[Explicit Module Builds] When '-explain-module-dependency' encounters the target Swift module, continue enumerating other possible paths

Author: artemcm

Sources/SwiftDriver/ExplicitModuleBuilds/InterModuleDependencies/CommonDependencyOperations.swift

@@ -252,22 +252,22 @@ extension InterModuleDependencyGraph {
 internal extension InterModuleDependencyGraph {
   func explainDependency(dependencyModuleName: String) throws -> [[ModuleDependencyId]]? {
     guard modules.contains(where: { $0.key.moduleName == dependencyModuleName }) else { return nil }
-    var results = [[ModuleDependencyId]]()
+    var results = Set<[ModuleDependencyId]>()
     try findAllPaths(source: .swift(mainModuleName),
                      to: dependencyModuleName,
                      pathSoFar: [.swift(mainModuleName)],
                      results: &results)
-    return Array(results)
+    return results.sorted(by: { $0.count < $1.count })
   }
 
 
   private func findAllPaths(source: ModuleDependencyId,
                             to moduleName: String,
                             pathSoFar: [ModuleDependencyId],
-                            results: inout [[ModuleDependencyId]]) throws {
+                            results: inout Set<[ModuleDependencyId]>) throws {
     let sourceInfo = try moduleInfo(of: source)
     // If the source is our target, we are done
-    guard source.moduleName != moduleName else {
+    if source.moduleName == moduleName {
       // If the source is a target Swift module, also check if it
       // depends on a corresponding Clang module with the same name.
       // If it does, add it to the path as well.
@@ -276,8 +276,7 @@ internal extension InterModuleDependencyGraph {
          dependencies.contains(.clang(moduleName)) {
         completePath.append(.clang(moduleName))
       }
-      results.append(completePath)
-      return
+      results.insert(completePath)
     }
 
     var allDependencies = sourceInfo.directDependencies ?? []

Tests/SwiftDriverTests/ExplicitModuleBuildTests.swift

@@ -2003,6 +2003,7 @@ final class ExplicitModuleBuildTests: XCTestCase {
         print(diag.behavior)
         print(diag.message)
       }
+      XCTAssertEqual(driver.diagnosticEngine.diagnostics.filter { $0.behavior == .note}.count, 2)
       XCTAssertTrue(driver.diagnosticEngine.diagnostics.contains { $0.behavior == .note &&
                                                                    $0.message.text == "[testTraceDependency] -> [A] -> [A](ObjC)"})
       XCTAssertTrue(driver.diagnosticEngine.diagnostics.contains { $0.behavior == .note &&