Upgrade to 0.12

[github/fretlink/terraform-provider-statuscake.git] / vendor / github.com / hashicorp / hcl2 / hcldec / spec.go

package hcldec

import (
        "bytes"
        "fmt"
        "sort"

        "github.com/hashicorp/hcl2/hcl"
        "github.com/zclconf/go-cty/cty"
        "github.com/zclconf/go-cty/cty/convert"
        "github.com/zclconf/go-cty/cty/function"
)

// A Spec is a description of how to decode a hcl.Body to a cty.Value.
//
// The various other types in this package whose names end in "Spec" are
// the spec implementations. The most common top-level spec is ObjectSpec,
// which decodes body content into a cty.Value of an object type.
type Spec interface {
        // Perform the decode operation on the given body, in the context of
        // the given block (which might be null), using the given eval context.
        //
        // "block" is provided only by the nested calls performed by the spec
        // types that work on block bodies.
        decode(content *hcl.BodyContent, blockLabels []blockLabel, ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics)

        // Return the cty.Type that should be returned when decoding a body with
        // this spec.
        impliedType() cty.Type

        // Call the given callback once for each of the nested specs that would
        // get decoded with the same body and block as the receiver. This should
        // not descend into the nested specs used when decoding blocks.
        visitSameBodyChildren(cb visitFunc)

        // Determine the source range of the value that would be returned for the
        // spec in the given content, in the context of the given block
        // (which might be null). If the corresponding item is missing, return
        // a place where it might be inserted.
        sourceRange(content *hcl.BodyContent, blockLabels []blockLabel) hcl.Range
}

type visitFunc func(spec Spec)

// An ObjectSpec is a Spec that produces a cty.Value of an object type whose
// attributes correspond to the keys of the spec map.
type ObjectSpec map[string]Spec

// attrSpec is implemented by specs that require attributes from the body.
type attrSpec interface {
        attrSchemata() []hcl.AttributeSchema
}

// blockSpec is implemented by specs that require blocks from the body.
type blockSpec interface {
        blockHeaderSchemata() []hcl.BlockHeaderSchema
        nestedSpec() Spec
}

// specNeedingVariables is implemented by specs that can use variables
// from the EvalContext, to declare which variables they need.
type specNeedingVariables interface {
        variablesNeeded(content *hcl.BodyContent) []hcl.Traversal
}

func (s ObjectSpec) visitSameBodyChildren(cb visitFunc) {
        for _, c := range s {
                cb(c)
        }
}

func (s ObjectSpec) decode(content *hcl.BodyContent, blockLabels []blockLabel, ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
        vals := make(map[string]cty.Value, len(s))
        var diags hcl.Diagnostics

        for k, spec := range s {
                var kd hcl.Diagnostics
                vals[k], kd = spec.decode(content, blockLabels, ctx)
                diags = append(diags, kd...)
        }

        return cty.ObjectVal(vals), diags
}

func (s ObjectSpec) impliedType() cty.Type {
        if len(s) == 0 {
                return cty.EmptyObject
        }

        attrTypes := make(map[string]cty.Type)
        for k, childSpec := range s {
                attrTypes[k] = childSpec.impliedType()
        }
        return cty.Object(attrTypes)
}

func (s ObjectSpec) sourceRange(content *hcl.BodyContent, blockLabels []blockLabel) hcl.Range {
        // This is not great, but the best we can do. In practice, it's rather
        // strange to ask for the source range of an entire top-level body, since
        // that's already readily available to the caller.
        return content.MissingItemRange
}

// A TupleSpec is a Spec that produces a cty.Value of a tuple type whose
// elements correspond to the elements of the spec slice.
type TupleSpec []Spec

func (s TupleSpec) visitSameBodyChildren(cb visitFunc) {
        for _, c := range s {
                cb(c)
        }
}

func (s TupleSpec) decode(content *hcl.BodyContent, blockLabels []blockLabel, ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
        vals := make([]cty.Value, len(s))
        var diags hcl.Diagnostics

        for i, spec := range s {
                var ed hcl.Diagnostics
                vals[i], ed = spec.decode(content, blockLabels, ctx)
                diags = append(diags, ed...)
        }

        return cty.TupleVal(vals), diags
}

func (s TupleSpec) impliedType() cty.Type {
        if len(s) == 0 {
                return cty.EmptyTuple
        }

        attrTypes := make([]cty.Type, len(s))
        for i, childSpec := range s {
                attrTypes[i] = childSpec.impliedType()
        }
        return cty.Tuple(attrTypes)
}

func (s TupleSpec) sourceRange(content *hcl.BodyContent, blockLabels []blockLabel) hcl.Range {
        // This is not great, but the best we can do. In practice, it's rather
        // strange to ask for the source range of an entire top-level body, since
        // that's already readily available to the caller.
        return content.MissingItemRange
}

// An AttrSpec is a Spec that evaluates a particular attribute expression in
// the body and returns its resulting value converted to the requested type,
// or produces a diagnostic if the type is incorrect.
type AttrSpec struct {
        Name     string
        Type     cty.Type
        Required bool
}

func (s *AttrSpec) visitSameBodyChildren(cb visitFunc) {
        // leaf node
}

// specNeedingVariables implementation
func (s *AttrSpec) variablesNeeded(content *hcl.BodyContent) []hcl.Traversal {
        attr, exists := content.Attributes[s.Name]
        if !exists {
                return nil
        }

        return attr.Expr.Variables()
}

// attrSpec implementation
func (s *AttrSpec) attrSchemata() []hcl.AttributeSchema {
        return []hcl.AttributeSchema{
                {
                        Name:     s.Name,
                        Required: s.Required,
                },
        }
}

func (s *AttrSpec) sourceRange(content *hcl.BodyContent, blockLabels []blockLabel) hcl.Range {
        attr, exists := content.Attributes[s.Name]
        if !exists {
                return content.MissingItemRange
        }

        return attr.Expr.Range()
}

func (s *AttrSpec) decode(content *hcl.BodyContent, blockLabels []blockLabel, ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
        attr, exists := content.Attributes[s.Name]
        if !exists {
                // We don't need to check required and emit a diagnostic here, because
                // that would already have happened when building "content".
                return cty.NullVal(s.Type), nil
        }

        val, diags := attr.Expr.Value(ctx)

