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TaskHost file access reporting ignores BuildParameters.ReportFileAccesses #14826

Open
#14871
Open
TaskHost file access reporting ignores BuildParameters.ReportFileAccesses#14826
#14871

Description

@JanProvaznik
JanProvaznik
opened on Aug 25, 2026

Summary

When a task runs in a TaskHost, file accesses reported through EngineServices.ReportFileAccess are collected and replayed unconditionally, ignoring BuildParameters.ReportFileAccesses. The equivalent in-proc code path does honor the flag. The same task therefore behaves differently depending only on where it happens to be scheduled.

This was found while investigating #14824, and it is the reason that defect crashed builds which had never asked for file-access reporting.

Details

The in-proc engine gates on the build parameter (src/Build/BackEnd/Components/RequestBuilder/TaskHost.cs):

publicvoidReportFileAccess(FileAccessDatafileAccessData){IBuildComponentHostbuildComponentHost=_taskHost._host;if(buildComponentHost.BuildParameters.ReportFileAccesses){((IFileAccessManager)buildComponentHost.GetComponent(BuildComponentType.FileAccessManager)).ReportFileAccess(fileAccessData,buildComponentHost.BuildParameters.NodeId);}}

The TaskHost process does not (src/MSBuild/OutOfProcTaskHostNode.cs):

publicvoidReportFileAccess(FileAccessDatafileAccessData){_taskHost._fileAccessData.Add(fileAccessData);}

Neither does the replay in the owning worker node (src/Build/Instance/TaskFactories/TaskHostTask.cs):

privatevoidHandleTaskHostTaskComplete(TaskHostTaskCompletetaskHostTaskComplete){
#if FEATURE_REPORTFILEACCESSESif(taskHostTaskComplete.FileAccessData?.Count>0){IFileAccessManagerfileAccessManager=((IFileAccessManager)_buildComponentHost.GetComponent(BuildComponentType.FileAccessManager));foreach(FileAccessDatafileAccessDataintaskHostTaskComplete.FileAccessData){fileAccessManager.ReportFileAccess(fileAccessData,_buildComponentHost.BuildParameters.NodeId);}}
#endif

TaskHostConfiguration carries no equivalent of ReportFileAccesses, so the TaskHost has no way to know the flag is off.

Impact

  1. Inconsistent behavior. A task that calls ReportFileAccess is a no-op in-proc when reporting is disabled, but is collected, serialized across the pipe and replayed into the FileAccessManager when the same task runs in a TaskHost — which now happens by default for every task not annotated with MSBuildMultiThreadableTaskAttribute under -mt.
  2. Wasted work. Every TaskHost task completion pays for serializing a List<FileAccessData> even when nothing will consume it.
  3. It turned TaskHost file-access data is corrupted under multithreaded MSBuild #14824 from "corrupted data for opted-in users" into "builds crash with MSB4018 / MSB1025 even without -reportfileaccesses". I reproduced that crash with MSBuild.exe repro.proj using nothing but a TaskHostFactoryUsingTask — no -mt, no -reportfileaccesses.

Expected behavior

ReportFileAccess should be a no-op end to end when BuildParameters.ReportFileAccesses is false, regardless of where the task executes.

Suggested fix

Plumb the flag into TaskHostConfiguration so OutOfProcTaskHostNode.EngineServicesImpl.ReportFileAccess can skip collection entirely, and gate the replay in TaskHostTask.HandleTaskHostTaskComplete on _buildComponentHost.BuildParameters.ReportFileAccesses for older/mismatched task hosts.

Note that gating alone would only have hidden #14824; the deserialization fix there is still required.

