hcldec: New function ChildBlockTypes

This function returns a map describing all of the child block types
declared inside a spec. This can be used for recursive decoding of bodies
using the low-level HCL API, though in most cases callers should just use
Decode which does recursive decoding of an entire nested structure in
a single call.

hcldec/public.go

@@ -51,3 +51,28 @@ func ImpliedType(spec Spec) cty.Type {
 func SourceRange(body hcl.Body, spec Spec) hcl.Range {
  return sourceRange(body, nil, spec)
 }
+
+// ChildBlockTypes returns a map of all of the child block types declared
+// by the given spec, with block type names as keys and the associated
+// nested body specs as values.
+func ChildBlockTypes(spec Spec) map[string]Spec {
+ ret := map[string]Spec{}
+
+ // visitSameBodyChildren walks through the spec structure, calling
+ // the given callback for each descendent spec encountered. We are
+ // interested in the specs that reference attributes and blocks.
+ var visit visitFunc
+ visit = func(s Spec) {
+ if bs, ok := s.(blockSpec); ok {
+ for _, blockS := range bs.blockHeaderSchemata() {
+ ret[blockS.Type] = bs.nestedSpec()
+ }
+ }
+
+ s.visitSameBodyChildren(visit)
+ }
+
+ visit(spec)
+
+ return ret
+}

hcldec/spec.go

@@ -52,6 +52,7 @@ type attrSpec interface {
 // 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
@@ -298,6 +299,11 @@ func (s *BlockSpec) blockHeaderSchemata() []hcl.BlockHeaderSchema {
  }
 }
 
+// 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
@@ -409,6 +415,11 @@ func (s *BlockListSpec) blockHeaderSchemata() []hcl.BlockHeaderSchema {
  }
 }
 
+// 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
@@ -519,6 +530,11 @@ func (s *BlockSetSpec) blockHeaderSchemata() []hcl.BlockHeaderSchema {
  }
 }
 
+// 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
@@ -631,6 +647,11 @@ func (s *BlockMapSpec) blockHeaderSchemata() []hcl.BlockHeaderSchema {
  }
 }
 
+// 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

hcldec/spec_test.go

@@ -1,14 +1,21 @@
 package hcldec
 
 // Verify that all of our spec types implement the necessary interfaces
-var objectSpecAsSpec Spec = ObjectSpec(nil)
-var tupleSpecAsSpec Spec = TupleSpec(nil)
-var attrSpecAsSpec Spec = (*AttrSpec)(nil)
-var literalSpecAsSpec Spec = (*LiteralSpec)(nil)
-var exprSpecAsSpec Spec = (*ExprSpec)(nil)
-var blockSpecAsSpec Spec = (*BlockSpec)(nil)
-var blockListSpecAsSpec Spec = (*BlockListSpec)(nil)
-var blockSetSpecAsSpec Spec = (*BlockSetSpec)(nil)
-var blockMapSpecAsSpec Spec = (*BlockMapSpec)(nil)
-var blockLabelSpecAsSpec Spec = (*BlockLabelSpec)(nil)
-var defaultSpecAsSpec Spec = (*DefaultSpec)(nil)
+var _ Spec = ObjectSpec(nil)
+var _ Spec = TupleSpec(nil)
+var _ Spec = (*AttrSpec)(nil)
+var _ Spec = (*LiteralSpec)(nil)
+var _ Spec = (*ExprSpec)(nil)
+var _ Spec = (*BlockSpec)(nil)
+var _ Spec = (*BlockListSpec)(nil)
+var _ Spec = (*BlockSetSpec)(nil)
+var _ Spec = (*BlockMapSpec)(nil)
+var _ Spec = (*BlockLabelSpec)(nil)
+var _ Spec = (*DefaultSpec)(nil)
+
+var _ attrSpec = (*AttrSpec)(nil)
+
+var _ blockSpec = (*BlockSpec)(nil)
+var _ blockSpec = (*BlockListSpec)(nil)
+var _ blockSpec = (*BlockSetSpec)(nil)
+var _ blockSpec = (*BlockMapSpec)(nil)