        convVal, err := convert.Convert(val, s.Type)
        if err != nil {
                diags = append(diags, &hcl.Diagnostic{
                        Severity: hcl.DiagError,
                        Summary:  "Incorrect attribute value type",
                        Detail: fmt.Sprintf(
                                "Inappropriate value for attribute %q: %s.",
                                s.Name, err.Error(),
                        ),
                        Subject: attr.Expr.StartRange().Ptr(),
                        Context: hcl.RangeBetween(attr.NameRange, attr.Expr.StartRange()).Ptr(),
                })
                // We'll return an unknown value of the _correct_ type so that the
                // incomplete result can still be used for some analysis use-cases.
                val = cty.UnknownVal(s.Type)
        } else {
                val = convVal
        }

        return val, diags
}

func (s *AttrSpec) impliedType() cty.Type {
        return s.Type
}

// A LiteralSpec is a Spec that produces the given literal value, ignoring
// the given body.
type LiteralSpec struct {
        Value cty.Value
}

func (s *LiteralSpec) visitSameBodyChildren(cb visitFunc) {
        // leaf node
}

func (s *LiteralSpec) decode(content *hcl.BodyContent, blockLabels []blockLabel, ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
        return s.Value, nil
}

func (s *LiteralSpec) impliedType() cty.Type {
        return s.Value.Type()
}

func (s *LiteralSpec) sourceRange(content *hcl.BodyContent, blockLabels []blockLabel) hcl.Range {
        // No sensible range to return for a literal, so the caller had better
        // ensure it doesn't cause any diagnostics.
        return hcl.Range{
                Filename: "<unknown>",
        }
}

// An ExprSpec is a Spec that evaluates the given expression, ignoring the
// given body.
type ExprSpec struct {
        Expr hcl.Expression
}

func (s *ExprSpec) visitSameBodyChildren(cb visitFunc) {
        // leaf node
}

// specNeedingVariables implementation
func (s *ExprSpec) variablesNeeded(content *hcl.BodyContent) []hcl.Traversal {
        return s.Expr.Variables()
}

func (s *ExprSpec) decode(content *hcl.BodyContent, blockLabels []blockLabel, ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
        return s.Expr.Value(ctx)
}

func (s *ExprSpec) impliedType() cty.Type {
        // We can't know the type of our expression until we evaluate it
        return cty.DynamicPseudoType
}

func (s *ExprSpec) sourceRange(content *hcl.BodyContent, blockLabels []blockLabel) hcl.Range {
        return s.Expr.Range()
}

// A BlockSpec is a Spec that produces a cty.Value by decoding the contents
// of a single nested block of a given type, using a nested spec.
//
// If the Required flag is not set, the nested block may be omitted, in which
// case a null value is produced. If it _is_ set, an error diagnostic is
// produced if there are no nested blocks of the given type.
type BlockSpec struct {
        TypeName string
        Nested   Spec
        Required bool
}

func (s *BlockSpec) visitSameBodyChildren(cb visitFunc) {
        // leaf node ("Nested" does not use the same body)
}

// blockSpec implementation
func (s *BlockSpec) blockHeaderSchemata() []hcl.BlockHeaderSchema {
        return []hcl.BlockHeaderSchema{
                {
                        Type:       s.TypeName,
                        LabelNames: findLabelSpecs(s.Nested),
                },
        }
}

// blockSpec implementation
func (s *BlockSpec) nestedSpec() Spec {
        return s.Nested
}

// specNeedingVariables implementation
func (s *BlockSpec) variablesNeeded(content *hcl.BodyContent) []hcl.Traversal {
        var childBlock *hcl.Block
        for _, candidate := range content.Blocks {
                if candidate.Type != s.TypeName {
                        continue
                }

                childBlock = candidate
                break
        }

        if childBlock == nil {
                return nil
        }

        return Variables(childBlock.Body, s.Nested)
}

func (s *BlockSpec) decode(content *hcl.BodyContent, blockLabels []blockLabel, ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
        var diags hcl.Diagnostics

        var childBlock *hcl.Block
        for _, candidate := range content.Blocks {
                if candidate.Type != s.TypeName {
                        continue
                }

                if childBlock != nil {
                        diags = append(diags, &hcl.Diagnostic{
                                Severity: hcl.DiagError,
                                Summary:  fmt.Sprintf("Duplicate %s block", s.TypeName),
                                Detail: fmt.Sprintf(
                                        "Only one block of type %q is allowed. Previous definition was at %s.",
                                        s.TypeName, childBlock.DefRange.String(),
                                ),
                                Subject: &candidate.DefRange,
                        })
                        break
                }

                childBlock = candidate
        }

        if childBlock == nil {
                if s.Required {
                        diags = append(diags, &hcl.Diagnostic{
                                Severity: hcl.DiagError,
                                Summary:  fmt.Sprintf("Missing %s block", s.TypeName),
                                Detail: fmt.Sprintf(
                                        "A block of type %q is required here.", s.TypeName,
                                ),
                                Subject: &content.MissingItemRange,
                        })
                }
                return cty.NullVal(s.Nested.impliedType()), diags
        }

        if s.Nested == nil {
                panic("BlockSpec with no Nested Spec")
        }
        val, _, childDiags := decode(childBlock.Body, labelsForBlock(childBlock), ctx, s.Nested, false)
        diags = append(diags, childDiags...)
        return val, diags
}

func (s *BlockSpec) impliedType() cty.Type {
        return s.Nested.impliedType()
}

func (s *BlockSpec) sourceRange(content *hcl.BodyContent, blockLabels []blockLabel) hcl.Range {
        var childBlock *hcl.Block
        for _, candidate := range content.Blocks {
                if candidate.Type != s.TypeName {
                        continue
                }

                childBlock = candidate
                break
        }

        if childBlock == nil {
                return content.MissingItemRange
        }

        return sourceRange(childBlock.Body, labelsForBlock(childBlock), s.Nested)
}

// A BlockListSpec is a Spec that produces a cty list of the results of
// decoding all of the nested blocks of a given type, using a nested spec.
type BlockListSpec struct {
        TypeName string
        Nested   Spec
        MinItems int
        MaxItems int
}

func (s *BlockListSpec) visitSameBodyChildren(cb visitFunc) {
        // leaf node ("Nested" does not use the same body)
}

// blockSpec implementation
func (s *BlockListSpec) blockHeaderSchemata() []hcl.BlockHeaderSchema {
        return []hcl.BlockHeaderSchema{
                {
                        Type:       s.TypeName,
                        LabelNames: findLabelSpecs(s.Nested),
                },
        }
}

