[flang] Support NAMELIST input of short arrays

NAMELIST array input does not need to fully define an array.
If another input item begins after at least one element,
it ends input into the array and the remaining items are
not modified.

The tricky part of supporting this feature is that it's not
always easy to determine whether the next non-blank thing in
the input is a value or the next item's name, esp. in the case
of logical data where T and F can be names.  E.g.,

  &group logicalArray = t f f t
      = 1 /

should read three elements into "logicalArray" and then read
an integer or real variable named "t".

So the I/O runtime has to do some look-ahead to determine whether
the next thing in the input is a name followed by '=', '(', or '%'.
Since the '=' may be on a later record, possibly with intervening
NAMELIST comments, the runtime has to support a general form of
saving and restoring its current position.  The infrastructure
in the I/O runtime already has to support repositioning for
list-directed repetition, even on non-positionable input sources
like terminals and sockets; this patch adds an internal RAII API
to make it easier to save a position and then do arbitrary
look-ahead.

Differential Revision: https://reviews.llvm.org/D112245

flang/runtime/connection.h

@@ -66,5 +66,32 @@ struct ConnectionState : public ConnectionAttributes {
   // Mutable modes set at OPEN() that can be overridden in READ/WRITE & FORMAT
   MutableModes modes; // BLANK=, DECIMAL=, SIGN=, ROUND=, PAD=, DELIM=, kP
 };
+
+// Utility class for capturing and restoring a position in an input stream.
+class SavedPosition {
+public:
+  explicit SavedPosition(ConnectionState &c)
+      : connection_{c}, positionInRecord_{c.positionInRecord},
+        furthestPositionInRecord_{c.furthestPositionInRecord},
+        leftTabLimit_{c.leftTabLimit}, previousResumptionRecordNumber_{
+                                           c.resumptionRecordNumber} {
+    c.resumptionRecordNumber = c.currentRecordNumber;
+  }
+  ~SavedPosition() {
+    connection_.currentRecordNumber = *connection_.resumptionRecordNumber;
+    connection_.resumptionRecordNumber = previousResumptionRecordNumber_;
+    connection_.leftTabLimit = leftTabLimit_;
+    connection_.furthestPositionInRecord = furthestPositionInRecord_;
+    connection_.positionInRecord = positionInRecord_;
+  }
+
+private:
+  ConnectionState &connection_;
+  std::int64_t positionInRecord_;
+  std::int64_t furthestPositionInRecord_;
+  std::optional<std::int64_t> leftTabLimit_;
+  std::optional<std::int64_t> previousResumptionRecordNumber_;
+};
+
 } // namespace Fortran::runtime::io
 #endif // FORTRAN_RUNTIME_IO_CONNECTION_H_

