tfprotov5+tfprotov6: Introduce ValueType() methods for Schema types (#158)

Reference: #128
Reference: #157

This methods implement standard conversion logic from `Schema*` types into their associated `tftypes.Type` equivalent. For example, these can be used to prepare calls to the `(DynamicValue).Unmarshal()` method, which is necessary in many RPCs.

Preferably, these methods would have been named `Type()`, however the `SchemaAttribute` type implements a `Type` field and Go does not permit overlapping field and method names. Instead, the name `ValueType()` was chosen as an alternate designation as the `tftypes.Type` really represents a data value type, instead of a type constraint (sometimes also referred to as a schema type).

Author: bflad

.changelog/158.txt

@@ -0,0 +1,7 @@
+```release-note:enhancement
+tfprotov5: Added `ValueType()` methods to `Schema`, `SchemaAttribute`, `SchemaBlock`, and `SchemaNestedBlock` types.
+```
+
+```release-note:enhancement
+tfprotov6: Added `ValueType()` methods to `Schema`, `SchemaAttribute`, `SchemaBlock`, `SchemaNestedBlock`, and `SchemaObject` types.
+```

tfprotov5/schema.go

@@ -68,6 +68,19 @@ type Schema struct {
 	Block *SchemaBlock
 }
 
+// ValueType returns the tftypes.Type for a Schema.
+//
+// If Schema is missing, an empty Object is returned.
+func (s *Schema) ValueType() tftypes.Type {
+	if s == nil {
+		return tftypes.Object{
+			AttributeTypes: map[string]tftypes.Type{},
+		}
+	}
+
+	return s.Block.ValueType()
+}
+
 // SchemaBlock represents a block in a schema. Blocks are how Terraform creates
 // groupings of attributes. In configurations, they don't use the equals sign
 // and use dynamic instead of list comprehensions.
@@ -105,6 +118,51 @@ type SchemaBlock struct {
 	Deprecated bool
 }
 
+// ValueType returns the tftypes.Type for a SchemaBlock.
+//
+// If SchemaBlock is missing, an empty Object is returned.
+func (s *SchemaBlock) ValueType() tftypes.Type {
+	if s == nil {
+		return tftypes.Object{
+			AttributeTypes: map[string]tftypes.Type{},
+		}
+	}
+
+	attributeTypes := map[string]tftypes.Type{}
+
+	for _, attribute := range s.Attributes {
+		if attribute == nil {
+			continue
+		}
+
+		attributeType := attribute.ValueType()
+
+		if attributeType == nil {
+			continue
+		}
+
+		attributeTypes[attribute.Name] = attributeType
+	}
+
+	for _, block := range s.BlockTypes {
+		if block == nil {
+			continue
+		}
+
+		blockType := block.ValueType()
+
+		if blockType == nil {
+			continue
+		}
+
+		attributeTypes[block.TypeName] = blockType
+	}
+
+	return tftypes.Object{
+		AttributeTypes: attributeTypes,
+	}
+}
+
 // SchemaAttribute represents a single attribute within a schema block.
 // Attributes are the fields users can set in configuration using the equals
 // sign, can assign to variables, can interpolate, and can use list
@@ -162,6 +220,17 @@ type SchemaAttribute struct {
 	Deprecated bool
 }
 
+// ValueType returns the tftypes.Type for a SchemaAttribute.
+//
+// If SchemaAttribute is missing, nil is returned.
+func (s *SchemaAttribute) ValueType() tftypes.Type {
+	if s == nil {
+		return nil
+	}
+
+	return s.Type
+}
+
 // SchemaNestedBlock is a nested block within another block. See SchemaBlock
 // for more information on blocks.
 type SchemaNestedBlock struct {
@@ -198,6 +267,39 @@ type SchemaNestedBlock struct {
 	MaxItems int64
 }
 
+// ValueType returns the tftypes.Type for a SchemaNestedBlock.
+//
+// If SchemaNestedBlock is missing or the Nesting mode is invalid, nil is
+// returned.
+func (s *SchemaNestedBlock) ValueType() tftypes.Type {
+	if s == nil {
+		return nil
+	}
+
+	blockType := s.Block.ValueType()
+
+	switch s.Nesting {
+	case SchemaNestedBlockNestingModeGroup:
+		return blockType
+	case SchemaNestedBlockNestingModeList:
+		return tftypes.List{
+			ElementType: blockType,
+		}
+	case SchemaNestedBlockNestingModeMap:
+		return tftypes.Map{
+			ElementType: blockType,
+		}
+	case SchemaNestedBlockNestingModeSet:
+		return tftypes.Set{
+			ElementType: blockType,
+		}
+	case SchemaNestedBlockNestingModeSingle:
+		return blockType
+	default:
+		return nil
+	}
+}
+
 // SchemaNestedBlockNestingMode indicates the nesting mode for
 // SchemaNestedBlocks. The nesting mode determines the number of instances of
 // the block allowed, how many labels the block expects, and the data structure