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TaskHost file access reporting ignores BuildParameters.ReportFileAccesses · Issue #14826 · dotnet/msbuild · GitHub
      Skip to content
      TaskHost file access reporting ignores BuildParameters.ReportFileAccesses #14826
      Open
      #14871
      Open
      TaskHost file access reporting ignores BuildParameters.ReportFileAccesses#14826
      #14871
      Description
      @JanProvaznik
      JanProvaznik
      opened on Aug 25, 2026
      Summary
      When a task runs in a TaskHost, file accesses reported through EngineServices.ReportFileAccess are collected and replayed unconditionally, ignoring BuildParameters.ReportFileAccesses. The equivalent in-proc code path does honor the flag. The same task therefore behaves differently depending only on where it happens to be scheduled.
      This was found while investigating #14824, and it is the reason that defect crashed builds which had never asked for file-access reporting.
      Details
      The in-proc engine gates on the build parameter (src/Build/BackEnd/Components/RequestBuilder/TaskHost.cs):
      publicvoidReportFileAccess(FileAccessDatafileAccessData){IBuildComponentHostbuildComponentHost=_taskHost._host;if(buildComponentHost.BuildParameters.ReportFileAccesses){((IFileAccessManager)buildComponentHost.GetComponent(BuildComponentType.FileAccessManager)).ReportFileAccess(fileAccessData,buildComponentHost.BuildParameters.NodeId);}}
      The TaskHost process does not (src/MSBuild/OutOfProcTaskHostNode.cs):
      publicvoidReportFileAccess(FileAccessDatafileAccessData){_taskHost._fileAccessData.Add(fileAccessData);}
      Neither does the replay in the owning worker node (src/Build/Instance/TaskFactories/TaskHostTask.cs):
      privatevoidHandleTaskHostTaskComplete(TaskHostTaskCompletetaskHostTaskComplete){
#if FEATURE_REPORTFILEACCESSESif(taskHostTaskComplete.FileAccessData?.Count>0){IFileAccessManagerfileAccessManager=((IFileAccessManager)_buildComponentHost.GetComponent(BuildComponentType.FileAccessManager));foreach(FileAccessDatafileAccessDataintaskHostTaskComplete.FileAccessData){fileAccessManager.ReportFileAccess(fileAccessData,_buildComponentHost.BuildParameters.NodeId);}}
#endif
      TaskHostConfiguration carries no equivalent of ReportFileAccesses, so the TaskHost has no way to know the flag is off.
      Impact
      1. Inconsistent behavior. A task that calls ReportFileAccess is a no-op in-proc when reporting is disabled, but is collected, serialized across the pipe and replayed into the FileAccessManager when the same task runs in a TaskHost — which now happens by default for every task not annotated with MSBuildMultiThreadableTaskAttribute under -mt.
      2. Wasted work. Every TaskHost task completion pays for serializing a List<FileAccessData> even when nothing will consume it.
      3. It turned TaskHost file-access data is corrupted under multithreaded MSBuild #14824 from "corrupted data for opted-in users" into "builds crash with MSB4018 / MSB1025 even without -reportfileaccesses". I reproduced that crash with MSBuild.exe repro.proj using nothing but a TaskHostFactoryUsingTask — no -mt, no -reportfileaccesses.
      Expected behavior
      ReportFileAccess should be a no-op end to end when BuildParameters.ReportFileAccesses is false, regardless of where the task executes.
      Suggested fix
      Plumb the flag into TaskHostConfiguration so OutOfProcTaskHostNode.EngineServicesImpl.ReportFileAccess can skip collection entirely, and gate the replay in TaskHostTask.HandleTaskHostTaskComplete on _buildComponentHost.BuildParameters.ReportFileAccesses for older/mismatched task hosts.
      Note that gating alone would only have hidden #14824; the deserialization fix there is still required.
      Metadata
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TaskHost file access reporting ignores BuildParameters.ReportFileAccesses · Issue #14826 · dotnet/msbuild · GitHub
          Skip to content
          TaskHost file access reporting ignores BuildParameters.ReportFileAccesses #14826
