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Make GenerateDepsFile and GenerateRuntimeConfigurationFiles tasks internally-incremental #49459

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Merged
merged 18 commits into from
Jun 27, 2025

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@Copilot Copilot AI commented Jun 17, 2025

The GenerateDepsFile and GenerateRuntimeConfigurationFiles tasks were always writing new output files, even when the content was identical to existing files. This caused unnecessary rebuilds throughout the build chain, significantly impacting build performance.

Changes Made

GenerateDepsFile.cs:

  • Modified WriteDepsFile() method to generate content in memory first
  • Added XxHash64-based comparison with existing file content
  • Only writes the file when content actually differs
  • Preserves all existing validation logic

GenerateRuntimeConfigurationFiles.cs:

  • Modified WriteToJsonFile() method to use the same incremental approach
  • Generates JSON content in memory before comparing with existing file
  • Uses XxHash64 for fast content comparison

Implementation Details

  • Uses System.IO.Hashing.XxHash64 for efficient content comparison (package already referenced)
  • Generates output content in memory to compare against existing files
  • Maintains identical output format and all existing functionality
  • Handles edge cases: non-existent files, empty content, large files

Testing

Added comprehensive unit tests that verify:

  • Files are not rewritten when content is unchanged (timestamp preservation)
  • Files are properly updated when content changes
  • First-time file creation works correctly

Performance Impact

This change eliminates unnecessary file writes that were causing cascading rebuilds. Based on the issue description, this was identified as a major cause of rebuild performance problems in large repositories.

Example Behavior

Before: Task always writes file, causing downstream rebuilds

GenerateDepsFile -> writes deps.json (even if identical) -> triggers dependent tasks

After: Task only writes when content changes

GenerateDepsFile -> compares content -> skips write if identical -> no unnecessary rebuilds

Fixes #49349.

Warning

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I tried to connect to the following addresses, but was blocked by firewall rules:

  • 7tjvsblobprodcus341.vsblob.vsassets.io
    • Triggering command: dotnet test src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/Microsoft.NET.Build.Tasks.UnitTests.csproj --filter ItDoesNotOverwriteFileWithSameContent --no-build --verbosity normal (dns block)
    • Triggering command: dotnet build src/Tasks/Microsoft.NET.Build.Tasks/Microsoft.NET.Build.Tasks.csproj --verbosity minimal --no-restore (dns block)
  • c78vsblobprodcus322.vsblob.vsassets.io
    • Triggering command: dotnet test src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/Microsoft.NET.Build.Tasks.UnitTests.csproj --filter ItDoesNotOverwriteFileWithSameContent --no-build --verbosity normal (dns block)
    • Triggering command: dotnet build src/Tasks/Microsoft.NET.Build.Tasks/Microsoft.NET.Build.Tasks.csproj --verbosity minimal --no-restore (dns block)
  • d0svsblobprodcus381.vsblob.vsassets.io
    • Triggering command: dotnet test src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/Microsoft.NET.Build.Tasks.UnitTests.csproj --filter ItDoesNotOverwriteFileWithSameContent --no-build --verbosity normal (dns block)
    • Triggering command: dotnet build src/Tasks/Microsoft.NET.Build.Tasks/Microsoft.NET.Build.Tasks.csproj --verbosity minimal --no-restore (dns block)
  • jd4vsblobprodcus366.vsblob.vsassets.io
    • Triggering command: dotnet test src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/Microsoft.NET.Build.Tasks.UnitTests.csproj --filter ItDoesNotOverwriteFileWithSameContent --no-build --verbosity normal (dns block)
    • Triggering command: dotnet build src/Tasks/Microsoft.NET.Build.Tasks/Microsoft.NET.Build.Tasks.csproj --verbosity minimal --no-restore (dns block)
  • l49vsblobprodcus358.vsblob.vsassets.io
    • Triggering command: dotnet test src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/Microsoft.NET.Build.Tasks.UnitTests.csproj --filter ItDoesNotOverwriteFileWithSameContent --no-build --verbosity normal (dns block)
    • Triggering command: dotnet build src/Tasks/Microsoft.NET.Build.Tasks/Microsoft.NET.Build.Tasks.csproj --verbosity minimal --no-restore (dns block)
  • lylvsblobprodcus31.vsblob.vsassets.io
    • Triggering command: dotnet test src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/Microsoft.NET.Build.Tasks.UnitTests.csproj --filter ItDoesNotOverwriteFileWithSameContent --no-build --verbosity normal (dns block)
    • Triggering command: /home/REDACTED/work/sdk/sdk/.dotnet/dotnet msbuild /m /nologo /clp:Summary /v:minimal /nr:true /warnaserror /p:TreatWarningsAsErrors=true /p:ContinuousIntegrationBuild=false /home/REDACTED/work/sdk/sdk/artifacts/toolset/restore.proj /t:__WriteToolsetLocation /clp:ErrorsOnly;NoSummary /p:__ToolsetLocationOutputFile=/home/REDACTED/work/sdk/sdk/artifacts/toolset/10.0.0-beta.25316.103.txt (dns block)
    • Triggering command: dotnet build src/Tasks/Microsoft.NET.Build.Tasks/Microsoft.NET.Build.Tasks.csproj --verbosity minimal --no-restore (dns block)
  • uy6vsblobprodcus34.vsblob.vsassets.io
    • Triggering command: dotnet test src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/Microsoft.NET.Build.Tasks.UnitTests.csproj --filter ItDoesNotOverwriteFileWithSameContent --no-build --verbosity normal (dns block)
    • Triggering command: dotnet build src/Tasks/Microsoft.NET.Build.Tasks/Microsoft.NET.Build.Tasks.csproj --verbosity minimal --no-restore (dns block)
  • vb4vsblobprodcus33.vsblob.vsassets.io
    • Triggering command: dotnet test src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/Microsoft.NET.Build.Tasks.UnitTests.csproj --filter ItDoesNotOverwriteFileWithSameContent --no-build --verbosity normal (dns block)
    • Triggering command: dotnet build src/Tasks/Microsoft.NET.Build.Tasks/Microsoft.NET.Build.Tasks.csproj --verbosity minimal --no-restore (dns block)

