What causes "%s%s: block schema is nil" in hashicorp/terraform?

Provide a full *NestedBlock (with a non-nil inner Block and a valid Nesting mode) for every key.

%s%s: block schema is nil

Error message

%s%s: block schema is nil

What it means

A nil entry exists in a Block's BlockTypes map (b.BlockTypes[name] == nil, checked at line 50). Analogous to 809 but for nested blocks; the validator skips recursion (`continue`) and records the error. Means a nested-block placeholder was left nil.

Source

Thrown at internal/configs/configschema/internal_validate.go:51

		multiErr = errors.Join(multiErr, fmt.Errorf("top-level block: DeprecationMessage must not be set when Deprecated is false"))
	}

	for name, attrS := range b.Attributes {
		if attrS == nil {
			multiErr = errors.Join(multiErr, fmt.Errorf("%s%s: attribute schema is nil", prefix, name))
			continue
		}
		multiErr = errors.Join(multiErr, attrS.internalValidate(name, prefix))

		// all attributes within a computed block must also be computed
		if b.Computed && !attrS.Computed {
			multiErr = errors.Join(multiErr, fmt.Errorf("%s%s: all attributes within computed blocks must also be computed", prefix, name))
		}
	}

	for name, blockS := range b.BlockTypes {
		if blockS == nil {
			multiErr = errors.Join(multiErr, fmt.Errorf("%s%s: block schema is nil", prefix, name))
			continue
		}

		if _, isAttr := b.Attributes[name]; isAttr {
			multiErr = errors.Join(multiErr, fmt.Errorf("%s%s: name defined as both attribute and child block type", prefix, name))
		} else if !validName.MatchString(name) {
			multiErr = errors.Join(multiErr, fmt.Errorf("%s%s: name may contain only lowercase letters, digits and underscores", prefix, name))
		}
		if !blockS.Deprecated && blockS.DeprecationMessage != "" {
			multiErr = errors.Join(multiErr, fmt.Errorf("%s%s: DeprecationMessage must not be set when Deprecated is false", prefix, name))
		}

		if blockS.MinItems < 0 || blockS.MaxItems < 0 {
			multiErr = errors.Join(multiErr, fmt.Errorf("%s%s: MinItems and MaxItems must both be greater than zero", prefix, name))
		}

		// any nested blocks within a computed block must also be computed
		if b.Computed && !blockS.Computed {

View on GitHub (pinned to c9def3e214)

Solutions

Provide a full *NestedBlock (with a non-nil inner Block and a valid Nesting mode) for every key.
Omit the key if the nested block shouldn't exist.

Example fix

// before
BlockTypes: map[string]*configschema.NestedBlock{
    "settings": nil,
}

// after
BlockTypes: map[string]*configschema.NestedBlock{
    "settings": {Nesting: configschema.NestingSingle, Block: configschema.Block{Attributes: map[string]*configschema.Attribute{"x": {Type: cty.String, Optional: true}}}},
}

Defensive patterns

Strategy: validation

Validate before calling

for k, nb := range block.BlockTypes {
    if nb == nil { return fmt.Errorf("nested block %q is nil", k) }
}

Prevention

Never store nil in BlockTypes; omit the entry instead.
Validate nested-block construction returns a populated *NestedBlock before insertion.

When it happens

Trigger: Building BlockTypes with `"settings": nil` or assigning a nil *NestedBlock from a helper that didn't populate it.

Common situations: Generated schemas, conditional nested-block construction returning nil, refactor leftovers.

Related errors

AI-assisted analysis of hashicorp/terraform@c9def3e214 (2026-08-07). Data as JSON: /api/errors/76dd6b11beb13f5a. Report an issue: GitHub.