hcl: New GetAttr and ApplyPath functions
These make it easier for calling applications to get the same result as operators within HCL expressions both for individual attribute accesses and when processing whole cty.Paths. (We previously had an Index function which did the same thing for indexing, and ApplyPath is just a wrapper around calling GetAttr and Index in a loop.)
This commit is contained in:
Martin Atkins
parent
93fb31f28b
commit
89dbc5eb3d
119
hcl/ops.go
119
hcl/ops.go
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@ -145,3 +145,122 @@ func Index(collection, key cty.Value, srcRange *Range) (cty.Value, Diagnostics)
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}
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}
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// GetAttr is a helper function that performs the same operation as the
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// attribute access in the HCL expression language. That is, the result is the
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// same as it would be for obj.attr in a configuration expression.
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//
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// This is exported so that applications can access attributes in a manner
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// consistent with how the language does it, including handling of null and
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// unknown values, etc.
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//
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// Diagnostics are produced if the given combination of values is not valid.
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// Therefore a pointer to a source range must be provided to use in diagnostics,
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// though nil can be provided if the calling application is going to
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// ignore the subject of the returned diagnostics anyway.
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func GetAttr(obj cty.Value, attrName string, srcRange *Range) (cty.Value, Diagnostics) {
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if obj.IsNull() {
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return cty.DynamicVal, Diagnostics{
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{
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Severity: DiagError,
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Summary: "Attempt to get attribute from null value",
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Detail: "This value is null, so it does not have any attributes.",
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Subject: srcRange,
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},
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}
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}
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ty := obj.Type()
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switch {
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case ty.IsObjectType():
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if !ty.HasAttribute(attrName) {
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return cty.DynamicVal, Diagnostics{
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{
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Severity: DiagError,
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Summary: "Unsupported attribute",
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Detail: fmt.Sprintf("This object does not have an attribute named %q.", attrName),
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Subject: srcRange,
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},
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}
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}
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if !obj.IsKnown() {
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return cty.UnknownVal(ty.AttributeType(attrName)), nil
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}
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return obj.GetAttr(attrName), nil
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case ty.IsMapType():
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if !obj.IsKnown() {
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return cty.UnknownVal(ty.ElementType()), nil
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}
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idx := cty.StringVal(attrName)
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if obj.HasIndex(idx).False() {
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return cty.DynamicVal, Diagnostics{
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{
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Severity: DiagError,
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Summary: "Missing map element",
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Detail: fmt.Sprintf("This map does not have an element with the key %q.", attrName),
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Subject: srcRange,
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},
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}
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}
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return obj.Index(idx), nil
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case ty == cty.DynamicPseudoType:
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return cty.DynamicVal, nil
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default:
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return cty.DynamicVal, Diagnostics{
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{
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Severity: DiagError,
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Summary: "Unsupported attribute",
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Detail: "This value does not have any attributes.",
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Subject: srcRange,
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},
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}
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}
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}
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// ApplyPath is a helper function that applies a cty.Path to a value using the
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// indexing and attribute access operations from HCL.
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//
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// This is similar to calling the path's own Apply method, but ApplyPath uses
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// the more relaxed typing rules that apply to these operations in HCL, rather
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// than cty's relatively-strict rules. ApplyPath is implemented in terms of
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// Index and GetAttr, and so it has the same behavior for individual steps
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// but will stop and return any errors returned by intermediate steps.
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//
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// Diagnostics are produced if the given path cannot be applied to the given
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// value. Therefore a pointer to a source range must be provided to use in
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// diagnostics, though nil can be provided if the calling application is going
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// to ignore the subject of the returned diagnostics anyway.
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func ApplyPath(val cty.Value, path cty.Path, srcRange *Range) (cty.Value, Diagnostics) {
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var diags Diagnostics
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for _, step := range path {
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var stepDiags Diagnostics
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switch ts := step.(type) {
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case cty.IndexStep:
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val, stepDiags = Index(val, ts.Key, srcRange)
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case cty.GetAttrStep:
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val, stepDiags = GetAttr(val, ts.Name, srcRange)
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default:
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// Should never happen because the above are all of the step types.
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diags = diags.Append(&Diagnostic{
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Severity: DiagError,
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Summary: "Invalid path step",
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Detail: fmt.Sprintf("Go type %T is not a valid path step. This is a bug in this program.", step),
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Subject: srcRange,
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})
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return cty.DynamicVal, diags
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}
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diags = append(diags, stepDiags...)