flang/runtime/descriptor-io.h

@@ -49,6 +49,7 @@ inline bool FormattedIntegerIO(
   SubscriptValue subscripts[maxRank];
   descriptor.GetLowerBounds(subscripts);
   using IntType = CppTypeFor<TypeCategory::Integer, KIND>;
+  bool anyInput{false};
   for (std::size_t j{0}; j < numElements; ++j) {
     if (auto edit{io.GetNextDataEdit()}) {
       IntType &x{ExtractElement<IntType>(io, descriptor, subscripts)};
@@ -57,8 +58,10 @@ inline bool FormattedIntegerIO(
           return false;
         }
       } else if (edit->descriptor != DataEdit::ListDirectedNullValue) {
-        if (!EditIntegerInput(io, *edit, reinterpret_cast<void *>(&x), KIND)) {
+        if (EditIntegerInput(io, *edit, reinterpret_cast<void *>(&x), KIND)) {
-          return false;
+          anyInput = true;
+        } else {
+          return anyInput && edit->IsNamelist();
         }
       }
       if (!descriptor.IncrementSubscripts(subscripts) && j + 1 < numElements) {
@@ -79,6 +82,7 @@ inline bool FormattedRealIO(
   SubscriptValue subscripts[maxRank];
   descriptor.GetLowerBounds(subscripts);
   using RawType = typename RealOutputEditing<KIND>::BinaryFloatingPoint;
+  bool anyInput{false};
   for (std::size_t j{0}; j < numElements; ++j) {
     if (auto edit{io.GetNextDataEdit()}) {
       RawType &x{ExtractElement<RawType>(io, descriptor, subscripts)};
@@ -87,8 +91,10 @@ inline bool FormattedRealIO(
           return false;
         }
       } else if (edit->descriptor != DataEdit::ListDirectedNullValue) {
-        if (!EditRealInput<KIND>(io, *edit, reinterpret_cast<void *>(&x))) {
+        if (EditRealInput<KIND>(io, *edit, reinterpret_cast<void *>(&x))) {
-          return false;
+          anyInput = true;
+        } else {
+          return anyInput && edit->IsNamelist();
         }
       }
       if (!descriptor.IncrementSubscripts(subscripts) && j + 1 < numElements) {
@@ -111,6 +117,7 @@ inline bool FormattedComplexIO(
   bool isListOutput{
       io.get_if<ListDirectedStatementState<Direction::Output>>() != nullptr};
   using RawType = typename RealOutputEditing<KIND>::BinaryFloatingPoint;
+  bool anyInput{false};
   for (std::size_t j{0}; j < numElements; ++j) {
     RawType *x{&ExtractElement<RawType>(io, descriptor, subscripts)};
     if (isListOutput) {
@@ -132,9 +139,11 @@ inline bool FormattedComplexIO(
           }
         } else if (edit->descriptor == DataEdit::ListDirectedNullValue) {
           break;
-        } else if (!EditRealInput<KIND>(
+        } else if (EditRealInput<KIND>(
                        io, *edit, reinterpret_cast<void *>(x))) {
-          return false;
+          anyInput = true;
+        } else {
+          return anyInput && edit->IsNamelist();
         }
       }
     }
@@ -154,6 +163,7 @@ inline bool FormattedCharacterIO(
   descriptor.GetLowerBounds(subscripts);
   std::size_t length{descriptor.ElementBytes() / sizeof(A)};
   auto *listOutput{io.get_if<ListDirectedStatementState<Direction::Output>>()};
+  bool anyInput{false};
   for (std::size_t j{0}; j < numElements; ++j) {
     A *x{&ExtractElement<A>(io, descriptor, subscripts)};
     if (listOutput) {
@@ -167,8 +177,10 @@ inline bool FormattedCharacterIO(
         }
       } else {
         if (edit->descriptor != DataEdit::ListDirectedNullValue) {
-          if (!EditDefaultCharacterInput(io, *edit, x, length)) {
+          if (EditDefaultCharacterInput(io, *edit, x, length)) {
-            return false;
+            anyInput = true;
+          } else {
+            return anyInput && edit->IsNamelist();
           }
         }
       }
@@ -191,6 +203,7 @@ inline bool FormattedLogicalIO(
   descriptor.GetLowerBounds(subscripts);
   auto *listOutput{io.get_if<ListDirectedStatementState<Direction::Output>>()};
   using IntType = CppTypeFor<TypeCategory::Integer, KIND>;
+  bool anyInput{false};
   for (std::size_t j{0}; j < numElements; ++j) {
     IntType &x{ExtractElement<IntType>(io, descriptor, subscripts)};
     if (listOutput) {
@@ -207,8 +220,9 @@ inline bool FormattedLogicalIO(
           bool truth{};
           if (EditLogicalInput(io, *edit, truth)) {
             x = truth;
+            anyInput = true;
           } else {
-            return false;
+            return anyInput && edit->IsNamelist();
           }
         }
       }

flang/runtime/edit-input.cpp

@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "edit-input.h"
+#include "namelist.h"
 #include "flang/Common/real.h"
 #include "flang/Common/uint128.h"
 #include <algorithm>
@@ -69,6 +70,10 @@ bool EditIntegerInput(
   RUNTIME_CHECK(io.GetIoErrorHandler(), kind >= 1 && !(kind & (kind - 1)));
   switch (edit.descriptor) {
   case DataEdit::ListDirected:
+    if (IsNamelistName(io)) {
+      return false;
+    }
+    break;
   case 'G':
   case 'I':
     break;
@@ -298,6 +303,10 @@ bool EditRealInput(IoStatementState &io, const DataEdit &edit, void *n) {
   constexpr int binaryPrecision{common::PrecisionOfRealKind(KIND)};
   switch (edit.descriptor) {
   case DataEdit::ListDirected:
+    if (IsNamelistName(io)) {
+      return false;
+    }
+    return EditCommonRealInput<KIND>(io, edit, n);
   case DataEdit::ListDirectedRealPart:
   case DataEdit::ListDirectedImaginaryPart:
   case 'F':
@@ -326,6 +335,10 @@ bool EditRealInput(IoStatementState &io, const DataEdit &edit, void *n) {
 bool EditLogicalInput(IoStatementState &io, const DataEdit &edit, bool &x) {
   switch (edit.descriptor) {
   case DataEdit::ListDirected:
+    if (IsNamelistName(io)) {
+      return false;
+    }
+    break;
   case 'L':
   case 'G':
     break;
@@ -407,6 +420,9 @@ static bool EditListDirectedDefaultCharacterInput(
     io.HandleRelativePosition(1);
     return EditDelimitedCharacterInput(io, x, length, *ch);
   }
+  if (IsNamelistName(io)) {
+    return false;
+  }
   // Undelimited list-directed character input: stop at a value separator
   // or the end of the current record.
   std::optional<int> remaining{length};

flang/runtime/format.h

@@ -51,6 +51,9 @@ struct DataEdit {
     return descriptor == ListDirected || descriptor == ListDirectedRealPart ||
         descriptor == ListDirectedImaginaryPart;
   }
+  constexpr bool IsNamelist() const {
+    return IsListDirected() && modes.inNamelist;
+  }
 
   static constexpr char DefinedDerivedType{'d'}; // DT user-defined derived type
 

flang/runtime/io-stmt.h

@@ -229,10 +229,10 @@ public:
   std::optional<DataEdit> GetNextDataEdit(
       IoStatementState &, int maxRepeat = 1);
 
