TrailingCommaRule only triggers when multi-line

CHANGELOG.md

@@ -6,7 +6,11 @@
 
 ##### Enhancements
 
-* None.
+* `TrailingCommaRule` now only triggers when a declaration is multi-line
+  when using `mandatory_comma: true`.  
+  [Marcelo Fabri](https://github.com/marcelofabri)
+  [#910](https://github.com/realm/SwiftLint/issues/910)
+  [#911](https://github.com/realm/SwiftLint/issues/911)
 
 ##### Bug Fixes
 

Source/SwiftLintFramework/Rules/TrailingCommaRule.swift

@@ -22,7 +22,8 @@ public struct TrailingCommaRule: ASTRule, ConfigurationProviderRule {
             "let foo = [1, 2, 3]\n",
             "let foo = []\n",
             "let foo = [:]\n",
-            "let foo = [1: 2, 2: 3]\n"
+            "let foo = [1: 2, 2: 3]\n",
+            "let foo = [Void]()\n"
         ],
         triggeringExamples: [
             "let foo = [1, 2, 3↓,]\n",
@@ -61,6 +62,13 @@ public struct TrailingCommaRule: ASTRule, ConfigurationProviderRule {
             return []
         }
 
+        if let (startLine, _) =  file.contents.lineAndCharacterForByteOffset(bodyOffset),
+            (endLine, _) =  file.contents.lineAndCharacterForByteOffset(lastPosition)
+            where configuration.mandatoryComma && startLine == endLine {
+            // shouldn't trigger if mandatory comma style and is a single-line declaration 
+            return []
+        }
+
         let length = bodyLength + bodyOffset - lastPosition
         let contentsAfterLastElement = file.contents
             .substringWithByteRange(start: lastPosition, length: length) ?? ""

Tests/SwiftLintFramework/RulesTests.swift

@@ -265,14 +265,21 @@ class RulesTests: XCTestCase {
                 "let foo = [1, 2, 3, ]\n",
                 "let foo = [1, 2, 3   ,]\n",
                 "let foo = [1: 2, 2: 3, ]\n",
-                "struct Bar {\n let foo = [1: 2, 2: 3,]\n}\n"
+                "struct Bar {\n let foo = [1: 2, 2: 3,]\n}\n",
+                "let foo = [Void]()\n",
+                "let foo = [(Void, Void)]()\n",
+                "let foo = [1, 2, 3]\n",
+                "let foo = [1: 2, 2: 3]\n",
+                "let foo = [1: 2, 2: 3   ]\n",
+                "struct Bar {\n let foo = [1: 2, 2: 3]\n}\n",
+                "let foo = [1, 2, 3] + [4, 5, 6]\n"
             ],
             triggeringExamples: [
-                "let foo = [1, 2, 3↓]\n",
-                "let foo = [1: 2, 2: 3↓]\n",
-                "let foo = [1: 2, 2: 3↓   ]\n",
-                "struct Bar {\n let foo = [1: 2, 2: 3↓]\n}\n",
-                "let foo = [1, 2, 3↓] + [4, 5, 6↓]\n"
+                "let foo = [1, 2,\n 3↓]\n",
+                "let foo = [1: 2,\n 2: 3↓]\n",
+                "let foo = [1: 2,\n 2: 3↓   ]\n",
+                "struct Bar {\n let foo = [1: 2,\n 2: 3↓]\n}\n",
+                "let foo = [1, 2,\n 3↓] + [4,\n 5, 6↓]\n"
             ]
         )