[472] Add path signature unique validator

src/Microsoft.OpenApi/Properties/SRResource.resx

@@ -210,6 +210,9 @@
   <data name="Validation_PathItemMustBeginWithSlash" xml:space="preserve">
     <value>The path item name '{0}' MUST begin with a slash.</value>
   </data>
+  <data name="Validation_PathSignatureMustBeUnique" xml:space="preserve">
+    <value>The path signature '{0}' MUST be unique.</value>
+  </data>
   <data name="Validation_RuleAddTwice" xml:space="preserve">
     <value>The same rule cannot be in the same rule set twice.</value>
   </data>
@@ -222,4 +225,4 @@
   <data name="WorkspaceRequredForExternalReferenceResolution" xml:space="preserve">
     <value>OpenAPI document must be added to an OpenApiWorkspace to be able to resolve external references.</value>
   </data>
-</root>
+</root>

src/Microsoft.OpenApi/Services/OpenApiWalker.cs

@@ -229,6 +229,7 @@ internal void Walk(OpenApiPaths paths)
                     _visitor.CurrentKeys.Path = null;
                 }
             }
+
         }
 
         /// <summary>
@@ -1058,6 +1059,7 @@ internal void Walk(IOpenApiElement element)
                 case OpenApiOAuthFlow e: Walk(e); break;
                 case OpenApiOperation e: Walk(e); break;
                 case OpenApiParameter e: Walk(e); break;
+                case OpenApiPaths e: Walk(e); break;
                 case OpenApiRequestBody e: Walk(e); break;
                 case OpenApiResponse e: Walk(e); break;
                 case OpenApiSchema e: Walk(e); break;

src/Microsoft.OpenApi/Validations/Rules/OpenApiPathsRules.cs

@@ -1,6 +1,9 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT license.
 
+using System;
+using System.Collections.Generic;
+using System.Text.RegularExpressions;
 using Microsoft.OpenApi.Models;
 using Microsoft.OpenApi.Properties;
 
@@ -23,7 +26,7 @@ public static class OpenApiPathsRules
                     {
                         context.Enter(pathName);
 
-                        if (pathName == null || !pathName.StartsWith("/"))
+                        if (pathName == null || !pathName.StartsWith("/", StringComparison.OrdinalIgnoreCase))
                         {
                             context.CreateError(nameof(PathNameMustBeginWithSlash),
                                 string.Format(SRResource.Validation_PathItemMustBeginWithSlash, pathName));
@@ -33,6 +36,30 @@ public static class OpenApiPathsRules
                     }
                 });
 
+        private static readonly Regex regexPath = new Regex("\\{([^/]+)\\}", RegexOptions.Compiled, TimeSpan.FromMilliseconds(100));
+        /// <summary>
+        /// A relative path to an individual endpoint. The field name MUST begin with a slash.
+        /// </summary>
+        public static ValidationRule<OpenApiPaths> PathMustBeUnique =>
+            new ValidationRule<OpenApiPaths>(
+                (context, item) =>
+                {
+                    var hashSet = new HashSet<string>();
+
+                    foreach (var path in item.Keys)
+                    {
+                        context.Enter(path);
+
+                        var pathSignature = regexPath.Replace(path, "{}");
+
+                        if (!hashSet.Add(pathSignature))
+                            context.CreateError(nameof(PathMustBeUnique),
+                                string.Format(SRResource.Validation_PathSignatureMustBeUnique, pathSignature));
+
+                        context.Exit();
+                    }
+                });
+
         // add more rules
     }
 }

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

@@ -1431,6 +1431,7 @@ namespace Microsoft.OpenApi.Validations.Rules
     [Microsoft.OpenApi.Validations.Rules.OpenApiRule]
     public static class OpenApiPathsRules
     {
+        public static Microsoft.OpenApi.Validations.ValidationRule<Microsoft.OpenApi.Models.OpenApiPaths> PathMustBeUnique { get; }
         public static Microsoft.OpenApi.Validations.ValidationRule<Microsoft.OpenApi.Models.OpenApiPaths> PathNameMustBeginWithSlash { get; }
     }
     [Microsoft.OpenApi.Validations.Rules.OpenApiRule]

test/Microsoft.OpenApi.Tests/Validations/OpenApiPathsValidationTests.cs

@@ -0,0 +1,49 @@
+using System.Linq;
+using FluentAssertions;
+using Microsoft.OpenApi.Extensions;
+using Microsoft.OpenApi.Models;
+using Microsoft.OpenApi.Properties;
+using Xunit;
+
+namespace Microsoft.OpenApi.Validations.Tests
+{
+    public class OpenApiPathsValidationTests
+    {
+        [Fact]
+        public void ValidatePathsMustBeginWithSlash()
+        {
+            // Arrange
+            var error = string.Format(SRResource.Validation_PathItemMustBeginWithSlash, "pets/{petId}");
+            var paths = new OpenApiPaths
+            {
+                {"pets/{petId}",new OpenApiPathItem() }
+            };
+
+            // Act
+            var errors = paths.Validate(ValidationRuleSet.GetDefaultRuleSet());
+
+            // Assert
+            errors.Should().NotBeEmpty();
+            errors.Select(e => e.Message).Should().BeEquivalentTo(error);
+        }
+
+        [Fact]
+        public void ValidatePathsAreUnique()
+        {
+            // Arrange
+            var error = string.Format(SRResource.Validation_PathSignatureMustBeUnique, "/pets/{}");
+            var paths = new OpenApiPaths
+            {
+                {"/pets/{petId}",new OpenApiPathItem() },
+                {"/pets/{name}",new OpenApiPathItem() }
+            };
+
+            // Act
+            var errors = paths.Validate(ValidationRuleSet.GetDefaultRuleSet());
+
+            // Assert
+            errors.Should().NotBeEmpty();
+            errors.Select(e => e.Message).Should().BeEquivalentTo(error);
+        }
+    }
+}

test/Microsoft.OpenApi.Tests/Validations/ValidationRuleSetTests.cs

@@ -35,7 +35,7 @@ public void DefaultRuleSetPropertyReturnsTheCorrectRules()
             Assert.NotEmpty(rules);
 
             // Update the number if you add new default rule(s).
-            Assert.Equal(22, rules.Count);
+            Assert.Equal(23, rules.Count);
         }
     }
 }