[flang] Extend runtime API for PAUSE to allow a stop code

[klausler]

Summary

Support integer and default character stop codes on PAUSE
statements. Add length argument to STOP statement with a
character stop code.

flang/runtime/stop.h

 #include "entry-names.h"
 #include <stdlib.h>
 
 FORTRAN_EXTERN_C_BEGIN
 
 // Program-initiated image stop
 NORETURN void RTNAME(StopStatement)(int code DEFAULT_VALUE(EXIT_SUCCESS),
     bool isErrorStop DEFAULT_VALUE(false), bool quiet DEFAULT_VALUE(false));
-NORETURN void RTNAME(StopStatementText)(const char *,
+NORETURN void RTNAME(StopStatementText)(const char *, size_t,
     bool isErrorStop DEFAULT_VALUE(false), bool quiet DEFAULT_VALUE(false));
 void RTNAME(PauseStatement)(NO_ARGUMENTS);
+void RTNAME(PauseStatementInt)(int);
+void RTNAME(PauseStatementText)(const char *, size_t);
 NORETURN void RTNAME(FailImageStatement)(NO_ARGUMENTS);
 NORETURN void RTNAME(ProgramEndStatement)(NO_ARGUMENTS);
 
 FORTRAN_EXTERN_C_END
 
 #endif // FORTRAN_RUNTIME_STOP_H_

flang/runtime/stop.cpp

if (!quiet) {
     }
     std::fputc('\n', stderr);
     DescribeIEEESignaledExceptions();
   }
   std::exit(code);
 }
 
 [[noreturn]] void RTNAME(StopStatementText)(
-    const char *code, bool isErrorStop, bool quiet) {
+    const char *code, std::size_t length, bool isErrorStop, bool quiet) {
   CloseAllExternalUnits("STOP statement");
   if (!quiet) {
-    std::fprintf(
-        stderr, "Fortran %s: %s\n", isErrorStop ? "ERROR STOP" : "STOP", code);
+    std::fprintf(stderr, "Fortran %s: %.*s\n",
+        isErrorStop ? "ERROR STOP" : "STOP", static_cast<int>(length), code);
     DescribeIEEESignaledExceptions();
   }
   std::exit(EXIT_FAILURE);
 }
 
-void RTNAME(PauseStatement)() {
+static bool StartPause() {
   if (Fortran::runtime::io::IsATerminal(0)) {
     Fortran::runtime::io::IoErrorHandler handler{"PAUSE statement"};
     Fortran::runtime::io::ExternalFileUnit::FlushAll(handler);
-    std::fputs("Fortran PAUSE: hit RETURN to continue:", stderr);
-    std::fflush(nullptr);
-    if (std::fgetc(stdin) == EOF) {
-      CloseAllExternalUnits("PAUSE statement");
-      std::exit(EXIT_SUCCESS);
-    }
-  }
+    return true;
+  }
+  return false;
+}
+
+static void EndPause() {
+
+void RTNAME(PauseStatement)() {
+  if (StartPause()) {
+    std::fputs("Fortran PAUSE: hit RETURN to continue:", stderr);
+    EndPause();
+  }
+}
+
+void RTNAME(PauseStatementInt)(int code) {
+  if (StartPause()) {
+    std::fprintf(stderr, "Fortran PAUSE %d: hit RETURN to continue:", code);
+    EndPause();
+  }
+}
+
+void RTNAME(PauseStatementText)(const char *code, std::size_t length) {
+  if (StartPause()) {
+    std::fprintf(stderr,
+        "Fortran PAUSE %.*s: hit RETURN to continue:", static_cast<int>(length),
+        code);
+    EndPause();
+  }
 }
 
 [[noreturn]] void RTNAME(FailImageStatement)() {
   Fortran::runtime::NotifyOtherImagesOfFailImageStatement();
   CloseAllExternalUnits("FAIL IMAGE statement");
   std::exit(EXIT_FAILURE);
 }
 
 [[noreturn]] void RTNAME(ProgramEndStatement)() {
   CloseAllExternalUnits("END statement");
   std::exit(EXIT_SUCCESS);
 }
 }