[Macros] Add frontend flag to dump macro expansions for diagnostics.

Add frontend flag `-emit-macro-expansion-files diagnostics` to emit any
macro expansion buffers referenced by diagnostics into files in a
temporary directory. This makes debugging type-checking failures in
macro expansions far easier, because you can see them after the
compiler process has exited.

Author: DougGregor

include/swift/Basic/DiagnosticOptions.h

@@ -73,6 +73,9 @@ class DiagnosticOptions {
   /// descriptive style that's specific to Swift (currently experimental).
   FormattingStyle PrintedFormattingStyle = FormattingStyle::LLVM;
 
+  /// Whether to emit macro expansion buffers into separate, temporary files.
+  bool EmitMacroExpansionFiles = false;
+
   std::string DiagnosticDocumentationPath = "";
 
   std::string LocalizationCode = "";

include/swift/Basic/SourceManager.h

@@ -350,7 +350,8 @@ class SourceManager {
   llvm::SMDiagnostic GetMessage(SourceLoc Loc, llvm::SourceMgr::DiagKind Kind,
                                 const Twine &Msg,
                                 ArrayRef<llvm::SMRange> Ranges,
-                                ArrayRef<llvm::SMFixIt> FixIts) const;
+                                ArrayRef<llvm::SMFixIt> FixIts,
+                                bool EmitMacroExpansionFiles = false) const;
 
   /// Verifies that all buffers are still valid.
   void verifyAllBuffers() const;

include/swift/Frontend/PrintingDiagnosticConsumer.h

@@ -33,6 +33,7 @@ class PrintingDiagnosticConsumer : public DiagnosticConsumer {
   llvm::raw_ostream &Stream;
   bool ForceColors = false;
   bool PrintEducationalNotes = false;
+  bool EmitMacroExpansionFiles = false;
   bool DidErrorOccur = false;
   DiagnosticOptions::FormattingStyle FormattingStyle =
       DiagnosticOptions::FormattingStyle::LLVM;
@@ -77,6 +78,10 @@ class PrintingDiagnosticConsumer : public DiagnosticConsumer {
     FormattingStyle = style;
   }
 
+  void setEmitMacroExpansionFiles(bool ShouldEmit) {
+    EmitMacroExpansionFiles = ShouldEmit;
+  }
+
   bool didErrorOccur() {
     return DidErrorOccur;
   }

include/swift/Frontend/SerializedDiagnosticConsumer.h

@@ -36,7 +36,7 @@ namespace swift {
     ///
     /// \returns A new diagnostic consumer that serializes diagnostics.
     std::unique_ptr<DiagnosticConsumer>
-    createConsumer(llvm::StringRef outputPath);
+    createConsumer(llvm::StringRef outputPath, bool emitMacroExpansionFiles);
   }
 }
 

include/swift/Option/FrontendOptions.td

@@ -342,6 +342,8 @@ def debug_requirement_machine : Joined<["-"], "debug-requirement-machine=">,
 
 def dump_macro_expansions : Flag<["-"], "dump-macro-expansions">,
   HelpText<"Dumps the results of each macro expansion">;
+def emit_macro_expansion_files : Separate<["-"], "emit-macro-expansion-files">,
+  HelpText<"Specify when to emit macro expansion file: 'none', 'debug', or 'diagnostics'">;
 
 def analyze_requirement_machine : Flag<["-"], "analyze-requirement-machine">,
   Flags<[FrontendOption, HelpHidden, DoesNotAffectIncrementalBuild]>,

lib/DriverTool/swift_api_digester_main.cpp

@@ -1846,7 +1846,7 @@ createDiagConsumer(llvm::raw_ostream &OS, bool &FailOnError, bool DisableFailOnE
   if (!SerializedDiagPath.empty()) {
     FailOnError = !DisableFailOnError;
     results.emplace_back(std::make_unique<PrintingDiagnosticConsumer>());
-    results.emplace_back(serialized_diagnostics::createConsumer(SerializedDiagPath));
+    results.emplace_back(serialized_diagnostics::createConsumer(SerializedDiagPath, false));
   } else if (CompilerStyleDiags) {
     FailOnError = !DisableFailOnError;
     results.emplace_back(std::make_unique<PrintingDiagnosticConsumer>());

lib/Frontend/CompilerInvocation.cpp

@@ -1476,6 +1476,15 @@ static bool ParseDiagnosticArgs(DiagnosticOptions &Opts, ArgList &Args,
     }
   }
 