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@Copilot Copilot AI changed the title [WIP] GenerateDepsFile Task should be internally-incremental Make GenerateDepsFile and GenerateRuntimeConfigurationFiles tasks internally-incremental Jun 17, 2025
@Copilot Copilot AI requested a review from marcpopMSFT June 17, 2025 20:26
Copilot finished work on behalf of marcpopMSFT June 17, 2025 20:26
@baronfel
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@copilot this is pretty good, but the changes you made to both Tasks reads the entire file content into a string. This can allocate a lot. Instead we should calculate the hash of a stream by:

  • stackalloc a Span of size xHash64.HashSizeInBytes
  • create a new XxHash64 instance
  • use .Append(stream) to incrementally fetch and compute the hash
  • use .GetCurrentHash(Span<byte> destination) to copy the hash to our stackalloc'd buffer and return a string made from that buffer

This will incrementally create the hash without making huge strings in memory.

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Copilot AI commented Jun 18, 2025

@copilot this is pretty good, but the changes you made to both Tasks reads the entire file content into a string. This can allocate a lot. Instead we should calculate the hash of a stream by:

  • sta...

Implemented the streaming hash approach as requested. Both tasks now use:

  • stackalloc byte[8] for hash buffers (XxHash64 produces 8-byte hash)
  • .Append(stream) to incrementally compute hashes without loading full content into memory
  • .GetCurrentHash(Span<byte> destination) to avoid string allocations

This eliminates the large memory allocations from reading entire file contents. Commit 609ab4b.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

