[Dependency Scanning] Diagnose an error when only finding incompatible Swift binary modules

When querying a Swift module, the scanner now also keeps track of all discovered candidate binary modules which are not compatible with current compilation.

- If a Swift dependency is successfully resolved to a compatible binary module or a textual interface, a warning is emitted for every incompatible binary Swift module discovered along the way.
- If a Swift dependency is not resolved, but incompatible module candidates were found, an error is emitted - while it is likely that the scan would fail downstream, it is also possible that an underlying Clang module dependency (with the same name) is successfuly resolved and the Swift lookup failure is ignored, which is still going to lead to failures most of the time if the client code assumes the presence of the Swift overlay module in this scenario.

This change refactors common error reporting by the scanner into a 'ModuleDependencyIssueReporter' class, which also keeps track of all diagnosed failed lookups to avoid repeating diagnostics.

Author: artemcm

include/swift/AST/DiagnosticsSema.def

@@ -1290,15 +1290,6 @@ REMARK(module_api_import_aliases,none,
        "%select{, which reexports definition from %2|}3",
        (const Decl *, ModuleDecl *, ModuleDecl *, bool))
 
-REMARK(dependency_scan_skip_module_invalid,none,
-       "module file '%0' skipped by the dependency scan because it is "
-       "incompatible with this Swift compiler: %1", (StringRef, StringRef))
-WARNING(skip_module_not_testable,none,
-        "ignore swiftmodule built without '-enable-testing': %0", (StringRef))
-WARNING(dependency_scan_module_incompatible, none,
-        "module file '%0' is incompatible with this Swift compiler: %1",
-        (StringRef, StringRef))
-
 REMARK(macro_loaded,none,
        "loaded macro implementation module %0 from "
        "%select{shared library '%2'|executable '%2'|"
@@ -2377,9 +2368,11 @@ ERROR(alignment_not_power_of_two,none,
       "alignment value must be a power of two", ())
 
 // Dependency Scanning
-ERROR(dependency_scan_module_not_found, none, "Unable to find module dependency: '%0'", (StringRef))
+ERROR(dependency_scan_module_not_found, none, "unable to resolve module dependency: '%0'", (StringRef))
+
 GROUPED_ERROR(dependency_scan_module_not_found_on_specified_search_paths, MissingModuleOnKnownPaths, none,
-              "Compilation search paths unable to resolve module dependency: '%0'", (StringRef))
+              "compilation search paths unable to resolve module dependency: '%0'", (StringRef))
+
 NOTE(unresolved_import_location,none,
      "also imported here", ())
 NOTE(dependency_as_imported_by_main_module,none,
@@ -2388,10 +2381,21 @@ NOTE(dependency_as_imported_by, none,
      "a dependency of %select{Swift|Clang}2 module '%0': '%1'", (StringRef, StringRef, bool))
 NOTE(inherited_search_path_resolves_module,none,
      "'%0' can be found using a search path that was specified when building module '%1' ('%2'). "
-     "This search path was not explicitly specified on the current compilation.", (StringRef, StringRef, StringRef))
+     "This search path was not explicitly specified on the current compilation", (StringRef, StringRef, StringRef))
+
+ERROR(dependency_scan_compatible_swift_module_not_found, none,
+      "unable to resolve Swift module dependency to a compatible module: '%0'",
+      (StringRef))
+NOTE(dependency_scan_incompatible_module_found,none,
+     "found incompatible module '%0': %1", (StringRef, StringRef))
+
+WARNING(dependency_scan_module_incompatible, none,
+        "module file '%0' is incompatible with this Swift compiler: %1",
+        (StringRef, StringRef))
+
+ERROR(clang_dependency_scan_error, none, "clang dependency scanning failure: %0", (StringRef))
 
-ERROR(clang_dependency_scan_error, none, "Clang dependency scanner failure: %0", (StringRef))
-ERROR(clang_header_dependency_scan_error, none, "Bridging header dependency scan failure: %0", (StringRef))
+ERROR(clang_header_dependency_scan_error, none, "bridging header dependency scanning failure: %0", (StringRef))
 
 // Enum annotations
 ERROR(indirect_case_without_payload,none,

include/swift/AST/ModuleDependencies.h

@@ -133,6 +133,10 @@ struct ScannerImportStatementInfo {
     uint32_t columnNumber;
   };
 
+  ScannerImportStatementInfo(std::string importIdentifier)
+      : importIdentifier(importIdentifier), importLocations(),
+        isExported(false), accessLevel(AccessLevel::Public) {}
+
   ScannerImportStatementInfo(std::string importIdentifier, bool isExported,
                              AccessLevel accessLevel)
       : importIdentifier(importIdentifier), importLocations(),

include/swift/DependencyScan/ModuleDependencyScanner.h

@@ -43,7 +43,7 @@ class ModuleDependencyScanningWorker {
           &alreadySeenModules);
 
   /// Retrieve the module dependencies for the Swift module with the given name.
-  ModuleDependencyVector scanFilesystemForSwiftModuleDependency(
+  SwiftModuleScannerQueryResult scanFilesystemForSwiftModuleDependency(
       Identifier moduleName, bool isTestableImport = false);
 
   /// Query dependency information for header dependencies
@@ -112,6 +112,46 @@ class ModuleDependencyScanningWorker {
   friend class ModuleDependencyScanner;
 };
 
