command: New -compact-warnings option

[apparentlymart]

When warnings appear in isolation (not accompanied by an error) it's reasonable to want to defer resolving them for a while because they are not actually blocking immediate work.

However, our warning messages tend to be long by default in order to include all of the necessary context to understand the implications of the warning, and that can make them overwhelming when combined with other output.

As a compromise, this adds a new CLI option -compact-warnings which is supported for all the main operation commands and which uses a more compact format to print out warnings as long as they aren't also accompanied by errors. This is mainly intended for use in automation scenarios where work is being sent to production, as opposed local development scenarios while working on changes to a module, but it can be used in either context. The intent is to ensure that the warnings still stay visible (or else the warning mechanism would become useless) while minimizing their weight in the overall output.

This also includes a change to the default behavior to consolidate warnings further so that there's only one instance of each distinct summary in the output. Aside from that additional consolidation, the default behavior is unchanged so that the warning messages can be presented with contextual information initially.

Full warning messages are always shown if there's at least one error included in the diagnostic set too, because in that case the warning message could contain additional context to help understand the error.

---

Warnings:

- Quoted type constraints are deprecated
  on deprecated-interp.tf line 3 (and 2 more)
- Interpolation-only expressions are deprecated
  on deprecated-interp.tf line 18

To see the full warning notes, run Terraform without -compact-warnings.

[jbardin]

If we only want to upgrade the output on errors, couldn't this just be HasErrors()?

[apparentlymart]

This is some future-proofing for a possible future scenario where there is a third diagnostic severity. My goal here is to explicitly check that the entire diagnostic set is warnings, as required by the contract of DiagnosticWarningsCompact, rather than to indirectly check it by assuming that error is the only non-warning severity.

(If this comes up again, perhaps we can add an OnlyWarnings accessor to Diagnostics to encapsulate this, but so far I don't recall us needing this check anywhere else.)

[nazarewk]

@apparentlymart can this be used by default with environment variable?

[apparentlymart]

Hi @nazarewk,

All command line options can be specified as environment variables:

export TF_CLI_ARGS_plan="-compact-warnings"
export TF_CLI_ARGS_apply="-compact-warnings"

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