add validation for variables import JSON structure

[rjgoyln]

Summary

This PR improves validation and error handling for the variables import command.

Previously, the implementation assumed that the input JSON was always a dictionary,
which could lead to unexpected AttributeError when processing invalid inputs.
This PR introduces explicit validation to ensure safer and more predictable behavior.

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Changes

• Validate that the top-level JSON structure is a dictionary
• Enforce presence of "value" field for nested variable objects
• Add unit tests to cover invalid input scenarios

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---

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[bugraoz93]

We were aiming to add validation to the entire stack of airflowctl. Adding high-level field validation here #65092 (issue attached) for generic cases and handling with more granular exceptions for all, what do you think?

[bugraoz93]

Maybe just keeping the JSON part to see if it is valid JSON, or not, but that was already handled above.

...
    if not os.path.exists(args.file):
        rich.print(f"[red]Missing variable file: {args.file}")
        sys.exit(1)
    with open(args.file) as var_file:
        try:
            var_json = json.load(var_file)
        except json.JSONDecodeError:
            rich.print(f"[red]Invalid variable file: {args.file}")
            sys.exit(1)
...

I would say let's merge the generic solution for everything and close this. Many thanks for the PR! This could cause confusion, double validation of fields, etc.
Or if you think we can somehow combine, open to any ideas :)

[rjgoyln]

Maybe just keeping the JSON part to see if it is valid JSON, or not, but that was already handled above.

...
    if not os.path.exists(args.file):
        rich.print(f"[red]Missing variable file: {args.file}")
        sys.exit(1)
    with open(args.file) as var_file:
        try:
            var_json = json.load(var_file)
        except json.JSONDecodeError:
            rich.print(f"[red]Invalid variable file: {args.file}")
            sys.exit(1)
...

I would say let's merge the generic solution for everything and close this. Many thanks for the PR! This could cause confusion, double validation of fields, etc. Or if you think we can somehow combine, open to any ideas :)

Thanks for the feedback! I agree that avoiding double validation and keeping the logic unified is better for the codebase. I’ll close this PR.