// blockSpec implementation
func (s *BlockListSpec) nestedSpec() Spec {
        return s.Nested
}

// specNeedingVariables implementation
func (s *BlockListSpec) variablesNeeded(content *hcl.BodyContent) []hcl.Traversal {
        var ret []hcl.Traversal

        for _, childBlock := range content.Blocks {
                if childBlock.Type != s.TypeName {
                        continue
                }

                ret = append(ret, Variables(childBlock.Body, s.Nested)...)
        }

        return ret
}

func (s *BlockListSpec) decode(content *hcl.BodyContent, blockLabels []blockLabel, ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
        var diags hcl.Diagnostics

        if s.Nested == nil {
                panic("BlockListSpec with no Nested Spec")
        }

        var elems []cty.Value
        var sourceRanges []hcl.Range
        for _, childBlock := range content.Blocks {
                if childBlock.Type != s.TypeName {
                        continue
                }

                val, _, childDiags := decode(childBlock.Body, labelsForBlock(childBlock), ctx, s.Nested, false)
                diags = append(diags, childDiags...)
                elems = append(elems, val)
                sourceRanges = append(sourceRanges, sourceRange(childBlock.Body, labelsForBlock(childBlock), s.Nested))
        }

        if len(elems) < s.MinItems {
                diags = append(diags, &hcl.Diagnostic{
                        Severity: hcl.DiagError,
                        Summary:  fmt.Sprintf("Insufficient %s blocks", s.TypeName),
                        Detail:   fmt.Sprintf("At least %d %q blocks are required.", s.MinItems, s.TypeName),
                        Subject:  &content.MissingItemRange,
                })
        } else if s.MaxItems > 0 && len(elems) > s.MaxItems {
                diags = append(diags, &hcl.Diagnostic{
                        Severity: hcl.DiagError,
                        Summary:  fmt.Sprintf("Too many %s blocks", s.TypeName),
                        Detail:   fmt.Sprintf("No more than %d %q blocks are allowed", s.MaxItems, s.TypeName),
                        Subject:  &sourceRanges[s.MaxItems],
                })
        }

        var ret cty.Value

        if len(elems) == 0 {
                ret = cty.ListValEmpty(s.Nested.impliedType())
        } else {
                // Since our target is a list, all of the decoded elements must have the
                // same type or cty.ListVal will panic below. Different types can arise
                // if there is an attribute spec of type cty.DynamicPseudoType in the
                // nested spec; all given values must be convertable to a single type
                // in order for the result to be considered valid.
                etys := make([]cty.Type, len(elems))
                for i, v := range elems {
                        etys[i] = v.Type()
                }
                ety, convs := convert.UnifyUnsafe(etys)
                if ety == cty.NilType {
                        // FIXME: This is a pretty terrible error message.
                        diags = append(diags, &hcl.Diagnostic{
                                Severity: hcl.DiagError,
                                Summary:  fmt.Sprintf("Unconsistent argument types in %s blocks", s.TypeName),
                                Detail:   "Corresponding attributes in all blocks of this type must be the same.",
                                Subject:  &sourceRanges[0],
                        })
                        return cty.DynamicVal, diags
                }
                for i, v := range elems {
                        if convs[i] != nil {
                                newV, err := convs[i](v)
                                if err != nil {
                                        // FIXME: This is a pretty terrible error message.
                                        diags = append(diags, &hcl.Diagnostic{
                                                Severity: hcl.DiagError,
                                                Summary:  fmt.Sprintf("Unconsistent argument types in %s blocks", s.TypeName),
                                                Detail:   fmt.Sprintf("Block with index %d has inconsistent argument types: %s.", i, err),
                                                Subject:  &sourceRanges[i],
                                        })
                                        // Bail early here so we won't panic below in cty.ListVal
                                        return cty.DynamicVal, diags
                                }
                                elems[i] = newV
                        }
                }

                ret = cty.ListVal(elems)
        }

        return ret, diags
}

func (s *BlockListSpec) impliedType() cty.Type {
        return cty.List(s.Nested.impliedType())
}

func (s *BlockListSpec) sourceRange(content *hcl.BodyContent, blockLabels []blockLabel) hcl.Range {
        // We return the source range of the _first_ block of the given type,
        // since they are not guaranteed to form a contiguous range.

        var childBlock *hcl.Block
        for _, candidate := range content.Blocks {
                if candidate.Type != s.TypeName {
                        continue
                }

                childBlock = candidate
                break
        }

        if childBlock == nil {
                return content.MissingItemRange
        }

        return sourceRange(childBlock.Body, labelsForBlock(childBlock), s.Nested)
}

// A BlockTupleSpec is a Spec that produces a cty tuple of the results of
// decoding all of the nested blocks of a given type, using a nested spec.
//
// This is similar to BlockListSpec, but it permits the nested blocks to have
// different result types in situations where cty.DynamicPseudoType attributes
// are present.
type BlockTupleSpec struct {
        TypeName string
        Nested   Spec
        MinItems int
        MaxItems int
}

func (s *BlockTupleSpec) visitSameBodyChildren(cb visitFunc) {
        // leaf node ("Nested" does not use the same body)
}

// blockSpec implementation
func (s *BlockTupleSpec) blockHeaderSchemata() []hcl.BlockHeaderSchema {
        return []hcl.BlockHeaderSchema{
                {
                        Type:       s.TypeName,
                        LabelNames: findLabelSpecs(s.Nested),
                },
        }
}

// blockSpec implementation
func (s *BlockTupleSpec) nestedSpec() Spec {
        return s.Nested
}

