From 852ad8df87e27fd9a39bf4def70742f7832b7240 Mon Sep 17 00:00:00 2001
From: "N. Taylor Mullen" <nimullen@microsoft.com>
Date: Wed, 29 Aug 2018 15:45:44 -0700
Subject: [PATCH] Allow content to be written after caught exception from child
 TagHelper.

- The issue was that the `executeChildContentAsync` call was stopping the invocation of the `_endTagHelperWritingScope`. Therefore, we'd never finish the TagHelper content scope and all following content would be ignored.
- Added two tests to validate the new functionality.

#2561
---
 .../TagHelpers/TagHelperExecutionContext.cs   | 20 ++++++--
 .../TagHelperExecutionContextTest.cs          | 47 +++++++++++++++++++
 2 files changed, 63 insertions(+), 4 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Runtime/Runtime/TagHelpers/TagHelperExecutionContext.cs b/src/Microsoft.AspNetCore.Razor.Runtime/Runtime/TagHelpers/TagHelperExecutionContext.cs
index 030e898b44..140c90597e 100644
--- a/src/Microsoft.AspNetCore.Razor.Runtime/Runtime/TagHelpers/TagHelperExecutionContext.cs
+++ b/src/Microsoft.AspNetCore.Razor.Runtime/Runtime/TagHelpers/TagHelperExecutionContext.cs
@@ -258,8 +258,14 @@ namespace Microsoft.AspNetCore.Razor.Runtime.TagHelpers
             if (childContent == null)
             {
                 _startTagHelperWritingScope(null);
-                await _executeChildContentAsync();
-                childContent = _endTagHelperWritingScope();
+                try
+                {
+                    await _executeChildContentAsync();
+                }
+                finally
+                {
+                    childContent = _endTagHelperWritingScope();
+                }
             }
 
             Debug.Assert(!Output.IsContentModified);
@@ -292,8 +298,14 @@ namespace Microsoft.AspNetCore.Razor.Runtime.TagHelpers
             if (!useCachedResult || childContent == null)
             {
                 _startTagHelperWritingScope(encoder);
-                await _executeChildContentAsync();
-                childContent = _endTagHelperWritingScope();
+                try
+                {
+                    await _executeChildContentAsync();
+                }
+                finally
+                {
+                    childContent = _endTagHelperWritingScope();
+                }
 
                 if (encoder == null)
                 {
diff --git a/test/Microsoft.AspNetCore.Razor.Runtime.Test/Runtime/TagHelpers/TagHelperExecutionContextTest.cs b/test/Microsoft.AspNetCore.Razor.Runtime.Test/Runtime/TagHelpers/TagHelperExecutionContextTest.cs
index a071832ba2..5f81c88cb6 100644
--- a/test/Microsoft.AspNetCore.Razor.Runtime.Test/Runtime/TagHelpers/TagHelperExecutionContextTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Runtime.Test/Runtime/TagHelpers/TagHelperExecutionContextTest.cs
@@ -15,6 +15,53 @@ namespace Microsoft.AspNetCore.Razor.Runtime.TagHelpers
 {
     public class TagHelperExecutionContextTest
     {
+        [Fact]
+        public async Task SetOutputContentAsync_CanHandleExceptionThrowingChildContent()
+        {
+            // Arrange
+            var calledEnd = false;
+            var executionContext = new TagHelperExecutionContext(
+                "p",
+                tagMode: TagMode.StartTagAndEndTag,
+                items: new Dictionary<object, object>(),
+                uniqueId: string.Empty,
+                executeChildContentAsync: () => throw new Exception(),
+                startTagHelperWritingScope: _ => { },
+                endTagHelperWritingScope: () =>
+                {
+                    calledEnd = true;
+                    return new DefaultTagHelperContent();
+                });
+
+            // Act & Assert
+            await Assert.ThrowsAsync<Exception>(async () => await executionContext.SetOutputContentAsync());
+            Assert.True(calledEnd);
+        }
+
+        [Fact]
+        public async Task GetChildContentAsync_CanHandleExceptionThrowingChildContent()
+        {
+            // Arrange
+            var calledEnd = false;
+            var executionContext = new TagHelperExecutionContext(
+                "p",
+                tagMode: TagMode.StartTagAndEndTag,
+                items: new Dictionary<object, object>(),
+                uniqueId: string.Empty,
+                executeChildContentAsync: () => throw new Exception(),
+                startTagHelperWritingScope: _ => { },
+                endTagHelperWritingScope: () =>
+                {
+                    calledEnd = true;
+                    return new DefaultTagHelperContent();
+                });
+
+            // Act & Assert
+            await Assert.ThrowsAsync<Exception>(
+                async () => await executionContext.GetChildContentAsync(useCachedResult: false, encoder: null));
+            Assert.True(calledEnd);
+        }
+
         [Fact]
         public async Task SetOutputContentAsync_SetsOutputsContent()
         {