Fix overlapping plugins/products build database access (#7273)

This regression was introduced in
https://github.com/apple/swift-package-manager/pull/7164/files#diff-7d5950f89d75bc14a591deb8270ebd32308c18248892c7abcb9d0ee3c6b14fd5L201.

We can restore the previous behavior in a hacky way by making sure that
build parameters passed to plugin builds and invocations have the
database path set in the same way as previously. This somewhat defeats
the point of tools/products build parameters isolation, but we're able
to isolate it only to a few lines in a single function.

I've added an explicit test case for this in new
`PluginsBuildPlanTests.swift` file, so we can be sure it doesn't regress
again.

Resolves rdar://120560817

Author: MaxDesiatov

Sources/Build/BuildOperation.swift

@@ -455,9 +455,16 @@ public final class BuildOperation: PackageStructureDelegate, SPMBuildCore.BuildS
         let prebuildCommandResults: [ResolvedTarget.ID: [PrebuildCommandResult]]
         // Invoke any build tool plugins in the graph to generate prebuild commands and build commands.
         if let pluginConfiguration, !self.productsBuildParameters.shouldSkipBuilding {
+            // Hacky workaround for rdar://120560817, but it replicates precisely enough the original behavior before
+            // products/tools build parameters were split. Ideally we want to have specify the correct path at the time
+            // when `toolsBuildParameters` is initialized, but we have too many places in the codebase where that's
+            // done, which makes it hard to realign them all at once.
+            var pluginsBuildParameters = self.toolsBuildParameters
+            pluginsBuildParameters.dataPath = pluginsBuildParameters.dataPath.parentDirectory.appending(components: ["plugins", "tools"])
             let buildOperationForPluginDependencies = BuildOperation(
-                productsBuildParameters: self.productsBuildParameters,
-                toolsBuildParameters: self.toolsBuildParameters,
+                // FIXME: this doesn't maintain the products/tools split cleanly
+                productsBuildParameters: pluginsBuildParameters,
+                toolsBuildParameters: pluginsBuildParameters,
                 cacheBuildManifest: false,
                 packageGraphLoader: { return graph },
                 additionalFileRules: self.additionalFileRules,
@@ -469,7 +476,7 @@ public final class BuildOperation: PackageStructureDelegate, SPMBuildCore.BuildS
             )
             buildToolPluginInvocationResults = try graph.invokeBuildToolPlugins(
                 outputDir: pluginConfiguration.workDirectory.appending("outputs"),
-                buildParameters: self.toolsBuildParameters,
+                buildParameters: pluginsBuildParameters,
                 additionalFileRules: self.additionalFileRules,
                 toolSearchDirectories: [self.toolsBuildParameters.toolchain.swiftCompilerPath.parentDirectory],
                 pkgConfigDirectories: self.pkgConfigDirectories,

Tests/BuildTests/PluginsBuildPlanTests.swift

@@ -0,0 +1,25 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2014-2024 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 Basics
+import SPMTestSupport
+import XCTest
+
+final class PluginsBuildPlanTests: XCTestCase {
+    func testBuildToolsDatabasePath() throws {
+        try fixture(name: "Miscellaneous/Plugins/MySourceGenPlugin") { fixturePath in
+            let (stdout, stderr) = try executeSwiftBuild(fixturePath)
+            XCTAssertMatch(stdout, .contains("Build complete!"))
+            XCTAssertTrue(localFileSystem.exists(fixturePath.appending(RelativePath(".build/plugins/tools/build.db"))))
+        }
+    }
+}