Compiler: Reduce allocations in tag helper matching #12134
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It's unnecessary to create a new List<TagHelperDescriptor> for the TagHelperIntermediateNode.TagHelpers property and add tag helpers to it. Since TagHelperBinding.Descriptors is already an ImmutableArray<TagHelperDescriptor>, it can just be assigned to TagHelperIntermediateNode.TagHelpers.
Many intermediate nodes store several related tag helper objects. For example, TagHelperPropertyIntermediateNode stores both a BoundAttributeDesccriptor and a TagHelperDescriptor. However, for all intermediate nodes, the tag helper objects are always have a parent-child relationship. Now that tag helper objects actually provide a Parent property, we can use that and avoid extra fields.
TagHelperMatchingConventions.TryGetFirstBoundAttributeMatch(...) has four out parameters. This change consolidates them into a single out parameter of type TagHelperAttributeMatch. This allows some logic based on the out parameters to be encapsulated, such as whether a match expects a boolean or string value.
Add helper method to collect matches and use it throughout DefaultRazorIntermediateNodeLoweringPhase to reduce LINQ-related allocations.
The polyfill extension method in SpanExtensions were causing ambiguities on .NET builds.
Introduce DirectiveAttributeName helper struct that uses spans to defer creating strings until necessary.
- Enable nullability - Make Children property lazy - Remove unnecessary argument-null checks - Add constructor that takes an TagHelperAttributeMatch and verifies that its a parameter match. - Change IsIndexerNameMatch and BoundAttributeParameter properties to computed properties that return values from TagHelperAttributeMatch. - Change other properties to init-only - Make AttributeName, AttributeNameWithoutParameter, OriginalAttributeName, and AttributeStructure as required.
- Enable nullability - Make Children property lazy - Remove unnecessary argument-null checks - Add constructor that takes an TagHelperAttributeMatch - Change IsIndexerNameMatch and BoundAttribute properties to computed properties that return values from TagHelperAttributeMatch. - Change other properties to init-only - Make AttributeName, OriginalAttributeName, and AttributeStructure as required.
- Enable nullability - Make Children property lazy - Remove unnecessary argument-null checks - Add constructor that takes an TagHelperAttributeMatch - Change IsIndexerNameMatch and BoundAttribute properties to computed properties that return values from TagHelperAttributeMatch. - Change other properties to init-only - Make AttributeName, and AttributeStructure as required.
- Enable nullability - Make Children property lazy - Remove unnecessary argument-null checks - Change properties to init-only - Mark AttributeName, and AttributeStructure as required.
- Enable nullability - Make Children property lazy - Remove unnecessary argument-null checks - Change properties to init-only - Mark TagMode, and TagName as required.
ToddGrun
reviewed
Aug 21, 2025
...Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/Language/Legacy/TagHelperBlockRewriter.cs
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ToddGrun
reviewed
Aug 21, 2025
...rosoft.CodeAnalysis.Razor.Compiler/src/Language/DefaultRazorIntermediateNodeLoweringPhase.cs
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333fred
approved these changes
Aug 21, 2025
davidwengier
approved these changes
Aug 22, 2025
This was referenced Aug 26, 2025
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This change simplifies and reduces allocations during tag helper matching in
DefaultRazorIntermediateNodeLoweringPhase. In addition, a handful of related intermediate nodes have been cleaned up somewhat, reducing the number of fields and making things a bit lazier. I recommend reviewing commit-by-commit as each commit has a descriptive message.CI Build: https://dev.azure.com/dnceng/internal/_build/results?buildId=2777461&view=results
Test Insertion: https://dev.azure.com/devdiv/DevDiv/_git/VS/pullrequest/663965
Toolset Run: https://dev.azure.com/dnceng/internal/_build/results?buildId=2777462&view=results