configs/configschema: add new NestedType to attribute

This commit adds a new field, NestedType, to the Attribute schema, and
extends the current Attribute decoderSpec to account for the new type.
The codepaths are mostly unused and included in a separate commit to
verify that the included changes do not impact any other tests yet.

configs/configschema/decoder_spec.go

@@ -6,6 +6,7 @@ import (
 	"unsafe"
 
 	"github.com/hashicorp/hcl/v2/hcldec"
+	"github.com/zclconf/go-cty/cty"
 )
 
 var mapLabelNames = []string{"key"}
@@ -183,9 +184,48 @@ func (b *Block) DecoderSpec() hcldec.Spec {
 }
 
 func (a *Attribute) decoderSpec(name string) hcldec.Spec {
-	return &hcldec.AttrSpec{
+	ret := &hcldec.AttrSpec{Name: name}
-		Name:     name,
+	if a == nil {
-		Type:     a.Type,
+		return ret
-		Required: a.Required,
 	}
+
+	if a.NestedType != nil {
+		// FIXME: a panic() is a bad UX. Fix this, probably by extending
+		// InternalValidate() to check Attribute schemas as well and calling it
+		// when we get the schema from the provider in Context().
+		if a.Type != cty.NilType {
+			panic("Invalid attribute schema: NestedType and Type cannot both be set. This is a bug in the provider.")
+		}
+
+		var optAttrs []string
+		optAttrs = listOptionalAttrsFromObject(a.NestedType, optAttrs)
+		ty := a.NestedType.ImpliedType()
+
+		switch a.NestedType.Nesting {
+		case NestingList:
+			ret.Type = cty.List(ty)
+		case NestingSet:
+			ret.Type = cty.Set(ty)
+		case NestingMap:
+			ret.Type = cty.Map(ty)
+		default: // NestingSingle, NestingGroup, or no NestingMode
+			ret.Type = ty
+		}
+		ret.Required = a.NestedType.MinItems > 0
+		return ret
+	}
+
+	ret.Type = a.Type
+	ret.Required = a.Required
+	return ret
+}
+
+func listOptionalAttrsFromObject(o *Object, optAttrs []string) []string {
+	for name, attr := range o.Attributes {
+		if attr.Optional == true {
+			optAttrs = append(optAttrs, name)
+		}
+	}
+
+	return optAttrs
 }

