helper/schema: ValidateFunc

Allows provider authors to implement arbitrary per-field validation
warnings or errors.

helper/schema/schema.go

@@ -131,6 +131,9 @@ type Schema struct {
 	// This string is the message shown to the user with instructions on
 	// what do to about the removed attribute.
 	Removed string
+
+	// ValidateFunc allows individual fields to validate
+	ValidateFunc SchemaValidateFunc
 }
 
 // SchemaDefaultFunc is a function called to return a default value for
@@ -173,6 +176,10 @@ type SchemaSetFunc func(interface{}) int
 // to be stored in the state.
 type SchemaStateFunc func(interface{}) string
 
+// SchemaValidateFunc is a function used to validate a single field in the
+// schema.
+type SchemaValidateFunc func(interface{}) ([]string, []error)
+
 func (s *Schema) GoString() string {
 	return fmt.Sprintf("*%#v", *s)
 }
@@ -1176,6 +1183,16 @@ func (m schemaMap) validateType(
 			"%q: [REMOVED] %s", k, schema.Removed))
 	}
 
+	if schema.ValidateFunc != nil {
+		ws2, es2 := schema.ValidateFunc(raw)
+		for _, w := range ws2 {
+			ws = append(ws, fmt.Sprintf("%q: %s", k, w))
+		}
+		for _, e := range es2 {
+			es = append(es, fmt.Errorf("%q: %s", k, e))
+		}
+	}
+
 	return ws, es
 }
 

helper/schema/schema_test.go

@@ -3399,7 +3399,43 @@ func TestSchemaMap_Validate(t *testing.T) {
 
 			Err: true,
 			Errors: []error{
-				fmt.Errorf("\"optional_att\": conflicts with required_att (\"required-val\")"),
+				fmt.Errorf(`"optional_att": conflicts with required_att ("required-val")`),
+			},
+		},
+
+		"Good with ValidateFunc": {
+			Schema: map[string]*Schema{
+				"validate_me": &Schema{
+					Type:     TypeString,
+					Required: true,
+					ValidateFunc: func(v interface{}) (ws []string, es []error) {
+						return
+					},
+				},
+			},
+			Config: map[string]interface{}{
+				"validate_me": "valid",
+			},
+			Err: false,
+		},
+
+		"Bad with ValidateFunc": {
+			Schema: map[string]*Schema{
+				"validate_me": &Schema{
+					Type:     TypeString,
+					Required: true,
+					ValidateFunc: func(v interface{}) (ws []string, es []error) {
+						es = append(es, fmt.Errorf("something is not right here"))
+						return
+					},
+				},
+			},
+			Config: map[string]interface{}{
+				"validate_me": "invalid",
+			},
+			Err: true,
+			Errors: []error{
+				fmt.Errorf(`"validate_me": something is not right here`),
 			},
 		},
 	}