feat: support Terraform override files in template preview#196
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Implement Terraform's override file semantics (override.tf, *_override.tf) by merging override blocks into primary files before evaluation. Related to: coder/coder#21991
Emyrk
reviewed
Mar 5, 2026
Override merging should not be stricter than Trivy, which accepts duplicate blocks without error. Additionally, replicating Terraform's duplicate detection correctly requires per-block-type semantics — complexity that isn't justified for something that's not our responsibility. Invalid duplicates will still be caught by `terraform plan`. 'terraform' block overrides are rare and the merging semantics are not straightforward, so we just skip them for now (with a warning).
Emyrk
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Mar 23, 2026
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The fallback behavior if it fails is great 👍
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| if ext == ".tf.json" { | ||
| if isOverrideFile(d.Name()) { | ||
| warnings = warnings.Append(&hcl.Diagnostic{ | ||
| Severity: hcl.DiagWarning, | ||
| Summary: "Unmerged .tf.json override file", | ||
| Detail: fmt.Sprintf("Not merging override file %q that uses JSON format", p), | ||
| }) |
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| // Override merging is best-effort; downgrade all override error | ||
| // diagnostics to warnings so they never abort the preview. |
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Implements https://developer.hashicorp.com/terraform/language/files/override (override.tf, *_override.tf) by merging override content into primary .tf files before Trivy evaluation.
Block merging
localsblocks are merged at the individual attribute level across all primary files, matching Terraform's per-attribute semanticsterraformblocks in overrides are skipped with a warning - their override semantics are too nuanced to replicate correctlyvariable "x" {}) are handled correctly by forcing multi-line formatting before attribute insertionFilesystem layer
How it works
Related to: coder/coder#21991