Enhancements

• ext/tryfunc: Optional functions try and can to include in your hcl.EvalContext when evaluating expressions, which allow users to make decisions based on the success of expressions. (#330)
• ext/typeexpr: Now has an optional function convert which you can include in your hcl.EvalContext when evaluating expressions, allowing users to convert values to specific type constraints using the type constraint expression syntax. (#330)
• ext/typeexpr: A new cty capsule type typeexpr.TypeConstraintType which, when used as either a type constraint for a function parameter or as a type constraint for a hcldec attribute specification will cause the given expression to be interpreted as a type constraint expression rather than a value expression. (#330)
• ext/customdecode: An optional extension that allows overriding the static decoding behavior for expressions either in function arguments or hcldec attribute specifications. (#330)
• ext/customdecode: New cty capsuletypes customdecode.ExpressionType and customdecode.ExpressionClosureType which, when used as either a type constraint for a function parameter or as a type constraint for a hcldec attribute specification will cause the given expression (and, for the closure type, also the hcl.EvalContext it was evaluated in) to be captured for later analysis, rather than immediately evaluated. (#330)

Enhancements

• hcldec: Attribute evaluation (as part of AttrSpec or BlockAttrsSpec) now captures expression evaluation metadata in any errors it produces during type conversions, allowing for better feedback in calling applications that are able to make use of this metadata when printing diagnostic messages. (#329)

Bugs Fixed

• hclsyntax: IndexExpr, SplatExpr, and RelativeTraversalExpr will now report a source range that covers all of their child expression nodes. Previously they would report only the operator part, such as ["foo"], [*], or .foo, which was problematic for callers using source ranges for code analysis. (#328)
• hclwrite: Parser will no longer panic when the input includes index, splat, or relative traversal syntax. (#328)

Enhancements

• gohcl: When decoding into a struct value with some fields already populated, those values will be retained if not explicitly overwritten in the given HCL body, with similar overriding/merging behavior as json.Unmarshal in the Go standard library.
• hclwrite: New interface to set the expression for an attribute to be a raw token sequence, with no special processing. This has some caveats, so if you intend to use it please refer to the godoc comments. (#320)

Bugs Fixed

• hclwrite: The Body.Blocks method was returing the blocks in an indefined order, rather than preserving the order of declaration in the source input. (#313)
• hclwrite: The TokensForTraversal function (and thus in turn the Body.SetAttributeTraversal method) was not correctly handling index steps in traversals, and thus producing invalid results. (#319)

Initial release of HCL 2, which is a new implementation combining the HCL 1 language with the HIL expression language to produce a single language supporting both nested configuration structures and arbitrary expressions.

HCL 2 has an entirely new Go library API and so is not a drop-in upgrade relative to HCL 1. It's possible to import both versions of HCL into a single program using Go's semantic import versioning mechanism:

import (
    hcl1 "github.com/hashicorp/hcl"
    hcl2 "github.com/hashicorp/hcl/v2"
)