[flang] Detect and report parsing failure

flang/lib/Frontend/FrontendAction.cpp

@@ -232,6 +232,19 @@ bool FrontendAction::reportFatalErrors(const char (&message)[N]) {
                                            instance->getAllCookedSources());
     return true;
   }
+  if (instance->getParsing().parseTree().has_value() &&
+      !instance->getParsing().consumedWholeFile()) {
+    // Parsing failed without error.
+    const unsigned diagID = instance->getDiagnostics().getCustomDiagID(
+        clang::DiagnosticsEngine::Error, message);
+    instance->getDiagnostics().Report(diagID) << getCurrentFileOrBufferName();
+    instance->getParsing().messages().Emit(llvm::errs(),
+                                           instance->getAllCookedSources());
+    instance->getParsing().EmitMessage(
+        llvm::errs(), instance->getParsing().finalRestingPlace(),
+        "parser FAIL (final position)", "error: ", llvm::raw_ostream::RED);
+    return true;
+  }
   return false;
 }
 

flang/lib/Frontend/FrontendActions.cpp

@@ -566,9 +566,11 @@ void DebugMeasureParseTreeAction::executeAction() {
   // Parse. In case of failure, report and return.
   ci.getParsing().Parse(llvm::outs());
 
-  if (!ci.getParsing().messages().empty() &&
-      (ci.getInvocation().getWarnAsErr() ||
-       ci.getParsing().messages().AnyFatalError())) {
+  if ((ci.getParsing().parseTree().has_value() &&
+       !ci.getParsing().consumedWholeFile()) ||
+      (!ci.getParsing().messages().empty() &&
+       (ci.getInvocation().getWarnAsErr() ||
+        ci.getParsing().messages().AnyFatalError()))) {
     unsigned diagID = ci.getDiagnostics().getCustomDiagID(
         clang::DiagnosticsEngine::Error, "Could not parse %0");
     ci.getDiagnostics().Report(diagID) << getCurrentFileOrBufferName();

flang/test/Integration/debug-local-var-2.f90

@@ -107,4 +107,4 @@ function fn2(a2, b2, c2) result (res2)
   end function
 end program
 
-LINEONLY-NOT: DILocalVariable
+! LINEONLY-NOT: DILocalVariable

flang/test/Parser/at-process.f

@@ -1,4 +1,4 @@
-! RUN: %flang_fc1 -fsyntax-only %s 2>&1 | FileCheck %s
+! RUN: not %flang_fc1 -fsyntax-only %s 2>&1 | FileCheck %s
 
 ! Test ignoring @PROCESS directive in fixed source form
 
@@ -18,3 +18,5 @@ subroutine f()
 
 !CHECK: Character in fixed-form label field must be a digit
 @precoss 
+
+!CHECK: at-process.f:14:1: error: parser FAIL (final position)

flang/test/Parser/unparseable.f90

@@ -0,0 +1,5 @@
+! RUN: not %flang_fc1 -fsyntax-only %s 2>&1 | FileCheck %s
+! CHECK: unparseable.f90:5:1: error: parser FAIL (final position)
+module m
+end
+select type (barf)