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package hcl
import (
"fmt"
"github.com/zclconf/go-cty/cty"
)
// A Traversal is a description of traversing through a value through a
// series of operations such as attribute lookup, index lookup, etc.
//
// It is used to look up values in scopes, for example.
//
// The traversal operations are implementations of interface Traverser.
// This is a closed set of implementations, so the interface cannot be
// implemented from outside this package.
//
// A traversal can be absolute (its first value is a symbol name) or relative
// (starts from an existing value).
type Traversal []Traverser
// TraversalJoin appends a relative traversal to an absolute traversal to
// produce a new absolute traversal.
func TraversalJoin(abs Traversal, rel Traversal) Traversal {
if abs.IsRelative() {
panic("first argument to TraversalJoin must be absolute")
}
if !rel.IsRelative() {
panic("second argument to TraversalJoin must be relative")
}
ret := make(Traversal, len(abs)+len(rel))
copy(ret, abs)
copy(ret[len(abs):], rel)
return ret
}
// TraverseRel applies the receiving traversal to the given value, returning
// the resulting value. This is supported only for relative traversals,
// and will panic if applied to an absolute traversal.
func (t Traversal) TraverseRel(val cty.Value) (cty.Value, Diagnostics) {
if !t.IsRelative() {
panic("can't use TraverseRel on an absolute traversal")
}
current := val
var diags Diagnostics
for _, tr := range t {
var newDiags Diagnostics
current, newDiags = tr.TraversalStep(current)
diags = append(diags, newDiags...)
if newDiags.HasErrors() {
return cty.DynamicVal, diags
}
}
return current, diags
}
// TraverseAbs applies the receiving traversal to the given eval context,
// returning the resulting value. This is supported only for absolute
// traversals, and will panic if applied to a relative traversal.
func (t Traversal) TraverseAbs(ctx *EvalContext) (cty.Value, Diagnostics) {
if t.IsRelative() {
panic("can't use TraverseAbs on a relative traversal")
}
split := t.SimpleSplit()
root := split.Abs[0].(TraverseRoot)
name := root.Name
thisCtx := ctx
hasNonNil := false
for thisCtx != nil {
if thisCtx.Variables == nil {
thisCtx = thisCtx.parent
continue
}
hasNonNil = true
val, exists := thisCtx.Variables[name]
if exists {
return split.Rel.TraverseRel(val)
}
thisCtx = thisCtx.parent
}
if !hasNonNil {
return cty.DynamicVal, Diagnostics{
{
Severity: DiagError,
Summary: "Variables not allowed",
Detail: "Variables may not be used here.",
Subject: &root.SrcRange,
},
}
}
suggestions := make([]string, 0, len(ctx.Variables))
thisCtx = ctx
for thisCtx != nil {
for k := range thisCtx.Variables {
suggestions = append(suggestions, k)
}
thisCtx = thisCtx.parent
}
suggestion := nameSuggestion(name, suggestions)
if suggestion != "" {
suggestion = fmt.Sprintf(" Did you mean %q?", suggestion)
}
return cty.DynamicVal, Diagnostics{
{
Severity: DiagError,
Summary: "Unknown variable",
Detail: fmt.Sprintf("There is no variable named %q.%s", name, suggestion),
Subject: &root.SrcRange,
},
}
}
// IsRelative returns true if the receiver is a relative traversal, or false
// otherwise.
func (t Traversal) IsRelative() bool {
if len(t) == 0 {
return true
}
if _, firstIsRoot := t[0].(TraverseRoot); firstIsRoot {
return false
}
return true
}
// SimpleSplit returns a TraversalSplit where the name lookup is the absolute
// part and the remainder is the relative part. Supported only for
// absolute traversals, and will panic if applied to a relative traversal.