+  for (const Arg *arg: Args.filtered(OPT_emit_macro_expansion_files)) {
+    StringRef contents = arg->getValue();
+    bool negated = contents.startswith("no-");
+    if (negated)
+      contents = contents.drop_front(3);
+    if (contents == "diagnostics")
+      Opts.EmitMacroExpansionFiles = !negated;
+  }
+
   Opts.FixitCodeForAllDiagnostics |= Args.hasArg(OPT_fixit_all);
   Opts.SuppressWarnings |= Args.hasArg(OPT_suppress_warnings);
   Opts.SuppressRemarks |= Args.hasArg(OPT_suppress_remarks);

lib/Frontend/PrintingDiagnosticConsumer.cpp

@@ -1182,15 +1182,17 @@ void PrintingDiagnosticConsumer::printDiagnostic(SourceManager &SM,
                                            Info.FormatArgs);
   }
 
-  auto Msg = SM.GetMessage(Info.Loc, SMKind, Text, Ranges, FixIts);
+  auto Msg = SM.GetMessage(Info.Loc, SMKind, Text, Ranges, FixIts,
+                           EmitMacroExpansionFiles);
   rawSM.PrintMessage(out, Msg, ForceColors);
 }
 
 llvm::SMDiagnostic
 SourceManager::GetMessage(SourceLoc Loc, llvm::SourceMgr::DiagKind Kind,
                           const Twine &Msg,
                           ArrayRef<llvm::SMRange> Ranges,
-                          ArrayRef<llvm::SMFixIt> FixIts) const {
+                          ArrayRef<llvm::SMFixIt> FixIts,
+                          bool EmitMacroExpansionFiles) const {
 
   // First thing to do: find the current buffer containing the specified
   // location to pull out the source line.
@@ -1200,7 +1202,7 @@ SourceManager::GetMessage(SourceLoc Loc, llvm::SourceMgr::DiagKind Kind,
   std::string LineStr;
 
   if (Loc.isValid()) {
-    BufferID = getDisplayNameForLoc(Loc);
+    BufferID = getDisplayNameForLoc(Loc, EmitMacroExpansionFiles);
     auto CurMB = LLVMSourceMgr.getMemoryBuffer(findBufferContainingLoc(Loc));
 
     // Scan backward to find the start of the line.

lib/Frontend/SerializedDiagnosticConsumer.cpp

@@ -103,12 +103,15 @@ struct SharedState : llvm::RefCountedBase<SharedState> {
 class SerializedDiagnosticConsumer : public DiagnosticConsumer {
   /// State shared among the various clones of this diagnostic consumer.
   llvm::IntrusiveRefCntPtr<SharedState> State;
+  bool EmitMacroExpansionFiles = false;
   bool CalledFinishProcessing = false;
   bool CompilationWasComplete = true;
 
 public:
-  SerializedDiagnosticConsumer(StringRef serializedDiagnosticsPath)
-      : State(new SharedState(serializedDiagnosticsPath)) {
+  SerializedDiagnosticConsumer(StringRef serializedDiagnosticsPath,
+                               bool emitMacroExpansionFiles)
+      : State(new SharedState(serializedDiagnosticsPath)),
+        EmitMacroExpansionFiles(emitMacroExpansionFiles) {
     emitPreamble();
   }
 
