From 7f6b05149de4bf024f91eb49f8d5b131c600992a Mon Sep 17 00:00:00 2001
From: Ajay Bhargav Baaskaran <ajbaaska@microsoft.com>
Date: Wed, 11 Jul 2018 15:31:37 -0700
Subject: [PATCH] Generate deterministic unique ids for tag helpers

---
 .../DefaultTagHelperTargetExtension.cs        | 12 +++++++++-
 .../IntegrationTests/BuildIntegrationTest.cs  | 23 ++++++++++++++++++-
 .../DefaultTagHelperTargetExtensionTest.cs    | 14 +++++++++++
 3 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Extensions/DefaultTagHelperTargetExtension.cs b/src/Microsoft.AspNetCore.Razor.Language/Extensions/DefaultTagHelperTargetExtension.cs
index ad85ebf807..884ef07df5 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Extensions/DefaultTagHelperTargetExtension.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Extensions/DefaultTagHelperTargetExtension.cs
@@ -99,7 +99,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
                 var uniqueId = (string)context.Items[CodeRenderingContext.SuppressUniqueIds];
                 if (uniqueId == null)
                 {
-                    uniqueId = Guid.NewGuid().ToString("N");
+                    uniqueId = GetDeterministicId(context);
                 }
 
                 context.CodeWriter.WriteStringLiteral(node.TagName)
@@ -637,6 +637,16 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
             return builder.ToString();
         }
 
+        // Internal for testing
+        internal static string GetDeterministicId(CodeRenderingContext context)
+        {
+            // Use the file checksum along with the absolute position in the generated code to create a unique id for each tag helper call site.
+            var checksum = Checksum.BytesToString(context.SourceDocument.GetChecksum());
+            var uniqueId = checksum + context.CodeWriter.Location.AbsoluteIndex;
+
+            return uniqueId;
+        }
+
         private static string GetPropertyAccessor(DefaultTagHelperPropertyIntermediateNode node)
         {
             var propertyAccessor = $"{node.FieldName}.{node.PropertyName}";
diff --git a/test/Microsoft.AspNetCore.Razor.Design.Test/IntegrationTests/BuildIntegrationTest.cs b/test/Microsoft.AspNetCore.Razor.Design.Test/IntegrationTests/BuildIntegrationTest.cs
index 030f55dd7b..878f5bba42 100644
--- a/test/Microsoft.AspNetCore.Razor.Design.Test/IntegrationTests/BuildIntegrationTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Design.Test/IntegrationTests/BuildIntegrationTest.cs
@@ -4,7 +4,6 @@
 using System;
 using System.IO;
 using System.Linq;
-using System.Reflection;
 using System.Runtime.InteropServices;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Testing.xunit;
@@ -568,6 +567,28 @@ namespace Microsoft.AspNetCore.Razor.Design.IntegrationTests
             Assert.FileExists(result, IntermediateOutputPath, "SimpleMvc.Views.pdb");
         }
 
+        [Fact]
+        [InitializeTestProject("SimpleMvc")]
+        public async Task Build_WithDeterministicFlagSet_OutputsDeterministicViewsAssembly()
+        {
+            // Build 1
+            var result = await DotnetMSBuild("Build", $"/p:Deterministic=true");
+
+            Assert.BuildPassed(result);
+            Assert.FileExists(result, IntermediateOutputPath, "SimpleMvc.Views.dll");
+            var filePath = Path.Combine(result.Project.DirectoryPath, IntermediateOutputPath, "SimpleMvc.Views.dll");
+            var firstAssemblyBytes = File.ReadAllBytes(filePath);
+
+            // Build 2
+            result = await DotnetMSBuild("Rebuild", $"/p:Deterministic=true");
+
+            Assert.BuildPassed(result);
+            Assert.FileExists(result, IntermediateOutputPath, "SimpleMvc.Views.dll");
+            var secondAssemblyBytes = File.ReadAllBytes(filePath);
+
+            Assert.Equal(firstAssemblyBytes, secondAssemblyBytes);
+        }
+
         private static DependencyContext ReadDependencyContext(string depsFilePath)
         {
             var reader = new DependencyContextJsonReader();
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Extensions/DefaultTagHelperTargetExtensionTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Extensions/DefaultTagHelperTargetExtensionTest.cs
index 6372657d9c..ccf5e5ca7e 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Extensions/DefaultTagHelperTargetExtensionTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Extensions/DefaultTagHelperTargetExtensionTest.cs
@@ -1118,6 +1118,20 @@ private global::Microsoft.AspNetCore.Razor.Runtime.TagHelpers.TagHelperScopeMana
                 ignoreLineEndingDifferences: true);
         }
 
+        [Fact]
+        public void GetDeterministicId_IsDeterministic()
+        {
+            // Arrange
+            var context = TestCodeRenderingContext.CreateRuntime(suppressUniqueIds: null);
+
+            // Act
+            var firstId = DefaultTagHelperTargetExtension.GetDeterministicId(context);
+            var secondId = DefaultTagHelperTargetExtension.GetDeterministicId(context);
+
+            // Assert
+            Assert.Equal(firstId, secondId);
+        }
+
         private static void Push(CodeRenderingContext context, TagHelperIntermediateNode node)
         {
             ((DefaultCodeRenderingContext)context).AncestorsInternal.Push(node);