resource/schema: Initial package

[bflad]

Reference: #132
Reference: #326
Reference: #437
Reference: #491
Reference: #508
Reference: #532

This change introduces a new resource/schema package, which contains schema interfaces and types relevant to resources. This new schema implementation also provides strongly typed attributes, nested attributes, and blocks with customizable types. Nested attributes and blocks are exposed with a separate nested object for customization, plan modification, and validation.

The implementation leans heavily on the design choice of the framework being responsible for preventing provider developer runtime errors. The tailored fields no longer expose functionality that is not available for resources. The framework design will also raise compiler-time errors for errant typing of validators.

No changes are required for data handling in any other resource.Resource methods.

Example definition:

package test

import (
	"context"

	"github.com/bflad/terraform-plugin-framework-type-time/timetypes"
	"github.com/hashicorp/terraform-plugin-framework-validators/float64validator"
	"github.com/hashicorp/terraform-plugin-framework-validators/listvalidator"
	"github.com/hashicorp/terraform-plugin-framework-validators/stringvalidator"
	"github.com/hashicorp/terraform-plugin-framework/resource"
	"github.com/hashicorp/terraform-plugin-framework/resource/schema"
	"github.com/hashicorp/terraform-plugin-framework/schema/validator"
	"github.com/hashicorp/terraform-plugin-framework/types"
)

type ThingResource struct{}

func (r ThingResource) Schema(ctx context.Context, req resource.SchemaRequest, resp *resource.SchemaResponse) {
	resp.Schema = schema.Schema{
		Attributes: map[string]schema.Attribute{
			"string_attribute": schema.StringAttribute{
				Required: true,
				Validators: []validator.String{
					stringvalidator.LengthBetween(3, 256),
				},
			},
			"custom_string_attribute": schema.StringAttribute{
				CustomType: timetypes.RFC3339Type,
				Optional:   true,
			},
			"list_attribute": schema.ListAttribute{
				ElementType: types.StringType,
				Optional:    true,
			},
			"list_nested_attribute": schema.ListNestedAttribute{
				NestedObject: schema.NestedAttributeObject{
					Attributes: map[string]schema.Attribute{
						"bool_attribute": schema.BoolAttribute{
							Optional: true,
						},
					},
					Validators: []validator.Object{ /*...*/ },
				},
				Optional: true,
				Validators: []validator.List{
					listvalidator.SizeAtMost(2),
				},
			},
			"single_nested_attribute": schema.SingleNestedAttribute{
				Attributes: map[string]schema.Attribute{
					"int64_attribute": schema.Int64Attribute{
						Optional: true,
					},
				},
				Optional: true,
			},
		},
		Blocks: map[string]schema.Block{
			"list_block": schema.ListNestedBlock{
				NestedObject: schema.NestedBlockObject{
					Attributes: map[string]schema.Attribute{
						"float64_attribute": schema.Float64Attribute{
							Optional: true,
							Validators: []validator.Float64{
								float64validator.OneOf(1.2, 2.4),
							},
						},
					},
					Validators: []validator.Object{ /*...*/ },
				},
				Validators: []validator.List{
					listvalidator.SizeAtMost(2),
				},
			},
		},
	}
}

To migrate a resource schema:

• Add github.com/hashicorp/terraform-plugin-framework/resource/schema to the import statement
• Switch the resource.Resource implementation GetSchema method to Schema whose response includes a schema.Schema from the new package.

Prior implementation:

func (r ThingResource) GetSchema(ctx context.Context) (tfsdk.Schema, diag.Diagnostics) {
  return tfsdk.Schema{/* ... */}, nil
}

Migrated implementation:

func (r ThingResource) Schema(ctx context.Context, req resource.SchemaRequest, resp *resource.SchemaResponse) {
  resp.Schema = schema.Schema{/*...*/}
}

If the resource requires no schema, the method can be entirely empty.

• Switch map[string]tfsdk.Attribute with map[string]schema.Attribute
• Switch map[string]tfsdk.Block with map[string]schema.Block
• Switch individual attribute and block definitions. Unless the code was already taking advantage of custom attribute types (uncommon so far), the Type field will be removed and the map entries must declare the typed implementation, e.g. a tfsdk.Attribute with Type: types.StringType is equivalent to schema.StringAttribute. Custom attribute types can be specified via the CustomType field in each of the implementations.

Prior primitive type (types.BoolType, types.Float64Type, types.Int64Type, types.NumberType, types.StringType) attribute implementation:

// The "tfsdk.Attribute" could be omitted inside a map[string]tfsdk.Attribute
tfsdk.Attribute{
  Required: true,
  Type: types.StringType,
}

Migrated implementation:

// The schema.XXXAttribute must be declared inside map[string]schema.Attribute
schema.StringAttribute{
  Required: true,
}

Prior collection type (types.ListType, types.MapType, types.SetType) attribute implementation:

// The "tfsdk.Attribute" could be omitted inside a map[string]tfsdk.Attribute
tfsdk.Attribute{
  Required: true,
  Type: types.ListType{
    ElemType: types.StringType,
  },
}

Migrated implementation:

// The schema.XXXAttribute must be declared inside map[string]schema.Attribute
schema.ListAttribute{
  ElementType: types.StringType,
  Required: true,
}

Prior single nested attributes type (tfsdk.SingleNestedAttributes()) attribute implementation:

// The "tfsdk.Attribute" could be omitted inside a map[string]tfsdk.Attribute
tfsdk.Attribute{
  Attributes: tfsdk.SingleNestedAttributes(map[string]tfsdk.Attribute{/*...*/}),
  Required: true,
},

Migrated implementation:

// The schema.XXXAttribute must be declared inside map[string]schema.Attribute
schema.SingleNestedAttribute{
  Attributes: map[string]schema.Attribute{/*...*/},
  Required: true,
}

Prior collection nested attributes type (tfsdk.ListNestedAttributes(), tfsdk.MapNestedAttributes(), tfsdk.SetNestedAttributes()) attribute implementation:

// The "tfsdk.Attribute" could be omitted inside a map[string]tfsdk.Attribute
tfsdk.Attribute{
  Attributes: tfsdk.ListNestedAttributes(map[string]tfsdk.Attribute{/*...*/}),
  Required: true,
},

Migrated implementation:

// The schema.XXXAttribute must be declared inside map[string]schema.Attribute
schema.ListNestedAttribute{
  NestedObject: schema.NestedAttributeObject{
    Attributes: map[string]schema.Attribute{/*...*/},
  },
  Required: true,
}

Prior collection blocks type (tfsdk.Block) attribute implementation:

// The "tfsdk.Block" could be omitted inside a map[string]tfsdk.Block
tfsdk.Block{
  Attributes: map[string]tfsdk.Attribute{/*...*/},
  Blocks: map[string]tfsdk.Block{/*...*/},
  NestingMode: tfsdk.BlockNestingModeList,
},

Migrated implementation:

// The schema.XXXBlock must be declared inside map[string]schema.Block
schema.ListNestedBlock{
  NestedObject: schema.NestedBlockObject{
    Attributes: map[string]schema.Attribute{/*...*/},
    Blocks: map[string]schema.Block{/*...*/},
  },
}

[bendbennett]

LGTM 👍

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