Implement fileAffectsSwiftOrClangBuildSettings with the logic from LLBuildManifestBuilder

Instead of inspecting file extensions to decide whether a file might affect build settings, check which files are in directories that are affecting compilation. This is the same logic that `LLBuildManifestBuilder` uses and should be more stable. In particular, this stops us from reloading the package manifest in SourceKit-LSP when a header file is written to a `.build` directory.

rdar://128573306

Author: ahoppen

Sources/Build/BuildManifest/LLBuildManifestBuilder.swift

@@ -173,28 +173,11 @@ public class LLBuildManifestBuilder {
 
 extension LLBuildManifestBuilder {
     private func addPackageStructureCommand() {
-        let inputs = self.plan.graph.rootPackages.flatMap { package -> [Node] in
-            var inputs = package.modules
-                .map(\.sources.root)
-                .sorted()
-                .map { Node.directoryStructure($0) }
-
-            // Add the output paths of any prebuilds that were run, so that we redo the plan if they change.
-            var derivedSourceDirPaths: [AbsolutePath] = []
-            for result in self.plan.prebuildCommandResults.values.flatMap({ $0 }) {
-                derivedSourceDirPaths.append(contentsOf: result.outputDirectories)
+        let inputs = self.plan.inputs.map {
+            switch $0 {
+            case .directoryStructure(let path): return Node.directoryStructure(path)
+            case .file(let path): return Node.file(path)
             }
-            inputs.append(contentsOf: derivedSourceDirPaths.sorted().map { Node.directoryStructure($0) })
-
-            // FIXME: Need to handle version-specific manifests.
-            inputs.append(file: package.manifest.path)
-
-            // FIXME: This won't be the location of Package.resolved for multiroot packages.
-            inputs.append(file: package.path.appending("Package.resolved"))
-
-            // FIXME: Add config file as an input
-
-            return inputs
         }
 
         let name = "PackageStructure"
@@ -214,7 +197,7 @@ extension LLBuildManifestBuilder {
 extension LLBuildManifestBuilder {
     // Creates commands for copying all binary artifacts depended on in the plan.
     private func addBinaryDependencyCommands() {
-        // Make sure we don't have multiple copy commands for each destination by mapping each destination to 
+        // Make sure we don't have multiple copy commands for each destination by mapping each destination to
         // its source binary.
         var destinations = [AbsolutePath: AbsolutePath]()
         for target in self.plan.targetMap.values {

Sources/Build/BuildPlan/BuildPlan.swift

@@ -163,6 +163,14 @@ extension BuildParameters {
 
 /// A build plan for a package graph.
 public class BuildPlan: SPMBuildCore.BuildPlan {
+    /// Return value of `inputs()`
+    package enum Input {
+        /// Any file in this directory affects the build plan
+        case directoryStructure(AbsolutePath)
+        /// The file at the given path affects the build plan
+        case file(AbsolutePath)
+    }
+
     public enum Error: Swift.Error, CustomStringConvertible, Equatable {
         /// There is no buildable target in the graph.
         case noBuildableTarget
@@ -171,7 +179,7 @@ public class BuildPlan: SPMBuildCore.BuildPlan {
             switch self {
             case .noBuildableTarget:
                 return """
-                The package does not contain a buildable target. 
+                The package does not contain a buildable target.
                 Add at least one `.target` or `.executableTarget` to your `Package.swift`.
                 """
             }
@@ -654,6 +662,34 @@ public class BuildPlan: SPMBuildCore.BuildPlan {
         }
         return try description.symbolGraphExtractArguments()
     }
+
+    /// Returns the files and directories that affect the build process of this build plan.
+    package var inputs: [Input] {
+        var inputs: [Input] = []
+        for package in self.graph.rootPackages {
+            inputs += package.modules
+                .map(\.sources.root)
+                .sorted()
+                .map { .directoryStructure($0) }
+
+            // Add the output paths of any prebuilds that were run, so that we redo the plan if they change.
+            var derivedSourceDirPaths: [AbsolutePath] = []
+            for result in self.prebuildCommandResults.values.flatMap({ $0 }) {
+                derivedSourceDirPaths.append(contentsOf: result.outputDirectories)
+            }
+            inputs.append(contentsOf: derivedSourceDirPaths.sorted().map { .directoryStructure($0) })
+
+            // FIXME: Need to handle version-specific manifests.
+            inputs.append(.file(package.manifest.path))
+
+            // FIXME: This won't be the location of Package.resolved for multiroot packages.
+            inputs.append(.file(package.path.appending("Package.resolved")))
+
+            // FIXME: Add config file as an input
+
+        }
+        return inputs
+    }
 }
 
 extension Basics.Diagnostic {

Sources/SourceKitLSPAPI/BuildDescription.swift

@@ -103,9 +103,14 @@ private struct WrappedSwiftTargetBuildDescription: BuildTarget {
 public struct BuildDescription {
     private let buildPlan: Build.BuildPlan
 
+    /// The inputs of the build plan so we don't need to re-compute them  on every call to
+    /// `fileAffectsSwiftOrClangBuildSettings`.
+    private let inputs: [BuildPlan.Input]
+
     // FIXME: should not use `BuildPlan` in the public interface
     public init(buildPlan: Build.BuildPlan) {
         self.buildPlan = buildPlan
+        self.inputs = buildPlan.inputs
     }
 
     // FIXME: should not use `ResolvedTarget` in the public interface
@@ -142,4 +147,26 @@ public struct BuildDescription {
             getBuildTarget(for: $0, in: modulesGraph)
         }
     }
+
+    /// Returns `true` if the file at the given path might influence build settings for a `swiftc` or `clang` invocation
+    /// generated by SwiftPM.
+    public func fileAffectsSwiftOrClangBuildSettings(_ url: URL) -> Bool {
+        guard let filePath = try? AbsolutePath(validating: url.path) else {
+            return false
+        }
+
+        for input in self.inputs {
+            switch input {
+            case .directoryStructure(let path):
+                if path.isAncestor(of: filePath) {
+                    return true
+                }
+            case .file(let path):
+                if filePath == path {
+                    return true
+                }
+            }
+        }
+        return false
+    }
 }

Sources/Workspace/Workspace.swift

@@ -1240,15 +1240,6 @@ extension Workspace {
         }
     }
 
-    /// Returns `true` if the file at the given path might influence build settings for a `swiftc` or `clang` invocation
-    /// generated by SwiftPM.
-    public func fileAffectsSwiftOrClangBuildSettings(filePath: AbsolutePath, packageGraph: ModulesGraph) -> Bool {
-        // TODO: Implement a more sophisticated check that also verifies if the file is in the sources directories of the passed in `packageGraph`.
-        FileRuleDescription.builtinRules.contains { fileRuleDescription in
-            fileRuleDescription.match(path: filePath, toolsVersion: self.currentToolsVersion)
-        }
-    }
-
     public func acceptIdentityChange(
         package: PackageIdentity,
         version: Version,