Add option to build a single dynamic library containing all swift-syntax modules

My previous approach of building each product as a dynamic library did not work because SwiftPM includes symbols from all dependencies in each `.dll`. Because of this, we ended up with duplicate symbols for each type in eg. SwiftSyntax at runtime.

Build a single `.dll` with all required products instead to avoid that issue.

To enforce that this is an internal target that should not be relied upon, only enable it when an environment variable is set.

Author: ahoppen

Contributor Documentation/Environment variables.md

@@ -7,7 +7,7 @@ The following environment variables can be used to control some behavior in swif
 - `SWIFT_BUILD_SCRIPT_ENVIRONMENT`: Enable assertions in release builds and remove the dependency of swift-syntax on os_log.
 - `SWIFTCI_USE_LOCAL_DEPS`: Assume that all of SourceKit-LSP’s dependencies are checked out next to it and use those instead of cloning the repositories. Primarily intended for CI environments that check out related branches.
 - `SWIFTPARSER_ENABLE_ALTERNATE_TOKEN_INTROSPECTION`: Mutate the input of `assertParse` test cases. See [CONTRIBUTING](../CONTRIBUTING.md) for more information.
-- `SWIFTSYNTAX_BUILD_DYNAMIC_LIBRARIES`: Build all libraries as *dynamic* instead of *automatic*. This allows us to build swift-syntax as dynamic libraries, which in turn allows us to build SourceKit-LSP using SwiftPM on Windows. Linking swift-syntax statically into sourcekit-lsp exceeds the maximum number of exported symbols on Windows.
+- `SWIFTSYNTAX_BUILD_DYNAMIC_LIBRARY`: Instead of building object files for all modules to be statically linked, build a single dynamic library. This allows us to build swift-syntax as dynamic libraries, which in turn allows us to build SourceKit-LSP using SwiftPM on Windows. Linking swift-syntax statically into sourcekit-lsp exceeds the maximum number of exported symbols on Windows.
 - `SWIFTSYNTAX_ENABLE_RAWSYNTAX_VALIDATION`: Check that the layout of the syntax tree is correct when creating or modifying nodes. See [CONTRIBUTING](../CONTRIBUTING.md) for more information.
 