// specNeedingVariables implementation
func (s *BlockTupleSpec) variablesNeeded(content *hcl.BodyContent) []hcl.Traversal {
        var ret []hcl.Traversal

        for _, childBlock := range content.Blocks {
                if childBlock.Type != s.TypeName {
                        continue
                }

                ret = append(ret, Variables(childBlock.Body, s.Nested)...)
        }

        return ret
}

func (s *BlockTupleSpec) decode(content *hcl.BodyContent, blockLabels []blockLabel, ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
        var diags hcl.Diagnostics

        if s.Nested == nil {
                panic("BlockListSpec with no Nested Spec")
        }

        var elems []cty.Value
        var sourceRanges []hcl.Range
        for _, childBlock := range content.Blocks {
                if childBlock.Type != s.TypeName {
                        continue
                }

                val, _, childDiags := decode(childBlock.Body, labelsForBlock(childBlock), ctx, s.Nested, false)
                diags = append(diags, childDiags...)
                elems = append(elems, val)
                sourceRanges = append(sourceRanges, sourceRange(childBlock.Body, labelsForBlock(childBlock), s.Nested))
        }

        if len(elems) < s.MinItems {
                diags = append(diags, &hcl.Diagnostic{
                        Severity: hcl.DiagError,
                        Summary:  fmt.Sprintf("Insufficient %s blocks", s.TypeName),
                        Detail:   fmt.Sprintf("At least %d %q blocks are required.", s.MinItems, s.TypeName),
                        Subject:  &content.MissingItemRange,
                })
        } else if s.MaxItems > 0 && len(elems) > s.MaxItems {
                diags = append(diags, &hcl.Diagnostic{
                        Severity: hcl.DiagError,
                        Summary:  fmt.Sprintf("Too many %s blocks", s.TypeName),
                        Detail:   fmt.Sprintf("No more than %d %q blocks are allowed", s.MaxItems, s.TypeName),
                        Subject:  &sourceRanges[s.MaxItems],
                })
        }

        var ret cty.Value

        if len(elems) == 0 {
                ret = cty.EmptyTupleVal
        } else {
                ret = cty.TupleVal(elems)
        }

        return ret, diags
}

func (s *BlockTupleSpec) impliedType() cty.Type {
        // We can't predict our type, because we don't know how many blocks
        // there will be until we decode.
        return cty.DynamicPseudoType
}

func (s *BlockTupleSpec) sourceRange(content *hcl.BodyContent, blockLabels []blockLabel) hcl.Range {
        // We return the source range of the _first_ block of the given type,
        // since they are not guaranteed to form a contiguous range.

        var childBlock *hcl.Block
        for _, candidate := range content.Blocks {
                if candidate.Type != s.TypeName {
                        continue
                }

                childBlock = candidate
                break
        }

        if childBlock == nil {
                return content.MissingItemRange
        }

        return sourceRange(childBlock.Body, labelsForBlock(childBlock), s.Nested)
}

// A BlockSetSpec is a Spec that produces a cty set of the results of
// decoding all of the nested blocks of a given type, using a nested spec.
type BlockSetSpec struct {
        TypeName string
        Nested   Spec
        MinItems int
        MaxItems int
}

func (s *BlockSetSpec) visitSameBodyChildren(cb visitFunc) {
        // leaf node ("Nested" does not use the same body)
}

// blockSpec implementation
func (s *BlockSetSpec) blockHeaderSchemata() []hcl.BlockHeaderSchema {
        return []hcl.BlockHeaderSchema{
                {
                        Type:       s.TypeName,
                        LabelNames: findLabelSpecs(s.Nested),
                },
        }
}

// blockSpec implementation
func (s *BlockSetSpec) nestedSpec() Spec {
        return s.Nested
}

// specNeedingVariables implementation
func (s *BlockSetSpec) variablesNeeded(content *hcl.BodyContent) []hcl.Traversal {
        var ret []hcl.Traversal

        for _, childBlock := range content.Blocks {
                if childBlock.Type != s.TypeName {
                        continue
                }

                ret = append(ret, Variables(childBlock.Body, s.Nested)...)
        }

        return ret
}

func (s *BlockSetSpec) decode(content *hcl.BodyContent, blockLabels []blockLabel, ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
        var diags hcl.Diagnostics

        if s.Nested == nil {
                panic("BlockSetSpec with no Nested Spec")
        }

        var elems []cty.Value
        var sourceRanges []hcl.Range
        for _, childBlock := range content.Blocks {
                if childBlock.Type != s.TypeName {
                        continue
                }

                val, _, childDiags := decode(childBlock.Body, labelsForBlock(childBlock), ctx, s.Nested, false)
                diags = append(diags, childDiags...)
                elems = append(elems, val)
                sourceRanges = append(sourceRanges, sourceRange(childBlock.Body, labelsForBlock(childBlock), s.Nested))
        }

        if len(elems) < s.MinItems {
                diags = append(diags, &hcl.Diagnostic{
                        Severity: hcl.DiagError,
                        Summary:  fmt.Sprintf("Insufficient %s blocks", s.TypeName),
                        Detail:   fmt.Sprintf("At least %d %q blocks are required.", s.MinItems, s.TypeName),
                        Subject:  &content.MissingItemRange,
                })
        } else if s.MaxItems > 0 && len(elems) > s.MaxItems {
                diags = append(diags, &hcl.Diagnostic{
                        Severity: hcl.DiagError,
                        Summary:  fmt.Sprintf("Too many %s blocks", s.TypeName),
                        Detail:   fmt.Sprintf("No more than %d %q blocks are allowed", s.MaxItems, s.TypeName),
                        Subject:  &sourceRanges[s.MaxItems],
                })
        }

        var ret cty.Value

        if len(elems) == 0 {
                ret = cty.SetValEmpty(s.Nested.impliedType())
        } else {
                // Since our target is a set, all of the decoded elements must have the
                // same type or cty.SetVal will panic below. Different types can arise
                // if there is an attribute spec of type cty.DynamicPseudoType in the
                // nested spec; all given values must be convertable to a single type
                // in order for the result to be considered valid.
                etys := make([]cty.Type, len(elems))
                for i, v := range elems {
                        etys[i] = v.Type()
                }
                ety, convs := convert.UnifyUnsafe(etys)
                if ety == cty.NilType {
                        // FIXME: This is a pretty terrible error message.
                        diags = append(diags, &hcl.Diagnostic{
                                Severity: hcl.DiagError,
                                Summary:  fmt.Sprintf("Unconsistent argument types in %s blocks", s.TypeName),
                                Detail:   "Corresponding attributes in all blocks of this type must be the same.",
                                Subject:  &sourceRanges[0],
                        })
                        return cty.DynamicVal, diags
                }
                for i, v := range elems {
                        if convs[i] != nil {
                                newV, err := convs[i](v)
                                if err != nil {
                                        // FIXME: This is a pretty terrible error message.
                                        diags = append(diags, &hcl.Diagnostic{
                                                Severity: hcl.DiagError,
                                                Summary:  fmt.Sprintf("Unconsistent argument types in %s blocks", s.TypeName),
                                                Detail:   fmt.Sprintf("Block with index %d has inconsistent argument types: %s.", i, err),
                                                Subject:  &sourceRanges[i],
                                        })
                                        // Bail early here so we won't panic below in cty.ListVal
                                        return cty.DynamicVal, diags
                                }
                                elems[i] = newV
                        }
                }

                ret = cty.SetVal(elems)
        }

        return ret, diags
}

func (s *BlockSetSpec) impliedType() cty.Type {
        return cty.Set(s.Nested.impliedType())
}

func (s *BlockSetSpec) sourceRange(content *hcl.BodyContent, blockLabels []blockLabel) hcl.Range {
        // We return the source range of the _first_ block of the given type,
        // since they are not guaranteed to form a contiguous range.