configs/configschema/decoder_spec_test.go

@@ -426,3 +426,363 @@ func TestBlockDecoderSpec(t *testing.T) {
 		})
 	}
 }
+
+func TestAttributeDecoderSpec(t *testing.T) {
+	tests := map[string]struct {
+		Schema    *Attribute
+		TestBody  hcl.Body
+		Want      cty.Value
+		DiagCount int
+	}{
+		"empty": {
+			&Attribute{},
+			hcl.EmptyBody(),
+			cty.NilVal,
+			0,
+		},
+		"nil": {
+			nil,
+			hcl.EmptyBody(),
+			cty.NilVal,
+			0,
+		},
+		"optional string (null)": {
+			&Attribute{
+				Type:     cty.String,
+				Optional: true,
+			},
+			hcl.EmptyBody(),
+			cty.NullVal(cty.String),
+			0,
+		},
+		"optional string": {
+			&Attribute{
+				Type:     cty.String,
+				Optional: true,
+			},
+			hcltest.MockBody(&hcl.BodyContent{
+				Attributes: hcl.Attributes{
+					"attr": {
+						Name: "attr",
+						Expr: hcltest.MockExprLiteral(cty.StringVal("bar")),
+					},
+				},
+			}),
+			cty.StringVal("bar"),
+			0,
+		},
+		"NestedType with required string": {
+			&Attribute{
+				NestedType: &Object{
+					Attributes: map[string]*Attribute{
+						"foo": {
+							Type:     cty.String,
+							Required: true,
+						},
+					},
+				},
+				Optional: true,
+			},
+			hcltest.MockBody(&hcl.BodyContent{
+				Attributes: hcl.Attributes{
+					"attr": {
+						Name: "attr",
+						Expr: hcltest.MockExprLiteral(cty.ObjectVal(map[string]cty.Value{
+							"foo": cty.StringVal("bar"),
+						})),
+					},
+				},
+			}),
+			cty.ObjectVal(map[string]cty.Value{
+				"foo": cty.StringVal("bar"),
+			}),
+			0,
+		},
+		"NestedType with optional attributes": {
+			&Attribute{
+				NestedType: &Object{
+					Attributes: map[string]*Attribute{
+						"foo": {
+							Type:     cty.String,
+							Optional: true,
+						},
+						"bar": {
+							Type:     cty.String,
+							Optional: true,
+						},
+					},
+				},
+				Optional: true,
+			},
+			hcltest.MockBody(&hcl.BodyContent{
+				Attributes: hcl.Attributes{
+					"attr": {
+						Name: "attr",
+						Expr: hcltest.MockExprLiteral(cty.ObjectVal(map[string]cty.Value{
+							"foo": cty.StringVal("bar"),
+						})),
+					},
+				},
+			}),
+			cty.ObjectVal(map[string]cty.Value{
+				"foo": cty.StringVal("bar"),
+				"bar": cty.NullVal(cty.String),
+			}),
+			0,
+		},
+		"NestedType with missing required string": {
+			&Attribute{
+				NestedType: &Object{
+					Attributes: map[string]*Attribute{
+						"foo": {
+							Type:     cty.String,
+							Required: true,
+						},
+					},
+				},
+				Optional: true,
+			},
+			hcltest.MockBody(&hcl.BodyContent{
+				Attributes: hcl.Attributes{
+					"attr": {
+						Name: "attr",
+						Expr: hcltest.MockExprLiteral(cty.EmptyObjectVal),
+					},
+				},
+			}),
+			cty.UnknownVal(cty.Object(map[string]cty.Type{
+				"foo": cty.String,
+			})),
+			1,
+		},
+		// NestedModes
+		"NestedType NestingModeList valid": {
+			&Attribute{
+				NestedType: &Object{
+					Nesting: NestingList,
+					Attributes: map[string]*Attribute{
+						"foo": {
+							Type:     cty.String,
+							Required: true,
+						},
+					},
+				},
+				Optional: true,
+			},
+			hcltest.MockBody(&hcl.BodyContent{
+				Attributes: hcl.Attributes{
+					"attr": {
+						Name: "attr",
+						Expr: hcltest.MockExprLiteral(cty.ListVal([]cty.Value{
+							cty.ObjectVal(map[string]cty.Value{
+								// "foo" should be a string, not a list
+								"foo": cty.StringVal("bar"),
+							}),
+							cty.ObjectVal(map[string]cty.Value{
+								// "foo" should be a string, not a list
+								"foo": cty.StringVal("baz"),
+							}),
+						})),
+					},
+				},
+			}),
+			cty.ListVal([]cty.Value{
+				cty.ObjectVal(map[string]cty.Value{"foo": cty.StringVal("bar")}),
+				cty.ObjectVal(map[string]cty.Value{"foo": cty.StringVal("baz")}),
+			}),
+			0,
+		},
+		"NestedType NestingModeList invalid": {
+			&Attribute{
+				NestedType: &Object{
+					Nesting: NestingList,
+					Attributes: map[string]*Attribute{
+						"foo": {
+							Type:     cty.String,
+							Required: true,
+						},
+					},
+				},
+				Optional: true,
+			},
+			hcltest.MockBody(&hcl.BodyContent{
+				Attributes: hcl.Attributes{
+					"attr": {
+						Name: "attr",
+						Expr: hcltest.MockExprLiteral(cty.ListVal([]cty.Value{cty.ObjectVal(map[string]cty.Value{
+							// "foo" should be a string, not a list
+							"foo": cty.ListVal([]cty.Value{cty.StringVal("bar"), cty.StringVal("baz")}),
+						})})),
+					},
+				},
+			}),
+			cty.UnknownVal(cty.List(cty.Object(map[string]cty.Type{"foo": cty.String}))),
+			1,
+		},
+		"NestedType NestingModeSet valid": {
+			&Attribute{
+				NestedType: &Object{
