[DependencyScanner] Drop macro search path if not needed

When scanning swift modules and constructing their build commands, there
is no need to pass any external plugin search paths if there are no macro
dependencies for the module.

rdar://135221984

Author: cachemeifyoucan

include/swift/AST/ModuleDependencies.h

@@ -813,6 +813,9 @@ class ModuleDependencyInfo {
   void addMacroDependency(StringRef macroModuleName, StringRef libraryPath,
                           StringRef executablePath);
 
+  /// For a Source/Textual dependency, if it Has macro dependency.
+  bool hasMacroDependencies() const;
+
   /// Whether or not a queried module name is a `@Testable` import dependency
   /// of this module. Can only return `true` for Swift source modules.
   bool isTestableImport(StringRef moduleName) const;

lib/AST/ModuleDependencies.cpp

@@ -120,6 +120,18 @@ void ModuleDependencyInfo::addMacroDependency(StringRef macroModuleName,
     llvm_unreachable("Unexpected dependency kind");
 }
 
+bool ModuleDependencyInfo::hasMacroDependencies() const {
+  if (auto sourceModule =
+          dyn_cast<SwiftSourceModuleDependenciesStorage>(storage.get()))
+    return !sourceModule->textualModuleDetails.macroDependencies.empty();
+
+  if (auto interfaceModule =
+          dyn_cast<SwiftInterfaceModuleDependenciesStorage>(storage.get()))
+    return !interfaceModule->textualModuleDetails.macroDependencies.empty();
+
+  llvm_unreachable("Unexpected dependency kind");
+}
+
 bool ModuleDependencyInfo::isTestableImport(StringRef moduleName) const {
   if (auto swiftSourceDepStorage = getAsSwiftSourceModule())
     return swiftSourceDepStorage->testableImports.contains(moduleName);

lib/DependencyScan/ScanDependencies.cpp

@@ -159,6 +159,24 @@ parseBatchScanInputFile(ASTContext &ctx, StringRef batchInputPath,
   return result;
 }
 
+static void removeMacroSearchPaths(std::vector<std::string> &cmd) {
+  // Macro search path options.
+  static const llvm::StringSet<> macroSearchOptions = {
+      "-plugin-path",
+      "-external-plugin-path",
+      "-load-plugin-library",
+      "-load-plugin-executable",
+      "-in-process-plugin-server-path",
+  };
+
+  // Remove macro search path option and its argument.
+  for (auto it = cmd.begin(), ie=cmd.end(); it != ie; ++it) {
+    if (macroSearchOptions.contains(*it) && it + 1 != ie) {
+      it = cmd.erase(it, it + 2);
+    }
+  }
+}
+
 static llvm::Expected<llvm::cas::ObjectRef>
 updateModuleCacheKey(ModuleDependencyInfo &depInfo,
                      ModuleDependenciesCache &cache,
@@ -378,9 +396,15 @@ static llvm::Error resolveExplicitModuleInputs(
     // Update build command line.
     if (resolvingDepInfo.isSwiftInterfaceModule() ||
         resolvingDepInfo.isSwiftSourceModule()) {
-      // Update with casfs option.
       std::vector<std::string> newCommandLine =
           dependencyInfoCopy.getCommandline();
+
+      // If there are no external macro dependencies, drop all plugin search
+      // paths.
+      if (!resolvingDepInfo.hasMacroDependencies())
+        removeMacroSearchPaths(newCommandLine);
+
+      // Update with casfs option.
       for (auto rootID : rootIDs) {
         newCommandLine.push_back("-cas-fs");
         newCommandLine.push_back(rootID);
@@ -390,6 +414,7 @@ static llvm::Error resolveExplicitModuleInputs(
         newCommandLine.push_back("-clang-include-tree-root");
         newCommandLine.push_back(tree);
       }
+
       dependencyInfoCopy.updateCommandLine(newCommandLine);
     }
 

test/CAS/macro_deps.swift

@@ -29,6 +29,11 @@
 // RUN: %swift_frontend_plain @%t/SwiftShims.cmd
 // RUN: %S/Inputs/BuildCommandExtractor.py %t/deps.json Foo > %t/Foo.cmd
 // RUN: %swift_frontend_plain @%t/Foo.cmd
+// RUN: %S/Inputs/BuildCommandExtractor.py %t/deps.json Bar > %t/Bar.cmd
+// RUN: %swift_frontend_plain @%t/Bar.cmd
+
+// RUN: %FileCheck %s --check-prefix=PLUGIN_SEARCH --input-file=%t/Bar.cmd
+// PLUGIN_SEARCH-NOT: -external-plugin-path
 
 // RUN: %S/Inputs/BuildCommandExtractor.py %t/deps.json MyApp > %t/MyApp.cmd
 // RUN: %{python} %S/Inputs/GenerateExplicitModuleMap.py %t/deps.json > %t/map.json
@@ -87,6 +92,11 @@ public func assertFalse() {
     #assert(false)
 }
 
+//--- include/Bar.swiftinterface
+// swift-interface-format-version: 1.0
+// swift-module-flags: -enable-library-evolution -swift-version 5 -O -module-name Bar -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib
+public func bar()
+
 //--- test.swift
 import Foo
 @inlinable
@@ -96,6 +106,7 @@ public func test() {
 
 //--- main.swift
 import Test
+import Bar
 @freestanding(expression) macro stringify<T>(_ value: T) -> (T, String) = #externalMacro(module: "MacroTwo", type: "StringifyMacro")
 
 func appTest() {