Extend swift-parser-cli with option to apply a static build configuration

Introduce the option "--build-configuration" to this test program. The
input is JSON for a static build configuration, and that configuration
will be applied to the parse tree to remove all inactive #if regions
before doing anything else with the parse command (printing
diagnostics, printing the tree, etc.).

Also add a "print" subcommand that prints back the tree after applying
whatever transformations are described above. One can use this to
implement a basic "preprocess" step that removes all inactive #if
regions from the source code.

Author: DougGregor

SwiftParserCLI/Package.swift

@@ -25,6 +25,7 @@ let package = Package(
         "InstructionCounter",
         .product(name: "SwiftBasicFormat", package: "swift-syntax"),
         .product(name: "SwiftDiagnostics", package: "swift-syntax"),
+        .product(name: "SwiftIfConfig", package: "swift-syntax"),
         .product(name: "SwiftOperators", package: "swift-syntax"),
         .product(name: "SwiftParser", package: "swift-syntax"),
         .product(name: "SwiftParserDiagnostics", package: "swift-syntax"),

SwiftParserCLI/Sources/swift-parser-cli/Commands/Print.swift

@@ -0,0 +1,34 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org 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 https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import ArgumentParser
+import SwiftParser
+import SwiftSyntax
+
+struct Print: ParsableCommand, ParseCommand {
+  static var configuration = CommandConfiguration(
+    commandName: "print",
+    abstract: "Print the parsed source file after applying any other arguments"
+  )
+
+  @OptionGroup
+  var arguments: ParseArguments
+
+  @Flag(name: .long, help: "Include trivia in the output")
+  var includeTrivia: Bool = false
+
+  func run() throws {
+    try withParsedSourceFile(wantDiagnostics: false) { (tree, _) in
+      print(tree.description)
+    }
+  }
+}

SwiftParserCLI/Sources/swift-parser-cli/Commands/PrintDiags.swift

@@ -28,13 +28,7 @@ struct PrintDiags: ParsableCommand, ParseCommand {
   var colorize: Bool = false
 
   func run() throws {
-    try sourceFileContents.withUnsafeBufferPointer { sourceBuffer in
-      let tree = Parser.parse(source: sourceBuffer)
-      var diags = ParseDiagnosticsGenerator.diagnostics(for: tree)
-      if foldSequences {
-        diags += foldAllSequences(tree).1
-      }
-
+    try withParsedSourceFile { (tree, diags) in
       var group = GroupedDiagnostics()
       group.addSourceFile(tree: tree, displayName: sourceFileName, diagnostics: diags)
       let annotatedSource = DiagnosticsFormatter.annotateSources(

SwiftParserCLI/Sources/swift-parser-cli/Commands/PrintTree.swift

@@ -27,17 +27,8 @@ struct PrintTree: ParsableCommand, ParseCommand {
   var includeTrivia: Bool = false
 
   func run() throws {
-    try sourceFileContents.withUnsafeBufferPointer { sourceBuffer in
-      let tree = Parser.parse(source: sourceBuffer)
-
-      let resultTree: Syntax
-      if foldSequences {
-        resultTree = foldAllSequences(tree).0
-      } else {
-        resultTree = Syntax(tree)
-      }
-
-      print(resultTree.debugDescription(includeTrivia: includeTrivia))
+    try withParsedSourceFile(wantDiagnostics: false) { (tree, _) in
+      print(tree.debugDescription(includeTrivia: includeTrivia))
     }
   }
 }

SwiftParserCLI/Sources/swift-parser-cli/ParseCommand.swift

@@ -11,6 +11,12 @@
 //===----------------------------------------------------------------------===//
 
 import ArgumentParser
+import Foundation
+import SwiftDiagnostics
+import SwiftIfConfig
+import SwiftParser
+import SwiftParserDiagnostics
+import SwiftSyntax
 
 struct ParseArguments: ParsableArguments {
   @Argument(help: "The source file that should be parsed; if omitted, use stdin")
@@ -21,6 +27,9 @@ struct ParseArguments: ParsableArguments {
 
   @Flag(name: .long, help: "Perform sequence folding with the standard operators")
   var foldSequences: Bool = false
+
+  @Option(help: "Apply the given static build configuration to the source text before further processing")
+  var buildConfiguration: String?
 }
 
 /// A command  that has arguments to parse source code
@@ -50,4 +59,52 @@ extension ParseCommand {
 
   /// Whether sequence folding using standard operators should be performed
   var foldSequences: Bool { arguments.foldSequences }
+
+  /// Parse the source file, applying any additional configuration options
+  /// such as sequence folding, and provide it to the given closure.
+  func withParsedSourceFile<R>(
+    wantDiagnostics: Bool = true,
+    body: (SourceFileSyntax, [Diagnostic]) throws -> R
+  ) throws -> R {
+    return try sourceFileContents.withUnsafeBufferPointer { sourceBuffer in
+      // Parse the sources
+      var tree = Parser.parse(source: sourceBuffer)
+
+      // If we want diagnostics, gather them from the parser.
+      var diags: [Diagnostic] = []
+      if wantDiagnostics {
+        diags += ParseDiagnosticsGenerator.diagnostics(for: tree)
+      }
+
+      // If we are supposed to fold sequences, do it now.
+      if foldSequences {
+        let (folded, foldDiags) = foldAllSequences(tree)
+
+        tree = folded.cast(SourceFileSyntax.self)
+        if wantDiagnostics {
+          diags += foldDiags
+        }
+      }
+
+      // If we are supposed to apply a build configuration, do it now.
+      if let buildConfiguration = arguments.buildConfiguration {
+        // Load the build configuration.
+        let buildConfigurationText = try Data(contentsOf: URL(fileURLWithPath: buildConfiguration))
+        let staticBuildConfiguration = try JSONDecoder().decode(
+          StaticBuildConfiguration.self,
+          from: buildConfigurationText
+        )
+
+        // Apply the build configuration.
+        let (configured, configuredDiags) = tree.removingInactive(in: staticBuildConfiguration)
+
+        tree = configured.cast(SourceFileSyntax.self)
+        if wantDiagnostics {
+          diags += configuredDiags
+        }
+      }
+
+      return try body(tree, diags)
+    }
+  }
 }

SwiftParserCLI/Sources/swift-parser-cli/swift-parser-cli.swift

@@ -32,6 +32,7 @@ class SwiftParserCli: ParsableCommand {
     subcommands: [
       BasicFormat.self,
       PerformanceTest.self,
+      Print.self,
       PrintDiags.self,
       PrintTree.self,
       Reduce.self,