+					Nesting: NestingSet,
+					Attributes: map[string]*Attribute{
+						"foo": {
+							Type:     cty.String,
+							Required: true,
+						},
+					},
+				},
+				Optional: true,
+			},
+			hcltest.MockBody(&hcl.BodyContent{
+				Attributes: hcl.Attributes{
+					"attr": {
+						Name: "attr",
+						Expr: hcltest.MockExprLiteral(cty.SetVal([]cty.Value{
+							cty.ObjectVal(map[string]cty.Value{
+								// "foo" should be a string, not a list
+								"foo": cty.StringVal("bar"),
+							}),
+							cty.ObjectVal(map[string]cty.Value{
+								// "foo" should be a string, not a list
+								"foo": cty.StringVal("baz"),
+							}),
+						})),
+					},
+				},
+			}),
+			cty.SetVal([]cty.Value{
+				cty.ObjectVal(map[string]cty.Value{"foo": cty.StringVal("bar")}),
+				cty.ObjectVal(map[string]cty.Value{"foo": cty.StringVal("baz")}),
+			}),
+			0,
+		},
+		"NestedType NestingModeSet invalid": {
+			&Attribute{
+				NestedType: &Object{
+					Nesting: NestingSet,
+					Attributes: map[string]*Attribute{
+						"foo": {
+							Type:     cty.String,
+							Required: true,
+						},
+					},
+				},
+				Optional: true,
+			},
+			hcltest.MockBody(&hcl.BodyContent{
+				Attributes: hcl.Attributes{
+					"attr": {
+						Name: "attr",
+						Expr: hcltest.MockExprLiteral(cty.SetVal([]cty.Value{cty.ObjectVal(map[string]cty.Value{
+							// "foo" should be a string, not a list
+							"foo": cty.ListVal([]cty.Value{cty.StringVal("bar"), cty.StringVal("baz")}),
+						})})),
+					},
+				},
+			}),
+			cty.UnknownVal(cty.Set(cty.Object(map[string]cty.Type{"foo": cty.String}))),
+			1,
+		},
+		"NestedType NestingModeMap valid": {
+			&Attribute{
+				NestedType: &Object{
+					Nesting: NestingMap,
+					Attributes: map[string]*Attribute{
+						"foo": {
+							Type:     cty.String,
+							Required: true,
+						},
+					},
+				},
+				Optional: true,
+			},
+			hcltest.MockBody(&hcl.BodyContent{
+				Attributes: hcl.Attributes{
+					"attr": {
+						Name: "attr",
+						Expr: hcltest.MockExprLiteral(cty.MapVal(map[string]cty.Value{
+							"one": cty.ObjectVal(map[string]cty.Value{
+								// "foo" should be a string, not a list
+								"foo": cty.StringVal("bar"),
+							}),
+							"two": cty.ObjectVal(map[string]cty.Value{
+								// "foo" should be a string, not a list
+								"foo": cty.StringVal("baz"),
+							}),
+						})),
+					},
+				},
+			}),
+			cty.MapVal(map[string]cty.Value{
+				"one": cty.ObjectVal(map[string]cty.Value{"foo": cty.StringVal("bar")}),
+				"two": cty.ObjectVal(map[string]cty.Value{"foo": cty.StringVal("baz")}),
+			}),
+			0,
+		},
+		"NestedType NestingModeMap invalid": {
+			&Attribute{
+				NestedType: &Object{
+					Nesting: NestingMap,
+					Attributes: map[string]*Attribute{
+						"foo": {
+							Type:     cty.String,
+							Required: true,
+						},
+					},
+				},
+				Optional: true,
+			},
+			hcltest.MockBody(&hcl.BodyContent{
+				Attributes: hcl.Attributes{
+					"attr": {
+						Name: "attr",
+						Expr: hcltest.MockExprLiteral(cty.MapVal(map[string]cty.Value{
+							"one": cty.ObjectVal(map[string]cty.Value{
+								// "foo" should be a string, not a list
+								"foo": cty.ListVal([]cty.Value{cty.StringVal("bar"), cty.StringVal("baz")}),
+							}),
+						})),
+					},
+				},
+			}),
+			cty.UnknownVal(cty.Map(cty.Object(map[string]cty.Type{"foo": cty.String}))),
+			1,
+		},
+	}
+
+	for name, test := range tests {
+		t.Run(name, func(t *testing.T) {
+			spec := test.Schema.decoderSpec("attr")
+			got, diags := hcldec.Decode(test.TestBody, spec, nil)
+			if len(diags) != test.DiagCount {
+				t.Errorf("wrong number of diagnostics %d; want %d", len(diags), test.DiagCount)
+				for _, diag := range diags {
+					t.Logf("- %s", diag.Error())
+				}
+			}
+
+			if !got.RawEquals(test.Want) {
+				t.Logf("[INFO] implied schema is %s", spew.Sdump(hcldec.ImpliedSchema(spec)))
+				t.Errorf("wrong result\ngot:  %s\nwant: %s", dump.Value(got), dump.Value(test.Want))
+			}
+		})
+	}
+
+}
+
+// TestAttributeDecodeSpec_panic is a temporary test which verifies that
+// decoderSpec panics when an invalid Attribute schema is encountered. It will
+// be removed when InternalValidate() is extended to validate Attribute specs
+// (and is used). See the #FIXME in decoderSpec.
+func TestAttributeDecoderSpec_panic(t *testing.T) {
+	attrS := &Attribute{
+		Type: cty.Object(map[string]cty.Type{
+			"nested_attribute": cty.String,
+		}),
+		NestedType: &Object{},
+		Optional:   true,
+	}
+
+	defer func() { recover() }()
+	attrS.decoderSpec("attr")
+	t.Errorf("expected panic")
+}

