[flang] More information on generic resolution failures (llvm#164738)

When a generic procedure reference does not match any of its specific
procedures, run through them and emit the errors for each attempted
match, so that the user has more information to resolve the problem by
adjusting the actual arguments.

Author: klausler

flang/include/flang/Evaluate/call.h

@@ -112,6 +112,7 @@ class ActualArgument {
   int Rank() const;
   bool operator==(const ActualArgument &) const;
   llvm::raw_ostream &AsFortran(llvm::raw_ostream &) const;
+  std::string AsFortran() const;
 
   std::optional<parser::CharBlock> keyword() const { return keyword_; }
   ActualArgument &set_keyword(parser::CharBlock x) {

flang/include/flang/Semantics/expression.h

@@ -367,11 +367,16 @@ class ExpressionAnalyzer {
   using AdjustActuals =
       std::optional<std::function<bool(const Symbol &, ActualArguments &)>>;
   const Symbol *ResolveForward(const Symbol &);
-  std::pair<const Symbol *, bool /* failure due ambiguity */> ResolveGeneric(
-      const Symbol &, const ActualArguments &, const AdjustActuals &,
-      bool isSubroutine, bool mightBeStructureConstructor = false);
-  void EmitGenericResolutionError(
-      const Symbol &, bool dueToNullActuals, bool isSubroutine);
+  struct GenericResolution {
+    const Symbol *specific{nullptr};
+    bool failedDueToAmbiguity{false};
+    SymbolVector tried{};
+  };
+  GenericResolution ResolveGeneric(const Symbol &, const ActualArguments &,
+      const AdjustActuals &, bool isSubroutine, SymbolVector &&tried,
+      bool mightBeStructureConstructor = false);
+  void EmitGenericResolutionError(const Symbol &, bool dueToNullActuals,
+      bool isSubroutine, ActualArguments &, const SymbolVector &);
   const Symbol &AccessSpecific(
       const Symbol &originalGeneric, const Symbol &specific);
   std::optional<CalleeAndArguments> GetCalleeAndArguments(const parser::Name &,

flang/lib/Evaluate/formatting.cpp

@@ -252,6 +252,13 @@ llvm::raw_ostream &ActualArgument::AsFortran(llvm::raw_ostream &o) const {
   return o;
 }
 
+std::string ActualArgument::AsFortran() const {
+  std::string result;
+  llvm::raw_string_ostream sstream(result);
+  AsFortran(sstream);
+  return result;
+}
+
 llvm::raw_ostream &SpecificIntrinsic::AsFortran(llvm::raw_ostream &o) const {
   return o << name;
 }

flang/lib/Semantics/check-call.cpp

@@ -2241,10 +2241,9 @@ static void CheckSpecificIntrinsic(const characteristics::Procedure &proc,
   }
 }
 
-static parser::Messages CheckExplicitInterface(
-    const characteristics::Procedure &proc, evaluate::ActualArguments &actuals,
-    SemanticsContext &context, const Scope *scope,
-    const evaluate::SpecificIntrinsic *intrinsic,
+parser::Messages CheckExplicitInterface(const characteristics::Procedure &proc,
+    evaluate::ActualArguments &actuals, SemanticsContext &context,
+    const Scope *scope, const evaluate::SpecificIntrinsic *intrinsic,
     bool allowActualArgumentConversions, bool extentErrors,
     bool ignoreImplicitVsExplicit) {
   evaluate::FoldingContext &foldingContext{context.foldingContext()};

flang/lib/Semantics/check-call.h

@@ -12,11 +12,8 @@
 #define FORTRAN_SEMANTICS_CHECK_CALL_H_
 
 #include "flang/Evaluate/call.h"
+#include "flang/Parser/message.h"
 
-namespace Fortran::parser {
-class Messages;
-class ContextualMessages;
-} // namespace Fortran::parser
 namespace Fortran::evaluate::characteristics {
 struct Procedure;
 }
@@ -47,6 +44,12 @@ bool CheckArgumentIsConstantExprInRange(
     const evaluate::ActualArguments &actuals, int index, int lowerBound,
     int upperBound, parser::ContextualMessages &messages);
 
+parser::Messages CheckExplicitInterface(
+    const evaluate::characteristics::Procedure &, evaluate::ActualArguments &,
+    SemanticsContext &, const Scope *, const evaluate::SpecificIntrinsic *,
+    bool allowActualArgumentConversions, bool extentErrors,
+    bool ignoreImplicitVsExplicit);
+
 // Checks actual arguments for the purpose of resolving a generic interface.
 bool CheckInterfaceForGeneric(const evaluate::characteristics::Procedure &,
     evaluate::ActualArguments &, SemanticsContext &,

flang/lib/Semantics/expression.cpp

@@ -2552,11 +2552,12 @@ auto ExpressionAnalyzer::AnalyzeProcedureComponentRef(
                 }
                 return true;
               }};
-          auto pair{
-              ResolveGeneric(generic, arguments, adjustment, isSubroutine)};
-          sym = pair.first;
+          auto result{ResolveGeneric(
+              generic, arguments, adjustment, isSubroutine, SymbolVector{})};
+          sym = result.specific;
           if (!sym) {
-            EmitGenericResolutionError(generic, pair.second, isSubroutine);
+            EmitGenericResolutionError(generic, result.failedDueToAmbiguity,
+                isSubroutine, arguments, result.tried);
             return std::nullopt;
           }
           // re-resolve the name to the specific binding
@@ -2886,10 +2887,10 @@ const Symbol *ExpressionAnalyzer::ResolveForward(const Symbol &symbol) {
 