          Open
          #14871
          Open
          TaskHost file access reporting ignores BuildParameters.ReportFileAccesses#14826
          #14871
          Description
          @JanProvaznik
          JanProvaznik
          opened on Aug 25, 2026
          Summary
          When a task runs in a TaskHost, file accesses reported through EngineServices.ReportFileAccess are collected and replayed unconditionally, ignoring BuildParameters.ReportFileAccesses. The equivalent in-proc code path does honor the flag. The same task therefore behaves differently depending only on where it happens to be scheduled.
          This was found while investigating #14824, and it is the reason that defect crashed builds which had never asked for file-access reporting.
          Details
          The in-proc engine gates on the build parameter (src/Build/BackEnd/Components/RequestBuilder/TaskHost.cs):
          publicvoidReportFileAccess(FileAccessDatafileAccessData){IBuildComponentHostbuildComponentHost=_taskHost._host;if(buildComponentHost.BuildParameters.ReportFileAccesses){((IFileAccessManager)buildComponentHost.GetComponent(BuildComponentType.FileAccessManager)).ReportFileAccess(fileAccessData,buildComponentHost.BuildParameters.NodeId);}}
          The TaskHost process does not (src/MSBuild/OutOfProcTaskHostNode.cs):
          publicvoidReportFileAccess(FileAccessDatafileAccessData){_taskHost._fileAccessData.Add(fileAccessData);}
          Neither does the replay in the owning worker node (src/Build/Instance/TaskFactories/TaskHostTask.cs):
          privatevoidHandleTaskHostTaskComplete(TaskHostTaskCompletetaskHostTaskComplete){
#if FEATURE_REPORTFILEACCESSESif(taskHostTaskComplete.FileAccessData?.Count>0){IFileAccessManagerfileAccessManager=((IFileAccessManager)_buildComponentHost.GetComponent(BuildComponentType.FileAccessManager));foreach(FileAccessDatafileAccessDataintaskHostTaskComplete.FileAccessData){fileAccessManager.ReportFileAccess(fileAccessData,_buildComponentHost.BuildParameters.NodeId);}}
#endif
          TaskHostConfiguration carries no equivalent of ReportFileAccesses, so the TaskHost has no way to know the flag is off.
          Impact
          1. Inconsistent behavior. A task that calls ReportFileAccess is a no-op in-proc when reporting is disabled, but is collected, serialized across the pipe and replayed into the FileAccessManager when the same task runs in a TaskHost — which now happens by default for every task not annotated with MSBuildMultiThreadableTaskAttribute under -mt.
          2. Wasted work. Every TaskHost task completion pays for serializing a List<FileAccessData> even when nothing will consume it.
          3. It turned TaskHost file-access data is corrupted under multithreaded MSBuild #14824 from "corrupted data for opted-in users" into "builds crash with MSB4018 / MSB1025 even without -reportfileaccesses". I reproduced that crash with MSBuild.exe repro.proj using nothing but a TaskHostFactoryUsingTask — no -mt, no -reportfileaccesses.
          Expected behavior
          ReportFileAccess should be a no-op end to end when BuildParameters.ReportFileAccesses is false, regardless of where the task executes.
          Suggested fix
          Plumb the flag into TaskHostConfiguration so OutOfProcTaskHostNode.EngineServicesImpl.ReportFileAccess can skip collection entirely, and gate the replay in TaskHostTask.HandleTaskHostTaskComplete on _buildComponentHost.BuildParameters.ReportFileAccesses for older/mismatched task hosts.
          Note that gating alone would only have hidden #14824; the deserialization fix there is still required.
          Metadata
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try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
TaskHost file access reporting ignores BuildParameters.ReportFileAccesses · Issue #14826 · dotnet/msbuild · GitHub
              Skip to content
              TaskHost file access reporting ignores BuildParameters.ReportFileAccesses #14826
              Open
              #14871
              Open