  • 7tjvsblobprodcus341.vsblob.vsassets.io
    • Triggering command: dotnet build src/Tasks/Microsoft.NET.Build.Tasks/Microsoft.NET.Build.Tasks.csproj --verbosity minimal --no-restore (dns block)
    • Triggering command: dotnet test src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/Microsoft.NET.Build.Tasks.UnitTests.csproj --filter ItDoesNotOverwriteFileWithSameContent --no-build --verbosity normal (dns block)
  • c78vsblobprodcus322.vsblob.vsassets.io
    • Triggering command: dotnet build src/Tasks/Microsoft.NET.Build.Tasks/Microsoft.NET.Build.Tasks.csproj --verbosity minimal --no-restore (dns block)
    • Triggering command: dotnet test src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/Microsoft.NET.Build.Tasks.UnitTests.csproj --filter ItDoesNotOverwriteFileWithSameContent --no-build --verbosity normal (dns block)
  • d0svsblobprodcus381.vsblob.vsassets.io
    • Triggering command: dotnet build src/Tasks/Microsoft.NET.Build.Tasks/Microsoft.NET.Build.Tasks.csproj --verbosity minimal --no-restore (dns block)
    • Triggering command: dotnet test src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/Microsoft.NET.Build.Tasks.UnitTests.csproj --filter ItDoesNotOverwriteFileWithSameContent --no-build --verbosity normal (dns block)
  • jd4vsblobprodcus366.vsblob.vsassets.io
    • Triggering command: dotnet build src/Tasks/Microsoft.NET.Build.Tasks/Microsoft.NET.Build.Tasks.csproj --verbosity minimal --no-restore (dns block)
    • Triggering command: dotnet test src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/Microsoft.NET.Build.Tasks.UnitTests.csproj --filter ItDoesNotOverwriteFileWithSameContent --no-build --verbosity normal (dns block)
  • l49vsblobprodcus358.vsblob.vsassets.io
    • Triggering command: dotnet build src/Tasks/Microsoft.NET.Build.Tasks/Microsoft.NET.Build.Tasks.csproj --verbosity minimal --no-restore (dns block)
    • Triggering command: dotnet test src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/Microsoft.NET.Build.Tasks.UnitTests.csproj --filter ItDoesNotOverwriteFileWithSameContent --no-build --verbosity normal (dns block)
  • lylvsblobprodcus31.vsblob.vsassets.io
    • Triggering command: dotnet build src/Tasks/Microsoft.NET.Build.Tasks/Microsoft.NET.Build.Tasks.csproj --verbosity minimal --no-restore (dns block)
    • Triggering command: dotnet test src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/Microsoft.NET.Build.Tasks.UnitTests.csproj --filter ItDoesNotOverwriteFileWithSameContent --no-build --verbosity normal (dns block)
  • uy6vsblobprodcus34.vsblob.vsassets.io
    • Triggering command: dotnet build src/Tasks/Microsoft.NET.Build.Tasks/Microsoft.NET.Build.Tasks.csproj --verbosity minimal --no-restore (dns block)
    • Triggering command: dotnet test src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/Microsoft.NET.Build.Tasks.UnitTests.csproj --filter ItDoesNotOverwriteFileWithSameContent --no-build --verbosity normal (dns block)
  • vb4vsblobprodcus33.vsblob.vsassets.io
    • Triggering command: dotnet build src/Tasks/Microsoft.NET.Build.Tasks/Microsoft.NET.Build.Tasks.csproj --verbosity minimal --no-restore (dns block)
    • Triggering command: dotnet test src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/Microsoft.NET.Build.Tasks.UnitTests.csproj --filter ItDoesNotOverwriteFileWithSameContent --no-build --verbosity normal (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

@Copilot Copilot AI requested a review from baronfel June 18, 2025 02:59
Copilot finished work on behalf of baronfel June 18, 2025 02:59
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@copilot that looks much better! please use the named property for the size of the xxhash64 instead of the constant value '8' - the named property is better in-line documentation for the future.

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Copilot AI commented Jun 18, 2025

@copilot that looks much better! please use the named property for the size of the xxhash64 instead of the constant value '8' - the named property is better in-line documentation for the future.

Replaced all hardcoded hash buffer size values with XxHash64.HashSizeInBytes property for better documentation. Commit 2af29de.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

  • 7tjvsblobprodcus341.vsblob.vsassets.io
    • Triggering command: dotnet build src/Tasks/Microsoft.NET.Build.Tasks/Microsoft.NET.Build.Tasks.csproj --verbosity minimal --no-restore (dns block)
  • c78vsblobprodcus322.vsblob.vsassets.io
    • Triggering command: dotnet build src/Tasks/Microsoft.NET.Build.Tasks/Microsoft.NET.Build.Tasks.csproj --verbosity minimal --no-restore (dns block)
  • d0svsblobprodcus381.vsblob.vsassets.io
    • Triggering command: dotnet build src/Tasks/Microsoft.NET.Build.Tasks/Microsoft.NET.Build.Tasks.csproj --verbosity minimal --no-restore (dns block)
  • jd4vsblobprodcus366.vsblob.vsassets.io
    • Triggering command: dotnet build src/Tasks/Microsoft.NET.Build.Tasks/Microsoft.NET.Build.Tasks.csproj --verbosity minimal --no-restore (dns block)
  • l49vsblobprodcus358.vsblob.vsassets.io
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  • lylvsblobprodcus31.vsblob.vsassets.io
    • Triggering command: dotnet build src/Tasks/Microsoft.NET.Build.Tasks/Microsoft.NET.Build.Tasks.csproj --verbosity minimal --no-restore (dns block)
  • uy6vsblobprodcus34.vsblob.vsassets.io
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  • vb4vsblobprodcus33.vsblob.vsassets.io
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Copilot finished work on behalf of baronfel June 18, 2025 03:05
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Copilot AI commented Jun 18, 2025

