[flang] Whether a procedure's interface is explicit or not is not a d… (#82796)

…istinguishing characteristic

We note whether a procedure's interface is explicit or implicit as an
attribute of its characteristics, so that other semantics can be checked
appropriately, but this internal attribute should not be used as a
distinguishing characteristic in itself.

Fixes https://github.com/llvm/llvm-project/issues/81876.

11 files changed, 116 insertions, 32 deletions

diff --git a/flang/include/flang/Evaluate/characteristics.h b/flang/include/flang/Evaluate/characteristics.h
index 04a0d71e1ade..f2f37866ecde 100644
--- a/flang/include/flang/Evaluate/characteristics.h
+++ b/flang/include/flang/Evaluate/characteristics.h
@@ -381,8 +381,8 @@ struct Procedure {
   int FindPassIndex(std::optional<parser::CharBlock>) const;
   bool CanBeCalledViaImplicitInterface(std::string *whyNot = nullptr) const;
   bool CanOverride(const Procedure &, std::optional<int> passIndex) const;
-  bool IsCompatibleWith(const Procedure &, std::string *whyNot = nullptr,
-      const SpecificIntrinsic * = nullptr,
+  bool IsCompatibleWith(const Procedure &, bool ignoreImplicitVsExplicit,
+      std::string *whyNot = nullptr, const SpecificIntrinsic * = nullptr,
       std::optional<std::string> *warning = nullptr) const;
 
   llvm::raw_ostream &Dump(llvm::raw_ostream &) const;
diff --git a/flang/include/flang/Evaluate/tools.h b/flang/include/flang/Evaluate/tools.h
index d257da1a7096..53896072675a 100644
--- a/flang/include/flang/Evaluate/tools.h
+++ b/flang/include/flang/Evaluate/tools.h
@@ -1094,7 +1094,7 @@ std::optional<parser::MessageFixedText> CheckProcCompatibility(bool isCall,
     const std::optional<characteristics::Procedure> &lhsProcedure,
     const characteristics::Procedure *rhsProcedure,
     const SpecificIntrinsic *specificIntrinsic, std::string &whyNotCompatible,
-    std::optional<std::string> &warning);
+    std::optional<std::string> &warning, bool ignoreImplicitVsExplicit);
 
 // Scalar constant expansion
 class ScalarConstantExpander {
diff --git a/flang/lib/Evaluate/characteristics.cpp b/flang/lib/Evaluate/characteristics.cpp
index 5ec9f757b681..688a856220a1 100644
--- a/flang/lib/Evaluate/characteristics.cpp
+++ b/flang/lib/Evaluate/characteristics.cpp
@@ -534,7 +534,8 @@ bool DummyProcedure::IsCompatibleWith(
     }
     return false;
   }
-  if (!procedure.value().IsCompatibleWith(actual.procedure.value(), whyNot)) {
+  if (!procedure.value().IsCompatibleWith(actual.procedure.value(),
+          /*ignoreImplicitVsExplicit=*/false, whyNot)) {
     if (whyNot) {
       *whyNot = "incompatible dummy procedure interfaces: "s + *whyNot;
     }
@@ -1207,7 +1208,8 @@ bool FunctionResult::IsCompatibleWith(
     CHECK(ifaceProc != nullptr);
     if (const auto *actualProc{
             std::get_if<CopyableIndirection<Procedure>>(&actual.u)}) {
-      if (ifaceProc->value().IsCompatibleWith(actualProc->value(), whyNot)) {
+      if (ifaceProc->value().IsCompatibleWith(actualProc->value(),
+              /*ignoreImplicitVsExplicit=*/false, whyNot)) {
         return true;
       }
       if (whyNot) {
@@ -1252,7 +1254,8 @@ bool Procedure::operator==(const Procedure &that) const {
       cudaSubprogramAttrs == that.cudaSubprogramAttrs;
 }
 