@@ -213,8 +216,11 @@ class SerializedDiagnosticConsumer : public DiagnosticConsumer {
 
 namespace swift {
 namespace serialized_diagnostics {
-  std::unique_ptr<DiagnosticConsumer> createConsumer(StringRef outputPath) {
-    return std::make_unique<SerializedDiagnosticConsumer>(outputPath);
+  std::unique_ptr<DiagnosticConsumer> createConsumer(
+      StringRef outputPath, bool emitMacroExpansionFiles
+  ) {
+    return std::make_unique<SerializedDiagnosticConsumer>(
+        outputPath, emitMacroExpansionFiles);
   }
 } // namespace serialized_diagnostics
 } // namespace swift
@@ -256,7 +262,8 @@ unsigned SerializedDiagnosticConsumer::getEmitFile(
   // The source range that this buffer was generated from, expressed as
   // offsets into the original buffer.
   if (generatedInfo->originalSourceRange.isValid()) {
-    auto originalFilename = SM.getDisplayNameForLoc(generatedInfo->originalSourceRange.Start);
+    auto originalFilename = SM.getDisplayNameForLoc(generatedInfo->originalSourceRange.Start,
+                                EmitMacroExpansionFiles);
     addRangeToRecord(
         Lexer::getCharSourceRangeFromSourceRange(
             SM, generatedInfo->originalSourceRange),
@@ -532,7 +539,7 @@ emitDiagnosticMessage(SourceManager &SM,
 
   StringRef filename = "";
   if (Loc.isValid())
-    filename = SM.getDisplayNameForLoc(Loc);
+    filename = SM.getDisplayNameForLoc(Loc, EmitMacroExpansionFiles);
 
   // Emit the RECORD_DIAG record.
   Record.clear();

lib/FrontendTool/FrontendTool.cpp

@@ -1929,15 +1929,19 @@ createDispatchingDiagnosticConsumerIfNeeded(
 /// If no serialized diagnostics are being produced, returns null.
 static std::unique_ptr<DiagnosticConsumer>
 createSerializedDiagnosticConsumerIfNeeded(
-    const FrontendInputsAndOutputs &inputsAndOutputs) {
+    const FrontendInputsAndOutputs &inputsAndOutputs,
+    bool emitMacroExpansionFiles
+) {
   return createDispatchingDiagnosticConsumerIfNeeded(
       inputsAndOutputs,
-      [](const InputFile &input) -> std::unique_ptr<DiagnosticConsumer> {
+      [emitMacroExpansionFiles](
+          const InputFile &input
+      ) -> std::unique_ptr<DiagnosticConsumer> {
         auto serializedDiagnosticsPath = input.getSerializedDiagnosticsPath();
         if (serializedDiagnosticsPath.empty())
           return nullptr;
         return serialized_diagnostics::createConsumer(
-            serializedDiagnosticsPath);
+            serializedDiagnosticsPath, emitMacroExpansionFiles);
       });
 }
 
@@ -2268,7 +2272,8 @@ int swift::performFrontend(ArrayRef<const char *> Args,
   // See https://github.com/apple/swift/issues/45288 for details.
   std::unique_ptr<DiagnosticConsumer> SerializedConsumerDispatcher =
       createSerializedDiagnosticConsumerIfNeeded(
-        Invocation.getFrontendOptions().InputsAndOutputs);
+        Invocation.getFrontendOptions().InputsAndOutputs,
+        Invocation.getDiagnosticOptions().EmitMacroExpansionFiles);
   if (SerializedConsumerDispatcher)
     Instance->addDiagnosticConsumer(SerializedConsumerDispatcher.get());
 
@@ -2286,6 +2291,9 @@ int swift::performFrontend(ArrayRef<const char *> Args,
   PDC.setFormattingStyle(
       Invocation.getDiagnosticOptions().PrintedFormattingStyle);
 
+  PDC.setEmitMacroExpansionFiles(
+      Invocation.getDiagnosticOptions().EmitMacroExpansionFiles);
+
   if (Invocation.getFrontendOptions().PrintStats) {
     llvm::EnableStatistics();
   }