        var childBlock *hcl.Block
        for _, candidate := range content.Blocks {
                if candidate.Type != s.TypeName {
                        continue
                }

                childBlock = candidate
                break
        }

        if childBlock == nil {
                return content.MissingItemRange
        }

        return sourceRange(childBlock.Body, labelsForBlock(childBlock), s.Nested)
}

// A BlockMapSpec is a Spec that produces a cty map of the results of
// decoding all of the nested blocks of a given type, using a nested spec.
//
// One level of map structure is created for each of the given label names.
// There must be at least one given label name.
type BlockMapSpec struct {
        TypeName   string
        LabelNames []string
        Nested     Spec
}

func (s *BlockMapSpec) visitSameBodyChildren(cb visitFunc) {
        // leaf node ("Nested" does not use the same body)
}

// blockSpec implementation
func (s *BlockMapSpec) blockHeaderSchemata() []hcl.BlockHeaderSchema {
        return []hcl.BlockHeaderSchema{
                {
                        Type:       s.TypeName,
                        LabelNames: append(s.LabelNames, findLabelSpecs(s.Nested)...),
                },
        }
}

// blockSpec implementation
func (s *BlockMapSpec) nestedSpec() Spec {
        return s.Nested
}

// specNeedingVariables implementation
func (s *BlockMapSpec) variablesNeeded(content *hcl.BodyContent) []hcl.Traversal {
        var ret []hcl.Traversal

        for _, childBlock := range content.Blocks {
                if childBlock.Type != s.TypeName {
                        continue
                }

                ret = append(ret, Variables(childBlock.Body, s.Nested)...)
        }

        return ret
}

func (s *BlockMapSpec) decode(content *hcl.BodyContent, blockLabels []blockLabel, ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
        var diags hcl.Diagnostics

        if s.Nested == nil {
                panic("BlockMapSpec with no Nested Spec")
        }
        if ImpliedType(s).HasDynamicTypes() {
                panic("cty.DynamicPseudoType attributes may not be used inside a BlockMapSpec")
        }

        elems := map[string]interface{}{}
        for _, childBlock := range content.Blocks {
                if childBlock.Type != s.TypeName {
                        continue
                }

                childLabels := labelsForBlock(childBlock)
                val, _, childDiags := decode(childBlock.Body, childLabels[len(s.LabelNames):], ctx, s.Nested, false)
                targetMap := elems
                for _, key := range childBlock.Labels[:len(s.LabelNames)-1] {
                        if _, exists := targetMap[key]; !exists {
                                targetMap[key] = make(map[string]interface{})
                        }
                        targetMap = targetMap[key].(map[string]interface{})
                }

                diags = append(diags, childDiags...)

                key := childBlock.Labels[len(s.LabelNames)-1]
                if _, exists := targetMap[key]; exists {
                        labelsBuf := bytes.Buffer{}
                        for _, label := range childBlock.Labels {
                                fmt.Fprintf(&labelsBuf, " %q", label)
                        }
                        diags = append(diags, &hcl.Diagnostic{
                                Severity: hcl.DiagError,
                                Summary:  fmt.Sprintf("Duplicate %s block", s.TypeName),
                                Detail: fmt.Sprintf(
                                        "A block for %s%s was already defined. The %s labels must be unique.",
                                        s.TypeName, labelsBuf.String(), s.TypeName,
                                ),
                                Subject: &childBlock.DefRange,
                        })
                        continue
                }

                targetMap[key] = val
        }

        if len(elems) == 0 {
                return cty.MapValEmpty(s.Nested.impliedType()), diags
        }

        var ctyMap func(map[string]interface{}, int) cty.Value
        ctyMap = func(raw map[string]interface{}, depth int) cty.Value {
                vals := make(map[string]cty.Value, len(raw))
                if depth == 1 {
                        for k, v := range raw {
                                vals[k] = v.(cty.Value)
                        }
                } else {
                        for k, v := range raw {
                                vals[k] = ctyMap(v.(map[string]interface{}), depth-1)
                        }
                }
                return cty.MapVal(vals)
        }

        return ctyMap(elems, len(s.LabelNames)), diags
}

func (s *BlockMapSpec) impliedType() cty.Type {
        ret := s.Nested.impliedType()
        for _ = range s.LabelNames {
                ret = cty.Map(ret)
        }
        return ret
}

func (s *BlockMapSpec) sourceRange(content *hcl.BodyContent, blockLabels []blockLabel) hcl.Range {
        // We return the source range of the _first_ block of the given type,
        // since they are not guaranteed to form a contiguous range.

        var childBlock *hcl.Block
        for _, candidate := range content.Blocks {
                if candidate.Type != s.TypeName {
                        continue
                }

                childBlock = candidate
                break
        }

        if childBlock == nil {
                return content.MissingItemRange
        }

        return sourceRange(childBlock.Body, labelsForBlock(childBlock), s.Nested)
}

// A BlockObjectSpec is a Spec that produces a cty object of the results of
// decoding all of the nested blocks of a given type, using a nested spec.
//
// One level of object structure is created for each of the given label names.
// There must be at least one given label name.
//
// This is similar to BlockMapSpec, but it permits the nested blocks to have
// different result types in situations where cty.DynamicPseudoType attributes
// are present.
type BlockObjectSpec struct {
        TypeName   string
        LabelNames []string
        Nested     Spec
}

func (s *BlockObjectSpec) visitSameBodyChildren(cb visitFunc) {
        // leaf node ("Nested" does not use the same body)
}