configs/configschema/empty_value.go

@@ -26,6 +26,18 @@ func (b *Block) EmptyValue() cty.Value {
 // the value that would be returned if there were no definition of the attribute
 // at all, ignoring any required constraint.
 func (a *Attribute) EmptyValue() cty.Value {
+	if a.NestedType != nil {
+		switch a.NestedType.Nesting {
+		case NestingList:
+			return cty.NullVal(cty.List(a.NestedType.ImpliedType()))
+		case NestingSet:
+			return cty.NullVal(cty.Set(a.NestedType.ImpliedType()))
+		case NestingMap:
+			return cty.NullVal(cty.Map(a.NestedType.ImpliedType()))
+		default: // NestingSingle, NestingGroup, or no NestingMode
+			return cty.NullVal(a.NestedType.ImpliedType())
+		}
+	}
 	return cty.NullVal(a.Type)
 }
 

configs/configschema/empty_value_test.go

@@ -168,3 +168,116 @@ func TestBlockEmptyValue(t *testing.T) {
 		})
 	}
 }
+
+// Attribute EmptyValue() is well covered by the Block tests above; these tests
+// focus on the behavior with NestedType field inside an Attribute
+func TestAttributeEmptyValue(t *testing.T) {
+	tests := []struct {
+		Schema *Attribute
+		Want   cty.Value
+	}{
+		{
+			&Attribute{},
+			cty.NilVal,
+		},
+		{
+			&Attribute{
+				Type: cty.String,
+			},
+			cty.NullVal(cty.String),
+		},
+		{
+			&Attribute{
+				NestedType: &Object{
+					// no Nesting set should behave the same as NestingSingle
+					Attributes: map[string]*Attribute{
+						"str": {Type: cty.String, Required: true},
+					},
+				},
+			},
+			cty.NullVal(cty.Object(map[string]cty.Type{
+				"str": cty.String,
+			})),
+		},
+		{
+			&Attribute{
+				NestedType: &Object{
+					Nesting: NestingSingle,
+					Attributes: map[string]*Attribute{
+						"str": {Type: cty.String, Required: true},
+					},
+				},
+			},
+			cty.NullVal(cty.Object(map[string]cty.Type{
+				"str": cty.String,
+			})),
+		},
+		{
+			&Attribute{
+				NestedType: &Object{
+					Nesting: NestingGroup, // functionally equivalent to NestingSingle in a NestedType
+					Attributes: map[string]*Attribute{
+						"str": {Type: cty.String, Required: true},
+					},
+				},
+			},
+			cty.NullVal(cty.Object(map[string]cty.Type{
+				"str": cty.String,
+			})),
+		},
+		{
+			&Attribute{
+				NestedType: &Object{
+					Nesting: NestingList,
+					Attributes: map[string]*Attribute{
+						"str": {Type: cty.String, Required: true},
+					},
+				},
+			},
+			cty.NullVal(cty.List(
+				cty.Object(map[string]cty.Type{
+					"str": cty.String,
+				}),
+			)),
+		},
+		{
+			&Attribute{
+				NestedType: &Object{
+					Nesting: NestingMap,
+					Attributes: map[string]*Attribute{
+						"str": {Type: cty.String, Required: true},
+					},
+				},
+			},
+			cty.NullVal(cty.Map(
+				cty.Object(map[string]cty.Type{
+					"str": cty.String,
+				}),
+			)),
+		},
+		{
+			&Attribute{
+				NestedType: &Object{
+					Nesting: NestingSet,
+					Attributes: map[string]*Attribute{
+						"str": {Type: cty.String, Required: true},
+					},
+				},
+			},
+			cty.NullVal(cty.Set(
+				cty.Object(map[string]cty.Type{
+					"str": cty.String,
+				}),
+			)),
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(fmt.Sprintf("%#v", test.Schema), func(t *testing.T) {
+			got := test.Schema.EmptyValue()
+			if !test.Want.RawEquals(got) {
+				t.Errorf("wrong result\nschema: %s\ngot: %s\nwant: %s", spew.Sdump(test.Schema), dump.Value(got), dump.Value(test.Want))
+			}
+		})
+	}
+}