              TaskHost file access reporting ignores BuildParameters.ReportFileAccesses#14826
              #14871
              Description
              @JanProvaznik
              JanProvaznik
              opened on Aug 25, 2026
              Summary
              When a task runs in a TaskHost, file accesses reported through EngineServices.ReportFileAccess are collected and replayed unconditionally, ignoring BuildParameters.ReportFileAccesses. The equivalent in-proc code path does honor the flag. The same task therefore behaves differently depending only on where it happens to be scheduled.
              This was found while investigating #14824, and it is the reason that defect crashed builds which had never asked for file-access reporting.
              Details
              The in-proc engine gates on the build parameter (src/Build/BackEnd/Components/RequestBuilder/TaskHost.cs):
              publicvoidReportFileAccess(FileAccessDatafileAccessData){IBuildComponentHostbuildComponentHost=_taskHost._host;if(buildComponentHost.BuildParameters.ReportFileAccesses){((IFileAccessManager)buildComponentHost.GetComponent(BuildComponentType.FileAccessManager)).ReportFileAccess(fileAccessData,buildComponentHost.BuildParameters.NodeId);}}
              The TaskHost process does not (src/MSBuild/OutOfProcTaskHostNode.cs):
              publicvoidReportFileAccess(FileAccessDatafileAccessData){_taskHost._fileAccessData.Add(fileAccessData);}
              Neither does the replay in the owning worker node (src/Build/Instance/TaskFactories/TaskHostTask.cs):
              privatevoidHandleTaskHostTaskComplete(TaskHostTaskCompletetaskHostTaskComplete){
#if FEATURE_REPORTFILEACCESSESif(taskHostTaskComplete.FileAccessData?.Count>0){IFileAccessManagerfileAccessManager=((IFileAccessManager)_buildComponentHost.GetComponent(BuildComponentType.FileAccessManager));foreach(FileAccessDatafileAccessDataintaskHostTaskComplete.FileAccessData){fileAccessManager.ReportFileAccess(fileAccessData,_buildComponentHost.BuildParameters.NodeId);}}
#endif
              TaskHostConfiguration carries no equivalent of ReportFileAccesses, so the TaskHost has no way to know the flag is off.
              Impact
              1. Inconsistent behavior. A task that calls ReportFileAccess is a no-op in-proc when reporting is disabled, but is collected, serialized across the pipe and replayed into the FileAccessManager when the same task runs in a TaskHost — which now happens by default for every task not annotated with MSBuildMultiThreadableTaskAttribute under -mt.
              2. Wasted work. Every TaskHost task completion pays for serializing a List<FileAccessData> even when nothing will consume it.
              3. It turned TaskHost file-access data is corrupted under multithreaded MSBuild #14824 from "corrupted data for opted-in users" into "builds crash with MSB4018 / MSB1025 even without -reportfileaccesses". I reproduced that crash with MSBuild.exe repro.proj using nothing but a TaskHostFactoryUsingTask — no -mt, no -reportfileaccesses.
              Expected behavior
              ReportFileAccess should be a no-op end to end when BuildParameters.ReportFileAccesses is false, regardless of where the task executes.
              Suggested fix
              Plumb the flag into TaskHostConfiguration so OutOfProcTaskHostNode.EngineServicesImpl.ReportFileAccess can skip collection entirely, and gate the replay in TaskHostTask.HandleTaskHostTaskComplete on _buildComponentHost.BuildParameters.ReportFileAccesses for older/mismatched task hosts.
              Note that gating alone would only have hidden #14824; the deserialization fix there is still required.
              Metadata
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, 'i');
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try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '
TaskHost file access reporting ignores BuildParameters.ReportFileAccesses · Issue #14826 · dotnet/msbuild · GitHub
                  Skip to content