-bool Procedure::IsCompatibleWith(const Procedure &actual, std::string *whyNot,
+bool Procedure::IsCompatibleWith(const Procedure &actual,
+    bool ignoreImplicitVsExplicit, std::string *whyNot,
     const SpecificIntrinsic *specificIntrinsic,
     std::optional<std::string> *warning) const {
   // 15.5.2.9(1): if dummy is not pure, actual need not be.
@@ -1266,6 +1269,9 @@ bool Procedure::IsCompatibleWith(const Procedure &actual, std::string *whyNot,
   }
   Attrs differences{attrs ^ actualAttrs};
   differences.reset(Attr::Subroutine); // dealt with specifically later
+  if (ignoreImplicitVsExplicit) {
+    differences.reset(Attr::ImplicitInterface);
+  }
   if (!differences.empty()) {
     if (whyNot) {
       auto sep{": "s};
diff --git a/flang/lib/Evaluate/tools.cpp b/flang/lib/Evaluate/tools.cpp
index 131bbd97ce16..e7fc651b9173 100644
--- a/flang/lib/Evaluate/tools.cpp
+++ b/flang/lib/Evaluate/tools.cpp
@@ -1083,7 +1083,7 @@ std::optional<parser::MessageFixedText> CheckProcCompatibility(bool isCall,
     const std::optional<characteristics::Procedure> &lhsProcedure,
     const characteristics::Procedure *rhsProcedure,
     const SpecificIntrinsic *specificIntrinsic, std::string &whyNotCompatible,
-    std::optional<std::string> &warning) {
+    std::optional<std::string> &warning, bool ignoreImplicitVsExplicit) {
   std::optional<parser::MessageFixedText> msg;
   if (!lhsProcedure) {
     msg = "In assignment to object %s, the target '%s' is a procedure"
@@ -1097,8 +1097,9 @@ std::optional<parser::MessageFixedText> CheckProcCompatibility(bool isCall,
           *rhsProcedure->functionResult, &whyNotCompatible)) {
     msg =
         "Function %s associated with incompatible function designator '%s': %s"_err_en_US;
-  } else if (lhsProcedure->IsCompatibleWith(*rhsProcedure, &whyNotCompatible,
-                 specificIntrinsic, &warning)) {
+  } else if (lhsProcedure->IsCompatibleWith(*rhsProcedure,
+                 ignoreImplicitVsExplicit, &whyNotCompatible, specificIntrinsic,
+                 &warning)) {
     // OK
   } else if (isCall) {
     msg = "Procedure %s associated with result of reference to function '%s'"
diff --git a/flang/lib/Semantics/check-call.cpp b/flang/lib/Semantics/check-call.cpp
index cd9150bdda4b..3adbd7cc4177 100644
--- a/flang/lib/Semantics/check-call.cpp
+++ b/flang/lib/Semantics/check-call.cpp
@@ -912,7 +912,7 @@ static void CheckExplicitDataArg(const characteristics::DummyDataObject &dummy,
 static void CheckProcedureArg(evaluate::ActualArgument &arg,
     const characteristics::Procedure &proc,
     const characteristics::DummyProcedure &dummy, const std::string &dummyName,
-    SemanticsContext &context) {
+    SemanticsContext &context, bool ignoreImplicitVsExplicit) {
   evaluate::FoldingContext &foldingContext{context.foldingContext()};
   parser::ContextualMessages &messages{foldingContext.messages()};
   auto restorer{
@@ -975,7 +975,8 @@ static void CheckProcedureArg(evaluate::ActualArgument &arg,
           if (interface.HasExplicitInterface()) {
             std::string whyNot;
             std::optional<std::string> warning;
-            if (!interface.IsCompatibleWith(argInterface, &whyNot,
+            if (!interface.IsCompatibleWith(argInterface,
+                    ignoreImplicitVsExplicit, &whyNot,
                     /*specificIntrinsic=*/nullptr, &warning)) {
               // 15.5.2.9(1): Explicit interfaces must match
               if (argInterface.HasExplicitInterface()) {
@@ -1081,7 +1082,8 @@ static void CheckExplicitInterfaceArg(evaluate::ActualArgument &arg,
     const characteristics::DummyArgument &dummy,
     const characteristics::Procedure &proc, SemanticsContext &context,
     const Scope *scope, const evaluate::SpecificIntrinsic *intrinsic,
-    bool allowActualArgumentConversions, bool extentErrors) {
+    bool allowActualArgumentConversions, bool extentErrors,
+    bool ignoreImplicitVsExplicit) {
   evaluate::FoldingContext &foldingContext{context.foldingContext()};
   auto &messages{foldingContext.messages()};
   std::string dummyName{"dummy argument"};
@@ -1185,7 +1187,8 @@ static void CheckExplicitInterfaceArg(evaluate::ActualArgument &arg,
           },
           [&](const characteristics::DummyProcedure &dummy) {
             if (!checkActualArgForLabel(arg)) {
-              CheckProcedureArg(arg, proc, dummy, dummyName, context);
+              CheckProcedureArg(arg, proc, dummy, dummyName, context,
+                  ignoreImplicitVsExplicit);
             }
           },
           [&](const characteristics::AlternateReturn &) {
@@ -1371,7 +1374,8 @@ static void CheckAssociated(evaluate::ActualArguments &arguments,
                           : nullptr};
                   std::optional<parser::MessageFixedText> msg{
                       CheckProcCompatibility(isCall, pointerProc, &*targetProc,
-                          specificIntrinsic, whyNot, warning)};
+                          specificIntrinsic, whyNot, warning,
+                          /*ignoreImplicitVsExplicit=*/false)};
                   if (!msg && warning &&
                       semanticsContext.ShouldWarn(
                           common::UsageWarning::ProcDummyArgShapes)) {
@@ -1740,7 +1744,8 @@ static parser::Messages CheckExplicitInterface(
     const characteristics::Procedure &proc, evaluate::ActualArguments &actuals,
     SemanticsContext &context, const Scope *scope,
     const evaluate::SpecificIntrinsic *intrinsic,
-    bool allowActualArgumentConversions, bool extentErrors) {
+    bool allowActualArgumentConversions, bool extentErrors,
+    bool ignoreImplicitVsExplicit) {
   evaluate::FoldingContext &foldingContext{context.foldingContext()};
   parser::ContextualMessages &messages{foldingContext.messages()};
   parser::Messages buffer;
@@ -1754,7 +1759,8 @@ static parser::Messages CheckExplicitInterface(
     const auto &dummy{proc.dummyArguments.at(index++)};
     if (actual) {
       CheckExplicitInterfaceArg(*actual, dummy, proc, context, scope, intrinsic,
-          allowActualArgumentConversions, extentErrors);
+          allowActualArgumentConversions, extentErrors,
+          ignoreImplicitVsExplicit);
     } else if (!dummy.IsOptional()) {
       if (dummy.name.empty()) {
         messages.Say(
@@ -1783,7 +1789,8 @@ bool CheckInterfaceForGeneric(const characteristics::Procedure &proc,
     bool allowActualArgumentConversions) {
   return proc.HasExplicitInterface() &&
       !CheckExplicitInterface(proc, actuals, context, nullptr, nullptr,
-          allowActualArgumentConversions, false /*extentErrors*/)
+          allowActualArgumentConversions, /*extentErrors=*/false,
+          /*ignoreImplicitVsExplicit=*/false)
            .AnyFatalError();
 }
 
