Initial implementation of the CommaWhitespace rule and tests (swiftlang#51)

Author: atamez31

Diff for: Sources/Rules/CommaWhitespace.swift

@@ -14,5 +14,39 @@ import SwiftSyntax
 ///
 /// - SeeAlso: https://google.github.io/swift#horizontal-whitespace
 public final class CommaWhitespace: SyntaxFormatRule {
+  public override func visit(_ token: TokenSyntax) -> Syntax {
+    guard let next = token.nextToken else { return token }
 
+    // Commas own their trailing spaces, so ensure it only has 1 if there's
+    // another token on the same line.
+    if token.tokenKind == .comma && !next.leadingTrivia.containsNewlines {
+      let numSpaces = token.trailingTrivia.numberOfSpaces
+      if numSpaces > 1 {
+        diagnose(.removeSpacesAfterComma(count: numSpaces - 1), on: token)
+      }
+      else if numSpaces == 0 {
+        diagnose(.addSpaceAfterComma, on: token)
+      }
+      return token.withOneTrailingSpace()
+    }
+
+    // Otherwise, comma-adjacent tokens should have 0 spaces after.
+    if next.tokenKind == .comma && token.trailingTrivia.containsSpaces {
+      diagnose(.noSpacesBeforeComma, on: next)
+      return token.withTrailingTrivia(token.trailingTrivia.withoutSpaces())
+    }
+    return token
+  }
+}
+
+extension Diagnostic.Message {
+  static func removeSpacesAfterComma(count: Int) -> Diagnostic.Message {
+    let ending = count == 1 ? "" : "s"
+    return Diagnostic.Message(.warning, "remove \(count) space\(ending) after ','")
+  }
+
+  static let addSpaceAfterComma =
+    Diagnostic.Message(.warning, "add one space after ','")
+  static let noSpacesBeforeComma =
+    Diagnostic.Message(.warning, "remove spaces before ','")
 }

Diff for: Tests/SwiftFormatTests/CommaWhitespaceTests.swift

@@ -0,0 +1,57 @@
+import SwiftSyntax
+import XCTest
+
+@testable import Rules
+
+public class CommaWhitespaceTests: DiagnosingTestCase {
+  public func testInvalidFuncCommaWhiteSpace() {
+    XCTAssertFormatting(
+      CommaWhitespace.self,
+      input: """
+             func testComma(paramA: Bool,paramB: Bool ,paramC: Bool , paramD: Bool) -> Bool {
+
+             if paramA,
+                !paramB ,
+                paramC   ,
+                paramD {
+              return true
+                }
+             return false
+             }
+             """,
+      expected: """
+                func testComma(paramA: Bool, paramB: Bool, paramC: Bool, paramD: Bool) -> Bool {
+
+                if paramA,
+                   !paramB,
+                   paramC,
+                   paramD {
+                 return true
+                   }
+                return false
+                }
+                """)
+  }
+  
+  public func testInvalidDeclCommaWhiteSpace() {
+    XCTAssertFormatting(
+      CommaWhitespace.self,
+      input: """
+             let numA = [1,2,3]
+             let numB = [1 ,2 ,3]
+             let numC = [1 , 2 , 3]
+             """,
+      expected: """
+                let numA = [1, 2, 3]
+                let numB = [1, 2, 3]
+                let numC = [1, 2, 3]
+                """)
+  }
+  
+  #if !os(macOS)
+  static let allTests = [
+    CommaWhitespaceTests.testInvalidFuncCommaWhiteSpace,
+    CommaWhitespaceTests.testInvalidDeclCommaWhiteSpace,
+    ]
+  #endif
+}