[Explicit Module Builds] Only specify '-fmodule-map-file' for bridging header Clang module dependencies

Relying on the corresponding field in the '-explicit-swift-module-map-file' provided by the driver.

Only bridging headers require a module map because that's what aids header include resolution. With lazy module loading today, '.modulemap' parsing which happens when instantiating Clang is responsible for associating headers with modules. Then upon encountering a header include inside the bridging header the compiler knows which module corresponds to said header and is then able to load explicitly-provided PCM for that module. For all other module dependencies, they are only ever queried by-name from Swift, so '.modulemap' parsing is not necessary.

Author: artemcm

include/swift/AST/SearchPathOptions.h

@@ -476,7 +476,7 @@ class SearchPathOptions {
   std::vector<std::string> CandidateCompiledModules;
 
   /// A map of explicit Swift module information.
-  std::string ExplicitSwiftModuleMap;
+  std::string ExplicitSwiftModuleMapPath;
 
   /// Module inputs specified with -swift-module-input,
   /// <ModuleName, Path to .swiftmodule file>

include/swift/Frontend/ModuleInterfaceLoader.h

@@ -269,9 +269,11 @@ struct ExplicitClangModuleInputInfo {
   ExplicitClangModuleInputInfo(
       std::string moduleMapPath, std::string modulePath,
       bool isFramework = false, bool isSystem = false,
+      bool isBridgingHeaderDependency = true,
       std::optional<std::string> moduleCacheKey = std::nullopt)
       : moduleMapPath(moduleMapPath), modulePath(modulePath),
         isFramework(isFramework), isSystem(isSystem),
+        isBridgingHeaderDependency(isBridgingHeaderDependency),
         moduleCacheKey(moduleCacheKey) {}
   // Path of the Clang module map file.
   std::string moduleMapPath;
@@ -281,6 +283,8 @@ struct ExplicitClangModuleInputInfo {
   bool isFramework = false;
   // A flag that indicates whether this module is a system module
   bool isSystem = false;
+  // A flag that indicates whether this is a module dependency of a textual header input
+  bool isBridgingHeaderDependency = true;
   // The cache key for clang module.
   std::optional<std::string> moduleCacheKey;
 };
@@ -367,7 +371,12 @@ class ExplicitModuleMapParser {
         swiftModuleSourceInfoPath, swiftModuleCacheKey, clangModuleCacheKey;
     std::optional<std::vector<std::string>> headerDependencyPaths;
     std::string clangModuleMapPath = "", clangModulePath = "";
-    bool isFramework = false, isSystem = false;
+    bool isFramework = false, isSystem = false,
+         // The default value is 'true' in case the build system does not yet
+         // support emitting this field, in which case we must be conservative and
+         // ensure all dependencies get '-fmodule-map-file', instead of strictly
+         // module dependencies of textual header inputs.
+         isBridgingHeaderDependency = true;
     for (auto &entry : *mapNode) {
       auto key = getScalaNodeText(entry.getKey());
       if (key == "prebuiltHeaderDependencyPaths") {
@@ -394,6 +403,8 @@ class ExplicitModuleMapParser {
           swiftModuleCacheKey = val.str();
         } else if (key == "clangModuleCacheKey") {
           clangModuleCacheKey = val.str();
+        } else if (key == "isBridgingHeaderDependency") {
+          isBridgingHeaderDependency = parseBoolValue(val);
         } else {
           // Being forgiving for future fields.
           continue;
@@ -423,6 +434,7 @@ class ExplicitModuleMapParser {
                                          clangModulePath,
                                          isFramework,
                                          isSystem,
+                                         isBridgingHeaderDependency,
                                          clangModuleCacheKey);
       clangModuleMap.try_emplace(moduleName, std::move(entry));
     }

lib/Frontend/CompilerInvocation.cpp

@@ -1982,7 +1982,7 @@ static bool ParseSearchPathArgs(SearchPathOptions &Opts,
       Args.hasArg(OPT_disable_modules_validate_system_headers);
 
   if (const Arg *A = Args.getLastArg(OPT_explicit_swift_module_map))
-    Opts.ExplicitSwiftModuleMap = A->getValue();
+    Opts.ExplicitSwiftModuleMapPath = A->getValue();
   for (auto A : Args.getAllArgValues(options::OPT_swift_module_file)) {
     if (validateSwiftModuleFileArgumentAndAdd(A, Diags,
                                               Opts.ExplicitSwiftModuleInputs))

lib/Frontend/Frontend.cpp

@@ -745,18 +745,18 @@ bool CompilerInstance::setUpModuleLoaders() {
   bool ExplicitModuleBuild =
       Invocation.getFrontendOptions().DisableImplicitModules;
   if (ExplicitModuleBuild ||
-      !Invocation.getSearchPathOptions().ExplicitSwiftModuleMap.empty() ||
+      !Invocation.getSearchPathOptions().ExplicitSwiftModuleMapPath.empty() ||
       !Invocation.getSearchPathOptions().ExplicitSwiftModuleInputs.empty()) {
     if (Invocation.getCASOptions().EnableCaching)
       ESML = ExplicitCASModuleLoader::create(
           *Context, getObjectStore(), getActionCache(), getDependencyTracker(),
-          MLM, Invocation.getSearchPathOptions().ExplicitSwiftModuleMap,
+          MLM, Invocation.getSearchPathOptions().ExplicitSwiftModuleMapPath,
           Invocation.getSearchPathOptions().ExplicitSwiftModuleInputs,
           IgnoreSourceInfoFile);
     else
       ESML = ExplicitSwiftModuleLoader::create(
           *Context, getDependencyTracker(), MLM,
-          Invocation.getSearchPathOptions().ExplicitSwiftModuleMap,
+          Invocation.getSearchPathOptions().ExplicitSwiftModuleMapPath,
           Invocation.getSearchPathOptions().ExplicitSwiftModuleInputs,
           IgnoreSourceInfoFile);
   }

lib/Frontend/ModuleInterfaceLoader.cpp

@@ -1847,8 +1847,8 @@ InterfaceSubContextDelegateImpl::InterfaceSubContextDelegateImpl(
   }
 