@@ -1876,6 +1883,7 @@ bool CheckPPCIntrinsic(const Symbol &generic, const Symbol &specific,
 bool CheckArguments(const characteristics::Procedure &proc,
     evaluate::ActualArguments &actuals, SemanticsContext &context,
     const Scope &scope, bool treatingExternalAsImplicit,
+    bool ignoreImplicitVsExplicit,
     const evaluate::SpecificIntrinsic *intrinsic) {
   bool explicitInterface{proc.HasExplicitInterface()};
   evaluate::FoldingContext foldingContext{context.foldingContext()};
@@ -1898,8 +1906,9 @@ bool CheckArguments(const characteristics::Procedure &proc,
     }
   }
   if (explicitInterface) {
-    auto buffer{CheckExplicitInterface(
-        proc, actuals, context, &scope, intrinsic, true, true)};
+    auto buffer{CheckExplicitInterface(proc, actuals, context, &scope,
+        intrinsic, /*allowArgumentConversions=*/true, /*extentErrors=*/true,
+        ignoreImplicitVsExplicit)};
     if (!buffer.empty()) {
       if (treatingExternalAsImplicit) {
         if (auto *msg{messages.Say(
diff --git a/flang/lib/Semantics/check-call.h b/flang/lib/Semantics/check-call.h
index 4275606225eb..8553f3a31efb 100644
--- a/flang/lib/Semantics/check-call.h
+++ b/flang/lib/Semantics/check-call.h
@@ -35,7 +35,7 @@ class SemanticsContext;
 // messages were created, true if all is well.
 bool CheckArguments(const evaluate::characteristics::Procedure &,
     evaluate::ActualArguments &, SemanticsContext &, const Scope &,
-    bool treatingExternalAsImplicit,
+    bool treatingExternalAsImplicit, bool ignoreImplicitVsExplicit,
     const evaluate::SpecificIntrinsic *intrinsic);
 
