[flang][runtime] Emit leading spaces in NAMELIST output (#76846)

As NAMELIST output is a variant of list-directed output, its editing
must produce leading spaces on (most) output records to effect carriage
control. These spaces are required by the language standard and
implemented by nearly all other Fortran compilers (except GNU).

Fixes https://github.com/llvm/llvm-project/issues/76798.

2 files changed, 21 insertions, 20 deletions

diff --git a/flang/runtime/namelist.cpp b/flang/runtime/namelist.cpp
index e6997bc..848ebcf 100644
--- a/flang/runtime/namelist.cpp
+++ b/flang/runtime/namelist.cpp
@@ -30,16 +30,15 @@ bool IONAME(OutputNamelist)(Cookie cookie, const NamelistGroup &group) {
   IoStatementState &io{*cookie};
   io.CheckFormattedStmtType<Direction::Output>("OutputNamelist");
   io.mutableModes().inNamelist = true;
-  char comma{static_cast<char>(GetComma(io))};
   ConnectionState &connection{io.GetConnectionState()};
-  // Internal functions to advance records and convert case
-  const auto EmitWithAdvance{[&](char ch) -> bool {
-    return (!connection.NeedAdvance(1) || io.AdvanceRecord()) &&
-        EmitAscii(io, &ch, 1);
-  }};
-  const auto EmitUpperCase{[&](const char *str) -> bool {
-    if (connection.NeedAdvance(std::strlen(str)) &&
-        !(io.AdvanceRecord() && EmitAscii(io, " ", 1))) {
+  // Internal function to advance records and convert case
+  const auto EmitUpperCase{[&](const char *prefix, std::size_t prefixLen,
+                               const char *str, char suffix) -> bool {
+    if ((connection.NeedAdvance(prefixLen) &&
+            !(io.AdvanceRecord() && EmitAscii(io, " ", 1))) ||
+        !EmitAscii(io, prefix, prefixLen) ||
+        (connection.NeedAdvance(std::strlen(str) + (suffix != ' ')) &&
+            !(io.AdvanceRecord() && EmitAscii(io, " ", 1)))) {
       return false;
     }
     for (; *str; ++str) {
@@ -49,23 +48,25 @@ bool IONAME(OutputNamelist)(Cookie cookie, const NamelistGroup &group) {
         return false;
       }
     }
-    return true;
+    return suffix == ' ' || EmitAscii(io, &suffix, 1);
   }};
   // &GROUP
-  if (!(EmitWithAdvance('&') && EmitUpperCase(group.groupName))) {
+  if (!EmitUpperCase(" &", 2, group.groupName, ' ')) {
     return false;
   }
   auto *listOutput{io.get_if<ListDirectedStatementState<Direction::Output>>()};
+  char comma{static_cast<char>(GetComma(io))};
+  char prefix{' '};
   for (std::size_t j{0}; j < group.items; ++j) {
     // [,]ITEM=...
     const NamelistGroup::Item &item{group.item[j]};
     if (listOutput) {
       listOutput->set_lastWasUndelimitedCharacter(false);
     }
-    if (!EmitWithAdvance(j == 0 ? ' ' : comma) || !EmitUpperCase(item.name) ||
-        !EmitWithAdvance('=')) {
+    if (!EmitUpperCase(&prefix, 1, item.name, '=')) {
       return false;
     }
+    prefix = comma;
     if (const auto *addendum{item.descriptor.Addendum()};
         addendum && addendum->derivedType()) {
       const NonTbpDefinedIoTable *table{group.nonTbpDefinedIo};
@@ -77,7 +78,7 @@ bool IONAME(OutputNamelist)(Cookie cookie, const NamelistGroup &group) {
     }
   }
   // terminal /
-  return EmitWithAdvance('/');
+  return EmitUpperCase("/", 1, "", ' ');
 }
 
 static constexpr bool IsLegalIdStart(char32_t ch) {
diff --git a/flang/unittests/Runtime/Namelist.cpp b/flang/unittests/Runtime/Namelist.cpp
index 5911d67..f95c5d2 100644
--- a/flang/unittests/Runtime/Namelist.cpp
+++ b/flang/unittests/Runtime/Namelist.cpp
@@ -88,7 +88,7 @@ TEST(NamelistTests, BasicSanity) {
   ASSERT_EQ(outStatus1, 0) << "Failed namelist output sanity, status "
                            << static_cast<int>(outStatus1);
 
-  static const std::string expect{"&GROUP1 INTS= 1 -2 4 -8 16 -32  "
+  static const std::string expect{" &GROUP1 INTS= 1 -2 4 -8 16 -32 "
                                   " 64 -128 256 -512 1024 -2048    "
                                   " 4096 -8192 16384 -32768 65536  "
                                   " -131072 262144 -524288,REALS=  "
@@ -157,7 +157,7 @@ TEST(NamelistTests, Subscripts) {
       << "Failed namelist output subscripts rewrite, status "
       << static_cast<int>(outStatus);
   std::string got{out, sizeof out};
-  static const std::string expect{"&JUSTA A= 0 2 0 0 0 1/                  "};
+  static const std::string expect{" &JUSTA A= 0 2 0 0 0 1/                 "};
   EXPECT_EQ(got, expect);
 }
 
@@ -213,7 +213,7 @@ TEST(NamelistTests, ScalarSubstring) {
   ASSERT_TRUE(IONAME(OutputNamelist)(outCookie, group));
   ASSERT_EQ(IONAME(EndIoStatement)(outCookie), IostatOk) << "namelist output";
   std::string got{out, sizeof out};
-  static const std::string expect{"&JUSTA A= 'aBCDEfgh'/           "};
+  static const std::string expect{" &JUSTA A= 'aBCDEfgh'/          "};
   EXPECT_EQ(got, expect);
 }
 
@@ -242,7 +242,7 @@ TEST(NamelistTests, ArraySubstring) {
   ASSERT_TRUE(IONAME(OutputNamelist)(outCookie, group));
   ASSERT_EQ(IONAME(EndIoStatement)(outCookie), IostatOk) << "namelist output";
   std::string got{out, sizeof out};
-  static const std::string expect{"&JUSTA A= 'aBCDEfgh' 'iJKLMnop'/        "};
+  static const std::string expect{" &JUSTA A= 'aBCDEfgh' 'iJKLMnop'/       "};
   EXPECT_EQ(got, expect);
 }
 
@@ -270,7 +270,7 @@ TEST(NamelistTests, Skip) {
   ASSERT_TRUE(IONAME(OutputNamelist)(outCookie, group));
   ASSERT_EQ(IONAME(EndIoStatement)(outCookie), IostatOk) << "namelist output";
   std::string got{out, sizeof out};
-  static const std::string expect{"&NML J= 123/        "};
+  static const std::string expect{" &NML J= 123/       "};
   EXPECT_EQ(got, expect);
 }
 
@@ -301,7 +301,7 @@ TEST(NamelistTests, Comma) {
   ASSERT_TRUE(IONAME(OutputNamelist)(outCookie, group));
   ASSERT_EQ(IONAME(EndIoStatement)(outCookie), IostatOk) << "namelist output";
   std::string got{out, sizeof out};
-  static const std::string expect{"&NML Z= (-1,;2,) (-3,;,5)/    "};
+  static const std::string expect{" &NML Z= (-1,;2,) (-3,;,5)/   "};
   EXPECT_EQ(got, expect);
 }