internal/fwschemadata: Migrate tfsdk GetAttribute and getAttributeVal…

…ue logic (hashicorp#453)

Reference: hashicorp#366

This change continues the migration of `tfsdk.Config`/`tfsdk.Plan`/`tfsdk.State` type logic into the `internal/fwschemadata` package `Data` type, so the implementation is shared and to potentially introduce other implementations.

internal/fwschemadata/data_get_at_path.go

@@ -0,0 +1,62 @@
+package fwschemadata
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/hashicorp/terraform-plugin-framework/attr"
+	"github.com/hashicorp/terraform-plugin-framework/diag"
+	"github.com/hashicorp/terraform-plugin-framework/internal/logging"
+	"github.com/hashicorp/terraform-plugin-framework/internal/reflect"
+	"github.com/hashicorp/terraform-plugin-framework/path"
+)
+
+// GetAtPath retrieves the attribute found at `path` and populates the
+// `target` with the value.
+func (d Data) GetAtPath(ctx context.Context, schemaPath path.Path, target any) diag.Diagnostics {
+	ctx = logging.FrameworkWithAttributePath(ctx, schemaPath.String())
+
+	attrValue, diags := d.ValueAtPath(ctx, schemaPath)
+
+	if diags.HasError() {
+		return diags
+	}
+
+	if attrValue == nil {
+		diags.AddAttributeError(
+			schemaPath,
+			"Config Read Error",
+			"An unexpected error was encountered trying to read an attribute from the configuration. This is always an error in the provider. Please report the following to the provider developer:\n\n"+
+				"Missing attribute value, however no error was returned. Preventing the panic from this situation.",
+		)
+		return diags
+	}
+
+	if reflect.IsGenericAttrValue(ctx, target) {
+		*(target.(*attr.Value)) = attrValue
+		return nil
+	}
+
+	raw, err := attrValue.ToTerraformValue(ctx)
+
+	if err != nil {
+		diags.AddAttributeError(
+			schemaPath,
+			"Error converting value",
+			fmt.Sprintf("An unexpected error was encountered converting a %T to its equivalent Terraform representation. This is always a bug in the provider.\n\n"+
+				"Error: %s", attrValue, err),
+		)
+		return diags
+	}
+
+	reflectDiags := reflect.Into(ctx, attrValue.Type(ctx), raw, target, reflect.Options{})
+
+	// reflect.Into does not have path information for its Diagnostics.
+	for idx, valueAsDiag := range reflectDiags {
+		reflectDiags[idx] = diag.WithPath(schemaPath, valueAsDiag)
+	}
+
+	diags.Append(reflectDiags...)
+
+	return diags
+}