[NFC] Remove redundant DependencyResolver protocol (#7127)

### Motivation:

This protocol doesn't define any requirements and was used for
nemaspacing a single tuple typealias. Instead of typealiasing this
fairly complex and pervasively used tuple, we should define a separate
struct for it. Then the protocol itself can be removed as completely
unused.

### Modifications:

Defined new `struct DependencyResolverBinding` with cleanly named
fields, which now avoids expressions that look like `binding.binding`
and re-declaration of this tuple in multiple places.

One other `typealias` in `protocol DependencyResolver` is unused, thus
the whole protocol is unused and now can be removed.

Also used this as an opportunity to clean up file naming and directory
layout in the `PackageGraph` module.


### Result:

This confusing protocol is removed from the codebase. Readability is
improved with explicit struct field names instead of ad-hoc tuple use.
Directory layout makes it more obvious the purpose of specific files for
potential new contributors and for existing contributors when reviewing
code retrospectively.

Author: MaxDesiatov

Sources/PackageGraph/CMakeLists.txt

@@ -9,8 +9,6 @@
 add_library(PackageGraph
   BoundVersion.swift
   DependencyMirrors.swift
-  DependencyResolutionNode.swift
-  DependencyResolver.swift
   Diagnostics.swift
   GraphLoadingNode.swift
   ModuleAliasTracker.swift
@@ -21,17 +19,21 @@ add_library(PackageGraph
   PackageModel+Extensions.swift
   PackageRequirement.swift
   PinsStore.swift
-  PubGrub/Assignment.swift
-  PubGrub/ContainerProvider.swift
-  PubGrub/DiagnosticReportBuilder.swift
-  PubGrub/Incompatibility.swift
-  PubGrub/PartialSolution.swift
-  PubGrub/PubGrubDependencyResolver.swift
-  PubGrub/PubGrubPackageContainer.swift
-  PubGrub/Term.swift  
-  ResolvedPackage.swift
-  ResolvedProduct.swift
-  ResolvedTarget.swift
+  Resolution/PubGrub/Assignment.swift
+  Resolution/PubGrub/ContainerProvider.swift
+  Resolution/PubGrub/DiagnosticReportBuilder.swift
+  Resolution/PubGrub/Incompatibility.swift
+  Resolution/PubGrub/PartialSolution.swift
+  Resolution/PubGrub/PubGrubDependencyResolver.swift
+  Resolution/PubGrub/PubGrubPackageContainer.swift
+  Resolution/PubGrub/Term.swift
+  Resolution/DependencyResolutionNode.swift
+  Resolution/DependencyResolverBinding.swift
+  Resolution/DependencyResolverDelegate.swift
+  Resolution/DependencyResolverError.swift
+  Resolution/ResolvedPackage.swift
+  Resolution/ResolvedProduct.swift
+  Resolution/ResolvedTarget.swift
   Version+Extensions.swift
   VersionSetSpecifier.swift)
 target_link_libraries(PackageGraph PUBLIC

Sources/PackageGraph/GraphLoadingNode.swift

@@ -18,7 +18,7 @@ import PackageModel
 ///
 /// This node uses the product filter that was already finalized during resolution.
 ///
-/// - SeeAlso: DependencyResolutionNode
+/// - SeeAlso: ``DependencyResolutionNode``
 public struct GraphLoadingNode: Equatable, Hashable {
 
     /// The package identity.

…kageGraph/DependencyResolutionNode.swift …esolution/DependencyResolutionNode.swiftSources/PackageGraph/DependencyResolutionNode.swift renamed to Sources/PackageGraph/Resolution/DependencyResolutionNode.swift Sources/PackageGraph/DependencyResolutionNode.swift renamed to Sources/PackageGraph/Resolution/DependencyResolutionNode.swift

@@ -18,7 +18,7 @@ import struct TSCUtility.Version
 ///
 /// See the documentation of each case for more detailed descriptions of each kind and how they interact.
 ///
-/// - SeeAlso: `GraphLoadingNode`
+/// - SeeAlso: ``GraphLoadingNode``
 public enum DependencyResolutionNode {
 
     /// An empty package node.

