fix(kustomize): Updated generator support for both EnvSources and FileSources using [{key}=]{path} syntax

[johanbcn]

Fixes: #9338 Related: n/a Merge before/after: n/a

Description When using kustomize during the render stage, if files must be mirrored before rendering because they require modifications (when using --set flags, for example), files defined in the env section of configMapGenerator and secretGenerator are omitted, and thus the render ends up failing because it cannot find all the required filed.

The error message in that case is similar to this:

running [kustomize build /var/folders/dy/qslwfy7n0jz3wp1gjxs3m32h0000gp/T/4251885249/Users/foobar/src/test/skaffold-set-issue/src/foobar/kustomize/overlays/issue1]
 - stdout: ""
 - stderr: "Error: loading KV pairs: env source files: [local.env]: evalsymlink failure on '/private/var/folders/dy/qslwfy7n0jz3wp1gjxs3m32h0000gp/T/4251885249/Users/foobar/src/test/skaffold-set-issue/src/foobar/kustomize/overlays/issue1/local.env' : lstat /private/var/folders/dy/qslwfy7n0jz3wp1gjxs3m32h0000gp/T/4251885249/Users/foobar/src/test/skaffold-set-issue/src/foobar/kustomize/overlays/issue1/local.env: no such file or directory\n"
 - cause: exit status 1

Moreover, both on the previous situation and when using skaffold in dev mode (using the skaffold dev command), files defined in the files section of the configMapGenerator and secretGenerator that make use of the [{key}=]{path} syntax aren't properly recognized and the files neither won't be copied when mirroring or watched upon for changes in dev mode.

The error message visible during the render stage is similar to this:

open /Users/foobar/src/test/skaffold-set-issue/src/foobar/kustomize/overlays/issue2/application.yaml=application-foobar.yaml: no such file or directory

An example of the [{key}=]{path} syntax can be seen in the second example from kustomize's reference documentation).

This PR adds additional test cases for the situations described above and the required fixes.

[gemini-code-assist[bot]]

Summary of Changes

Hello @johanbcn, I'm Gemini Code Assist[^1]! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses critical issues within Skaffold's Kustomize integration, specifically concerning how configMapGenerator and secretGenerator process file sources. It ensures that all referenced files, including environment sources and those using the [{key}=]{path} syntax, are correctly mirrored during the rendering process and properly tracked for changes in development mode. This prevents build failures and improves the reliability of Kustomize-based deployments within Skaffold.

Highlights

• Kustomize Generator Support: Enhanced Kustomize configMapGenerator and secretGenerator to correctly handle EnvSources and FileSources that use the [{key}=]{path} syntax.
• Fixes File Omission During Render: Resolved an issue where files defined in env sections of generators were omitted during the render stage, leading to 'no such file or directory' errors.
• Improved Dev Mode File Watching: Ensured that files specified with the [{key}=]{path} syntax in files sections of generators are properly recognized and watched for changes in skaffold dev mode.
• Comprehensive Test Coverage: Added new test cases to validate the correct mirroring and dependency detection for various generator configurations, including those using alternative keys and environment sources.

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[johanbcn]

The added tests brought up to light another issue when mirroring files in Windows systems, which didn't handle filesystem paths correctly.

I have updated the PR to fix that too.

[johanbcn]

I rebased the changes over the latest commits from main. Let me know if there is anything else that must be done.