[flang][driver] Add actions that execute despite semantic errors

[awarzynski]

Summary

This patch adds a new abstract class for frontend actions: PrescanAndSemaDebugAction. It's very similar to PrescanAndSemaAction, but in the presence of semantic errors it does not skip the corresponding ExecuteAction specialisation. Instead, it runs it as if there were no semantic errors. This class is for developer actions only (i.e. front-end driver options).

The new behaviour does not affect the return code from flang-new -fc1 when the input file is semantically incorrect. The return code is inferred from the number of driver diagnostics generated in CompilerInstance::ExecuteAction and this patch does not change that. More specifically, the semantic errors are still reported and hence the driver is able to correctly report that the compilation has failed (with a non-zero return code).

This new base class is meant for debug actions only and DebugDumpAllAction is updated to demonstrate the new behaviour. With this change, flang-new -fc1 -fdebug-dump-all dumps the parse tree and symbols for all input files, regardless of whether any semantic errors were found.

This patch addresses https://bugs.llvm.org/show_bug.cgi?id=52097.

[PeteSteinfeld]

LGTM

All looks good. Thanks for doing this!

[MatsPetersson]

flang/lib/Frontend/FrontendActions.cpp

45

Probably should fix the & to && in this one too, following the suggestion from FIR-Dev.

[awarzynski]

As per suggestion from @MatsPetersson, fixing the erroneous &.

[awarzynski]

Thanks Mats!

flang/lib/Frontend/FrontendActions.cpp

45

For our future selves: https://github.com/flang-compiler/f18-llvm-project/pull/1113#discussion_r724321121

[PeteSteinfeld]

flang/lib/Frontend/FrontendActions.cpp

45

Note that this line of code is also modified by https://reviews.llvm.org/D111395. Should these patches be combined?

[awarzynski]

flang/lib/Frontend/FrontendActions.cpp

45

https://reviews.llvm.org/D111395 fixes a bug on L40, so it's a different line.

This patch creates PrescanAndSemaDebugAction. It will work correctly without modifying PrescanAndSemaAction. https://reviews.llvm.org/D111395 fixes the latter, but that does not affect the former.

As the two changes are unrelated, I think that it's worthwhile to keep them in separate commits. This way it will be easier to track down the rationale for the fix.

[Leporacanthicus]

LGTM

flang/include/flang/Frontend/FrontendActions.h

 };
 
 class DebugDumpParseTreeNoSemaAction : public PrescanAndParseAction {
   void ExecuteAction() override;
 };
 
 //===----------------------------------------------------------------------===//
 // PrescanAndSema Actions
+//
+// These actions will parse the input, run the semantic checks and execute
+// their actions provided that no parsing or semantic errors were found.
 //===----------------------------------------------------------------------===//
 class PrescanAndSemaAction : public FrontendAction {
 
   void ExecuteAction() override = 0;
   bool BeginSourceFileAction() override;
 };
 
 class DebugUnparseWithSymbolsAction : public PrescanAndSemaAction {
   void ExecuteAction() override;
 };
 
 class DebugUnparseAction : public PrescanAndSemaAction {
   void ExecuteAction() override;
 };
 
 class DebugDumpSymbolsAction : public PrescanAndSemaAction {
   void ExecuteAction() override;
 };
 
 class DebugDumpParseTreeAction : public PrescanAndSemaAction {
   void ExecuteAction() override;
 };
 
-class DebugDumpAllAction : public PrescanAndSemaAction {
-  void ExecuteAction() override;
-};
-
 class DebugPreFIRTreeAction : public PrescanAndSemaAction {
   void ExecuteAction() override;
 };
 
 class GetDefinitionAction : public PrescanAndSemaAction {
   void ExecuteAction() override;
 };
 
 class GetSymbolsSourcesAction : public PrescanAndSemaAction {
   void ExecuteAction() override;
 };
 
 class ParseSyntaxOnlyAction : public PrescanAndSemaAction {
   void ExecuteAction() override;
 };
 
 class PluginParseTreeAction : public PrescanAndSemaAction {
   void ExecuteAction() override = 0;
 };
 
+//===----------------------------------------------------------------------===//
+// PrescanAndSemaDebug Actions
+//
+// These actions will parse the input, run the semantic checks and execute
+// their actions regardless of whether any semantic errors are found.
+//===----------------------------------------------------------------------===//
+class PrescanAndSemaDebugAction : public FrontendAction {
+
+  void ExecuteAction() override = 0;
+  bool BeginSourceFileAction() override;
+};
+
+class DebugDumpAllAction : public PrescanAndSemaDebugAction {
+  void ExecuteAction() override;
+};
+
 } // namespace Fortran::frontend
 
 #endif // LLVM_FLANG_FRONTEND_FRONTENDACTIONS_H

flang/lib/Frontend/FrontendActions.cpp

 bool PrescanAndParseAction::BeginSourceFileAction() {
   return RunPrescan() && RunParse();
 }
 
 bool PrescanAndSemaAction::BeginSourceFileAction() {
   return RunPrescan() && RunParse() && RunSemanticChecks();
 }
 
+bool PrescanAndSemaDebugAction::BeginSourceFileAction() {
+  // Semantic checks are made to succeed unconditionally.
+  return RunPrescan() && RunParse() && (RunSemanticChecks() || true);
+}
+
 //===----------------------------------------------------------------------===//
 // Custom ExecuteAction
 //===----------------------------------------------------------------------===//
 void InputOutputTestAction::ExecuteAction() {
   CompilerInstance &ci = instance();
 
   // Create a stream for errors
   std::string buf;

flang/test/Driver/dump-all-bad.f90

+! Verify that -fdebug-dump-all dumps both symbols and the parse tree, even when semantic errors are present
+
+!----------
+! RUN lines
+!----------
+! RUN: not %flang_fc1 -fdebug-dump-all %s 2>&1 | FileCheck %s
+
+!----------------
+! EXPECTED OUTPUT
+!----------------
+! CHECK: error: Semantic errors in
+! CHECK: Flang: parse tree dump
+! CHECK: Flang: symbols dump
+
+!-------
+! INPUT
+!-------
+program bad
+  real,pointer :: x
+  x = null()      ! Error - must be pointer assignment
+end