[flang][runtime] Reset the left tab limit when flushing output

When flushing output to a non-positionable tty or socket file, reset the
left tab limit.  Otherwise, non-advancing output to that file will contain
an increasing amount of leading spaces in each flush.  Also, detect
newline characters in stream output, and treat them as record
advancement.

Differential Revision: https://reviews.llvm.org/D148157

flang/runtime/emit-encoded.h

@@ -13,13 +13,28 @@
 
 #include "connection.h"
 #include "environment.h"
+#include "tools.h"
 #include "utf.h"
 
 namespace Fortran::runtime::io {
 
 template <typename CONTEXT, typename CHAR>
 bool EmitEncoded(CONTEXT &to, const CHAR *data, std::size_t chars) {
   ConnectionState &connection{to.GetConnectionState()};
+  if (connection.access == Access::Stream &&
+      connection.internalIoCharKind == 0) {
+    // Stream output: treat newlines as record advancements so that the left tab
+    // limit is correctly managed
+    while (const CHAR * nl{FindCharacter(data, CHAR{'\n'}, chars)}) {
+      auto pos{static_cast<std::size_t>(nl - data)};
+      if (!EmitEncoded(to, data, pos)) {
+        return false;
+      }
+      data += pos + 1;
+      chars -= pos + 1;
+      to.AdvanceRecord();
+    }
+  }
   if (connection.useUTF8<CHAR>()) {
     using UnsignedChar = std::make_unsigned_t<CHAR>;
     const UnsignedChar *uData{reinterpret_cast<const UnsignedChar *>(data)};
@@ -61,7 +76,8 @@ bool EmitEncoded(CONTEXT &to, const CHAR *data, std::size_t chars) {
 template <typename CONTEXT>
 bool EmitAscii(CONTEXT &to, const char *data, std::size_t chars) {
   ConnectionState &connection{to.GetConnectionState()};
-  if (connection.internalIoCharKind <= 1) {
+  if (connection.internalIoCharKind <= 1 &&
+      connection.access != Access::Stream) {
     return to.Emit(data, chars);
   } else {
     return EmitEncoded(to, data, chars);
@@ -74,7 +90,9 @@ bool EmitRepeated(CONTEXT &to, char ch, std::size_t n) {
     return true;
   }
   ConnectionState &connection{to.GetConnectionState()};
-  if (connection.internalIoCharKind <= 1) {
+  if (connection.internalIoCharKind <= 1 &&
+      connection.access != Access::Stream) {
+    // faster path, no encoding needed
     while (n-- > 0) {
       if (!to.Emit(&ch, 1)) {
         return false;

flang/runtime/tools.h

@@ -13,6 +13,7 @@
 #include "flang/Runtime/cpp-type.h"
 #include "flang/Runtime/descriptor.h"
 #include "flang/Runtime/memory.h"
+#include <cstring>
 #include <functional>
 #include <map>
 #include <type_traits>
@@ -356,5 +357,24 @@ using AccumulationType = CppTypeFor<CAT,
         ? std::max(KIND, static_cast<int>(sizeof(double)))
         : KIND>;
 
+// memchr() for any character type
+template <typename CHAR>
+static inline const CHAR *FindCharacter(
+    const CHAR *data, CHAR ch, std::size_t chars) {
+  const CHAR *end{data + chars};
+  for (const CHAR *p{data}; p < end; ++p) {
+    if (*p == ch) {
+      return p;
+    }
+  }
+  return nullptr;
+}
+
+template <>
+inline const char *FindCharacter(const char *data, char ch, std::size_t chars) {
+  return reinterpret_cast<const char *>(
+      std::memchr(data, static_cast<int>(ch), chars));
+}
+
 } // namespace Fortran::runtime
 #endif // FORTRAN_RUNTIME_TOOLS_H_

flang/runtime/unit.cpp

@@ -9,6 +9,7 @@
 #include "unit.h"
 #include "io-error.h"
 #include "lock.h"
+#include "tools.h"
 #include "unit-map.h"
 #include <cstdio>
 #include <limits>
@@ -417,8 +418,7 @@ bool ExternalFileUnit::SetVariableFormattedRecordLength() {
   } else if (FrameLength() > recordOffsetInFrame_) {
     const char *record{Frame() + recordOffsetInFrame_};
     std::size_t bytes{FrameLength() - recordOffsetInFrame_};
-    if (const char *nl{
-            reinterpret_cast<const char *>(std::memchr(record, '\n', bytes))}) {
+    if (const char *nl{FindCharacter(record, '\n', bytes)}) {
       recordLength = nl - record;
       if (*recordLength > 0 && record[*recordLength - 1] == '\r') {
         --*recordLength;
@@ -621,6 +621,7 @@ void ExternalFileUnit::FlushOutput(IoErrorHandler &handler) {
       // needs to advance frameOffsetInFile_ to prevent attempts at
       // impossible seeks
       CommitWrites();
+      leftTabLimit.reset();
     }
   }
   Flush(handler);