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• Issue: In ContentFileUtils.GetContentFileGroup the results list is initialized with contentFileGroups.Count as capacity, but the actual number of items added equals entryMappings.Count (which is the count of unique file paths across all groups). Since each content group typically contains multiple items, entryMappings.Count is significantly larger than contentFileGroups.Count, causing repeated list resizing and unnecessary LockFileContentFile[] allocations.
  Evidence:

  TypeAllocated!NuGet.ProjectModel.LockFileContentFile[]
  clr.dll!JIT_NewArr1
  mscorlib.dll!System.Collections.Generic.List`[System.__Canon].set_Capacity
  mscorlib.dll!System.Collections.Generic.List`[System.__Canon].EnsureCapacity
  mscorlib.dll!System.Collections.Generic.List`[System.__Canon].Add
  nuget.commands.dll!NuGet.Commands.ContentFileUtils.GetContentFileGroup
  

• Issue type: Specify an up-front capacity for collections if one is known

• Proposed fix: Move the results list initialization to after the entryMappings dictionary is fully populated, and change the capacity from contentFileGroups.Count to entryMappings.Count. This ensures the list is allocated with the exact required capacity, eliminating all resize-triggered array allocations.

Best practices wiki
See related failure in PRISM
ADO work item