Let the workflow give the backend type

[benlangfeld]

One of the two approaches offered in #443. The other is #444, which makes the inspection itself cheap. They are independent — this one needs the caller to opt in, #444 helps everyone — and either stands alone.

The change

setup() works out the backend type by parsing every file in the root module. Most workflows know the answer already, and it rarely changes.

- uses: dflook/terraform-plan@v3
  with:
    backend_type: s3

When set, the inspection is skipped:

if [[ -n "${INPUT_BACKEND_TYPE:-}" ]]; then
    # Given by the workflow, so the root module does not need inspecting.
    TERRAFORM_BACKEND_TYPE="$INPUT_BACKEND_TYPE"
    echo "Using the $TERRAFORM_BACKEND_TYPE backend given by the backend_type input"
else
    TERRAFORM_BACKEND_TYPE=$(terraform-backend)
    if [[ "$TERRAFORM_BACKEND_TYPE" != "" ]]; then
        echo "Detected $TERRAFORM_BACKEND_TYPE backend"
    fi
fi

The log distinguishes the two cases, since a type the caller gave was not detected.

Notes on the approach

backend_type is already defined in docs-gen/inputs/ and used by remote-state, so this reuses that input with required=False rather than adding a second one with the same name. It sorts immediately after path, which is where Action.assert_ordering already expects it.

Added to plan, apply and check — the three actions named in #443. actions.sh is shared, so extending it to the others is only a matter of listing the input on them; I have left that out rather than widen the diff, and am happy to add them if you would prefer it everywhere at once.

Generated files are regenerated with docs-gen/generate.py; the only change in them is the new input.

Effect

On the root module profiled in #443 — ~260 .tf files — this removes a 46 second step. For comparison, #444 takes the same work from 34.07s to 0.20s on a generated module of that shape, without needing the input.

Tests

pytest tests --ignore=tests/github_pr_comment gives 147 passed with 2 failures and 7 errors, identical to main — those need S3 and some environment variables I do not have. tests/github_pr_comment fails to collect identically before and after, on a missing TERRAFORM_ACTIONS_* variable. bash -n image/actions.sh is clean under bash 5.

A larger related saving

The same root module is parsed twice per step. terraform-version calls load_module() on it in its own process, immediately before terraform-backend does.

That the first one is a parse rather than the archive download is now measured rather than inferred: the reporter cached the archive with actions/cache and the time did not move at all, with gpg verification landing at the identical offset on a cold and a warm run. See #443 (comment).

Together the two parses are around 80 seconds of a ~5m30s plan.

#446 removes the first one for workflows that pin an exact version, by taking the existing argument fast path in main() when TERRAFORM_VERSION names a version rather than a constraint — which also skips the release index fetch. With this PR and #446 together, a large root module with a pinned version parses nothing at all before terraform runs.

🤖 Generated with Claude Code