 bool CheckPPCIntrinsic(const Symbol &generic, const Symbol &specific,
diff --git a/flang/lib/Semantics/check-declarations.cpp b/flang/lib/Semantics/check-declarations.cpp
index e9adc086402d..719bea34406a 100644
--- a/flang/lib/Semantics/check-declarations.cpp
+++ b/flang/lib/Semantics/check-declarations.cpp
@@ -1481,7 +1481,8 @@ void CheckHelper::CheckExternal(const Symbol &symbol) {
           if (auto globalChars{Characterize(*global)}) {
             if (chars->HasExplicitInterface()) {
               std::string whyNot;
-              if (!chars->IsCompatibleWith(*globalChars, &whyNot)) {
+              if (!chars->IsCompatibleWith(*globalChars,
+                      /*ignoreImplicitVsExplicit=*/false, &whyNot)) {
                 msg = WarnIfNotInModuleFile(
                     "The global subprogram '%s' is not compatible with its local procedure declaration (%s)"_warn_en_US,
                     global->name(), whyNot);
@@ -1507,7 +1508,8 @@ void CheckHelper::CheckExternal(const Symbol &symbol) {
       if (auto chars{Characterize(symbol)}) {
         if (auto previousChars{Characterize(previous)}) {
           std::string whyNot;
-          if (!chars->IsCompatibleWith(*previousChars, &whyNot)) {
+          if (!chars->IsCompatibleWith(*previousChars,
+                  /*ignoreImplicitVsExplicit=*/false, &whyNot)) {
             if (auto *msg{WarnIfNotInModuleFile(
                     "The external interface '%s' is not compatible with an earlier definition (%s)"_warn_en_US,
                     symbol.name(), whyNot)}) {
diff --git a/flang/lib/Semantics/expression.cpp b/flang/lib/Semantics/expression.cpp
index b957f773816b..0132562bc6c9 100644
--- a/flang/lib/Semantics/expression.cpp
+++ b/flang/lib/Semantics/expression.cpp
@@ -3129,7 +3129,8 @@ std::optional<characteristics::Procedure> ExpressionAnalyzer::CheckCall(
       if (auto iter{implicitInterfaces_.find(name)};
           iter != implicitInterfaces_.end()) {
         std::string whyNot;
-        if (!chars->IsCompatibleWith(iter->second.second, &whyNot)) {
+        if (!chars->IsCompatibleWith(iter->second.second,
+                /*ignoreImplicitVsExplicit=*/false, &whyNot)) {
           if (auto *msg{Say(callSite,
                   "Reference to the procedure '%s' has an implicit interface that is distinct from another reference: %s"_warn_en_US,
                   name, whyNot)}) {
@@ -3169,7 +3170,7 @@ std::optional<characteristics::Procedure> ExpressionAnalyzer::CheckCall(
     }
     ok &= semantics::CheckArguments(*chars, arguments, context_,
         context_.FindScope(callSite), treatExternalAsImplicit,
-        specificIntrinsic);
+        /*ignoreImplicitVsExplicit=*/false, specificIntrinsic);
   }
   if (procSymbol && !IsPureProcedure(*procSymbol)) {
     if (const semantics::Scope *
@@ -3188,7 +3189,8 @@ std::optional<characteristics::Procedure> ExpressionAnalyzer::CheckCall(
       if (auto globalChars{characteristics::Procedure::Characterize(
               *global, context_.foldingContext())}) {
         semantics::CheckArguments(*globalChars, arguments, context_,
-            context_.FindScope(callSite), true,
+            context_.FindScope(callSite), /*treatExternalAsImplicit=*/true,
+            /*ignoreImplicitVsExplicit=*/false,
             nullptr /*not specific intrinsic*/);
       }
     }
diff --git a/flang/lib/Semantics/pointer-assignment.cpp b/flang/lib/Semantics/pointer-assignment.cpp
index 4c293e85cf9d..58155a29da1e 100644
--- a/flang/lib/Semantics/pointer-assignment.cpp
+++ b/flang/lib/Semantics/pointer-assignment.cpp
@@ -362,7 +362,8 @@ bool PointerAssignmentChecker::Check(parser::CharBlock rhsName, bool isCall,
   std::optional<std::string> warning;
   CharacterizeProcedure();
   if (std::optional<MessageFixedText> msg{evaluate::CheckProcCompatibility(
-          isCall, procedure_, rhsProcedure, specific, whyNot, warning)}) {
+          isCall, procedure_, rhsProcedure, specific, whyNot, warning,
+          /*ignoreImplicitVsExplicit=*/isCall)}) {
     Say(std::move(*msg), description_, rhsName, whyNot);
     return false;
   }