                  TaskHost file access reporting ignores BuildParameters.ReportFileAccesses #14826
                  Open
                  #14871
                  Open
                  TaskHost file access reporting ignores BuildParameters.ReportFileAccesses#14826
                  #14871
                  Description
                  @JanProvaznik
                  JanProvaznik
                  opened on Aug 25, 2026
                  Summary
                  When a task runs in a TaskHost, file accesses reported through EngineServices.ReportFileAccess are collected and replayed unconditionally, ignoring BuildParameters.ReportFileAccesses. The equivalent in-proc code path does honor the flag. The same task therefore behaves differently depending only on where it happens to be scheduled.
                  This was found while investigating #14824, and it is the reason that defect crashed builds which had never asked for file-access reporting.
                  Details
                  The in-proc engine gates on the build parameter (src/Build/BackEnd/Components/RequestBuilder/TaskHost.cs):
                  publicvoidReportFileAccess(FileAccessDatafileAccessData){IBuildComponentHostbuildComponentHost=_taskHost._host;if(buildComponentHost.BuildParameters.ReportFileAccesses){((IFileAccessManager)buildComponentHost.GetComponent(BuildComponentType.FileAccessManager)).ReportFileAccess(fileAccessData,buildComponentHost.BuildParameters.NodeId);}}
                  The TaskHost process does not (src/MSBuild/OutOfProcTaskHostNode.cs):
                  publicvoidReportFileAccess(FileAccessDatafileAccessData){_taskHost._fileAccessData.Add(fileAccessData);}
                  Neither does the replay in the owning worker node (src/Build/Instance/TaskFactories/TaskHostTask.cs):
                  privatevoidHandleTaskHostTaskComplete(TaskHostTaskCompletetaskHostTaskComplete){
#if FEATURE_REPORTFILEACCESSESif(taskHostTaskComplete.FileAccessData?.Count>0){IFileAccessManagerfileAccessManager=((IFileAccessManager)_buildComponentHost.GetComponent(BuildComponentType.FileAccessManager));foreach(FileAccessDatafileAccessDataintaskHostTaskComplete.FileAccessData){fileAccessManager.ReportFileAccess(fileAccessData,_buildComponentHost.BuildParameters.NodeId);}}
#endif
                  TaskHostConfiguration carries no equivalent of ReportFileAccesses, so the TaskHost has no way to know the flag is off.
                  Impact
                  1. Inconsistent behavior. A task that calls ReportFileAccess is a no-op in-proc when reporting is disabled, but is collected, serialized across the pipe and replayed into the FileAccessManager when the same task runs in a TaskHost — which now happens by default for every task not annotated with MSBuildMultiThreadableTaskAttribute under -mt.
                  2. Wasted work. Every TaskHost task completion pays for serializing a List<FileAccessData> even when nothing will consume it.
                  3. It turned TaskHost file-access data is corrupted under multithreaded MSBuild #14824 from "corrupted data for opted-in users" into "builds crash with MSB4018 / MSB1025 even without -reportfileaccesses". I reproduced that crash with MSBuild.exe repro.proj using nothing but a TaskHostFactoryUsingTask — no -mt, no -reportfileaccesses.
                  Expected behavior
                  ReportFileAccess should be a no-op end to end when BuildParameters.ReportFileAccesses is false, regardless of where the task executes.
                  Suggested fix
                  Plumb the flag into TaskHostConfiguration so OutOfProcTaskHostNode.EngineServicesImpl.ReportFileAccess can skip collection entirely, and gate the replay in TaskHostTask.HandleTaskHostTaskComplete on _buildComponentHost.BuildParameters.ReportFileAccesses for older/mismatched task hosts.
                  Note that gating alone would only have hidden #14824; the deserialization fix there is still required.
                  Metadata
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                      Issue actions
                      
