Fix product lookup

Sources/PackageGraph/PackageGraph+Loading.swift

@@ -267,6 +267,7 @@ private func createResolvedPackages(
 
         var dependencies = OrderedCollections.OrderedDictionary<PackageIdentity, ResolvedPackageBuilder>()
         var dependenciesByNameForTargetDependencyResolution = [String: ResolvedPackageBuilder]()
+        var dependencyNamesForTargetDependencyResolutionOnly = [PackageIdentity: String]()
 
         // Establish the manifest-declared package dependencies.
         package.manifest.dependenciesRequired(for: packageBuilder.productFilter).forEach { dependency in
@@ -334,12 +335,14 @@ private func createResolvedPackages(
 
                 let nameForTargetDependencyResolution = dependency.explicitNameForTargetDependencyResolutionOnly ?? dependency.identity.description
                 dependenciesByNameForTargetDependencyResolution[nameForTargetDependencyResolution] = resolvedPackage
+                dependencyNamesForTargetDependencyResolutionOnly[resolvedPackage.package.identity] = nameForTargetDependencyResolution
 
                 dependencies[resolvedPackage.package.identity] = resolvedPackage
             }
         }
 
         packageBuilder.dependencies = Array(dependencies.values)
+        packageBuilder.dependencyNamesForTargetDependencyResolutionOnly = dependencyNamesForTargetDependencyResolutionOnly
 
         packageBuilder.defaultLocalization = package.manifest.defaultLocalization
 
@@ -441,7 +444,13 @@ private func createResolvedPackages(
 
         let productDependencyMap: [String: ResolvedProductBuilder]
         if lookupByProductIDs {
-            productDependencyMap = productDependencies.spm_createDictionary { ($0.product.identity, $0) }
+            productDependencyMap = try Dictionary(uniqueKeysWithValues: productDependencies.map {
+                guard let packageName = packageBuilder.dependencyNamesForTargetDependencyResolutionOnly[$0.packageBuilder.package.identity] else {
+                    throw InternalError("could not determine name for dependency on package '\($0.packageBuilder.package.identity)' from package '\(packageBuilder.package.identity)'")
+                }
+                let key = "\(packageName.lowercased())_\($0.product.name)"
+                return (key, $0)
+            })
         } else {
             productDependencyMap = try Dictionary(
                 productDependencies.map { ($0.product.name, $0) },
@@ -962,6 +971,9 @@ private final class ResolvedPackageBuilder: ResolvedBuilder<ResolvedPackage> {
     /// The dependencies of this package.
     var dependencies: [ResolvedPackageBuilder] = []
 
+    /// Map from package identity to the local name for target dependency resolution that has been given to that package through the dependency declaration.
+    var dependencyNamesForTargetDependencyResolutionOnly: [PackageIdentity: String] = [:]
+
     /// The defaultLocalization for this package.
     var defaultLocalization: String? = nil
 

Tests/PackageGraphTests/PackageGraphTests.swift

@@ -2550,6 +2550,43 @@ class PackageGraphTests: XCTestCase {
 
         XCTAssertEqual(observability.diagnostics.count, 0, "unexpected diagnostics: \(observability.diagnostics.map { $0.description })")
     }
+
+    func testCustomNameInPackageDependency() throws {
+        let fs = InMemoryFileSystem(emptyFiles:
+            "/Foo/Sources/Foo/source.swift",
+            "/Bar2/Sources/Bar/source.swift"
+        )
+
+        let observability = ObservabilitySystem.makeForTesting()
+        _ = try loadPackageGraph(
+            fileSystem: fs,
+            manifests: [
+                Manifest.createRootManifest(
+                    displayName: "Foo",
+                    path: .init(path: "/Foo"),
+                    toolsVersion: .v5_9,
+                    dependencies: [
+                        .fileSystem(deprecatedName: "Bar", path: "/Bar2"),
+                    ],
+                    targets: [
+                        TargetDescription(name: "Foo", dependencies: [.product(name: "Bar", package: "BAR")]),
+                    ]),
+                Manifest.createFileSystemManifest(
+                    displayName: "Bar",
+                    path: .init(path: "/Bar2"),
+                    toolsVersion: .v5_9,
+                    products: [
+                        ProductDescription(name: "Bar", type: .library(.automatic), targets: ["Bar"]),
+                    ],
+                    targets: [
+                        TargetDescription(name: "Bar"),
+                    ]),
+            ],
+            observabilityScope: observability.topScope
+        )
+
+        XCTAssertEqual(observability.diagnostics.count, 0, "unexpected diagnostics: \(observability.diagnostics.map { $0.description })")
+    }
 }