 ## Testing

Package.swift

@@ -3,6 +3,48 @@
 import Foundation
 import PackageDescription
 
+let products: [Product]
+
+if buildDynamicLibrary {
+  products = [
+    .library(
+      name: "_SwiftSyntaxDynamic",
+      type: .dynamic,
+      targets: [
+        "SwiftBasicFormat",
+        "SwiftDiagnostics",
+        "SwiftIDEUtils",
+        "SwiftParser",
+        "SwiftParserDiagnostics",
+        "SwiftRefactor",
+        "SwiftSyntax",
+        "SwiftSyntaxBuilder",
+      ]
+    )
+  ]
+} else {
+  products = [
+    .library(name: "SwiftBasicFormat", targets: ["SwiftBasicFormat"]),
+    .library(name: "SwiftCompilerPlugin", targets: ["SwiftCompilerPlugin"]),
+    .library(name: "SwiftDiagnostics", targets: ["SwiftDiagnostics"]),
+    .library(name: "SwiftIDEUtils", targets: ["SwiftIDEUtils"]),
+    .library(name: "SwiftIfConfig", targets: ["SwiftIfConfig"]),
+    .library(name: "SwiftLexicalLookup", targets: ["SwiftLexicalLookup"]),
+    .library(name: "SwiftOperators", targets: ["SwiftOperators"]),
+    .library(name: "SwiftParser", targets: ["SwiftParser"]),
+    .library(name: "SwiftParserDiagnostics", targets: ["SwiftParserDiagnostics"]),
+    .library(name: "SwiftRefactor", targets: ["SwiftRefactor"]),
+    .library(name: "SwiftSyntax", targets: ["SwiftSyntax"]),
+    .library(name: "SwiftSyntaxBuilder", targets: ["SwiftSyntaxBuilder"]),
+    .library(name: "SwiftSyntaxMacros", targets: ["SwiftSyntaxMacros"]),
+    .library(name: "SwiftSyntaxMacroExpansion", targets: ["SwiftSyntaxMacroExpansion"]),
+    .library(name: "SwiftSyntaxMacrosTestSupport", targets: ["SwiftSyntaxMacrosTestSupport"]),
+    .library(name: "SwiftSyntaxMacrosGenericTestSupport", targets: ["SwiftSyntaxMacrosGenericTestSupport"]),
+    .library(name: "_SwiftCompilerPluginMessageHandling", targets: ["SwiftCompilerPluginMessageHandling"]),
+    .library(name: "_SwiftLibraryPluginProvider", targets: ["SwiftLibraryPluginProvider"]),
+  ]
+}
+
 let package = Package(
   name: "swift-syntax",
   platforms: [
@@ -12,26 +54,7 @@ let package = Package(
     .watchOS(.v6),
     .macCatalyst(.v13),
   ],
-  products: [
-    .library(name: "SwiftBasicFormat", type: type, targets: ["SwiftBasicFormat"]),
-    .library(name: "SwiftCompilerPlugin", type: type, targets: ["SwiftCompilerPlugin"]),
-    .library(name: "SwiftDiagnostics", type: type, targets: ["SwiftDiagnostics"]),
-    .library(name: "SwiftIDEUtils", type: type, targets: ["SwiftIDEUtils"]),
-    .library(name: "SwiftIfConfig", type: type, targets: ["SwiftIfConfig"]),
-    .library(name: "SwiftLexicalLookup", type: type, targets: ["SwiftLexicalLookup"]),
-    .library(name: "SwiftOperators", type: type, targets: ["SwiftOperators"]),
-    .library(name: "SwiftParser", type: type, targets: ["SwiftParser"]),
-    .library(name: "SwiftParserDiagnostics", type: type, targets: ["SwiftParserDiagnostics"]),
-    .library(name: "SwiftRefactor", type: type, targets: ["SwiftRefactor"]),
-    .library(name: "SwiftSyntax", type: type, targets: ["SwiftSyntax"]),
-    .library(name: "SwiftSyntaxBuilder", type: type, targets: ["SwiftSyntaxBuilder"]),
-    .library(name: "SwiftSyntaxMacros", type: type, targets: ["SwiftSyntaxMacros"]),
-    .library(name: "SwiftSyntaxMacroExpansion", type: type, targets: ["SwiftSyntaxMacroExpansion"]),
-    .library(name: "SwiftSyntaxMacrosTestSupport", type: type, targets: ["SwiftSyntaxMacrosTestSupport"]),
-    .library(name: "SwiftSyntaxMacrosGenericTestSupport", type: type, targets: ["SwiftSyntaxMacrosGenericTestSupport"]),
-    .library(name: "_SwiftCompilerPluginMessageHandling", type: type, targets: ["SwiftCompilerPluginMessageHandling"]),
-    .library(name: "_SwiftLibraryPluginProvider", type: type, targets: ["SwiftLibraryPluginProvider"]),
-  ],
+  products: products,
   targets: [
     // MARK: - Internal helper targets
     .target(
@@ -407,17 +430,12 @@ var rawSyntaxValidation: Bool { hasEnvironmentVariable("SWIFTSYNTAX_ENABLE_RAWSY
 /// See CONTRIBUTING.md for more information
 var alternateTokenIntrospection: Bool { hasEnvironmentVariable("SWIFTPARSER_ENABLE_ALTERNATE_TOKEN_INTROSPECTION") }
 
-/// The types of libraries to build.
+/// Instead of building object files for all modules to be statically linked, build a single dynamic library.
 ///
 /// This allows us to build swift-syntax as dynamic libraries, which in turn allows us to build SourceKit-LSP using
 /// SwiftPM on Windows. Linking swift-syntax statically into sourcekit-lsp exceeds the maximum number of exported
 /// symbols on Windows.
-var type: Product.Library.LibraryType? {
-  if hasEnvironmentVariable("SWIFTSYNTAX_BUILD_DYNAMIC_LIBRARIES") {
-    return .dynamic
-  }
-  return nil
-}
+var buildDynamicLibrary: Bool { hasEnvironmentVariable("SWIFTSYNTAX_BUILD_DYNAMIC_LIBRARY") }
 
 // MARK: - Compute custom build settings