[Dependency Scanning] Filter out '-Xcc' search paths from Swift module compilation commands

These search paths will not get used during Swift module compilation and can only hinder module sharing among different targets.

Resolves rdar://119217774

Author: artemcm

include/swift/Basic/LangOptions.h

@@ -1001,6 +1001,16 @@ namespace swift {
 
     std::vector<std::string> getRemappedExtraArgs(
         std::function<std::string(StringRef)> pathRemapCallback) const;
+
+    /// For a swift module dependency, interface build command generation must
+    /// inherit
+    /// `-Xcc` flags used for configuration of the building instance's
+    /// `ClangImporter`. However, we can ignore Clang search path flags because
+    /// explicit Swift module build tasks will not rely on them and they may be
+    /// source-target-context-specific and hinder module sharing across
+    /// compilation source targets.
+    std::vector<std::string>
+    getReducedExtraArgsForSwiftModuleDependency() const;
   };
 
 } // end namespace swift

lib/Basic/LangOptions.cpp

@@ -672,26 +672,30 @@ DiagnosticBehavior LangOptions::getAccessNoteFailureLimit() const {
   llvm_unreachable("covered switch");
 }
 
+namespace {
+  static constexpr std::array<std::string_view, 16> knownSearchPathPrefiexes =
+       {"-I",
+        "-F",
+        "-fmodule-map-file=",
+        "-iquote",
+        "-idirafter",
+        "-iframeworkwithsysroot",
+        "-iframework",
+        "-iprefix",
+        "-iwithprefixbefore",
+        "-iwithprefix",
+        "-isystemafter",
+        "-isystem",
+        "-isysroot",
+        "-ivfsoverlay",
+        "-working-directory=",
+        "-working-directory"};
+}
+
 std::vector<std::string> ClangImporterOptions::getRemappedExtraArgs(
     std::function<std::string(StringRef)> pathRemapCallback) const {
   auto consumeIncludeOption = [](StringRef &arg, StringRef &prefix) {
-    static StringRef options[] = {"-I",
-                                  "-F",
-                                  "-fmodule-map-file=",
-                                  "-iquote",
-                                  "-idirafter",
-                                  "-iframeworkwithsysroot",
-                                  "-iframework",
-                                  "-iprefix",
-                                  "-iwithprefixbefore",
-                                  "-iwithprefix",
-                                  "-isystemafter",
-                                  "-isystem",
-                                  "-isysroot",
-                                  "-ivfsoverlay",
-                                  "-working-directory=",
-                                  "-working-directory"};
-    for (StringRef &option : options)
+    for (const auto &option : knownSearchPathPrefiexes)
       if (arg.consume_front(option)) {
         prefix = option;
         return true;
@@ -724,3 +728,34 @@ std::vector<std::string> ClangImporterOptions::getRemappedExtraArgs(
   }
   return args;
 }
+
+std::vector<std::string>
+ClangImporterOptions::getReducedExtraArgsForSwiftModuleDependency() const {
+  auto matchIncludeOption = [](StringRef &arg) {
+    for (const auto &option : knownSearchPathPrefiexes)
+      if (arg.consume_front(option))
+        return true;
+    return false;
+  };
+
+  std::vector<std::string> filtered_args;
+  bool skip_next = false;
+  std::vector<std::string> args;
+  for (auto A : ExtraArgs) {
+    StringRef arg(A);
+    if (skip_next) {
+      skip_next = false;
+      continue;
+    } else if (matchIncludeOption(arg)) {
+      if (arg.empty()) {
+        // Option pair
+        skip_next = true;
+      } // else non-pair option e.g. '-I/search/path'
+      continue;
+    } else {
+      filtered_args.push_back(A);
+    }
+  }
+
+  return filtered_args;
+}

lib/Frontend/ModuleInterfaceLoader.cpp

@@ -1756,17 +1756,32 @@ InterfaceSubContextDelegateImpl::InterfaceSubContextDelegateImpl(
     clangImporterOpts.DetailedPreprocessingRecord;
   subClangImporterOpts.CASOpts = clangImporterOpts.CASOpts;
 