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var __m = "*";
var __re = new RegExp('^' + ".*" + '
TaskHost file access reporting ignores BuildParameters.ReportFileAccesses · Issue #14826 · dotnet/msbuild · GitHub
                      Skip to content
                      TaskHost file access reporting ignores BuildParameters.ReportFileAccesses #14826
                      Open
                      #14871
                      Open
                      TaskHost file access reporting ignores BuildParameters.ReportFileAccesses#14826
                      #14871
                      Description
                      @JanProvaznik
                      JanProvaznik
                      opened on Aug 25, 2026
                      Summary
                      When a task runs in a TaskHost, file accesses reported through EngineServices.ReportFileAccess are collected and replayed unconditionally, ignoring BuildParameters.ReportFileAccesses. The equivalent in-proc code path does honor the flag. The same task therefore behaves differently depending only on where it happens to be scheduled.
                      This was found while investigating #14824, and it is the reason that defect crashed builds which had never asked for file-access reporting.
                      Details
                      The in-proc engine gates on the build parameter (src/Build/BackEnd/Components/RequestBuilder/TaskHost.cs):
                      publicvoidReportFileAccess(FileAccessDatafileAccessData){IBuildComponentHostbuildComponentHost=_taskHost._host;if(buildComponentHost.BuildParameters.ReportFileAccesses){((IFileAccessManager)buildComponentHost.GetComponent(BuildComponentType.FileAccessManager)).ReportFileAccess(fileAccessData,buildComponentHost.BuildParameters.NodeId);}}
                      The TaskHost process does not (src/MSBuild/OutOfProcTaskHostNode.cs):
                      publicvoidReportFileAccess(FileAccessDatafileAccessData){_taskHost._fileAccessData.Add(fileAccessData);}
                      Neither does the replay in the owning worker node (src/Build/Instance/TaskFactories/TaskHostTask.cs):
                      privatevoidHandleTaskHostTaskComplete(TaskHostTaskCompletetaskHostTaskComplete){
#if FEATURE_REPORTFILEACCESSESif(taskHostTaskComplete.FileAccessData?.Count>0){IFileAccessManagerfileAccessManager=((IFileAccessManager)_buildComponentHost.GetComponent(BuildComponentType.FileAccessManager));foreach(FileAccessDatafileAccessDataintaskHostTaskComplete.FileAccessData){fileAccessManager.ReportFileAccess(fileAccessData,_buildComponentHost.BuildParameters.NodeId);}}
#endif
                      TaskHostConfiguration carries no equivalent of ReportFileAccesses, so the TaskHost has no way to know the flag is off.
                      Impact
                      1. Inconsistent behavior. A task that calls ReportFileAccess is a no-op in-proc when reporting is disabled, but is collected, serialized across the pipe and replayed into the FileAccessManager when the same task runs in a TaskHost — which now happens by default for every task not annotated with MSBuildMultiThreadableTaskAttribute under -mt.
                      2. Wasted work. Every TaskHost task completion pays for serializing a List<FileAccessData> even when nothing will consume it.
                      3. It turned TaskHost file-access data is corrupted under multithreaded MSBuild #14824 from "corrupted data for opted-in users" into "builds crash with MSB4018 / MSB1025 even without -reportfileaccesses". I reproduced that crash with MSBuild.exe repro.proj using nothing but a TaskHostFactoryUsingTask — no -mt, no -reportfileaccesses.
                      Expected behavior
                      ReportFileAccess should be a no-op end to end when BuildParameters.ReportFileAccesses is false, regardless of where the task executes.
                      Suggested fix
                      Plumb the flag into TaskHostConfiguration so OutOfProcTaskHostNode.EngineServicesImpl.ReportFileAccess can skip collection entirely, and gate the replay in TaskHostTask.HandleTaskHostTaskComplete on _buildComponentHost.BuildParameters.ReportFileAccesses for older/mismatched task hosts.
                      Note that gating alone would only have hidden #14824; the deserialization fix there is still required.
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TaskHost file access reporting ignores BuildParameters.ReportFileAccesses · Issue #14826 · dotnet/msbuild · GitHub
                          Skip to content
                          TaskHost file access reporting ignores BuildParameters.ReportFileAccesses #14826
                          Open
                          #14871
                          Open
                          TaskHost file access reporting ignores BuildParameters.ReportFileAccesses#14826
                          #14871
                          Description