configs/configschema/implied_type.go

@@ -40,3 +40,37 @@ func (b *Block) ContainsSensitive() bool {
 	}
 	return false
 }
+
+// ImpliedType returns the cty.Type that would result from decoding a NestedType
+// Attribute using the receiving block schema.
+//
+// ImpliedType always returns a result, even if the given schema is
+// inconsistent. Code that creates configschema.Object objects should be tested
+// using the InternalValidate method to detect any inconsistencies that would
+// cause this method to fall back on defaults and assumptions.
+func (o *Object) ImpliedType() cty.Type {
+	if o == nil {
+		return cty.EmptyObject
+	}
+
+	attrTys := make(map[string]cty.Type, len(o.Attributes))
+	for name, attrS := range o.Attributes {
+		attrTys[name] = attrS.Type
+	}
+
+	var optAttrs []string
+	optAttrs = listOptionalAttrsFromObject(o, optAttrs)
+
+	return cty.ObjectWithOptionalAttrs(attrTys, optAttrs)
+}
+
+// ContainsSensitive returns true if any of the attributes of the receiving
+// Object are marked as sensitive.
+func (o *Object) ContainsSensitive() bool {
+	for _, attrS := range o.Attributes {
+		if attrS.Sensitive {
+			return true
+		}
+	}
+	return false
+}

configs/configschema/implied_type_test.go

@@ -122,3 +122,59 @@ func TestBlockImpliedType(t *testing.T) {
 		})
 	}
 }
+
+func TestObjectImpliedType(t *testing.T) {
+	tests := map[string]struct {
+		Schema *Object
+		Want   cty.Type
+	}{
+		"nil": {
+			nil,
+			cty.EmptyObject,
+		},
+		"empty": {
+			&Object{},
+			cty.EmptyObject,
+		},
+		"attributes": {
+			&Object{
+				Attributes: map[string]*Attribute{
+					"optional": {
+						Type:     cty.String,
+						Optional: true,
+					},
+					"required": {
+						Type:     cty.Number,
+						Required: true,
+					},
+					"computed": {
+						Type:     cty.List(cty.Bool),
+						Computed: true,
+					},
+					"optional_computed": {
+						Type:     cty.Map(cty.Bool),
+						Optional: true,
+					},
+				},
+			},
+			cty.ObjectWithOptionalAttrs(
+				map[string]cty.Type{
+					"optional":          cty.String,
+					"required":          cty.Number,
+					"computed":          cty.List(cty.Bool),
+					"optional_computed": cty.Map(cty.Bool),
+				},
+				[]string{"optional", "optional_computed"},
+			),
+		},
+	}
+
+	for name, test := range tests {
+		t.Run(name, func(t *testing.T) {
+			got := test.Schema.ImpliedType()
+			if !got.Equals(test.Want) {
+				t.Errorf("wrong result\ngot:  %#v\nwant: %#v", got, test.Want)
+			}
+		})
+	}
+}

configs/configschema/schema.go

@@ -38,8 +38,13 @@ type Block struct {
 // Attribute represents a configuration attribute, within a block.
 type Attribute struct {
 	// Type is a type specification that the attribute's value must conform to.
+	// It conflicts with NestedType.
 	Type cty.Type
 
+	// NestedType indicates that the attribute is a NestedBlock-style object.
+	// This field conflicts with Type.
+	NestedType *Object
+
 	// Description is an English-language description of the purpose and
 	// usage of the attribute. A description should be concise and use only
 	// one or two sentences, leaving full definition to longer-form
@@ -72,6 +77,25 @@ type Attribute struct {
 	Deprecated bool
 }
 
+// Object represents the embedding of a structural object inside an Attribute.
+type Object struct {
+	// Attributes describes the nested attributes which may appear inside the
+	// Object.
+	Attributes map[string]*Attribute
+
+	// Nesting provides the nesting mode for this Object, which determines how
+	// many instances of the Object are allowed, how many labels it expects, and
+	// how the resulting data will be converted into a data structure.
+	Nesting NestingMode
+
+	// MinItems and MaxItems set, for the NestingList and NestingSet nesting
+	// modes, lower and upper limits on the number of child blocks allowed
+	// of the given type. If both are left at zero, no limit is applied.
+	// These fields are ignored for other nesting modes and must both be left
+	// at zero.
+	MinItems, MaxItems int
+}
+
 // NestedBlock represents the embedding of one block within another.
 type NestedBlock struct {
 	// Block is the description of the block that's nested.
@@ -98,6 +122,8 @@ type NestedBlock struct {
 // blocks.
 type NestingMode int
 
+// Object represents the embedding of a NestedBl
+
 //go:generate go run golang.org/x/tools/cmd/stringer -type=NestingMode
 
 const (