Sources/PackageGraph/Resolution/DependencyResolverBinding.swift

@@ -0,0 +1,20 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2014-2023 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import enum PackageModel.ProductFilter
+import struct PackageModel.PackageReference
+
+public struct DependencyResolverBinding {
+    public let package: PackageReference
+    public let boundVersion: BoundVersion
+    public let products: ProductFilter
+}

…es/PackageGraph/DependencyResolver.swift …olution/DependencyResolverDelegate.swiftSources/PackageGraph/DependencyResolver.swift renamed to Sources/PackageGraph/Resolution/DependencyResolverDelegate.swift Sources/PackageGraph/DependencyResolver.swift renamed to Sources/PackageGraph/Resolution/DependencyResolverDelegate.swift

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift open source project
 //
-// Copyright (c) 2014-2017 Apple Inc. and the Swift project authors
+// Copyright (c) 2014-2023 Apple Inc. and the Swift project authors
 // Licensed under Apache License v2.0 with Runtime Library Exception
 //
 // See http://swift.org/LICENSE.txt for license information
@@ -16,25 +16,6 @@ import PackageModel
 
 import struct TSCUtility.Version
 
-public protocol DependencyResolver {
-    typealias Binding = (package: PackageReference, binding: BoundVersion, products: ProductFilter)
-    typealias Delegate = DependencyResolverDelegate
-}
-
-public enum DependencyResolverError: Error, Equatable {
-     /// A revision-based dependency contains a local package dependency.
-    case revisionDependencyContainsLocalPackage(dependency: String, localPackage: String)
-}
-
-extension DependencyResolverError: CustomStringConvertible {
-    public var description: String {
-        switch self {
-        case .revisionDependencyContainsLocalPackage(let dependency, let localPackage):
-            return "package '\(dependency)' is required using a revision-based requirement and it depends on local package '\(localPackage)', which is not supported"
-        }
-    }
-}
-
 public protocol DependencyResolverDelegate {
     func willResolve(term: Term)
     func didResolve(term: Term, version: Version, duration: DispatchTimeInterval)
@@ -44,7 +25,7 @@ public protocol DependencyResolverDelegate {
     func satisfied(term: Term, by assignment: Assignment, incompatibility: Incompatibility)
     func partiallySatisfied(term: Term, by assignment: Assignment, incompatibility: Incompatibility, difference: Term)
     func failedToResolve(incompatibility: Incompatibility)
-    func solved(result: [DependencyResolver.Binding])
+    func solved(result: [DependencyResolverBinding])
 }
 
 public struct ObservabilityDependencyResolverDelegate: DependencyResolverDelegate {
@@ -82,9 +63,9 @@ public struct ObservabilityDependencyResolverDelegate: DependencyResolverDelegat
         self.debug("\(term) is partially satisfied by '\(assignment)', which is caused by '\(assignment.cause?.description ?? "unknown cause")'. new incompatibility \(incompatibility)")
     }
 
-    public func solved(result: [DependencyResolver.Binding]) {
-        for (package, binding, _) in result {
-            self.debug("solved '\(package.identity)' (\(package.locationString)) at '\(binding)'")
+    public func solved(result: [DependencyResolverBinding]) {
+        for binding in result {
+            self.debug("solved '\(binding.package.identity)' (\(binding.package.locationString)) at '\(binding.boundVersion)'")
         }
         self.debug("dependency resolution complete!")
     }
@@ -129,7 +110,7 @@ public struct MultiplexResolverDelegate: DependencyResolverDelegate {
         underlying.forEach { $0.failedToResolve(incompatibility: incompatibility)  }
     }
 
-    public func solved(result: [(package: PackageReference, binding: BoundVersion, products: ProductFilter)]) {
+    public func solved(result: [DependencyResolverBinding]) {
         underlying.forEach { $0.solved(result: result)  }
     }
 

Sources/PackageGraph/Resolution/DependencyResolverError.swift

@@ -0,0 +1,27 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2014-2023 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import Foundation
+
+public enum DependencyResolverError: Error, Equatable {
+     /// A revision-based dependency contains a local package dependency.
+    case revisionDependencyContainsLocalPackage(dependency: String, localPackage: String)
+}
+
+extension DependencyResolverError: CustomStringConvertible {
+    public var description: String {
+        switch self {
+        case .revisionDependencyContainsLocalPackage(let dependency, let localPackage):
+            return "package '\(dependency)' is required using a revision-based requirement and it depends on local package '\(localPackage)', which is not supported"
+        }
+    }
+}