Avoid re-creating pre-existing folders.

[adreed-msft]

Description

• Feature / Bug Fix: (Brief description of the feature or issue being addressed)

• Related Links:

• PBI # 26906103

Type of Change

• Bug fix
• New feature
• Documentation update required
• Code quality improvement
• Other (describe):

How Has This Been Tested?

Test is written to interact with the folder creation tracker directly.

[Copilot]

Pull Request Overview

This PR implements a bug fix to avoid re-creating pre-existing folders, addressing performance issues with services like Azure Files that may complain about excessive directory creation requests.

Key Changes

• Introduces a new FolderExisted transfer status to distinguish between folders created by the current job versus pre-existing folders
• Modifies folder creation logic to return a sentinel error (FolderCreationErrorAlreadyExists) when a folder already exists, preventing redundant creation attempts
• Extends the NewFolderCreationTracker to create trackers for File and BlobFS destinations, not just when persisting folder properties

Reviewed Changes

Copilot reviewed 10 out of 11 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
ste/folderCreationTracker.go	Core logic changes: adds folder state tracking, new status enum, and logic to avoid re-creating existing folders
ste/folderCreationTracker_test.go	Adds test for folder existence detection and updates existing test structure
ste/sender-blobFS.go	Updates doEnsureDirExists to return FolderCreationErrorAlreadyExists when path already exists
ste/sender-azureFile.go	Updates CreateDirToRoot to return FolderCreationErrorAlreadyExists when resource already exists
ste/mgr-JobMgr.go	Passes fromTo parameter to NewFolderCreationTracker constructor
common/folderCreationTracker_interface.go	Defines new FolderCreationErrorAlreadyExists sentinel error type
common/fe-ste-models.go	Adds FolderExisted() status (value 4) and adjusts Restarted() to value 5
ste/JobPartPlan.go	Bumps data schema version from 19 to 20 for enum value changes
jobsAdmin/init.go	Includes FolderExisted status in job summary resurrection logic
go.mod, go.sum	Adds indirect dependencies (transitive from other packages)

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[Copilot]

The comparison ts == ts.FolderCreated() is comparing the variable against a method call on itself, which will always return false. This should be ts == common.ETransferStatus.FolderCreated() to properly check if the transfer status is FolderCreated.

Suggested change

	if ts := f.fetchTransfer(*state.Index).TransferStatus(); ts == ts.FolderCreated() {
	if ts := f.fetchTransfer(*state.Index).TransferStatus(); ts == common.ETransferStatus.FolderCreated() {

[Copilot]

When a new state is created (line 153) for a folder that isn't already in f.contents, it needs to be stored in the map. After updating the state's Status field (lines 156-160), add f.contents[folder] = state before line 174 to persist the state. Without this, the state is lost and subsequent calls to CreateFolder for the same folder won't see the previous status, defeating the purpose of tracking folder creation.

Suggested change

	f.contents[folder] = state

[Copilot]

The comment is misleading. The error is returned after doCreation has already been called and attempted to create the folder. It signals that the folder already existed, not that creation should be skipped. Consider rewording to: "FolderCreationErrorAlreadyExists is a signalling error that should be returned by doCreation when the folder already exists, allowing the tracker to mark it as FolderExisted rather than FolderCreated."

Suggested change

	// returned by doCreation on FolderCreationTracker.CreateFolder for supported folder-creators.
	// This will inform the folder creation tracker to _not_ try to create the folder.
	// returned by doCreation when the folder already exists, allowing the tracker to mark it as
	// FolderExisted rather than FolderCreated.