+class ModuleDependencyIssueReporter {
+private:
+  ModuleDependencyIssueReporter(DiagnosticEngine &Diagnostics)
+      : Diagnostics(Diagnostics) {}
+
+  /// Diagnose scanner failure and attempt to reconstruct the dependency
+  /// path from the main module to the missing dependency
+  void diagnoseModuleNotFoundFailure(
+      const ScannerImportStatementInfo &moduleImport,
+      const ModuleDependenciesCache &cache,
+      std::optional<ModuleDependencyID> dependencyOf,
+      std::optional<std::pair<ModuleDependencyID, std::string>>
+          resolvingSerializedSearchPath,
+      std::optional<
+          std::vector<SwiftModuleScannerQueryResult::IncompatibleCandidate>>
+          foundIncompatibleCandidates = std::nullopt);
+
+  /// Upon query failure, if incompatible binary module
+  /// candidates were found, emit a failure diagnostic
+  void diagnoseFailureOnOnlyIncompatibleCandidates(
+      const ScannerImportStatementInfo &moduleImport,
+      const std::vector<SwiftModuleScannerQueryResult::IncompatibleCandidate>
+          &candidates,
+      const ModuleDependenciesCache &cache,
+      std::optional<ModuleDependencyID> dependencyOf);
+
+  /// Emit warnings for each discovered binary Swift module
+  /// which was incompatible with the current compilation
+  /// when querying \c moduleName
+  void warnOnIncompatibleCandidates(
+      StringRef moduleName,
+      const std::vector<SwiftModuleScannerQueryResult::IncompatibleCandidate>
+          &candidates);
+
+  DiagnosticEngine &Diagnostics;
+  std::unordered_set<std::string> ReportedMissing;
+  // Restrict access to the parent scanner class.
+  friend class ModuleDependencyScanner;
+};
+
 class ModuleDependencyScanner {
 public:
   ModuleDependencyScanner(SwiftDependencyScanningService &ScanningService,
@@ -182,7 +222,7 @@ class ModuleDependencyScanner {
       StringRef mainModuleName, ModuleDependenciesCache &cache,
       llvm::function_ref<void(ModuleDependencyID)> action);
 
-  /// Performance BridgingHeader Chaining.
+  /// Perform Bridging Header Chaining.
   llvm::Error
   performBridgingHeaderChaining(const ModuleDependencyID &rootModuleID,
                                 ModuleDependenciesCache &cache,
@@ -197,12 +237,6 @@ class ModuleDependencyScanner {
   /// for a given module name.
   Identifier getModuleImportIdentifier(StringRef moduleName);
 
-  /// Diagnose scanner failure and attempt to reconstruct the dependency
-  /// path from the main module to the missing dependency.
-  void diagnoseScannerFailure(const ScannerImportStatementInfo &moduleImport,
-                              const ModuleDependenciesCache &cache,
-                              std::optional<ModuleDependencyID> dependencyOf);
-
   /// Assuming the \c `moduleImport` failed to resolve,
   /// iterate over all binary Swift module dependencies with serialized
   /// search paths and attempt to diagnose if the failed-to-resolve module
@@ -211,12 +245,12 @@ class ModuleDependencyScanner {
   std::optional<std::pair<ModuleDependencyID, std::string>>
   attemptToFindResolvingSerializedSearchPath(
       const ScannerImportStatementInfo &moduleImport,
-      const ModuleDependenciesCache &cache, const SourceLoc &importLoc);
+      const ModuleDependenciesCache &cache);
 
 private:
   const CompilerInvocation &ScanCompilerInvocation;
   ASTContext &ScanASTContext;
-  DiagnosticEngine &Diagnostics;
+  ModuleDependencyIssueReporter IssueReporter;
 
   /// The available pool of workers for filesystem module search
   unsigned NumThreads;

include/swift/Serialization/ScanningLoaders.h

@@ -18,6 +18,19 @@
 #include "swift/Serialization/SerializedModuleLoader.h"
 
 namespace swift {
+
+/// Result of looking up a Swift module on the current filesystem
+/// search paths.
+struct SwiftModuleScannerQueryResult {
+  struct IncompatibleCandidate {
+    std::string path;
+    std::string incompatibilityReason;
+  };
+
+  std::vector<IncompatibleCandidate> incompatibleCandidates;
+  std::optional<ModuleDependencyInfo> foundDependencyInfo;
+};
+
 /// A module "loader" that looks for .swiftinterface and .swiftmodule files
 /// for the purpose of determining dependencies, but does not attempt to
 /// load the module files.
@@ -60,7 +73,8 @@ class SwiftModuleScanner : public SerializedModuleLoaderBase {
   std::vector<std::string> swiftModuleClangCC1CommandLineArgs;
 
 public:
-  std::optional<ModuleDependencyInfo> dependencies;
+  std::vector<SwiftModuleScannerQueryResult::IncompatibleCandidate> incompatibleCandidates;
+  std::optional<ModuleDependencyInfo> foundDependencyInfo;
 
   SwiftModuleScanner(ASTContext &ctx, ModuleLoadingMode LoadMode,
                      InterfaceSubContextDelegate &astDelegate,
@@ -74,7 +88,7 @@ class SwiftModuleScanner : public SerializedModuleLoaderBase {
         swiftModuleClangCC1CommandLineArgs(swiftModuleClangCC1CommandLineArgs)  {}
 
   /// Perform a filesystem search for a Swift module with a given name
-  llvm::SmallVector<std::pair<ModuleDependencyID, ModuleDependencyInfo>, 1>
+  SwiftModuleScannerQueryResult
   lookupSwiftModule(Identifier moduleName, bool isTestableImport);
 };
 } // namespace swift