-  // If the compiler has been asked to be strict with ensuring downstream dependencies
-  // get the parent invocation's context, or this is an Explicit build, inherit the
-  // extra Clang arguments also.
-  if (LoaderOpts.strictImplicitModuleContext || LoaderOpts.disableImplicitSwiftModule ||
-      LoaderOpts.requestedAction == FrontendOptions::ActionType::ScanDependencies) {
-    // Inherit any clang-specific state of the compilation (macros, clang flags, etc.)
-    subClangImporterOpts.ExtraArgs = clangImporterOpts.ExtraArgs;
-    for (auto arg : subClangImporterOpts.ExtraArgs) {
-      GenericArgs.push_back("-Xcc");
-      GenericArgs.push_back(ArgSaver.save(arg));
-    }
+  std::vector<std::string> inheritedParentContextClangArgs;
+  if (LoaderOpts.requestedAction ==
+      FrontendOptions::ActionType::ScanDependencies) {
+    // For a dependency scanning action, interface build command generation must
+    // inherit
+    // `-Xcc` flags used for configuration of the building instance's
+    // `ClangImporter`. However, we can ignore Clang search path flags because
+    // explicit Swift module build tasks will not rely on them and they may be
+    // source-target-context-specific and hinder module sharing across
+    // compilation source targets.
+    // Clang module dependecies of this Swift dependency will be distinguished by
+    // their context hash for different variants, so would still cause a difference
+    // in the Swift compile commands, when different.
+    inheritedParentContextClangArgs =
+        clangImporterOpts.getReducedExtraArgsForSwiftModuleDependency();
+  } else if (LoaderOpts.strictImplicitModuleContext) {
+    // If the compiler has been asked to be strict with ensuring downstream
+    // dependencies get the parent invocation's context, inherit the extra Clang
+    // arguments also. Inherit any clang-specific state of the compilation
+    // (macros, clang flags, etc.)
+    inheritedParentContextClangArgs = clangImporterOpts.ExtraArgs;
+  }
+  subClangImporterOpts.ExtraArgs = inheritedParentContextClangArgs;
+  for (auto arg : subClangImporterOpts.ExtraArgs) {
+    GenericArgs.push_back("-Xcc");
+    GenericArgs.push_back(ArgSaver.save(arg));
   }
 
   subClangImporterOpts.EnableClangSPI = clangImporterOpts.EnableClangSPI;

test/ScanDependencies/FilterClangSearchPaths.swift

@@ -0,0 +1,35 @@
+// RUN: %empty-directory(%t)
+// RUN: %empty-directory(%t/clang-module-cache)
+
+// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -Xcc -fobjc-disable-direct-methods-for-testing -Xcc -I -Xcc /tmp/foo -Xcc -I/tmp/bar
+// Check the contents of the JSON output
+// RUN: %validate-json %t/deps.json | %FileCheck %s
+
+// REQUIRES: executable_test
+// REQUIRES: objc_interop
+
+import C
+
+// CHECK: "mainModuleName": "deps"
+/// --------Main module
+// CHECK-LABEL: "modulePath": "deps.swiftmodule",
+// CHECK-NEXT: sourceFiles
+// CHECK-NEXT: FilterClangSearchPaths.swift
+// CHECK-NEXT: ],
+// CHECK-NEXT: "directDependencies": [
+// CHECK-DAG:     "clang": "C"
+// CHECK-DAG:     "swift": "Swift"
+// CHECK-DAG:     "swift": "SwiftOnoneSupport"
+// CHECK-DAG:     "swift": "_Concurrency"
+// CHECK: ],
+
+// CHECK:     "swift": "A"
+// CHECK:        "swift": {
+// CHECK-NEXT:          "moduleInterfacePath": "{{.*}}{{/|\\}}Inputs{{/|\\}}Swift{{/|\\}}A.swiftinterface",
+// CHECK:          "commandLine": [
+// CHECK:            "-fobjc-disable-direct-methods-for-testing"
+// CHECK:            "-o",
+// CHECK-NEXT:       "{{.*}}{{/|\\}}A-{{.*}}.swiftmodule",
+// CHECK-NOT:        "/tmp/foo"
+// CHECK-NOT:        "-I/tmp/bar"
+// CHECK:          ]