[flang] Warn about assumed-rank items in I/O lists (#182957)

An assumed-rank dummy argument is not a conforming I/O list or NAMELIST
group item. Add a -pedantic warning and some documentation.

flang/docs/Extensions.md

@@ -483,6 +483,7 @@ end
   are to the same value.  Distinct initializations remain errors.
 * A pointer component that has no default initialization or explicit value
   in a structure constructor is defaulted to `NULL()`.
+* An assumed-rank entity is an acceptable `NAMELIST` group item.
 
 ### Extensions supported when enabled by options
 

flang/include/flang/Support/Fortran-features.h

@@ -57,7 +57,7 @@ ENUM_CLASS(LanguageFeature, BackslashEscapes, OldDebugLines,
     ForwardRefExplicitTypeDummy, InaccessibleDeferredOverride,
     CudaWarpMatchFunction, DoConcurrentOffload, TransferBOZ, Coarray,
     PointerPassObject, MultipleIdenticalDATA,
-    DefaultStructConstructorNullPointer)
+    DefaultStructConstructorNullPointer, AssumedRankIoItem)
 
 // Portability and suspicious usage warnings
 ENUM_CLASS(UsageWarning, Portability, PointerToUndefinable,

flang/lib/Semantics/check-io.cpp

@@ -327,10 +327,12 @@ void IoChecker::Enter(const parser::InputItem &spec) {
   }
   CheckForDefinableVariable(*var, "Input");
   if (auto expr{AnalyzeExpr(context_, *var)}) {
+    auto at{var->GetSource()};
+    CheckForAssumedRank(UnwrapWholeSymbolDataRef(*expr), at);
     CheckForBadIoType(*expr,
         flags_.test(Flag::FmtOrNml) ? common::DefinedIo::ReadFormatted
                                     : common::DefinedIo::ReadUnformatted,
-        var->GetSource());
+        at);
   }
 }
 
@@ -651,11 +653,14 @@ void IoChecker::Enter(const parser::OutputItem &item) {
       } else if (IsProcedure(*expr)) {
         context_.Say(parser::FindSourceLocation(*x),
             "Output item must not be a procedure"_err_en_US); // C1233
+      } else {
+        auto at{parser::FindSourceLocation(item)};
+        CheckForAssumedRank(UnwrapWholeSymbolDataRef(*expr), at);
+        CheckForBadIoType(*expr,
+            flags_.test(Flag::FmtOrNml) ? common::DefinedIo::WriteFormatted
+                                        : common::DefinedIo::WriteUnformatted,
+            at);
       }
-      CheckForBadIoType(*expr,
-          flags_.test(Flag::FmtOrNml) ? common::DefinedIo::WriteFormatted
-                                      : common::DefinedIo::WriteUnformatted,
-          parser::FindSourceLocation(item));
     }
   }
 }
@@ -1228,6 +1233,17 @@ parser::Message *IoChecker::CheckForBadIoType(const Symbol &symbol,
   return nullptr;
 }
 
+void IoChecker::CheckForAssumedRank(
+    const Symbol *symbol, parser::CharBlock namelistLocation) const {
+  if (symbol && IsAssumedRank(*symbol)) {
+    evaluate::AttachDeclaration(
+        context_.Say(namelistLocation,
+            "Assumed-rank object '%s' may not be an I/O list item"_err_en_US,
+            symbol->name()),
+        *symbol);
+  }
+}
+
 void IoChecker::CheckNamelist(const Symbol &namelist, common::DefinedIo which,
     parser::CharBlock namelistLocation) const {
   if (!context_.HasError(namelist)) {

flang/lib/Semantics/check-io.h

@@ -133,6 +133,7 @@ private:
       const SomeExpr &, common::DefinedIo, parser::CharBlock) const;
   parser::Message *CheckForBadIoType(
       const Symbol &, common::DefinedIo, parser::CharBlock) const;
+  void CheckForAssumedRank(const Symbol *, parser::CharBlock) const;
 
   void CheckNamelist(
       const Symbol &, common::DefinedIo, parser::CharBlock) const;

flang/lib/Semantics/resolve-names.cpp

@@ -7228,6 +7228,13 @@ void DeclarationVisitor::FinishNamelists() {
             } else if (!ConvertToObjectEntity(symbol->GetUltimate())) {
               SayWithDecl(name, *symbol, "'%s' is not a variable"_err_en_US);
               context().SetError(*groupSymbol);
+            } else if (IsAssumedRank(*symbol)) {
+              evaluate::AttachDeclaration(
+                  context().Warn(common::LanguageFeature::AssumedRankIoItem,
+                      name.source,
+                      "Assumed-rank object '%s' should not be a namelist group item"_port_en_US,
+                      symbol->name()),
+                  *symbol);
             }
             symbol->GetUltimate().set(Symbol::Flag::InNamelist);
             details->add_object(*symbol);

flang/test/Semantics/io16.f90

@@ -0,0 +1,15 @@
+! RUN: %python %S/test_errors.py %s %flang_fc1 -pedantic
+subroutine assumedRank(x, y)
+  real x(..), y(*)
+  !PORTABILITY: Assumed-rank object 'x' should not be a namelist group item [-Wassumed-rank-io-item]
+  !ERROR: A namelist group object 'y' must not be assumed-size
+  namelist /nml/x, y
+  !ERROR: Assumed-rank object 'x' may not be an I/O list item
+  !ERROR: Whole assumed-size array 'y' may not appear here without subscripts
+  read *, x, y
+  !ERROR: Assumed-rank object 'x' may not be an I/O list item
+  !ERROR: Whole assumed-size array 'y' may not appear here without subscripts
+  print *, x, y
+  read(*,nml=nml)
+  write(*,nml=nml)
+end