   // Pass down -explicit-swift-module-map-file
-  StringRef explicitSwiftModuleMap = searchPathOpts.ExplicitSwiftModuleMap;
-  genericSubInvocation.getSearchPathOptions().ExplicitSwiftModuleMap =
+  StringRef explicitSwiftModuleMap = searchPathOpts.ExplicitSwiftModuleMapPath;
+  genericSubInvocation.getSearchPathOptions().ExplicitSwiftModuleMapPath =
     explicitSwiftModuleMap.str();
 
   // Pass down VFSOverlay flags (do not need to inherit the options because
@@ -2194,6 +2194,7 @@ struct ExplicitSwiftModuleLoader::Implementation {
     for (auto &entry : ExplicitClangModuleMap) {
       const auto &moduleMapPath = entry.getValue().moduleMapPath;
       if (!moduleMapPath.empty() &&
+          entry.getValue().isBridgingHeaderDependency &&
           moduleMapsSeen.find(moduleMapPath) == moduleMapsSeen.end()) {
         moduleMapsSeen.insert(moduleMapPath);
         extraClangArgs.push_back(

test/ScanDependencies/bridging_header_modulemap_only.swift

@@ -0,0 +1,51 @@
+// REQUIRES: objc_interop
+// RUN: %empty-directory(%t)
+// RUN: %empty-directory(%t/TestInputs)
+// RUN: split-file %s %t
+
+// - Fixup the input module file map
+// RUN: sed -e "s|INPUTSDIR|%/t/TestInputs|g" %t/map.json.template > %t/map.json.template1
+// RUN: sed -e "s|STDLIBMOD|%/stdlib_module|g" %t/map.json.template1 > %t/map.json.template2
+// RUN: sed -e "s|ONONEMOD|%/ononesupport_module|g" %t/map.json.template2 > %t/map.json.template3
+// RUN: sed -e "s|CHEADERSDIR|%/S/Inputs/CHeaders|g" %t/map.json.template3 > %t/map.json.template4
+// RUN: sed -e "s|SWIFTLIBDIR|%swift-lib-dir|g" %t/map.json.template4 > %t/map.json
+
+// - Pre-compile explicit module dependency inputs
+// RUN: %target-swift-emit-pcm -module-name A -o %t/TestInputs/A.pcm %S/Inputs/CHeaders/module.modulemap
+// RUN: %target-swift-emit-pcm -module-name SwiftShims %swift-lib-dir/swift/shims/module.modulemap -o %t/TestInputs/SwiftShims.pcm
+
+// RUN: %target-swift-frontend -c -disable-implicit-swift-modules -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -explicit-swift-module-map-file %t/map.json -primary-file %t/bridging_header_modulemap_only.swift -o %t/bridging_header_modulemap_only.o -dump-clang-diagnostics 2>&1 | %FileCheck %s --check-prefix=CHECK-CLANG-COMMAND
+
+//--- map.json.template
+[
+  {
+      "moduleName": "Swift",
+      "modulePath": "STDLIBMOD",
+      "isFramework": false
+  },
+  {
+      "moduleName": "SwiftOnoneSupport",
+      "modulePath": "ONONEMOD",
+      "isFramework": false
+  },
+  {
+      "moduleName": "SwiftShims",
+      "isFramework": false,
+      "isBridgingHeaderDependency": false,
+      "clangModuleMapPath": "SWIFTLIBDIR/swift/shims/module.modulemap",
+      "clangModulePath": "INPUTSDIR/SwiftShims.pcm"
+  },
+  {
+      "moduleName": "A",
+      "isFramework": false,
+      "isBridgingHeaderDependency": true,      
+      "clangModulePath": "INPUTSDIR/A.pcm",
+      "clangModuleMapPath": "CHEADERSDIR/module.modulemap"
+  }
+]
+
+//--- bridging_header_modulemap_only.swift
+import A
+
+// CHECK-CLANG-COMMAND: -fmodule-map-file={{.*}}{{/|\\}}CHeaders{{/|\\}}module.modulemap
+// CHECK-CLANG-COMMAND-NOT: -fmodule-map-file={{.*}}{{/|\\}}swift{{/|\\}}shims{{/|\\}}module.modulemap

tools/swift-ide-test/swift-ide-test.cpp

@@ -4520,7 +4520,7 @@ int main(int argc, char *argv[]) {
     InitInvok.getLangOptions().addCustomConditionalCompilationFlag(ConfigName);
 
   if (!options::ExplicitSwiftModuleMap.empty()) {
-    InitInvok.getSearchPathOptions().ExplicitSwiftModuleMap =
+    InitInvok.getSearchPathOptions().ExplicitSwiftModuleMapPath =
       options::ExplicitSwiftModuleMap;
     InitInvok.getFrontendOptions().DisableImplicitModules = true;
   }