Fix duplicate key error when adding multiple labels with --without-selector

[isarns]

Description

Fixes a bug in the kustomize edit add label --without-selector command where adding multiple labels would fail with a "label already in kustomization file" error, even when the labels didn't actually exist.
Fixes: #5978

Problem

When running:

kustomize edit add label --without-selector test1:a test2:b

The command would fail with:

Error: label test2 already in kustomization file. Use --force to override.

Root Cause

The issue was in the writeToLabels function in addmetadata.go. The function was calling o.writeToMap(lbl.Pairs, kind) which attempts to add all metadata pairs to the lbl.Pairs map. However, since lbl.Pairs already contained pairs from previous iterations of the loop, it would find duplicates and throw the "already exists" error.

Solution

Changed line 186 from:

if err := o.writeToMap(lbl.Pairs, kind); err != nil {

To:

if err := o.writeToMapEntry(lbl.Pairs, k, v, kind); err != nil {

This ensures only the current key-value pair is added to the map, avoiding the duplicate key issue.

Testing

• Verified the fix works with multiple labels using --without-selector
• Existing tests continue to pass
• No regression in other label functionality

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

[k8s-ci-robot]

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[koba1t]

Hi @isarns
Thanks for your contribution!

So, Could you add testacases to check this change will be fix that problem?

[k8s-ci-robot]

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[koba1t]

@isarns
Could you check lint failure?

[koba1t]

/ok-to-test

[koba1t]

@isarns
Thanks for your contribution!

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: isarns, koba1t

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