// blockSpec implementation
func (s *BlockObjectSpec) blockHeaderSchemata() []hcl.BlockHeaderSchema {
        return []hcl.BlockHeaderSchema{
                {
                        Type:       s.TypeName,
                        LabelNames: append(s.LabelNames, findLabelSpecs(s.Nested)...),
                },
        }
}

// blockSpec implementation
func (s *BlockObjectSpec) nestedSpec() Spec {
        return s.Nested
}

// specNeedingVariables implementation
func (s *BlockObjectSpec) variablesNeeded(content *hcl.BodyContent) []hcl.Traversal {
        var ret []hcl.Traversal

        for _, childBlock := range content.Blocks {
                if childBlock.Type != s.TypeName {
                        continue
                }

                ret = append(ret, Variables(childBlock.Body, s.Nested)...)
        }

        return ret
}

func (s *BlockObjectSpec) decode(content *hcl.BodyContent, blockLabels []blockLabel, ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
        var diags hcl.Diagnostics

        if s.Nested == nil {
                panic("BlockObjectSpec with no Nested Spec")
        }

        elems := map[string]interface{}{}
        for _, childBlock := range content.Blocks {
                if childBlock.Type != s.TypeName {
                        continue
                }

                childLabels := labelsForBlock(childBlock)
                val, _, childDiags := decode(childBlock.Body, childLabels[len(s.LabelNames):], ctx, s.Nested, false)
                targetMap := elems
                for _, key := range childBlock.Labels[:len(s.LabelNames)-1] {
                        if _, exists := targetMap[key]; !exists {
                                targetMap[key] = make(map[string]interface{})
                        }
                        targetMap = targetMap[key].(map[string]interface{})
                }

                diags = append(diags, childDiags...)

                key := childBlock.Labels[len(s.LabelNames)-1]
                if _, exists := targetMap[key]; exists {
                        labelsBuf := bytes.Buffer{}
                        for _, label := range childBlock.Labels {
                                fmt.Fprintf(&labelsBuf, " %q", label)
                        }
                        diags = append(diags, &hcl.Diagnostic{
                                Severity: hcl.DiagError,
                                Summary:  fmt.Sprintf("Duplicate %s block", s.TypeName),
                                Detail: fmt.Sprintf(
                                        "A block for %s%s was already defined. The %s labels must be unique.",
                                        s.TypeName, labelsBuf.String(), s.TypeName,
                                ),
                                Subject: &childBlock.DefRange,
                        })
                        continue
                }

                targetMap[key] = val
        }

        if len(elems) == 0 {
                return cty.EmptyObjectVal, diags
        }

        var ctyObj func(map[string]interface{}, int) cty.Value
        ctyObj = func(raw map[string]interface{}, depth int) cty.Value {
                vals := make(map[string]cty.Value, len(raw))
                if depth == 1 {
                        for k, v := range raw {
                                vals[k] = v.(cty.Value)
                        }
                } else {
                        for k, v := range raw {
                                vals[k] = ctyObj(v.(map[string]interface{}), depth-1)
                        }
                }
                return cty.ObjectVal(vals)
        }

        return ctyObj(elems, len(s.LabelNames)), diags
}

func (s *BlockObjectSpec) impliedType() cty.Type {
        // We can't predict our type, since we don't know how many blocks are
        // present and what labels they have until we decode.
        return cty.DynamicPseudoType
}

func (s *BlockObjectSpec) sourceRange(content *hcl.BodyContent, blockLabels []blockLabel) hcl.Range {
        // We return the source range of the _first_ block of the given type,
        // since they are not guaranteed to form a contiguous range.

        var childBlock *hcl.Block
        for _, candidate := range content.Blocks {
                if candidate.Type != s.TypeName {
                        continue
                }

                childBlock = candidate
                break
        }

        if childBlock == nil {
                return content.MissingItemRange
        }

        return sourceRange(childBlock.Body, labelsForBlock(childBlock), s.Nested)
}

// A BlockAttrsSpec is a Spec that interprets a single block as if it were
// a map of some element type. That is, each attribute within the block
// becomes a key in the resulting map and the attribute's value becomes the
// element value, after conversion to the given element type. The resulting
// value is a cty.Map of the given element type.
//
// This spec imposes a validation constraint that there be exactly one block
// of the given type name and that this block may contain only attributes. The
// block does not accept any labels.
//
// This is an alternative to an AttrSpec of a map type for situations where
// block syntax is desired. Note that block syntax does not permit dynamic
// keys, construction of the result via a "for" expression, etc. In most cases
// an AttrSpec is preferred if the desired result is a map whose keys are
// chosen by the user rather than by schema.
type BlockAttrsSpec struct {
        TypeName    string
        ElementType cty.Type
        Required    bool
}

func (s *BlockAttrsSpec) visitSameBodyChildren(cb visitFunc) {
        // leaf node
}

// blockSpec implementation
func (s *BlockAttrsSpec) blockHeaderSchemata() []hcl.BlockHeaderSchema {
        return []hcl.BlockHeaderSchema{
                {
                        Type:       s.TypeName,
                        LabelNames: nil,
                },
        }
}

// blockSpec implementation
func (s *BlockAttrsSpec) nestedSpec() Spec {
        // This is an odd case: we aren't actually going to apply a nested spec
        // in this case, since we're going to interpret the body directly as
        // attributes, but we need to return something non-nil so that the
        // decoder will recognize this as a block spec. We won't actually be
        // using this for anything at decode time.
        return noopSpec{}
}

// specNeedingVariables implementation
func (s *BlockAttrsSpec) variablesNeeded(content *hcl.BodyContent) []hcl.Traversal {

        block, _ := s.findBlock(content)
        if block == nil {
                return nil
        }

        var vars []hcl.Traversal

        attrs, diags := block.Body.JustAttributes()
        if diags.HasErrors() {
                return nil
        }

        for _, attr := range attrs {
                vars = append(vars, attr.Expr.Variables()...)
        }

