Fix running analyze on Xcode 11 build outputs (realm#2912)

Xcode 11 started using _response files_ [0] to avoid exceeding command
line length limits. For SwiftLint's analyzer rules to find which
compiler arguments are needed for a given file being analyzed, we first
need to expand these response files to their contents.

This was ported over from jpsim/SourceKitten#613

[0]: swiftlang/swift#16362

CHANGELOG.md

@@ -37,7 +37,9 @@
 
 #### Bug Fixes
 
-* None.
+* Fix running analyzer rules on the output of builds performed with
+  Xcode 11 or later.  
+  [JP Simard](https://github.com/jpsim)
 
 ## 0.35.0: Secondary Lint Trap
 

Source/swiftlint/Helpers/CompilerArgumentsExtractor.swift

@@ -6,7 +6,11 @@ struct CompilerArgumentsExtractor {
         var compilerInvocations = [String]()
         compilerLogs.enumerateLines { line, _ in
             if let swiftcIndex = line.range(of: "swiftc ")?.upperBound, line.contains(" -module-name ") {
-                compilerInvocations.append(String(line[swiftcIndex...]))
+                let invocation = line[swiftcIndex...]
+                    .components(separatedBy: " ")
+                    .expandingResponseFiles
+                    .joined(separator: " ")
+                compilerInvocations.append(invocation)
             }
         }
 
@@ -118,3 +122,20 @@ private func filter(arguments args: [String]) -> [String] {
         return $0
     }
 }
+
+private extension Array where Element == String {
+    /// Return the full list of compiler arguments, replacing any response files with their contents.
+    var expandingResponseFiles: [String] {
+        return flatMap { arg -> [String] in
+            guard arg.starts(with: "@") else {
+                return [arg]
+            }
+            let responseFile = String(arg.dropFirst())
+            return (try? String(contentsOf: URL(fileURLWithPath: responseFile))).flatMap {
+                $0.trimmingCharacters(in: .newlines)
+                  .components(separatedBy: "\n")
+                  .expandingResponseFiles
+            } ?? [arg]
+        }
+    }
+}