159 lines
4 KiB
Go
159 lines
4 KiB
Go
package cty
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import (
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"bytes"
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"fmt"
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"hash/crc32"
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"math/big"
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"sort"
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)
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// setRules provides a Rules implementation for the ./set package that
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// respects the equality rules for cty values of the given type.
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//
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// This implementation expects that values added to the set will be
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// valid internal values for the given Type, which is to say that wrapping
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// the given value in a Value struct along with the ruleset's type should
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// produce a valid, working Value.
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type setRules struct {
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Type Type
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}
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// Hash returns a hash value for the receiver that can be used for equality
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// checks where some inaccuracy is tolerable.
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//
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// The hash function is value-type-specific, so it is not meaningful to compare
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// hash results for values of different types.
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//
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// This function is not safe to use for security-related applications, since
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// the hash used is not strong enough.
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func (val Value) Hash() int {
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hashBytes := makeSetHashBytes(val)
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return int(crc32.ChecksumIEEE(hashBytes))
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}
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func (r setRules) Hash(v interface{}) int {
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return Value{
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ty: r.Type,
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v: v,
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}.Hash()
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}
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func (r setRules) Equivalent(v1 interface{}, v2 interface{}) bool {
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v1v := Value{
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ty: r.Type,
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v: v1,
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}
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v2v := Value{
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ty: r.Type,
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v: v2,
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}
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eqv := v1v.Equals(v2v)
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// By comparing the result to true we ensure that an Unknown result,
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// which will result if either value is unknown, will be considered
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// as non-equivalent. Two unknown values are not equivalent for the
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// sake of set membership.
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return eqv.v == true
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}
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func makeSetHashBytes(val Value) []byte {
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var buf bytes.Buffer
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appendSetHashBytes(val, &buf)
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return buf.Bytes()
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}
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func appendSetHashBytes(val Value, buf *bytes.Buffer) {
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// Exactly what bytes we generate here don't matter as long as the following
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// constraints hold:
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// - Unknown and null values all generate distinct strings from
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// each other and from any normal value of the given type.
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// - The delimiter used to separate items in a compound structure can
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// never appear literally in any of its elements.
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// Since we don't support hetrogenous lists we don't need to worry about
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// collisions between values of different types, apart from
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// PseudoTypeDynamic.
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// If in practice we *do* get a collision then it's not a big deal because
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// the Equivalent function will still distinguish values, but set
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// performance will be best if we are able to produce a distinct string
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// for each distinct value, unknown values notwithstanding.
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if !val.IsKnown() {
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buf.WriteRune('?')
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return
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}
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if val.IsNull() {
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buf.WriteRune('~')
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return
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}
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switch val.ty {
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case Number:
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buf.WriteString(val.v.(*big.Float).String())
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return
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case Bool:
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if val.v.(bool) {
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buf.WriteRune('T')
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} else {
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buf.WriteRune('F')
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}
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return
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case String:
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buf.WriteString(fmt.Sprintf("%q", val.v.(string)))
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return
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}
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if val.ty.IsMapType() {
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buf.WriteRune('{')
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val.ForEachElement(func(keyVal, elementVal Value) bool {
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appendSetHashBytes(keyVal, buf)
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buf.WriteRune(':')
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appendSetHashBytes(elementVal, buf)
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buf.WriteRune(';')
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return false
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})
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buf.WriteRune('}')
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return
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}
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if val.ty.IsListType() || val.ty.IsSetType() {
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buf.WriteRune('[')
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val.ForEachElement(func(keyVal, elementVal Value) bool {
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appendSetHashBytes(elementVal, buf)
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buf.WriteRune(';')
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return false
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})
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buf.WriteRune(']')
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return
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}
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if val.ty.IsObjectType() {
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buf.WriteRune('<')
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attrNames := make([]string, 0, len(val.ty.AttributeTypes()))
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for attrName := range val.ty.AttributeTypes() {
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attrNames = append(attrNames, attrName)
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}
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sort.Strings(attrNames)
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for _, attrName := range attrNames {
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appendSetHashBytes(val.GetAttr(attrName), buf)
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buf.WriteRune(';')
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}
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buf.WriteRune('>')
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return
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}
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if val.ty.IsTupleType() {
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buf.WriteRune('<')
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val.ForEachElement(func(keyVal, elementVal Value) bool {
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appendSetHashBytes(elementVal, buf)
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buf.WriteRune(';')
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return false
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})
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buf.WriteRune('>')
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return
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}
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// should never get down here
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panic("unsupported type in set hash")
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}
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