        // We'll return the variables references in source order so that any
        // error messages that result are also in source order.
        sort.Slice(vars, func(i, j int) bool {
                return vars[i].SourceRange().Start.Byte < vars[j].SourceRange().Start.Byte
        })

        return vars
}

func (s *BlockAttrsSpec) decode(content *hcl.BodyContent, blockLabels []blockLabel, ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
        var diags hcl.Diagnostics

        block, other := s.findBlock(content)
        if block == nil {
                if s.Required {
                        diags = append(diags, &hcl.Diagnostic{
                                Severity: hcl.DiagError,
                                Summary:  fmt.Sprintf("Missing %s block", s.TypeName),
                                Detail: fmt.Sprintf(
                                        "A block of type %q is required here.", s.TypeName,
                                ),
                                Subject: &content.MissingItemRange,
                        })
                }
                return cty.NullVal(cty.Map(s.ElementType)), diags
        }
        if other != nil {
                diags = append(diags, &hcl.Diagnostic{
                        Severity: hcl.DiagError,
                        Summary:  fmt.Sprintf("Duplicate %s block", s.TypeName),
                        Detail: fmt.Sprintf(
                                "Only one block of type %q is allowed. Previous definition was at %s.",
                                s.TypeName, block.DefRange.String(),
                        ),
                        Subject: &other.DefRange,
                })
        }

        attrs, attrDiags := block.Body.JustAttributes()
        diags = append(diags, attrDiags...)

        if len(attrs) == 0 {
                return cty.MapValEmpty(s.ElementType), diags
        }

        vals := make(map[string]cty.Value, len(attrs))
        for name, attr := range attrs {
                attrVal, attrDiags := attr.Expr.Value(ctx)
                diags = append(diags, attrDiags...)

                attrVal, err := convert.Convert(attrVal, s.ElementType)
                if err != nil {
                        diags = append(diags, &hcl.Diagnostic{
                                Severity: hcl.DiagError,
                                Summary:  "Invalid attribute value",
                                Detail:   fmt.Sprintf("Invalid value for attribute of %q block: %s.", s.TypeName, err),
                                Subject:  attr.Expr.Range().Ptr(),
                        })
                        attrVal = cty.UnknownVal(s.ElementType)
                }

                vals[name] = attrVal
        }

        return cty.MapVal(vals), diags
}

func (s *BlockAttrsSpec) impliedType() cty.Type {
        return cty.Map(s.ElementType)
}

func (s *BlockAttrsSpec) sourceRange(content *hcl.BodyContent, blockLabels []blockLabel) hcl.Range {
        block, _ := s.findBlock(content)
        if block == nil {
                return content.MissingItemRange
        }
        return block.DefRange
}

func (s *BlockAttrsSpec) findBlock(content *hcl.BodyContent) (block *hcl.Block, other *hcl.Block) {
        for _, candidate := range content.Blocks {
                if candidate.Type != s.TypeName {
                        continue
                }
                if block != nil {
                        return block, candidate
                }
                block = candidate
        }

        return block, nil
}

// A BlockLabelSpec is a Spec that returns a cty.String representing the
// label of the block its given body belongs to, if indeed its given body
// belongs to a block. It is a programming error to use this in a non-block
// context, so this spec will panic in that case.
//
// This spec only works in the nested spec within a BlockSpec, BlockListSpec,
// BlockSetSpec or BlockMapSpec.
//
// The full set of label specs used against a particular block must have a
// consecutive set of indices starting at zero. The maximum index found
// defines how many labels the corresponding blocks must have in cty source.
type BlockLabelSpec struct {
        Index int
        Name  string
}

func (s *BlockLabelSpec) visitSameBodyChildren(cb visitFunc) {
        // leaf node
}

func (s *BlockLabelSpec) decode(content *hcl.BodyContent, blockLabels []blockLabel, ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
        if s.Index >= len(blockLabels) {
                panic("BlockListSpec used in non-block context")
        }

        return cty.StringVal(blockLabels[s.Index].Value), nil
}

func (s *BlockLabelSpec) impliedType() cty.Type {
        return cty.String // labels are always strings
}

func (s *BlockLabelSpec) sourceRange(content *hcl.BodyContent, blockLabels []blockLabel) hcl.Range {
        if s.Index >= len(blockLabels) {
                panic("BlockListSpec used in non-block context")
        }

        return blockLabels[s.Index].Range
}

func findLabelSpecs(spec Spec) []string {
        maxIdx := -1
        var names map[int]string

        var visit visitFunc
        visit = func(s Spec) {
                if ls, ok := s.(*BlockLabelSpec); ok {
                        if maxIdx < ls.Index {
                                maxIdx = ls.Index
                        }
                        if names == nil {
                                names = make(map[int]string)
                        }
                        names[ls.Index] = ls.Name
                }
                s.visitSameBodyChildren(visit)
        }

        visit(spec)

        if maxIdx < 0 {
                return nil // no labels at all
        }

        ret := make([]string, maxIdx+1)
        for i := range ret {
                name := names[i]
                if name == "" {
                        // Should never happen if the spec is conformant, since we require
                        // consecutive indices starting at zero.
                        name = fmt.Sprintf("missing%02d", i)
                }
                ret[i] = name
        }

        return ret
}

// DefaultSpec is a spec that wraps two specs, evaluating the primary first
// and then evaluating the default if the primary returns a null value.
//
// The two specifications must have the same implied result type for correct
// operation. If not, the result is undefined.
//
// Any requirements imposed by the "Default" spec apply even if "Primary" does
// not return null. For example, if the "Default" spec is for a required
// attribute then that attribute is always required, regardless of the result
// of the "Primary" spec.
//
// The "Default" spec must not describe a nested block, since otherwise the
// result of ChildBlockTypes would not be decidable without evaluation. If
// the default spec _does_ describe a nested block then the result is
// undefined.
type DefaultSpec struct {
        Primary Spec
        Default Spec
}

func (s *DefaultSpec) visitSameBodyChildren(cb visitFunc) {
        cb(s.Primary)
        cb(s.Default)
}

func (s *DefaultSpec) decode(content *hcl.BodyContent, blockLabels []blockLabel, ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
        val, diags := s.Primary.decode(content, blockLabels, ctx)
        if val.IsNull() {
                var moreDiags hcl.Diagnostics
                val, moreDiags = s.Default.decode(content, blockLabels, ctx)
                diags = append(diags, moreDiags...)
        }
        return val, diags
}

func (s *DefaultSpec) impliedType() cty.Type {
        return s.Primary.impliedType()
}

// attrSpec implementation
func (s *DefaultSpec) attrSchemata() []hcl.AttributeSchema {
        // We must pass through the union of both of our nested specs so that
        // we'll have both values available in the result.
        var ret []hcl.AttributeSchema
        if as, ok := s.Primary.(attrSpec); ok {
                ret = append(ret, as.attrSchemata()...)
        }
        if as, ok := s.Default.(attrSpec); ok {
                ret = append(ret, as.attrSchemata()...)
        }
        return ret
}