                          @JanProvaznik
                          JanProvaznik
                          opened on Aug 25, 2026
                          Summary
                          When a task runs in a TaskHost, file accesses reported through EngineServices.ReportFileAccess are collected and replayed unconditionally, ignoring BuildParameters.ReportFileAccesses. The equivalent in-proc code path does honor the flag. The same task therefore behaves differently depending only on where it happens to be scheduled.
                          This was found while investigating #14824, and it is the reason that defect crashed builds which had never asked for file-access reporting.
                          Details
                          The in-proc engine gates on the build parameter (src/Build/BackEnd/Components/RequestBuilder/TaskHost.cs):
                          publicvoidReportFileAccess(FileAccessDatafileAccessData){IBuildComponentHostbuildComponentHost=_taskHost._host;if(buildComponentHost.BuildParameters.ReportFileAccesses){((IFileAccessManager)buildComponentHost.GetComponent(BuildComponentType.FileAccessManager)).ReportFileAccess(fileAccessData,buildComponentHost.BuildParameters.NodeId);}}
                          The TaskHost process does not (src/MSBuild/OutOfProcTaskHostNode.cs):
                          publicvoidReportFileAccess(FileAccessDatafileAccessData){_taskHost._fileAccessData.Add(fileAccessData);}
                          Neither does the replay in the owning worker node (src/Build/Instance/TaskFactories/TaskHostTask.cs):
                          privatevoidHandleTaskHostTaskComplete(TaskHostTaskCompletetaskHostTaskComplete){
#if FEATURE_REPORTFILEACCESSESif(taskHostTaskComplete.FileAccessData?.Count>0){IFileAccessManagerfileAccessManager=((IFileAccessManager)_buildComponentHost.GetComponent(BuildComponentType.FileAccessManager));foreach(FileAccessDatafileAccessDataintaskHostTaskComplete.FileAccessData){fileAccessManager.ReportFileAccess(fileAccessData,_buildComponentHost.BuildParameters.NodeId);}}
#endif
                          TaskHostConfiguration carries no equivalent of ReportFileAccesses, so the TaskHost has no way to know the flag is off.
                          Impact
                          1. Inconsistent behavior. A task that calls ReportFileAccess is a no-op in-proc when reporting is disabled, but is collected, serialized across the pipe and replayed into the FileAccessManager when the same task runs in a TaskHost — which now happens by default for every task not annotated with MSBuildMultiThreadableTaskAttribute under -mt.
                          2. Wasted work. Every TaskHost task completion pays for serializing a List<FileAccessData> even when nothing will consume it.
                          3. It turned TaskHost file-access data is corrupted under multithreaded MSBuild #14824 from "corrupted data for opted-in users" into "builds crash with MSB4018 / MSB1025 even without -reportfileaccesses". I reproduced that crash with MSBuild.exe repro.proj using nothing but a TaskHostFactoryUsingTask — no -mt, no -reportfileaccesses.
                          Expected behavior
                          ReportFileAccess should be a no-op end to end when BuildParameters.ReportFileAccesses is false, regardless of where the task executes.
                          Suggested fix
                          Plumb the flag into TaskHostConfiguration so OutOfProcTaskHostNode.EngineServicesImpl.ReportFileAccess can skip collection entirely, and gate the replay in TaskHostTask.HandleTaskHostTaskComplete on _buildComponentHost.BuildParameters.ReportFileAccesses for older/mismatched task hosts.
                          Note that gating alone would only have hidden #14824; the deserialization fix there is still required.
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/* Invert everything except media */
html {
filter: invert(1) hue-rotate(180deg) !important;
background: #1a1a2e !important;
}
/* Restore images, videos, iframes, canvas */
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filter: invert(1) hue-rotate(180deg) !important;
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[data-theme="light"], [data-theme="light"],
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.monaco-editor, .monaco-editor *,
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filter: none !important;
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/* Fix common UI elements */
.modal, .popup, .dropdown-menu, .tooltip, .popover {
filter: invert(1) hue-rotate(180deg) !important;
background: #2d2d44 !important;
border-color: #444 !important;
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::-webkit-scrollbar-thumb { background: #444 !important; }
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/* Selection */
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';
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console.log('[Universal Dark Mode] Disabled');
