OpenTofu 1.13 Improves Plan-Time Resolution of Unknown Values and Adds Linting

Enhanced Plan-Time Resolution

OpenTofu version 1.13 introduces new capabilities for module authors to resolve expressions during the planning phase. Specifically, functions such as `convert` and `assumenotnull` address scenarios where `count` or `for_each` keys remain unknown due to dynamic inputs like `yamldecode` results. This allows the planner to determine the number of resource instances even when all their attributes are not yet known, preventing plan failures.

The `convert` function enables specifying a known type for values, even if the input is initially unknown, such as with `yamldecode`. When combined with `assumenotnull`, it allows `count` expressions based on nullness to resolve to zero or one, while the object's contents can remain unknown until the apply phase. This design aligns with a similar feature introduced in Terraform 1.15.

New Linting Capabilities

OpenTofu 1.13 includes experimental built-in linting rules, which can be enabled using the `-lint=all` flag with `tofu validate`, `tofu plan`, or `tofu apply`. These rules include `core:unused-variable` and `core:count-instead-enabled`. The maintainers noted that linting was a highly requested feature, with future plans for custom rules and broader policy checks. This feature complements existing static analysis tools like TFLint.

Symbol Libraries Experiment

An opt-in experimental feature called Symbol Libraries is also part of this release. It allows sharing functions and type definitions through `*.sym.hcl` files. While libraries cannot directly access resources, data sources, or provider functions, callers can pass resource values into library functions. The OpenTofu team aims to stabilize this feature in version 1.14.

Other Changes

Version 1.13 also removes Windows Remote Management (WinRM) support from `tofu`.