Handle eval errors on the client side

plugin/fromproto/fromproto.go

@@ -307,9 +307,9 @@ func Error(err error) error {
 	case *proto.ErrorDetail:
 		switch t.Code {
 		case proto.ErrorCode_ERROR_CODE_UNKNOWN_VALUE:
-			return fmt.Errorf("%s%w", st.Message(), tflint.ErrUnknownValue)
+			return tflint.ErrUnknownValue
 		case proto.ErrorCode_ERROR_CODE_NULL_VALUE:
-			return fmt.Errorf("%s%w", st.Message(), tflint.ErrNullValue)
+			return tflint.ErrNullValue
 		case proto.ErrorCode_ERROR_CODE_UNEVALUABLE:
 			return fmt.Errorf("%s%w", st.Message(), tflint.ErrUnevaluable)
 		case proto.ErrorCode_ERROR_CODE_SENSITIVE:

plugin/plugin2host/client.go

@@ -11,6 +11,7 @@ import (
 	"github.com/hashicorp/hcl/v2/hclsyntax"
 	hcljson "github.com/hashicorp/hcl/v2/json"
 	"github.com/terraform-linters/tflint-plugin-sdk/hclext"
+	"github.com/terraform-linters/tflint-plugin-sdk/logger"
 	"github.com/terraform-linters/tflint-plugin-sdk/plugin/fromproto"
 	"github.com/terraform-linters/tflint-plugin-sdk/plugin/proto"
 	"github.com/terraform-linters/tflint-plugin-sdk/plugin/toproto"
@@ -331,6 +332,27 @@ func (c *GRPCClient) EvaluateExpr(expr hcl.Expression, ret interface{}, opts *tf
 		return err
 	}
 
+	if ty == cty.DynamicPseudoType {
+		return gocty.FromCtyValue(val, ret)
+	}
+
+	// Returns an error if the value cannot be decoded to a Go value (e.g. unknown value, null).
+	// This allows the caller to handle the value by the errors package.
+	err = cty.Walk(val, func(path cty.Path, v cty.Value) (bool, error) {
+		if !v.IsKnown() {
+			logger.Debug(fmt.Sprintf("unknown value found in %s", expr.Range()))
+			return false, tflint.ErrUnknownValue
+		}
+		if v.IsNull() {
+			logger.Debug(fmt.Sprintf("null value found in %s", expr.Range()))
+			return false, tflint.ErrNullValue
+		}
+		return true, nil
+	})
+	if err != nil {
+		return err
+	}
+
 	return gocty.FromCtyValue(val, ret)
 }
 

tflint/errors.go

@@ -9,10 +9,11 @@ import (
 // inside the plugin system, so you usually don't have to worry about it.
 var (
 	// ErrUnknownValue is an error when an unknown value is referenced
-	ErrUnknownValue = errors.New("")
+	ErrUnknownValue = errors.New("unknown value found")
 	// ErrNullValue is an error when null value is referenced
-	ErrNullValue = errors.New("")
+	ErrNullValue = errors.New("null value found")
 	// ErrUnevaluable is an error when a received expression has unevaluable references.
+	// Deprecated: This error is no longer returned since TFLint v0.41.
 	ErrUnevaluable = errors.New("")
 	// ErrSensitive is an error when a received expression contains a sensitive value.
 	ErrSensitive = errors.New("")