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if (enabled && !document.getElementById('universal-dark-mode-style')) {
applyDarkMode();
}
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observer.observe(document.head, { childList: true });
console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');
})();
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();
TaskHost file access reporting ignores BuildParameters.ReportFileAccesses · Issue #14826 · dotnet/msbuild · GitHub
                              Skip to content
                              TaskHost file access reporting ignores BuildParameters.ReportFileAccesses #14826
                              Open
                              #14871
                              Open
                              TaskHost file access reporting ignores BuildParameters.ReportFileAccesses#14826
                              #14871
                              Description
                              @JanProvaznik
                              JanProvaznik
                              opened on Aug 25, 2026
                              Summary
                              When a task runs in a TaskHost, file accesses reported through EngineServices.ReportFileAccess are collected and replayed unconditionally, ignoring BuildParameters.ReportFileAccesses. The equivalent in-proc code path does honor the flag. The same task therefore behaves differently depending only on where it happens to be scheduled.
                              This was found while investigating #14824, and it is the reason that defect crashed builds which had never asked for file-access reporting.
                              Details
                              The in-proc engine gates on the build parameter (src/Build/BackEnd/Components/RequestBuilder/TaskHost.cs):
                              publicvoidReportFileAccess(FileAccessDatafileAccessData){IBuildComponentHostbuildComponentHost=_taskHost._host;if(buildComponentHost.BuildParameters.ReportFileAccesses){((IFileAccessManager)buildComponentHost.GetComponent(BuildComponentType.FileAccessManager)).ReportFileAccess(fileAccessData,buildComponentHost.BuildParameters.NodeId);}}
                              The TaskHost process does not (src/MSBuild/OutOfProcTaskHostNode.cs):
                              publicvoidReportFileAccess(FileAccessDatafileAccessData){_taskHost._fileAccessData.Add(fileAccessData);}
                              Neither does the replay in the owning worker node (src/Build/Instance/TaskFactories/TaskHostTask.cs):
                              privatevoidHandleTaskHostTaskComplete(TaskHostTaskCompletetaskHostTaskComplete){
#if FEATURE_REPORTFILEACCESSESif(taskHostTaskComplete.FileAccessData?.Count>0){IFileAccessManagerfileAccessManager=((IFileAccessManager)_buildComponentHost.GetComponent(BuildComponentType.FileAccessManager));foreach(FileAccessDatafileAccessDataintaskHostTaskComplete.FileAccessData){fileAccessManager.ReportFileAccess(fileAccessData,_buildComponentHost.BuildParameters.NodeId);}}
#endif
                              TaskHostConfiguration carries no equivalent of ReportFileAccesses, so the TaskHost has no way to know the flag is off.
                              Impact
                              1. Inconsistent behavior. A task that calls ReportFileAccess is a no-op in-proc when reporting is disabled, but is collected, serialized across the pipe and replayed into the FileAccessManager when the same task runs in a TaskHost — which now happens by default for every task not annotated with MSBuildMultiThreadableTaskAttribute under -mt.
                              2. Wasted work. Every TaskHost task completion pays for serializing a List<FileAccessData> even when nothing will consume it.
                              3. It turned TaskHost file-access data is corrupted under multithreaded MSBuild #14824 from "corrupted data for opted-in users" into "builds crash with MSB4018 / MSB1025 even without -reportfileaccesses". I reproduced that crash with MSBuild.exe repro.proj using nothing but a TaskHostFactoryUsingTask — no -mt, no -reportfileaccesses.
                              Expected behavior
                              ReportFileAccess should be a no-op end to end when BuildParameters.ReportFileAccesses is false, regardless of where the task executes.
                              Suggested fix
                              Plumb the flag into TaskHostConfiguration so OutOfProcTaskHostNode.EngineServicesImpl.ReportFileAccess can skip collection entirely, and gate the replay in TaskHostTask.HandleTaskHostTaskComplete on _buildComponentHost.BuildParameters.ReportFileAccesses for older/mismatched task hosts.
                              Note that gating alone would only have hidden #14824; the deserialization fix there is still required.
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