[ARM] Deployment stacks What-If support

[kalbert312]

Related command
az stack-whatif

Description
Adds stack-whatif commands to Az CLI. This is a new resource type in ARM that stores previews of operations on deployment stacks. This may become a subcommand, or a flag to existing stack commands in the future, depending on customer feedback. The reason this is not added as a subcommand now is there is a subcommand hierarchy conflict:
az stack what-if group conflicts with az stack group where what-if is an action vs group which is a scope.
az stack group what-if would operate on a what-if entity, not a stack, which conflicts with the hierarchy.
Happy to take other suggestions if az stack-whatif is not desired.

Testing Guide
See test_resource_stacks.py for live test examples. Note at the time of writing, these commands currently only work in Canary regions, but full prod availability is expected by the end of the month.

History Notes

[ARM] az stack-whatif group/sub/mg: Add deployment stacks what-if commands.

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[yonzhan]

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Please sync the latest code with latest dev branch (for azure-cli) or main branch (for azure-cli-extensions).
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[Copilot]

Pull request overview

Adds a new az stack-whatif command surface to the resource module to create/show/list/delete deployment stack What-If results across RG/subscription/management-group scopes, including a dedicated pretty-printer for stack What-If output and accompanying tests/recordings.

Changes:

• Register new stack-whatif {group|sub|mg} {create|show|list|delete} command groups and arguments, plus help text and linter exclusions.
• Add a stack What-If pretty formatter (DeploymentStacksWhatIfResultFormatter) and extend shared color/formatting utilities.
• Add live-scenario tests + recordings, and a unit test + sample JSON for formatter output.

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
src/azure-cli/service_name.json	Map az stack-whatif to the ARM “Resource Manager” service link.
src/azure-cli/azure/cli/command_modules/resource/tests/latest/test_stack_formatters.py	New unit test for stack What-If pretty formatting.
src/azure-cli/azure/cli/command_modules/resource/tests/latest/test_resource_stacks.py	New scenario tests for stack-whatif create/show/list/delete.
src/azure-cli/azure/cli/command_modules/resource/tests/latest/recordings/test_deployment_stack_what_if_at_subscription.yaml	Playback recording for subscription-scope stack-whatif scenario.
src/azure-cli/azure/cli/command_modules/resource/tests/latest/recordings/test_deployment_stack_what_if_at_resource_group.yaml	Playback recording for RG-scope stack-whatif scenario.
src/azure-cli/azure/cli/command_modules/resource/tests/latest/recordings/test_deployment_stack_what_if_at_management_group.yaml	Playback recording for MG-scope stack-whatif scenario.
src/azure-cli/azure/cli/command_modules/resource/tests/latest/data/stacks-what-if/what-if-1.json	Sample stack What-If payload used by formatter unit tests.
src/azure-cli/azure/cli/command_modules/resource/linter_exclusions.yml	Add linter exclusions for stack-whatif command groups/params.
src/azure-cli/azure/cli/command_modules/resource/custom.py	Implement stack-whatif create/show pretty-print behavior and wiring to the formatter.
src/azure-cli/azure/cli/command_modules/resource/commands.py	Register new stack-whatif command groups and operations.
src/azure-cli/azure/cli/command_modules/resource/_utils.py	Add str_lower_eq helper used by stack-whatif formatter comparisons.
src/azure-cli/azure/cli/command_modules/resource/_stacks_formatters.py	New pretty-printer for stack What-If results (stack-level + managed resource changes + diagnostics).
src/azure-cli/azure/cli/command_modules/resource/_params.py	Add --no-color, introduce --stack-id for stack-whatif, and share argument wiring across stack/stack-whatif.
src/azure-cli/azure/cli/command_modules/resource/_help.py	Add help entries + examples for az stack-whatif across scopes.
src/azure-cli/azure/cli/command_modules/resource/_formatters.py	Adjust deployment What-If formatter behavior around “Unknown” scopes / missing relative IDs.
src/azure-cli/azure/cli/command_modules/resource/_color.py	Extend color utilities (CYAN) and add indentation/insert helpers used by the new formatter.
src/azure-cli-core/azure/cli/core/helpIndex.latest.json	Add top-level help index entry for stack-whatif.
src/azure-cli-core/azure/cli/core/commandIndex.latest.json	Add stack-whatif to command index; also modifies network module mapping.

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[Copilot]

commandIndex.latest.json drops azure.cli.command_modules.privatedns from the network command group. Since azure/cli/command_modules/privatedns/ still exists, this likely breaks az network private-dns ... command loading under the optimized loader. Please regenerate the command index or re-add the privatedns module to the network entry.

Suggested change

	"azure.cli.command_modules.network"
	"azure.cli.command_modules.network",
	"azure.cli.command_modules.privatedns"

[kalbert312]

Not sure how this happened. I ran the script to update this.