Change path contain and canonical algorithm

Author: Pouya Yarandi

Sources/SwiftProtobuf/Google_Protobuf_FieldMask+Extensions.swift

@@ -242,10 +242,12 @@ extension Google_Protobuf_FieldMask {
   public var canonical: Google_Protobuf_FieldMask {
     var mask = Google_Protobuf_FieldMask()
     let sortedPaths = self.paths.sorted()
-    var set = Set<String>()
     for path in sortedPaths {
-      if !contains(path, in: set) {
-        set.insert(path)
+      if let lastPath = mask.paths.last {
+        if path != lastPath, !path.hasPrefix("\(lastPath).") {
+          mask.paths.append(path)
+        }
+      } else {
         mask.paths.append(path)
       }
     }
@@ -314,7 +316,12 @@ extension Google_Protobuf_FieldMask {
   /// - Parameter path: Path to be checked.
   /// - Returns: Boolean determines is path covered.
   public func contains(_ path: String) -> Bool {
-    contains(path, in: pathsSet)
+    for _path in paths {
+      if path.hasPrefix("\(_path).") || _path == path {
+        return true
+      }
+    }
+    return false
   }
 
   // Set containing paths of FieldMask
@@ -328,18 +335,6 @@ extension Google_Protobuf_FieldMask {
       comps[0...$0].joined(separator: ".")
     }
   }
-
-  private func contains(
-    _ path: String,
-    in set: Set<String>
-  ) -> Bool {
-    for level in levels(path: path) {
-      if set.contains(level) {
-        return true
-      }
-    }
-    return false
-  }
 }
 
 extension Google_Protobuf_FieldMask {

Tests/SwiftProtobufTests/Test_FieldMask.swift

@@ -206,14 +206,17 @@ final class Test_FieldMask: XCTestCase, PBTestHelpers {
     // Checks canonincal form of field mask.
     // 1. Sub-message with parent in the paths should be excluded.
     // 2. Canonincal form should be sorted.
-    // 3. More nested levels of paths.
+    // 3. More nested levels of paths with duplicates.
+    // 4. Two siblings with their parent should be excluded.
     func testCanonicalFieldMask() {
         let m1 = Google_Protobuf_FieldMask(protoPaths: ["a.b", "a", "b"])
         XCTAssertEqual(m1.canonical.paths, ["a", "b"])
         let m2 = Google_Protobuf_FieldMask(protoPaths: ["b", "a"])
         XCTAssertEqual(m2.canonical.paths, ["a", "b"])
-        let m3 = Google_Protobuf_FieldMask(protoPaths: ["c", "a.b.c", "a.b", "a.b.c.d"])
+        let m3 = Google_Protobuf_FieldMask(protoPaths: ["c", "a.b.c", "a.b", "a.b", "a.b.c.d"])
         XCTAssertEqual(m3.canonical.paths, ["a.b", "c"])
+        let m4 = Google_Protobuf_FieldMask(protoPaths: ["a.c", "a", "a.b"])
+        XCTAssertEqual(m4.canonical.paths, ["a"])
     }
 
     // Checks `addPath` func of fieldMask with: