[flang] Respect NO_STOP_MESSAGE=1 in runtime

[klausler]

Summary

When an environment variable NO_STOP_MESSAGE=1 is set,
assume that STOP statements with a successful code
have QUIET=.TRUE.

[jeanPerier]

LGTM

flang/runtime/environment.h

 struct ExecutionEnvironment {
   void Configure(int argc, const char *argv[], const char *envp[]);
   const char *GetEnv(
       const char *name, std::size_t name_length, const Terminator &terminator);
 
   int argc;
   const char **argv;
   const char **envp;
-  int listDirectedOutputLineLengthLimit;
+
+  int listDirectedOutputLineLengthLimit; // FORT_FMT_RECL
   enum decimal::FortranRounding defaultOutputRoundingMode;
-  Convert conversion;
+  Convert conversion; // FORT_CONVERT
+  bool noStopMessage; // NO_STOP_MESSAGE=1 inhibits "Fortran STOP"
 };
 extern ExecutionEnvironment executionEnvironment;
 } // namespace Fortran::runtime
 
 #endif // FORTRAN_RUNTIME_ENVIRONMENT_H_

flang/runtime/environment.cpp

if (auto *x{std::getenv("FORT_CONVERT")}) {
     if (auto convert{GetConvertFromString(x, std::strlen(x))}) {
       conversion = *convert;
     } else {
       std::fprintf(
           stderr, "Fortran runtime: FORT_CONVERT=%s is invalid; ignored\n", x);
     }
   }
 
+  if (auto *x{std::getenv("NO_STOP_MESSAGE")}) {
+    char *end;
+    auto n{std::strtol(x, &end, 10)};
+    if (n >= 0 && n <= 1 && *end == '\0') {
+      noStopMessage = n != 0;
+    } else {
+      std::fprintf(stderr,
+          "Fortran runtime: NO_STOP_MESSAGE=%s is invalid; ignored\n", x);
+    }
+  }
+
   // TODO: Set RP/ROUND='PROCESSOR_DEFINED' from environment
 }
 
 const char *ExecutionEnvironment::GetEnv(
     const char *name, std::size_t name_length, const Terminator &terminator) {
   RUNTIME_CHECK(terminator, name && name_length);
 
   OwningPtr<char> cStyleName{
       SaveDefaultCharacter(name, name_length, terminator)};
   RUNTIME_CHECK(terminator, cStyleName);
 
   return std::getenv(cStyleName.get());
 }
 } // namespace Fortran::runtime

flang/runtime/stop.cpp

 //===-- runtime/stop.cpp --------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/stop.h"
+#include "environment.h"
 #include "file.h"
 #include "io-error.h"
 #include "terminator.h"
 #include "unit.h"
 #include <cfenv>
 #include <cstdio>
 #include <cstdlib>
 

 static void CloseAllExternalUnits(const char *why) {
   Fortran::runtime::io::IoErrorHandler handler{why};
   Fortran::runtime::io::ExternalFileUnit::CloseAll(handler);
 }
 
 [[noreturn]] void RTNAME(StopStatement)(
     int code, bool isErrorStop, bool quiet) {
   CloseAllExternalUnits("STOP statement");
+  if (Fortran::runtime::executionEnvironment.noStopMessage && code == 0) {
+    quiet = true;
+  }
   if (!quiet) {
     std::fprintf(stderr, "Fortran %s", isErrorStop ? "ERROR STOP" : "STOP");
     if (code != EXIT_SUCCESS) {
       std::fprintf(stderr, ": code %d\n", code);
     }
     std::fputc('\n', stderr);
     DescribeIEEESignaledExceptions();
   }