TagHelperCollection Part 3: Optimize tag helper change detection logic in source generator #12506
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DustinCampbell
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This was referenced Nov 18, 2025
davidwengier
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chsienki
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| Prelude | [Part 1](#12504) | [Part 2](#12505) | [Part 3](#12506) | [Part 4](#12507) | [Part 5](#12509) | This is a set of support utilities and helpers added as part of the `TagHelperCollection` changes: - Added `InterlockedOperations.Initialize(...)` overloads for lock free initialization with a factory method. (f3686aa) - Added two `LazyValue` structs that use the new `InterlockedOperations.Initialize(...)` overloads. These are useful for lazily initializing a value without extra allocations or locks. (81795f5) - Added `OverloadResolutionPriorityAttribute` polyfill type. (27ab174) - Refactored `TagHelperCache` to extract `CleanableWeakCache<TKey, TValue>`. This caches items as weak references. When the number of items added reaches a configurable threshold, the cache is cleaned up, and any dead weak references are removed. (673a9b5) ---- CI Build: https://dev.azure.com/dnceng/internal/_build/results?buildId=2842136&view=results Toolset Run: https://dev.azure.com/dnceng/internal/_build/results?buildId=2842197&view=results
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| [Prelude](#12503) | Part 1 | [Part 2](#12505) | [Part 3](#12506) | [Part 4](#12507) | [Part 5](#12509) | This pull request represents all new code! It introduces a new immutable collection type, `TagHelperCollection`, that is designed to contain `TagHelperDescriptors`. It is built with the following principles: 1. Guarantee that collections never contain duplicate tag helpers. 2. Collections can be compared efficiently via checksums. 3. Multiple collections can be merged into a single collection efficiently, with minimal array copying. 4. Determining whether a collection contains a tag helper is efficient. > [!TIP] > Since this is all new code, I recommend reviewing commit-by-commit. Each commit represents a cohesive portion of new code. ---- CI Build: https://dev.azure.com/dnceng/internal/_build/results?buildId=2842145&view=results Toolset Run: https://dev.azure.com/dnceng/internal/_build/results?buildId=2842216&view=results
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| [Prelude](#12503) | [Part 1](#12504) | Part 2 | [Part 3](#12506) | [Part 4](#12507) | [Part 5](#12509) | > [!WARNING] > This pull request contains breaking changes for the RazorSdk. Once this is merged and flows to the VMR, dotnet/dotnet@9a7e708 will need to be cherry-picked to resolve build breaks in `src/sdk/src/RazorSdk`. These commits represent the (mostly) mechanical changes needed to integrate `TagHelperCollection` across the Razor code base. Most references to `ImmutableArrary<TagHelperDescriptor>`, `IReadOnlyList<TagHelperDescriptor>`, `IEnumerable<TagHelperDescriptor>`, and `TagHelperDescriptor[]` have been replaced with `TagHelperCollection`. This is **by far** the largest of the `TagHelperCollection` pull requests. While most of the commits contain mechanical changes across the code base, there are few that include more substantial work that require a bit more scrutiny: - **Update `RenameService` to remove `ImmutableArray<TagHelperDescriptor>`** (fa3ad2b) This includes a fair amount of refactoring in `RenameService` to fix bugs found when moving to `TagHelperCollection`. - **Update `TagHelperFacts` to use `TagHelperCollection`** Extra work was done in `DirectiveAttributeComplationItemProvider` to clean up a bit following #12473. ---- CI Build: https://dev.azure.com/dnceng/internal/_build/results?buildId=2842165&view=results Toolset Run: https://dev.azure.com/dnceng/internal/_build/results?buildId=2842237&view=results
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Refactors the tag helper change detection logic to be more efficient and avoid allocations by directly comparing collections rather than using LINQ's Except method.
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| [Prelude](#12503) | [Part 1](#12504) | [Part 2](#12505) | [Part 3](#12506) | Part 4 | [Part 5](#12509) | > [!WARNING] > This pull request contains breaking changes for the RazorSdk. Once this is merged and flows to the VMR, dotnet/dotnet@dc17a09 will need to be cherry-picked to resolve build breaks in `src/sdk/src/RazorSdk`. Previously, tag helpers were discovered by `ITagHelperDescriptorProvider`. Each provider was responsible for walking a compilation's assemblies and producing `TagHelperDescriptors` from the types within. This change inverts the tag helper discovery process by introducing `ITagHelperDiscoveryService` and moving the tag helper construction logic into a set of `TagHelperProducers`. The `ITagHelperDiscoveryService` performs a single walk of the compilation or assembly and calls the producers as needed. Importantly, the new process allows a more expansive cache to be maintained. There is now a per-assembly cache that holds onto `TagHelperCollection` instances. The old cache that was owned by providers via `TagHelperCollector` has been removed. To complete this change, `ITagHelperDescriptorProvider` and related types have been _deleted_. ---- CI Build: https://dev.azure.com/dnceng/internal/_build/results?buildId=2842196&view=results Toolset Run: https://dev.azure.com/dnceng/internal/_build/results?buildId=2842249&view=results
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…xt (#12509) | [Prelude](#12503) | [Part 1](#12504) | [Part 2](#12505) | [Part 3](#12506) | [Part 4](#12507) | Part 5 | This change introduces a weak cache for `TagHelperDocumentContext` keyed by the tag helper prefix string and `TagHelperCollection` checksum. This helps avoid creating new `TagHelperBinders` for the same set of tag helpers, since `TagHelperBinder` is expensive to create. ---- CI Build: https://dev.azure.com/dnceng/internal/_build/results?buildId=2842228&view=results Toolset Run: https://dev.azure.com/dnceng/internal/_build/results?buildId=2842250&view=results
This was referenced Nov 25, 2025
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| Prelude | Part 1 | Part 2 | Part 3 | Part 4 | Part 5 |
This is a relatively small change to remove LINQ from the Razor source generator and use
TagHelperCollectionwhen checking for added/removed tag helpers.CI Build: https://dev.azure.com/dnceng/internal/_build/results?buildId=2842169&view=results
Toolset Run: https://dev.azure.com/dnceng/internal/_build/results?buildId=2842240&view=results