ModuleInterface: refactor a utility function out for collecting candidate compiled modules. NFC

lib/Frontend/ModuleInterfaceLoader.cpp

@@ -590,12 +590,8 @@ class ModuleInterfaceLoaderImpl {
     return path.startswith(resourceDir);
   }
 
-  llvm::ErrorOr<DiscoveredModule>
-  discoverUpToDateCompiledModuleForInterface(SmallVectorImpl<FileDependency> &deps,
-                                             std::string &UsableModulePath) {
-    auto notFoundError =
-      std::make_error_code(std::errc::no_such_file_or_directory);
-
+  std::pair<std::string, std::string> getCompiledModuleCandidates() {
+    std::pair<std::string, std::string> result;
     // Keep track of whether we should attempt to load a .swiftmodule adjacent
     // to the .swiftinterface.
     bool shouldLoadAdjacentModule = true;
@@ -604,7 +600,7 @@ class ModuleInterfaceLoaderImpl {
     case ModuleLoadingMode::OnlyInterface:
       // Always skip both the caches and adjacent modules, and always build the
       // module interface.
-      return notFoundError;
+      return {};
     case ModuleLoadingMode::PreferInterface:
       // If we're in the load mode that prefers .swiftinterfaces, specifically
       // skip the module adjacent to the interface, but use the caches if
@@ -627,16 +623,48 @@ class ModuleInterfaceLoaderImpl {
     // diagnose it.
 
     if (shouldLoadAdjacentModule) {
-      auto adjacentModuleBuffer = fs.getBufferForFile(modulePath);
+      if (fs.exists(modulePath)) {
+        result.first = modulePath;
+      }
+    }
+
+    // If we have a prebuilt cache path, check that too if the interface comes
+    // from the SDK.
+    if (!prebuiltCacheDir.empty()) {
+      llvm::SmallString<256> scratch;
+      std::unique_ptr<llvm::MemoryBuffer> moduleBuffer;
+      Optional<StringRef> path = computePrebuiltModulePath(scratch);
+      if (!path) {
+        // Hack: deal with prebuilds of modules that still use the target-based
+        // names.
+        path = computeFallbackPrebuiltModulePath(scratch);
+      }
+      if (path) {
+        if (fs.exists(*path)) {
+          result.second = *path;
+        }
+      }
+    }
+
+    return result;
+  }
+
+  llvm::ErrorOr<DiscoveredModule>
+  discoverUpToDateCompiledModuleForInterface(SmallVectorImpl<FileDependency> &deps,
+                                             std::string &UsableModulePath) {
+    std::string adjacentMod, prebuiltMod;
+    std::tie(adjacentMod, prebuiltMod) = getCompiledModuleCandidates();
+    if (!adjacentMod.empty()) {
+      auto adjacentModuleBuffer = fs.getBufferForFile(adjacentMod);
       if (adjacentModuleBuffer) {
-        if (serializedASTBufferIsUpToDate(modulePath, *adjacentModuleBuffer.get(),
+        if (serializedASTBufferIsUpToDate(adjacentMod, *adjacentModuleBuffer.get(),
                                           deps)) {
           LLVM_DEBUG(llvm::dbgs() << "Found up-to-date module at "
-                                  << modulePath
+                                  << adjacentMod
                                   << "; deferring to serialized module loader\n");
-          UsableModulePath = modulePath.str();
+          UsableModulePath = adjacentMod;
           return std::make_error_code(std::errc::not_supported);
-        } else if (isInResourceDir(modulePath) &&
+        } else if (isInResourceDir(adjacentMod) &&
                    loadMode == ModuleLoadingMode::PreferSerialized) {
           // Special-case here: If we're loading a .swiftmodule from the resource
           // dir adjacent to the compiler, defer to the serialized loader instead
@@ -647,53 +675,40 @@ class ModuleInterfaceLoaderImpl {
           // we used to.
           LLVM_DEBUG(llvm::dbgs() << "Found out-of-date module in the "
                                      "resource-dir at "
-                                  << modulePath
+                                  << adjacentMod
                                   << "; deferring to serialized module loader "
                                      "to diagnose\n");
           return std::make_error_code(std::errc::not_supported);
         } else {
           LLVM_DEBUG(llvm::dbgs() << "Found out-of-date module at "
-                                  << modulePath << "\n");
-          rebuildInfo.setModuleKind(modulePath,
+                                  << adjacentMod << "\n");
+          rebuildInfo.setModuleKind(adjacentMod,
                                     ModuleRebuildInfo::ModuleKind::Normal);
         }
-      } else if (adjacentModuleBuffer.getError() != notFoundError) {
+      } else {
         LLVM_DEBUG(llvm::dbgs() << "Found unreadable module at "
-                                << modulePath
+                                << adjacentMod
                                 << "; deferring to serialized module loader\n");
         return std::make_error_code(std::errc::not_supported);
       }
     }
 
-    // If we have a prebuilt cache path, check that too if the interface comes
-    // from the SDK.
-    if (!prebuiltCacheDir.empty()) {
-      llvm::SmallString<256> scratch;
+    if(!prebuiltMod.empty()) {
       std::unique_ptr<llvm::MemoryBuffer> moduleBuffer;
-      Optional<StringRef> path = computePrebuiltModulePath(scratch);
-      if (!path) {
-        // Hack: deal with prebuilds of modules that still use the target-based
-        // names.
-        path = computeFallbackPrebuiltModulePath(scratch);
-      }
-      if (path) {
-        if (swiftModuleIsUpToDate(*path, deps, moduleBuffer)) {
-          LLVM_DEBUG(llvm::dbgs() << "Found up-to-date prebuilt module at "
-                                  << path->str() << "\n");
-          UsableModulePath = path->str();
-          return DiscoveredModule::prebuilt(*path, std::move(moduleBuffer));
-        } else {
-          LLVM_DEBUG(llvm::dbgs() << "Found out-of-date prebuilt module at "
-                                  << path->str() << "\n");
-          rebuildInfo.setModuleKind(*path,
-                                    ModuleRebuildInfo::ModuleKind::Prebuilt);
-        }
+      if (swiftModuleIsUpToDate(prebuiltMod, deps, moduleBuffer)) {
+        LLVM_DEBUG(llvm::dbgs() << "Found up-to-date prebuilt module at "
+                                << prebuiltMod << "\n");
+        UsableModulePath = prebuiltMod;
+        return DiscoveredModule::prebuilt(prebuiltMod, std::move(moduleBuffer));
+      } else {
+        LLVM_DEBUG(llvm::dbgs() << "Found out-of-date prebuilt module at "
+                                << prebuiltMod << "\n");
+        rebuildInfo.setModuleKind(prebuiltMod,
+                                  ModuleRebuildInfo::ModuleKind::Prebuilt);
       }
     }
-
-    // Couldn't find an up-to-date .swiftmodule, will need to build module from
-    // interface.
-    return notFoundError;
+    // We cannot find any proper compiled module to use.
+    return std::make_error_code(std::errc::no_such_file_or_directory);
   }
 
   /// Finds the most appropriate .swiftmodule, whose dependencies are up to