schema: Proof of concept Schema and Attribute validation

schema/attribute.go

@@ -1,9 +1,11 @@
 package schema
 
 import (
+	"context"
 	"errors"
 
 	"github.com/hashicorp/terraform-plugin-framework/attr"
+	"github.com/hashicorp/terraform-plugin-go/tfprotov6"
 	"github.com/hashicorp/terraform-plugin-go/tftypes"
 )
 
@@ -64,6 +66,9 @@ type Attribute struct {
 	// using this attribute, warning them that it is deprecated and
 	// instructing them on what upgrade steps to take.
 	DeprecationMessage string
+
+	// Validators defines validation functionality for the attribute.
+	Validators []AttributeValidator
 }
 
 // ApplyTerraform5AttributePathStep transparently calls
@@ -119,3 +124,62 @@ func (a Attribute) Equal(o Attribute) bool {
 	}
 	return true
 }
+
+func (a Attribute) Validate(ctx context.Context, req ValidateAttributeRequest, resp *ValidateAttributeResponse) {
+	if (a.Attributes == nil || len(a.Attributes.GetAttributes()) == 0) && a.Type == nil {
+		resp.Diagnostics = append(resp.Diagnostics, &tfprotov6.Diagnostic{
+			Severity:  tfprotov6.DiagnosticSeverityError,
+			Summary:   "Invalid Attribute Definition",
+			Detail:    "Attribute must define either Attributes or Type. This is always a problem with the provider and should be reported to the provider developer.",
+			Attribute: req.AttributePath,
+		})
+
+		return
+	}
+
+	if a.Attributes != nil && len(a.Attributes.GetAttributes()) > 0 && a.Type != nil {
+		resp.Diagnostics = append(resp.Diagnostics, &tfprotov6.Diagnostic{
+			Severity:  tfprotov6.DiagnosticSeverityError,
+			Summary:   "Invalid Attribute Definition",
+			Detail:    "Attribute cannot define both Attributes and Type. This is always a problem with the provider and should be reported to the provider developer.",
+			Attribute: req.AttributePath,
+		})
+
+		return
+	}
+
+	attributeConfig, err := req.Config.GetAttribute(ctx, req.AttributePath)
+
+	if err != nil {
+		resp.Diagnostics = append(resp.Diagnostics, &tfprotov6.Diagnostic{
+			Severity:  tfprotov6.DiagnosticSeverityError,
+			Summary:   "Attribute Value Error",
+			Detail:    "Attribute validation cannot read configuration value. Report this to the provider developer:\n\n" + err.Error(),
+			Attribute: req.AttributePath,
+		})
+
+		return
+	}
+
+	req.AttributeConfig = attributeConfig
+
+	for _, validator := range a.Validators {
+		validator.Validate(ctx, req, resp)
+	}
+
+	if a.Attributes != nil {
+		for nestedName, nestedAttr := range a.Attributes.GetAttributes() {
+			nestedAttrReq := ValidateAttributeRequest{
+				AttributePath: req.AttributePath.WithAttributeName(nestedName),
+				Config:        req.Config,
+			}
+			nestedAttrResp := &ValidateAttributeResponse{}
+
+			nestedAttr.Validate(ctx, nestedAttrReq, nestedAttrResp)
+
+			resp.Diagnostics = append(resp.Diagnostics, nestedAttrResp.Diagnostics...)
+		}
+	}
+
+	return
+}

schema/attribute_validation.go

@@ -0,0 +1,44 @@
+package schema
+
+import (
+	"context"
+
+	"github.com/hashicorp/terraform-plugin-framework/attr"
+	"github.com/hashicorp/terraform-plugin-framework/tfsdk"
+	"github.com/hashicorp/terraform-plugin-go/tfprotov6"
+	"github.com/hashicorp/terraform-plugin-go/tftypes"
+)
+
+// AttributeValidator describes reusable Attribute validation functionality.
+type AttributeValidator interface {
+	// Description describes the validation in plain text formatting.
+	Description(context.Context) string
+
+	// MarkdownDescription describes the validation in Markdown formatting.
+	MarkdownDescription(context.Context) string
+
+	// Validate performs the validation.
+	Validate(context.Context, ValidateAttributeRequest, *ValidateAttributeResponse)
+}
+
+// ValidateAttributeRequest repesents a request for
+type ValidateAttributeRequest struct {
+	// AttributePath contains the path of the attribute.
+	AttributePath *tftypes.AttributePath
+
+	// AttributeConfig contains the value of the attribute in the configuration.
+	AttributeConfig attr.Value
+
+	// Config contains the entire configuration of the data source, provider, or resource.
+	Config tfsdk.Config
+}
+
+// ValidateAttributeResponse represents a response to a
+// ValidateAttributeRequest. An instance of this response struct is
+// automatically passed through to each AttributeValidator.
+type ValidateAttributeResponse struct {
+	// Diagnostics report errors or warnings related to validating the data
+	// source configuration. An empty slice indicates success, with no warnings
+	// or errors generated.
+	Diagnostics []*tfprotov6.Diagnostic
+}

schema/schema.go

@@ -126,3 +126,19 @@ func (s Schema) AttributeAtPath(path *tftypes.AttributePath) (Attribute, error)
 	}
 	return a, nil
 }
+
+func (s Schema) Validate(ctx context.Context, req ValidateSchemaRequest, resp *ValidateSchemaResponse) {
+	for name, attribute := range s.Attributes {
+		attributeReq := ValidateAttributeRequest{
+			AttributePath: tftypes.NewAttributePath().WithAttributeName(name),
+			Config:        req.Config,
+		}
+		attributeResp := &ValidateAttributeResponse{}
+
+		attribute.Validate(ctx, attributeReq, attributeResp)
+
+		resp.Diagnostics = append(resp.Diagnostics, attributeResp.Diagnostics...)
+	}
+
+	return
+}

schema/schema_validation.go

@@ -0,0 +1,21 @@
+package schema
+
+import (
+	"github.com/hashicorp/terraform-plugin-framework/tfsdk"
+	"github.com/hashicorp/terraform-plugin-go/tfprotov6"
+)
+
+// ValidateSchemaRequest repesents a request for validating a Schema.
+type ValidateSchemaRequest struct {
+	// Config contains the entire configuration of the data source, provider, or resource.
+	Config tfsdk.Config
+}
+
+// ValidateSchemaResponse represents a response to a
+// ValidateSchemaRequest.
+type ValidateSchemaResponse struct {
+	// Diagnostics report errors or warnings related to validating the data
+	// source configuration. An empty slice indicates success, with no warnings
+	// or errors generated.
+	Diagnostics []*tfprotov6.Diagnostic
+}