// blockSpec implementation
func (s *DefaultSpec) blockHeaderSchemata() []hcl.BlockHeaderSchema {
        // Only the primary spec may describe a block, since otherwise
        // our nestedSpec method below can't know which to return.
        if bs, ok := s.Primary.(blockSpec); ok {
                return bs.blockHeaderSchemata()
        }
        return nil
}

// blockSpec implementation
func (s *DefaultSpec) nestedSpec() Spec {
        if bs, ok := s.Primary.(blockSpec); ok {
                return bs.nestedSpec()
        }
        return nil
}

func (s *DefaultSpec) sourceRange(content *hcl.BodyContent, blockLabels []blockLabel) hcl.Range {
        // We can't tell from here which of the two specs will ultimately be used
        // in our result, so we'll just assume the first. This is usually the right
        // choice because the default is often a literal spec that doesn't have a
        // reasonable source range to return anyway.
        return s.Primary.sourceRange(content, blockLabels)
}

// TransformExprSpec is a spec that wraps another and then evaluates a given
// hcl.Expression on the result.
//
// The implied type of this spec is determined by evaluating the expression
// with an unknown value of the nested spec's implied type, which may cause
// the result to be imprecise. This spec should not be used in situations where
// precise result type information is needed.
type TransformExprSpec struct {
        Wrapped      Spec
        Expr         hcl.Expression
        TransformCtx *hcl.EvalContext
        VarName      string
}

func (s *TransformExprSpec) visitSameBodyChildren(cb visitFunc) {
        cb(s.Wrapped)
}

func (s *TransformExprSpec) decode(content *hcl.BodyContent, blockLabels []blockLabel, ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
        wrappedVal, diags := s.Wrapped.decode(content, blockLabels, ctx)
        if diags.HasErrors() {
                // We won't try to run our function in this case, because it'll probably
                // generate confusing additional errors that will distract from the
                // root cause.
                return cty.UnknownVal(s.impliedType()), diags
        }

        chiCtx := s.TransformCtx.NewChild()
        chiCtx.Variables = map[string]cty.Value{
                s.VarName: wrappedVal,
        }
        resultVal, resultDiags := s.Expr.Value(chiCtx)
        diags = append(diags, resultDiags...)
        return resultVal, diags
}

func (s *TransformExprSpec) impliedType() cty.Type {
        wrappedTy := s.Wrapped.impliedType()
        chiCtx := s.TransformCtx.NewChild()
        chiCtx.Variables = map[string]cty.Value{
                s.VarName: cty.UnknownVal(wrappedTy),
        }
        resultVal, _ := s.Expr.Value(chiCtx)
        return resultVal.Type()
}

func (s *TransformExprSpec) sourceRange(content *hcl.BodyContent, blockLabels []blockLabel) hcl.Range {
        // We'll just pass through our wrapped range here, even though that's
        // not super-accurate, because there's nothing better to return.
        return s.Wrapped.sourceRange(content, blockLabels)
}

// TransformFuncSpec is a spec that wraps another and then evaluates a given
// cty function with the result. The given function must expect exactly one
// argument, where the result of the wrapped spec will be passed.
//
// The implied type of this spec is determined by type-checking the function
// with an unknown value of the nested spec's implied type, which may cause
// the result to be imprecise. This spec should not be used in situations where
// precise result type information is needed.
//
// If the given function produces an error when run, this spec will produce
// a non-user-actionable diagnostic message. It's the caller's responsibility
// to ensure that the given function cannot fail for any non-error result
// of the wrapped spec.
type TransformFuncSpec struct {
        Wrapped Spec
        Func    function.Function
}

func (s *TransformFuncSpec) visitSameBodyChildren(cb visitFunc) {
        cb(s.Wrapped)
}

func (s *TransformFuncSpec) decode(content *hcl.BodyContent, blockLabels []blockLabel, ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
        wrappedVal, diags := s.Wrapped.decode(content, blockLabels, ctx)
        if diags.HasErrors() {
                // We won't try to run our function in this case, because it'll probably
                // generate confusing additional errors that will distract from the
                // root cause.
                return cty.UnknownVal(s.impliedType()), diags
        }

        resultVal, err := s.Func.Call([]cty.Value{wrappedVal})
        if err != nil {
                // This is not a good example of a diagnostic because it is reporting
                // a programming error in the calling application, rather than something
                // an end-user could act on.
                diags = append(diags, &hcl.Diagnostic{
                        Severity: hcl.DiagError,
                        Summary:  "Transform function failed",
                        Detail:   fmt.Sprintf("Decoder transform returned an error: %s", err),
                        Subject:  s.sourceRange(content, blockLabels).Ptr(),
                })
                return cty.UnknownVal(s.impliedType()), diags
        }

        return resultVal, diags
}

func (s *TransformFuncSpec) impliedType() cty.Type {
        wrappedTy := s.Wrapped.impliedType()
        resultTy, err := s.Func.ReturnType([]cty.Type{wrappedTy})
        if err != nil {
                // Should never happen with a correctly-configured spec
                return cty.DynamicPseudoType
        }

        return resultTy
}

func (s *TransformFuncSpec) sourceRange(content *hcl.BodyContent, blockLabels []blockLabel) hcl.Range {
        // We'll just pass through our wrapped range here, even though that's
        // not super-accurate, because there's nothing better to return.
        return s.Wrapped.sourceRange(content, blockLabels)
}

// noopSpec is a placeholder spec that does nothing, used in situations where
// a non-nil placeholder spec is required. It is not exported because there is
// no reason to use it directly; it is always an implementation detail only.
type noopSpec struct {
}

func (s noopSpec) decode(content *hcl.BodyContent, blockLabels []blockLabel, ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
        return cty.NullVal(cty.DynamicPseudoType), nil
}

func (s noopSpec) impliedType() cty.Type {
        return cty.DynamicPseudoType
}

func (s noopSpec) visitSameBodyChildren(cb visitFunc) {
        // nothing to do
}

func (s noopSpec) sourceRange(content *hcl.BodyContent, blockLabels []blockLabel) hcl.Range {
        // No useful range for a noopSpec, and nobody should be calling this anyway.
        return hcl.Range{
                Filename: "noopSpec",
        }
}