[flang][runtime] Disable namelist storage sequence input when defined (#158708)

The runtime supports a near-universal extension to namelist input that
allows reading a sequence of values into a storage sequence beginning at
an array element, e.g. &NML A(2)=1. 2. 3. / .

Disable this extension when the type of the array has a defined
formatted READ subroutine defined. That defined input procedure may
itself not be using list-directed input, and might not notice a
following slash or new input item name as such.

Fixes https://github.com/llvm/llvm-project/issues/158496.

flang-rt/lib/runtime/namelist.cpp

diff --git a/flang-rt/lib/runtime/namelist.cpp b/flang-rt/lib/runtime/namelist.cpp
index 79dbe4b..47b1643 100644
--- a/flang-rt/lib/runtime/namelist.cpp
+++ b/flang-rt/lib/runtime/namelist.cpp
@@ -258,13 +258,40 @@
   return false;
 }
 
-static RT_API_ATTRS void StorageSequenceExtension(
-    Descriptor &desc, const Descriptor &source) {
+static RT_API_ATTRS bool HasDefinedIoSubroutine(common::DefinedIo definedIo,
+    typeInfo::SpecialBinding::Which specialBinding,
+    const typeInfo::DerivedType *derivedType,
+    const NonTbpDefinedIoTable *table) {
+  for (; derivedType; derivedType = derivedType->GetParentType()) {
+    if ((table && table->Find(*derivedType, definedIo) != nullptr) ||
+        derivedType->FindSpecialBinding(specialBinding)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+static RT_API_ATTRS bool HasDefinedIoSubroutine(common::DefinedIo definedIo,
+    typeInfo::SpecialBinding::Which specialBinding,
+    const Descriptor &descriptor, const NonTbpDefinedIoTable *table) {
+  const DescriptorAddendum *addendum{descriptor.Addendum()};
+  return addendum &&
+      HasDefinedIoSubroutine(
+          definedIo, specialBinding, addendum->derivedType(), table);
+}
+
+static RT_API_ATTRS void StorageSequenceExtension(Descriptor &desc,
+    const Descriptor &source, const io::NonTbpDefinedIoTable *table) {
   // Support the near-universal extension of NAMELIST input into a
   // designatable storage sequence identified by its initial scalar array
   // element.  For example, treat "A(1) = 1. 2. 3." as if it had been
   // "A(1:) = 1. 2. 3.".
-  if (desc.rank() == 0 && (source.rank() == 1 || source.IsContiguous())) {
+  // (But don't do this for derived types with defined formatted READs,
+  // since they might do non-list-directed input that won't stop at the
+  // next namelist input item name.)
+  if (desc.rank() == 0 && (source.rank() == 1 || source.IsContiguous()) &&
+      !HasDefinedIoSubroutine(common::DefinedIo::ReadFormatted,
+          typeInfo::SpecialBinding::Which::ReadFormatted, desc, table)) {
     if (auto stride{source.rank() == 1
                 ? source.GetDimension(0).ByteStride()
                 : static_cast<SubscriptValue>(source.ElementBytes())};
@@ -561,7 +588,8 @@
         next = io.GetCurrentChar(byteCount);
       } while (next && (*next == '(' || *next == '%'));
       if (lastSubscriptDescriptor) {
-        StorageSequenceExtension(*lastSubscriptDescriptor, *lastSubscriptBase);
+        StorageSequenceExtension(*lastSubscriptDescriptor, *lastSubscriptBase,
+            group.nonTbpDefinedIo);
       }
     }
     // Skip the '='

flang/docs/Extensions.md

diff --git a/flang/docs/Extensions.md b/flang/docs/Extensions.md
index cf528b8..c442a9c 100644
--- a/flang/docs/Extensions.md
+++ b/flang/docs/Extensions.md
@@ -930,3 +930,6 @@
   or contiguous array can be used as the initial element of a storage
   sequence.  For example, "&GRP A(1)=1. 2. 3./" is treated as if had been
   "&GRP A(1:)=1. 2. 3./".
+  This extension is necessarily disabled when the type of the array
+  has an accessible defined formatted READ subroutine.
+