Add a warning/error option to schema validation

Add new schema options to configure the warning/error level of validation functions.
This allows the following functions to be used as a warning-level diag instead of a fatal error:
"ConflictsWith", "AtLeastOneOf", "ExactlyOneOf", "RequiredWith".

The ConditionsMode allows provider developers to toggle between "warning" and "error" level messages.
The ConditionsMessage is an optional additional message to be displayed to users at run time.

Author: dak1n1

helper/schema/schema.go

@@ -198,6 +198,14 @@ type Schema struct {
 	AtLeastOneOf  []string
 	RequiredWith  []string
 
+	// ConditionsMode specifies the behavior of the SDK when one of the
+	// above conditions are met. (ConflictsWith, ExactlyOneOf, etc).
+	// When set to WARNING, a warning message is displayed to the user.
+	// When set to ERROR (default), a fatal error is returned.
+	// Optionally, a message can be returned with the warning or error.
+	ConditionsMode    string
+	ConditionsMessage string
+
 	// When Deprecated is set, this attribute is deprecated.
 	//
 	// A deprecated field still works, but will probably stop working in near
@@ -1449,22 +1457,29 @@ func (m schemaMap) validate(
 		ok = raw != nil
 	}
 
+	var conditionsMode diag.Severity
+	if schema.ConditionsMode == strings.ToLower("warning") {
+		conditionsMode = diag.Warning
+	} else {
+		conditionsMode = diag.Error
+	}
+
 	err := validateExactlyOneAttribute(k, schema, c)
 	if err != nil {
 		return append(diags, diag.Diagnostic{
-			Severity:      diag.Error,
+			Severity:      conditionsMode,
 			Summary:       "ExactlyOne",
-			Detail:        err.Error(),
+			Detail:        fmt.Sprintf("%s %s", schema.ConditionsMessage, err.Error()),
 			AttributePath: path,
 		})
 	}
 
 	err = validateAtLeastOneAttribute(k, schema, c)
 	if err != nil {
 		return append(diags, diag.Diagnostic{
-			Severity:      diag.Error,
+			Severity:      conditionsMode,
 			Summary:       "AtLeastOne",
-			Detail:        err.Error(),
+			Detail:        fmt.Sprintf("%s %s", schema.ConditionsMessage, err.Error()),
 			AttributePath: path,
 		})
 	}
@@ -1494,9 +1509,9 @@ func (m schemaMap) validate(
 	err = validateRequiredWithAttribute(k, schema, c)
 	if err != nil {
 		return append(diags, diag.Diagnostic{
-			Severity:      diag.Error,
+			Severity:      conditionsMode,
 			Summary:       "RequiredWith",
-			Detail:        err.Error(),
+			Detail:        fmt.Sprintf("%s %s", schema.ConditionsMessage, err.Error()),
 			AttributePath: path,
 		})
 	}
@@ -1521,9 +1536,9 @@ func (m schemaMap) validate(
 	err = validateConflictingAttributes(k, schema, c)
 	if err != nil {
 		return append(diags, diag.Diagnostic{
-			Severity:      diag.Error,
+			Severity:      conditionsMode,
 			Summary:       "ConflictsWith",
-			Detail:        err.Error(),
+			Detail:        fmt.Sprintf("%s %s", schema.ConditionsMessage, err.Error()),
 			AttributePath: path,
 		})
 	}

helper/schema/schema_test.go

@@ -5991,7 +5991,33 @@ func TestSchemaMap_Validate(t *testing.T) {
 
 			Err: true,
 			Errors: []error{
-				fmt.Errorf(`Error: ConflictsWith: "blacklist": conflicts with whitelist`),
+				fmt.Errorf(`Error: ConflictsWith:  "blacklist": conflicts with whitelist`),
+			},
+		},
+
+		"Conflicting attributes generate warning": {
+			Schema: map[string]*Schema{
+				"whitelist": {
+					Type:     TypeString,
+					Optional: true,
+				},
+				"blacklist": {
+					Type:              TypeString,
+					Optional:          true,
+					ConflictsWith:     []string{"whitelist"},
+					ConditionsMode:    "warning",
+					ConditionsMessage: "This functionality will be removed in a later release.",
+				},
+			},
+
+			Config: map[string]interface{}{
+				"whitelist": "white-val",
+				"blacklist": "black-val",
+			},
+
+			Err: false,
+			Warnings: []string{
+				`Warning: ConflictsWith: This functionality will be removed in a later release. "blacklist": conflicts with whitelist`,
 			},
 		},
 
@@ -6087,8 +6113,8 @@ func TestSchemaMap_Validate(t *testing.T) {
 
 			Err: true,
 			Errors: []error{
-				fmt.Errorf(`Error: ConflictsWith: "blacklist": conflicts with greenlist`),
-				fmt.Errorf(`Error: ConflictsWith: "greenlist": conflicts with blacklist`),
+				fmt.Errorf(`Error: ConflictsWith:  "blacklist": conflicts with greenlist`),
+				fmt.Errorf(`Error: ConflictsWith:  "greenlist": conflicts with blacklist`),
 			},
 		},
 
@@ -6132,7 +6158,7 @@ func TestSchemaMap_Validate(t *testing.T) {
 
 			Err: true,
 			Errors: []error{
-				fmt.Errorf(`Error: ConflictsWith: "optional_att": conflicts with required_att`),
+				fmt.Errorf(`Error: ConflictsWith:  "optional_att": conflicts with required_att`),
 			},
 		},
 
@@ -6159,8 +6185,8 @@ func TestSchemaMap_Validate(t *testing.T) {
 
 			Err: true,
 			Errors: []error{
-				fmt.Errorf(`Error: ConflictsWith: "bar_att": conflicts with foo_att`),
-				fmt.Errorf(`Error: ConflictsWith: "foo_att": conflicts with bar_att`),
+				fmt.Errorf(`Error: ConflictsWith:  "bar_att": conflicts with foo_att`),
+				fmt.Errorf(`Error: ConflictsWith:  "foo_att": conflicts with bar_att`),
 			},
 		},