//
// This can be used by applications that have a relatively-simple variable
// namespace where only the top-level is directly populated in the scope, with
// everything else handled by relative lookups from those initial values.
func (t Traversal) SimpleSplit() TraversalSplit {
if t.IsRelative() {
panic("can't use SimpleSplit on a relative traversal")
}
return TraversalSplit{
Abs: t[0:1],
Rel: t[1:],
}
}
// RootName returns the root name for a absolute traversal. Will panic if
// called on a relative traversal.
func (t Traversal) RootName() string {
if t.IsRelative() {
panic("can't use RootName on a relative traversal")
}
return t[0].(TraverseRoot).Name
}
// SourceRange returns the source range for the traversal.
func (t Traversal) SourceRange() Range {
if len(t) == 0 {
// Nothing useful to return here, but we'll return something
// that's correctly-typed at least.
return Range{}
}
return RangeBetween(t[0].SourceRange(), t[len(t)-1].SourceRange())
}
// TraversalSplit represents a pair of traversals, the first of which is
// an absolute traversal and the second of which is relative to the first.
//
// This is used by calling applications that only populate prefixes of the
// traversals in the scope, with Abs representing the part coming from the
// scope and Rel representing the remaining steps once that part is
// retrieved.
type TraversalSplit struct {
Abs Traversal
Rel Traversal
}
// TraverseAbs traverses from a scope to the value resulting from the
// absolute traversal.
func (t TraversalSplit) TraverseAbs(ctx *EvalContext) (cty.Value, Diagnostics) {
return t.Abs.TraverseAbs(ctx)
}
// TraverseRel traverses from a given value, assumed to be the result of
// TraverseAbs on some scope, to a final result for the entire split traversal.
func (t TraversalSplit) TraverseRel(val cty.Value) (cty.Value, Diagnostics) {
return t.Rel.TraverseRel(val)
}
// Traverse is a convenience function to apply TraverseAbs followed by
// TraverseRel.
func (t TraversalSplit) Traverse(ctx *EvalContext) (cty.Value, Diagnostics) {
v1, diags := t.TraverseAbs(ctx)
if diags.HasErrors() {
return cty.DynamicVal, diags
}
v2, newDiags := t.TraverseRel(v1)
diags = append(diags, newDiags...)
return v2, diags
}
// Join concatenates together the Abs and Rel parts to produce a single
// absolute traversal.
func (t TraversalSplit) Join() Traversal {
return TraversalJoin(t.Abs, t.Rel)
}
// RootName returns the root name for the absolute part of the split.
func (t TraversalSplit) RootName() string {
return t.Abs.RootName()
}
// A Traverser is a step within a Traversal.
type Traverser interface {
TraversalStep(cty.Value) (cty.Value, Diagnostics)
SourceRange() Range
isTraverserSigil() isTraverser
}
// Embed this in a struct to declare it as a Traverser
type isTraverser struct {
}
func (tr isTraverser) isTraverserSigil() isTraverser {
return isTraverser{}
}
// TraverseRoot looks up a root name in a scope. It is used as the first step
// of an absolute Traversal, and cannot itself be traversed directly.
type TraverseRoot struct {
isTraverser
Name string
SrcRange Range
}
// TraversalStep on a TraverseName immediately panics, because absolute
// traversals cannot be directly traversed.
func (tn TraverseRoot) TraversalStep(cty.Value) (cty.Value, Diagnostics) {
panic("Cannot traverse an absolute traversal")
}
func (tn TraverseRoot) SourceRange() Range {
return tn.SrcRange
}
// TraverseAttr looks up an attribute in its initial value.
type TraverseAttr struct {
isTraverser
Name string
SrcRange Range
}
func (tn TraverseAttr) TraversalStep(val cty.Value) (cty.Value, Diagnostics) {
return GetAttr(val, tn.Name, &tn.SrcRange)
}
func (tn TraverseAttr) SourceRange() Range {
return tn.SrcRange
}
// TraverseIndex applies the index operation to its initial value.
type TraverseIndex struct {
isTraverser
Key cty.Value
SrcRange Range
}
func (tn TraverseIndex) TraversalStep(val cty.Value) (cty.Value, Diagnostics) {
return Index(val, tn.Key, &tn.SrcRange)
}
func (tn TraverseIndex) SourceRange() Range {
return tn.SrcRange
}
// TraverseSplat applies the splat operation to its initial value.
type TraverseSplat struct {
isTraverser
Each Traversal
SrcRange Range
}
func (tn TraverseSplat) TraversalStep(val cty.Value) (cty.Value, Diagnostics) {
panic("TraverseSplat not yet implemented")
}
func (tn TraverseSplat) SourceRange() Range {
return tn.SrcRange
}
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