Allow swiftformat directive in middle of comment

Sources/Formatter.swift

@@ -72,20 +72,21 @@ public class Formatter: NSObject {
     // Process a comment token (which may contain directives)
     func processCommentBody(_ comment: String, at index: Int) {
         var prefix = "swiftformat:"
-        guard comment.hasPrefix(prefix) else {
+        guard let range = comment.range(of: prefix) else {
             return
         }
+        let comment = String(comment[range.upperBound...])
         guard let directive = ["disable", "enable", "options"].first(where: {
-            comment.hasPrefix("\(prefix)\($0)")
+            comment.hasPrefix($0)
         }) else {
             let parts = comment.components(separatedBy: ":")
-            var directive = parts[1]
+            var directive = parts[0]
             if let range = directive.rangeOfCharacter(from: .whitespacesAndNewlines) {
                 directive = String(directive[..<range.lowerBound])
             }
             return fatalError("Unknown directive swiftformat:\(directive)", at: index)
         }
-        prefix += directive
+        prefix = directive
         wasNextDirective = comment.hasPrefix("\(prefix):next")
         let offset = (wasNextDirective ? "\(prefix):next" : prefix).endIndex
         let argumentsString = String(comment[offset...])

Tests/FormatterTests.swift

@@ -120,6 +120,12 @@ class FormatterTests: XCTestCase {
         XCTAssertEqual(try format(input, rules: FormatRules.default), output)
     }
 
+    func testDirectiveInMiddleOfComment() {
+        let input = "//fixme: swiftformat:disable spaceAroundOperators - bug\nlet foo : Int=5;"
+        let output = "// FIXME: swiftformat:disable spaceAroundOperators - bug\nlet foo : Int=5\n"
+        XCTAssertEqual(try format(input, rules: FormatRules.default), output)
+    }
+
     func testDisableAndReEnableRules() {
         let input = """
         // swiftformat:disable indent blankLinesBetweenScopes redundantSelf