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if stepDiags.HasErrors() {
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return cty.DynamicVal, diags
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}
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}
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return val, diags
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}
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@ -0,0 +1,132 @@
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package hcl
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import (
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"fmt"
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"testing"
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"github.com/zclconf/go-cty/cty"
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)
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func TestApplyPath(t *testing.T) {
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tests := []struct {
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Start cty.Value
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Path cty.Path
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Want cty.Value
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WantErr string
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}{
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{
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cty.StringVal("hello"),
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nil,
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cty.StringVal("hello"),
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``,
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},
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{
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cty.StringVal("hello"),
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(cty.Path)(nil).Index(cty.StringVal("boop")),
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cty.NilVal,
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`Invalid index`,
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},
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{
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cty.StringVal("hello"),
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(cty.Path)(nil).Index(cty.NumberIntVal(0)),
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cty.NilVal,
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`Invalid index`,
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},
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{
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cty.ListVal([]cty.Value{
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cty.StringVal("hello"),
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}),
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(cty.Path)(nil).Index(cty.NumberIntVal(0)),
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cty.StringVal("hello"),
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``,
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},
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{
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cty.TupleVal([]cty.Value{
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cty.StringVal("hello"),
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}),
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(cty.Path)(nil).Index(cty.NumberIntVal(0)),
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cty.StringVal("hello"),
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``,
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},
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{
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cty.ListValEmpty(cty.String),
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(cty.Path)(nil).Index(cty.NumberIntVal(0)),
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cty.NilVal,
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`Invalid index`,
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},
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{
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cty.ListVal([]cty.Value{
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cty.StringVal("hello"),
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}),
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(cty.Path)(nil).Index(cty.NumberIntVal(1)),
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cty.NilVal,
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`Invalid index`,
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},
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{
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cty.ListVal([]cty.Value{
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cty.StringVal("hello"),
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}),
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(cty.Path)(nil).Index(cty.NumberIntVal(0)).GetAttr("foo"),
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cty.NilVal,
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`Unsupported attribute`,
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},
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{
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cty.ListVal([]cty.Value{
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cty.EmptyObjectVal,
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}),
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(cty.Path)(nil).Index(cty.NumberIntVal(0)).GetAttr("foo"),
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cty.NilVal,
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`Unsupported attribute`,
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},
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{
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cty.NullVal(cty.List(cty.String)),
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(cty.Path)(nil).Index(cty.NumberIntVal(0)),
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cty.NilVal,
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`Attempt to index null value`,
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},
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{
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cty.NullVal(cty.Map(cty.String)),
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(cty.Path)(nil).Index(cty.NumberIntVal(0)),
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cty.NilVal,
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`Attempt to index null value`,
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},
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{
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cty.NullVal(cty.EmptyObject),
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(cty.Path)(nil).GetAttr("foo"),
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cty.NilVal,
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`Attempt to get attribute from null value`,
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},
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}
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for _, test := range tests {
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t.Run(fmt.Sprintf("%#v %#v", test.Start, test.Path), func(t *testing.T) {
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got, diags := ApplyPath(test.Start, test.Path, nil)
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t.Logf("testing ApplyPath\nstart: %#v\npath: %#v", test.Start, test.Path)
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for _, diag := range diags {
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t.Logf(diag.Error())
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}
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if test.WantErr != "" {
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if !diags.HasErrors() {
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t.Fatalf("succeeded, but want error\nwant error: %s", test.WantErr)
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}
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if len(diags) != 1 {
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t.Fatalf("wrong number of diagnostics %d; want 1", len(diags))
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}
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if gotErrStr := diags[0].Summary; gotErrStr != test.WantErr {
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t.Fatalf("wrong error\ngot error: %s\nwant error: %s", gotErrStr, test.WantErr)
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}
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return
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}
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if diags.HasErrors() {
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t.Fatalf("failed, but want success\ngot diagnostics:\n%s", diags.Error())
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}
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if !test.Want.RawEquals(got) {
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t.Fatalf("wrong result\ngot: %#v\nwant: %#v", got, test.Want)
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}
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})
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}
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}
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@ -255,66 +255,7 @@ type TraverseAttr struct {
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}
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func (tn TraverseAttr) TraversalStep(val cty.Value) (cty.Value, Diagnostics) {
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if val.IsNull() {
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return cty.DynamicVal, Diagnostics{
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{
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Severity: DiagError,
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Summary: "Attempt to get attribute from null value",
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Detail: "This value is null, so it does not have any attributes.",
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Subject: &tn.SrcRange,
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},
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}
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}
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ty := val.Type()
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switch {
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case ty.IsObjectType():
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if !ty.HasAttribute(tn.Name) {
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return cty.DynamicVal, Diagnostics{
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{
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Severity: DiagError,
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Summary: "Unsupported attribute",
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Detail: fmt.Sprintf("This object does not have an attribute named %q.", tn.Name),
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Subject: &tn.SrcRange,
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},
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}
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}
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if !val.IsKnown() {
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return cty.UnknownVal(ty.AttributeType(tn.Name)), nil
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}
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return val.GetAttr(tn.Name), nil
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case ty.IsMapType():
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if !val.IsKnown() {
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return cty.UnknownVal(ty.ElementType()), nil
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}
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idx := cty.StringVal(tn.Name)
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if val.HasIndex(idx).False() {
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return cty.DynamicVal, Diagnostics{
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{
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Severity: DiagError,
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Summary: "Missing map element",
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Detail: fmt.Sprintf("This map does not have an element with the key %q.", tn.Name),
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Subject: &tn.SrcRange,
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},
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}
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}
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return val.Index(idx), nil
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case ty == cty.DynamicPseudoType:
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return cty.DynamicVal, nil
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default:
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return cty.DynamicVal, Diagnostics{
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{
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Severity: DiagError,
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Summary: "Unsupported attribute",
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Detail: "This value does not have any attributes.",
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Subject: &tn.SrcRange,
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},
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}
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}
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return GetAttr(val, tn.Name, &tn.SrcRange)
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}
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func (tn TraverseAttr) SourceRange() Range {
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