        private static readonly Dictionary<Type, Func<OpenApiSchema>> _simpleTypeToOpenApiSchema = new()
+        {
+            [typeof(bool)] = () => new OpenApiSchema { Type = "boolean" },
+            [typeof(byte)] = () => new OpenApiSchema { Type = "string", Format = "byte" },
+            [typeof(int)] = () => new OpenApiSchema { Type = "integer", Format = "int32" },
+            [typeof(uint)] = () => new OpenApiSchema { Type = "integer", Format = "int32" },
+            [typeof(long)] = () => new OpenApiSchema { Type = "integer", Format = "int64" },
+            [typeof(ulong)] = () => new OpenApiSchema { Type = "integer", Format = "int64" },
+            [typeof(float)] = () => new OpenApiSchema { Type = "number", Format = "float" },
+            [typeof(double)] = () => new OpenApiSchema { Type = "number", Format = "double" },
+            [typeof(decimal)] = () => new OpenApiSchema { Type = "number", Format = "double" },
+            [typeof(DateTime)] = () => new OpenApiSchema { Type = "string", Format = "date-time" },
+            [typeof(DateTimeOffset)] = () => new OpenApiSchema { Type = "string", Format = "date-time" },
+            [typeof(Guid)] = () => new OpenApiSchema { Type = "string", Format = "uuid" },
+            [typeof(char)] = () => new OpenApiSchema { Type = "string" },
+
+            // Nullable types
+            [typeof(bool?)] = () => new OpenApiSchema { Type = "boolean", Nullable = true },
+            [typeof(byte?)] = () => new OpenApiSchema { Type = "string", Format = "byte", Nullable = true },
+            [typeof(int?)] = () => new OpenApiSchema { Type = "integer", Format = "int32", Nullable = true },
+            [typeof(uint?)] = () => new OpenApiSchema { Type = "integer", Format = "int32", Nullable = true },
+            [typeof(long?)] = () => new OpenApiSchema { Type = "integer", Format = "int64", Nullable = true },
+            [typeof(ulong?)] = () => new OpenApiSchema { Type = "integer", Format = "int64", Nullable = true },
+            [typeof(float?)] = () => new OpenApiSchema { Type = "number", Format = "float", Nullable = true },
+            [typeof(double?)] = () => new OpenApiSchema { Type = "number", Format = "double", Nullable = true },
+            [typeof(decimal?)] = () => new OpenApiSchema { Type = "number", Format = "double", Nullable = true },
+            [typeof(DateTime?)] = () => new OpenApiSchema { Type = "string", Format = "date-time", Nullable = true },
+            [typeof(DateTimeOffset?)] = () => new OpenApiSchema { Type = "string", Format = "date-time", Nullable = true },
+            [typeof(Guid?)] = () => new OpenApiSchema { Type = "string", Format = "uuid", Nullable = true },
+            [typeof(char?)] = () => new OpenApiSchema { Type = "string", Nullable = true },
+
+            [typeof(Uri)] = () => new OpenApiSchema { Type = "string" }, // Uri is treated as simple string
+            [typeof(string)] = () => new OpenApiSchema { Type = "string" },
+            [typeof(object)] = () => new OpenApiSchema { Type = "object" }
+        };
+
+        /// <summary>
+        /// Maps a simple type to an OpenAPI data type and format.
+        /// </summary>
+        /// <param name="type">Simple type.</param>
+        /// <remarks>
+        /// All the following types from http://swagger.io/specification/#data-types-12 are supported.
+        /// Other types including nullables and URL are also supported.
+        /// Common Name      type    format      Comments
+        /// ===========      ======= ======      =========================================
+        /// integer          integer int32       signed 32 bits
+        /// long             integer int64       signed 64 bits
+        /// float            number  float
+        /// double           number  double
+        /// string           string  [empty]
+        /// byte             string  byte        base64 encoded characters
+        /// binary           string  binary      any sequence of octets
+        /// boolean          boolean [empty]
+        /// date             string  date        As defined by full-date - RFC3339
+        /// dateTime         string  date-time   As defined by date-time - RFC3339
+        /// password         string  password    Used to hint UIs the input needs to be obscured.
+        /// If the type is not recognized as "simple", System.String will be returned.
+        /// </remarks>
+        public static OpenApiSchema MapTypeToOpenApiPrimitiveType(this Type type)
+        {
+            if (type == null)
+            {
+                throw new ArgumentNullException(nameof(type));
+            }
+
+            return _simpleTypeToOpenApiSchema.TryGetValue(type, out var result)
+                ? result()
+                : new OpenApiSchema { Type = "string" };
+        }
+    }
+}

test/Microsoft.OpenApi.Tests/Extensions/OpenApiTypeMapperTests.cs

@@ -0,0 +1,35 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license. 
+
+using System;
+using System.Collections.Generic;
+using FluentAssertions;
+using Microsoft.OpenApi.Extensions;
+using Microsoft.OpenApi.Models;
+using Xunit;
+
+namespace Microsoft.OpenApi.Tests.Extensions
+{
+    public class OpenApiTypeMapperTests
+    {
+        [Theory]
+        [MemberData(nameof(PrimitiveTypeData))]
+        public void MapTypeToOpenApiPrimitiveTypeShouldSucceed(Type type, OpenApiSchema expected)
+        {
+            // Arrange & Act
+            var actual = OpenApiTypeMapper.MapTypeToOpenApiPrimitiveType(type);
+
+            // Assert
+            actual.Should().BeEquivalentTo(expected);
+        }
+
+        public static IEnumerable<object[]> PrimitiveTypeData => new List<object[]>
+        {
+            new object[] { typeof(int), new OpenApiSchema { Type = "integer", Format = "int32" } },
+            new object[] { typeof(string), new OpenApiSchema { Type = "string" } },
+            new object[] { typeof(double), new OpenApiSchema { Type = "number", Format = "double" } },
+            new object[] { typeof(float?), new OpenApiSchema { Type = "number", Format = "float", Nullable = true } },
+            new object[] { typeof(DateTimeOffset), new OpenApiSchema { Type = "string", Format = "date-time" } }
+        };
+    }
+}

test/Microsoft.OpenApi.Tests/PublicApi/PublicApi.approved.txt

@@ -282,6 +282,10 @@ namespace Microsoft.OpenApi.Extensions
         public static void SerializeAsYaml<T>(this T element, System.IO.Stream stream, Microsoft.OpenApi.OpenApiSpecVersion specVersion)
             where T : Microsoft.OpenApi.Interfaces.IOpenApiSerializable { }
     }
+    public static class OpenApiTypeMapper
+    {
+        public static Microsoft.OpenApi.Models.OpenApiSchema MapTypeToOpenApiPrimitiveType(this System.Type type) { }
+    }
     public static class StringExtensions
     {
         public static T GetEnumFromDisplayName<T>(this string displayName) { }