-  // Each NAMELIST input item is a distinct "list-directed"
+  // Each NAMELIST input item is treated like a distinct list-directed
-  // input statement.  This member function resets this state
+  // input statement.  This member function resets some state so that
-  // so that repetition and null values work correctly for each
+  // repetition and null values work correctly for each successive
-  // successive NAMELIST input item.
+  // NAMELIST input item.
   void ResetForNextNamelistItem() {
     remaining_ = 0;
     eatComma_ = false;

flang/runtime/namelist.cpp

@@ -333,7 +333,7 @@ bool IONAME(InputNamelist)(Cookie cookie, const NamelistGroup &group) {
       return false;
     }
     io.HandleRelativePosition(1);
-    // Read the values into the descriptor
+    // Read the values into the descriptor.  An array can be short.
     listInput->ResetForNextNamelistItem();
     if (!descr::DescriptorIO<Direction::Input>(io, *useDescriptor)) {
       return false;
@@ -352,4 +352,25 @@ bool IONAME(InputNamelist)(Cookie cookie, const NamelistGroup &group) {
   return true;
 }
 
+bool IsNamelistName(IoStatementState &io) {
+  if (io.get_if<ListDirectedStatementState<Direction::Input>>()) {
+    ConnectionState &connection{io.GetConnectionState()};
+    if (connection.modes.inNamelist) {
+      SavedPosition savedPosition{connection};
+      if (auto ch{io.GetNextNonBlank()}) {
+        if (IsLegalIdStart(*ch)) {
+          do {
+            io.HandleRelativePosition(1);
+            ch = io.GetCurrentChar();
+          } while (ch && IsLegalIdChar(*ch));
+          ch = io.GetNextNonBlank();
+          // TODO: how to deal with NaN(...) ambiguity?
+          return ch && (ch == '=' || ch == '(' || ch == '%');
+        }
+      }
+    }
+  }
+  return false;
+}
+
 } // namespace Fortran::runtime::io

flang/runtime/namelist.h

@@ -15,6 +15,7 @@
 
 namespace Fortran::runtime {
 class Descriptor;
+class IoStatementState;
 } // namespace Fortran::runtime
 
 namespace Fortran::runtime::io {
@@ -33,5 +34,11 @@ public:
   std::size_t items;
   const Item *item; // in original declaration order
 };
+
+// Look ahead on input for an identifier followed by a '=', '(', or '%'
+// character; for use in disambiguating a name-like value (e.g. F or T) from a
+// NAMELIST group item name.  Always false when not reading a NAMELIST.
+bool IsNamelistName(IoStatementState &);
+
 } // namespace Fortran::runtime::io
 #endif // FORTRAN_RUNTIME_NAMELIST_H_

flang/unittests/Runtime/Namelist.cpp

@@ -161,4 +161,32 @@ TEST(NamelistTests, Subscripts) {
   EXPECT_EQ(got, expect);
 }
 
+TEST(NamelistTests, ShortArrayInput) {
+  OwningPtr<Descriptor> aDesc{
+      MakeArray<TypeCategory::Integer, static_cast<int>(sizeof(int))>(
+          std::vector<int>{2}, std::vector<int>(2, -1))};
+  OwningPtr<Descriptor> bDesc{
+      MakeArray<TypeCategory::Integer, static_cast<int>(sizeof(int))>(
+          std::vector<int>{2}, std::vector<int>(2, -2))};
+  const NamelistGroup::Item items[]{{"a", *aDesc}, {"b", *bDesc}};
+  const NamelistGroup group{"nl", 2, items};
+  // Two 12-character lines of internal input
+  static char t1[]{"&nl a = 1 b "
+                   " = 2 /      "};
+  StaticDescriptor<1, true> statDesc;
+  Descriptor &internalDesc{statDesc.descriptor()};
+  SubscriptValue shape{2};
+  internalDesc.Establish(1, 12, t1, 1, &shape, CFI_attribute_pointer);
+  auto inCookie{IONAME(BeginInternalArrayListInput)(
+      internalDesc, nullptr, 0, __FILE__, __LINE__)};
+  ASSERT_TRUE(IONAME(InputNamelist)(inCookie, group));
+  auto inStatus{IONAME(EndIoStatement)(inCookie)};
+  ASSERT_EQ(inStatus, 0) << "Failed namelist input subscripts, status "
+                         << static_cast<int>(inStatus);
+  EXPECT_EQ(*aDesc->ZeroBasedIndexedElement<int>(0), 1);
+  EXPECT_EQ(*aDesc->ZeroBasedIndexedElement<int>(1), -1);
+  EXPECT_EQ(*bDesc->ZeroBasedIndexedElement<int>(0), 2);
+  EXPECT_EQ(*bDesc->ZeroBasedIndexedElement<int>(1), -2);
+}
+
 // TODO: Internal NAMELIST error tests