diff --git a/flang/lib/Semantics/resolve-names.cpp b/flang/lib/Semantics/resolve-names.cpp
index 87b613088080..4646bb01ee72 100644
--- a/flang/lib/Semantics/resolve-names.cpp
+++ b/flang/lib/Semantics/resolve-names.cpp
@@ -8595,16 +8595,25 @@ bool ResolveNamesVisitor::Pre(const parser::PointerAssignmentStmt &x) {
   const auto &bounds{std::get<parser::PointerAssignmentStmt::Bounds>(x.t)};
   const auto &expr{std::get<parser::Expr>(x.t)};
   ResolveDataRef(dataRef);
+  Symbol *ptrSymbol{parser::GetLastName(dataRef).symbol};
   Walk(bounds);
   // Resolve unrestricted specific intrinsic procedures as in "p => cos".
   if (const parser::Name * name{parser::Unwrap<parser::Name>(expr)}) {
     if (NameIsKnownOrIntrinsic(*name)) {
-      // If the name is known because it is an object entity from a host
-      // procedure, create a host associated symbol.
-      if (Symbol * symbol{name->symbol}; symbol &&
-          symbol->GetUltimate().has<ObjectEntityDetails>() &&
-          IsUplevelReference(*symbol)) {
-        MakeHostAssocSymbol(*name, *symbol);
+      if (Symbol * symbol{name->symbol}) {
+        if (IsProcedurePointer(ptrSymbol) &&
+            !ptrSymbol->test(Symbol::Flag::Function) &&
+            !ptrSymbol->test(Symbol::Flag::Subroutine)) {
+          if (symbol->test(Symbol::Flag::Function)) {
+            ApplyImplicitRules(*ptrSymbol);
+          }
+        }
+        // If the name is known because it is an object entity from a host
+        // procedure, create a host associated symbol.
+        if (symbol->GetUltimate().has<ObjectEntityDetails>() &&
+            IsUplevelReference(*symbol)) {
+          MakeHostAssocSymbol(*name, *symbol);
+        }
       }
       return false;
     }
diff --git a/flang/test/Semantics/implicit14.f90 b/flang/test/Semantics/implicit14.f90
new file mode 100644
index 000000000000..d688049a587f
--- /dev/null
+++ b/flang/test/Semantics/implicit14.f90
@@ -0,0 +1,54 @@
+! RUN: %python %S/test_errors.py %s %flang_fc1
+module m
+  type dt
+    procedure(explicit), pointer, nopass :: p
+  end type
+ contains
+  integer function one()
+    one = 1
+  end
+  function onePtr()
+    procedure(one), pointer :: onePtr
+    onePtr => one
+  end
+  function explicit
+    character(:), allocatable :: explicit
+    explicit = "abc"
+  end
+end
+
+program test
+  use m
+  procedure(), pointer :: p0
+  procedure(one), pointer :: p1
+  procedure(integer), pointer :: p2
+  procedure(explicit), pointer :: p3
+  external implicit
+  type(dt) x
+  p0 => one ! ok
+  p0 => onePtr() ! ok
+  p0 => implicit ! ok
+  !ERROR: Procedure pointer 'p0' with implicit interface may not be associated with procedure designator 'explicit' with explicit interface that cannot be called via an implicit interface
+  p0 => explicit
+  p1 => one ! ok
+  p1 => onePtr() ! ok
+  p1 => implicit ! ok
+  !ERROR: Function pointer 'p1' associated with incompatible function designator 'explicit': function results have incompatible attributes
+  p1 => explicit
+  p2 => one ! ok
+  p2 => onePtr() ! ok
+  p2 => implicit ! ok
+  !ERROR: Function pointer 'p2' associated with incompatible function designator 'explicit': function results have incompatible attributes
+  p2 => explicit
+  !ERROR: Function pointer 'p3' associated with incompatible function designator 'one': function results have incompatible attributes
+  p3 => one
+  !ERROR: Procedure pointer 'p3' associated with result of reference to function 'oneptr' that is an incompatible procedure pointer: function results have incompatible attributes
+  p3 => onePtr()
+  p3 => explicit ! ok
+  !ERROR: Procedure pointer 'p3' with explicit interface that cannot be called via an implicit interface cannot be associated with procedure designator with an implicit interface
+  p3 => implicit
+  !ERROR: Procedure pointer 'p' with explicit interface that cannot be called via an implicit interface cannot be associated with procedure designator with an implicit interface
+  x = dt(implicit)
+  !ERROR: Procedure pointer 'p' with explicit interface that cannot be called via an implicit interface cannot be associated with procedure designator with an implicit interface
+  x%p => implicit
+end