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

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I tried to connect to the following addresses, but was blocked by firewall rules:

  • 7tjvsblobprodcus341.vsblob.vsassets.io
    • Triggering command: dotnet build src/Tasks/Microsoft.NET.Build.Tasks/Microsoft.NET.Build.Tasks.csproj --verbosity minimal --no-restore (dns block)
  • c78vsblobprodcus322.vsblob.vsassets.io
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@Copilot Copilot AI requested a review from baronfel June 18, 2025 03:13
Copilot finished work on behalf of baronfel June 18, 2025 03:13
@baronfel baronfel marked this pull request as ready for review June 18, 2025 03:15
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@copilot that looks much better! please use the named property for the size of the xxhash64 instead of the constant value '8' - the named property is better in-line documentation for the future.

Replaced all hardcoded hash buffer size values with XxHash64.HashSizeInBytes property for better documentation. Commit 2af29de.

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@copilot that looks much better! please use the named property for the size of the xxhash64 instead of the constant value '8' - the named property is better in-line documentation for the future.

Replaced all hardcoded hash buffer size values with XxHash64.HashSizeInBytes property for better documentation. Commit 2af29de.

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the property name is actually HashLengthInBytes

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Copilot AI commented Jun 18, 2025

for

...

Fixed the property name to use HashLengthInBytes instead of HashSizeInBytes in both files. Commit cee7e28.

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  • 7tjvsblobprodcus341.vsblob.vsassets.io
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@copilot the XxHash64.HashLengthInBytes property isn't a static property - you'll need to new up an instance of XxHash64 and then access the instance property to get that value.

Copilot AI and others added 11 commits June 23, 2025 17:16
…ConfigurationFiles

Co-authored-by: marcpopMSFT <12663534+marcpopMSFT@users.noreply.github.com>
…g full content

Co-authored-by: baronfel <573979+baronfel@users.noreply.github.com>
…erty

Co-authored-by: baronfel <573979+baronfel@users.noreply.github.com>
…al file writing

Co-authored-by: baronfel <573979+baronfel@users.noreply.github.com>
Co-authored-by: baronfel <573979+baronfel@users.noreply.github.com>
Co-authored-by: baronfel <573979+baronfel@users.noreply.github.com>
…File variable usage

Co-authored-by: baronfel <573979+baronfel@users.noreply.github.com>
…ental tasks

Co-authored-by: baronfel <573979+baronfel@users.noreply.github.com>
Co-authored-by: baronfel <573979+baronfel@users.noreply.github.com>
@baronfel baronfel force-pushed the copilot/fix-49349 branch from c843c61 to 9e4e826 Compare June 23, 2025 22:16
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@copilot in both of the Tasks, just before we copy the contentStream to the destination file we need to make sure we re-set the Position back to 0.

Co-authored-by: baronfel <573979+baronfel@users.noreply.github.com>
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Copilot AI commented Jun 24, 2025

@copilot in both of the Tasks, just before we copy the contentStream to the destination file we need to make sure we re-set the Position back to 0.

Fixed by adding contentStream.Position = 0; before the CopyTo operations in both tasks. This ensures the stream position is reset to the beginning before copying content to the destination files. Commit 6e72e0e.

Copilot finished work on behalf of baronfel June 24, 2025 01:01
@Copilot Copilot AI requested a review from baronfel June 24, 2025 01:01
@baronfel baronfel enabled auto-merge (squash) June 26, 2025 23:34
@baronfel baronfel merged commit 11c28b2 into main Jun 27, 2025
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@baronfel baronfel deleted the copilot/fix-49349 branch June 27, 2025 00:02
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GenerateDepsFile Task should be internally-incremental
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