Do not use product identifier based lookup for older tools-versions (#6793)

When we introduced module aliasing, we tried to paper over the fact that there are no product aliases by changing the lookup under certain conditions. It looks like one of these conditions is "one package in the graph uses aliasing" which breaks if the graph contains any packages with pre-5.2 tools-versions because they lack the information to do a identity based lookup.

This changes opts packages with older tools-versions out of the identity based lookup. This implies that it is not possible to use aliasing in certain situations, but that seems preferrable to not being to use aliasing at all in affected package graphs.

rdar://113506853

Author: neonichu

Sources/PackageGraph/PackageGraph+Loading.swift

@@ -402,7 +402,11 @@ private func createResolvedPackages(
         }
     }
 
-    let dupProductsChecker = DuplicateProductsChecker(packageBuilders: packageBuilders)
+    let dupProductsChecker = DuplicateProductsChecker(
+        packageBuilders: packageBuilders,
+        moduleAliasingUsed: moduleAliasingUsed,
+        observabilityScope: observabilityScope
+    )
     try dupProductsChecker.run(lookupByProductIDs: moduleAliasingUsed, observabilityScope: observabilityScope)
 
     // The set of all target names.
@@ -430,7 +434,8 @@ private func createResolvedPackages(
                 return false
             })
 
-        let lookupByProductIDs = packageBuilder.package.manifest.disambiguateByProductIDs || moduleAliasingUsed
+        let packageDoesNotSupportProductAliases = packageBuilder.package.doesNotSupportProductAliases
+        let lookupByProductIDs = !packageDoesNotSupportProductAliases && (packageBuilder.package.manifest.disambiguateByProductIDs || moduleAliasingUsed)
 
         // Get all the products from dependencies of this package.
         let productDependencies = packageBuilder.dependencies
@@ -457,9 +462,11 @@ private func createResolvedPackages(
                 productDependencies.map { ($0.product.name, $0) },
                 uniquingKeysWith: { lhs, _ in
                     let duplicates = productDependencies.filter { $0.product.name == lhs.product.name }
-                    throw PackageGraphError.duplicateProduct(
-                        product: lhs.product.name,
-                        packages: duplicates.map(\.packageBuilder.package)
+                    throw emitDuplicateProductDiagnostic(
+                        productName: lhs.product.name,
+                        packages: duplicates.map(\.packageBuilder.package),
+                        moduleAliasingUsed: moduleAliasingUsed,
+                        observabilityScope: observabilityScope
                     )
                 }
             )
@@ -600,6 +607,31 @@ private func createResolvedPackages(
     return try packageBuilders.map{ try $0.construct() }
 }
 
+private func emitDuplicateProductDiagnostic(
+    productName: String,
+    packages: [Package],
+    moduleAliasingUsed: Bool,
+    observabilityScope: ObservabilityScope
+) -> PackageGraphError {
+    if moduleAliasingUsed {
+        packages.filter { $0.doesNotSupportProductAliases }.forEach {
+            // Emit an additional warning about product aliasing in case of older tools-versions.
+            observabilityScope.emit(warning: "product aliasing requires tools-version 5.2 or later, so it is not supported by '\($0.identity.description)'")
+        }
+    }
+    return PackageGraphError.duplicateProduct(
+        product: productName,
+        packages: packages
+    )
+}
+
+fileprivate extension Package {
+    var doesNotSupportProductAliases: Bool {
+        // We can never use the identity based lookup for older packages because they lack the necessary information.
+        return self.manifest.toolsVersion < .v5_2
+    }
+}
+
 fileprivate struct Pair: Hashable {
     let package1: Package
     let package2: Package
@@ -625,11 +657,16 @@ private class DuplicateProductsChecker {
     var packageIDToBuilder = [PackageIdentity: ResolvedPackageBuilder]()
     var checkedPkgIDs = [PackageIdentity]()
 
-    init(packageBuilders: [ResolvedPackageBuilder]) {
+    let moduleAliasingUsed: Bool
+    let observabilityScope: ObservabilityScope
+
+    init(packageBuilders: [ResolvedPackageBuilder], moduleAliasingUsed: Bool, observabilityScope: ObservabilityScope) {
         for packageBuilder in packageBuilders {
             let pkgID = packageBuilder.package.identity
             self.packageIDToBuilder[pkgID] = packageBuilder
         }
+        self.moduleAliasingUsed = moduleAliasingUsed
+        self.observabilityScope = observabilityScope
     }
 
     func run(lookupByProductIDs: Bool = false, observabilityScope: ObservabilityScope) throws {
@@ -657,9 +694,11 @@ private class DuplicateProductsChecker {
             }
             for (depIDOrName, depPkgs) in productToPkgMap.filter({Set($0.value).count > 1}) {
                 let name = depIDOrName.components(separatedBy: "_").dropFirst().joined(separator: "_")
-                throw PackageGraphError.duplicateProduct(
-                    product: name.isEmpty ? depIDOrName : name,
-                    packages: depPkgs.compactMap{ packageIDToBuilder[$0]?.package }
+                throw emitDuplicateProductDiagnostic(
+                    productName: name.isEmpty ? depIDOrName : name,
+                    packages: depPkgs.compactMap{ packageIDToBuilder[$0]?.package },
+                    moduleAliasingUsed: self.moduleAliasingUsed,
+                    observabilityScope: self.observabilityScope
                 )
             }
         }
@@ -683,9 +722,11 @@ private class DuplicateProductsChecker {
 
         let duplicates = productToPkgMap.filter{ $0.value.count > 1 }
         for (productName, pkgs) in duplicates {
-            throw PackageGraphError.duplicateProduct(
-                product: productName,
-                packages: pkgs.compactMap{ packageIDToBuilder[$0]?.package }
+            throw emitDuplicateProductDiagnostic(
+                productName: productName,
+                packages: pkgs.compactMap{ packageIDToBuilder[$0]?.package },
+                moduleAliasingUsed: self.moduleAliasingUsed,
+                observabilityScope: self.observabilityScope
             )
         }
     }