 // Resolve a call to a generic procedure with given actual arguments.
 // adjustActuals is called on procedure bindings to handle pass arg.
-std::pair<const Symbol *, bool> ExpressionAnalyzer::ResolveGeneric(
-    const Symbol &symbol, const ActualArguments &actuals,
-    const AdjustActuals &adjustActuals, bool isSubroutine,
-    bool mightBeStructureConstructor) {
+auto ExpressionAnalyzer::ResolveGeneric(const Symbol &symbol,
+    const ActualArguments &actuals, const AdjustActuals &adjustActuals,
+    bool isSubroutine, SymbolVector &&tried, bool mightBeStructureConstructor)
+    -> GenericResolution {
   const Symbol &ultimate{symbol.GetUltimate()};
   // Check for a match with an explicit INTRINSIC
   const Symbol *explicitIntrinsic{nullptr};
@@ -2948,7 +2949,7 @@ std::pair<const Symbol *, bool> ExpressionAnalyzer::ResolveGeneric(
               // cannot be unambiguously distinguished
               // Underspecified external procedure actual arguments can
               // also lead to ambiguity.
-              return {nullptr, true /* due to ambiguity */};
+              return {nullptr, true /* due to ambiguity */, std::move(tried)};
             }
           }
           if (!procedure->IsElemental()) {
@@ -2959,6 +2960,8 @@ std::pair<const Symbol *, bool> ExpressionAnalyzer::ResolveGeneric(
           }
           crtMatchingDistance = ComputeCudaMatchingDistance(
               context_.languageFeatures(), *procedure, localActuals);
+        } else {
+          tried.push_back(*specific);
         }
       }
     }
@@ -3038,11 +3041,12 @@ std::pair<const Symbol *, bool> ExpressionAnalyzer::ResolveGeneric(
   // Check parent derived type
   if (const auto *parentScope{symbol.owner().GetDerivedTypeParent()}) {
     if (const Symbol * extended{parentScope->FindComponent(symbol.name())}) {
-      auto pair{ResolveGeneric(
-          *extended, actuals, adjustActuals, isSubroutine, false)};
-      if (pair.first) {
-        return pair;
+      auto result{ResolveGeneric(*extended, actuals, adjustActuals,
+          isSubroutine, std::move(tried), false)};
+      if (result.specific != nullptr) {
+        return result;
       }
+      tried = std::move(result.tried);
     }
   }
   // Structure constructor?
@@ -3054,14 +3058,15 @@ std::pair<const Symbol *, bool> ExpressionAnalyzer::ResolveGeneric(
   if (!symbol.owner().IsGlobal() && !symbol.owner().IsDerivedType()) {
     if (const Symbol *
         outer{symbol.owner().parent().FindSymbol(symbol.name())}) {
-      auto pair{ResolveGeneric(*outer, actuals, adjustActuals, isSubroutine,
-          mightBeStructureConstructor)};
-      if (pair.first) {
-        return pair;
+      auto result{ResolveGeneric(*outer, actuals, adjustActuals, isSubroutine,
+          std::move(tried), mightBeStructureConstructor)};
+      if (result.specific) {
+        return result;
       }
+      tried = std::move(result.tried);
     }
   }
-  return {nullptr, false};
+  return {nullptr, false, std::move(tried)};
 }
 
 const Symbol &ExpressionAnalyzer::AccessSpecific(
@@ -3098,16 +3103,39 @@ const Symbol &ExpressionAnalyzer::AccessSpecific(
   }
 }
 
-void ExpressionAnalyzer::EmitGenericResolutionError(
-    const Symbol &symbol, bool dueToAmbiguity, bool isSubroutine) {
-  Say(dueToAmbiguity
-          ? "The actual arguments to the generic procedure '%s' matched multiple specific procedures, perhaps due to use of NULL() without MOLD= or an actual procedure with an implicit interface"_err_en_US
-          : semantics::IsGenericDefinedOp(symbol)
-          ? "No specific procedure of generic operator '%s' matches the actual arguments"_err_en_US
-          : isSubroutine
-          ? "No specific subroutine of generic '%s' matches the actual arguments"_err_en_US
-          : "No specific function of generic '%s' matches the actual arguments"_err_en_US,
-      symbol.name());
+void ExpressionAnalyzer::EmitGenericResolutionError(const Symbol &symbol,
+    bool dueToAmbiguity, bool isSubroutine, ActualArguments &arguments,
+    const SymbolVector &tried) {
+  if (auto *msg{Say(dueToAmbiguity
+              ? "The actual arguments to the generic procedure '%s' matched multiple specific procedures, perhaps due to use of NULL() without MOLD= or an actual procedure with an implicit interface"_err_en_US
+              : semantics::IsGenericDefinedOp(symbol)
+              ? "No specific procedure of generic operator '%s' matches the actual arguments"_err_en_US
+              : isSubroutine
+              ? "No specific subroutine of generic '%s' matches the actual arguments"_err_en_US
+              : "No specific function of generic '%s' matches the actual arguments"_err_en_US,
+          symbol.name())}) {
+    parser::ContextualMessages &messages{GetContextualMessages()};
+    semantics::Scope &scope{context_.FindScope(messages.at())};
+    for (const Symbol &specific : tried) {
+      if (auto procChars{characteristics::Procedure::Characterize(
+              specific, GetFoldingContext())}) {
+        if (procChars->HasExplicitInterface()) {
+          if (auto reasons{semantics::CheckExplicitInterface(*procChars,
+                  arguments, context_, &scope, /*intrinsic=*/nullptr,
+                  /*allocActualArgumentConversions=*/false,
+                  /*extentErrors=*/false,
+                  /*ignoreImplicitVsExplicit=*/false)};
+              !reasons.empty()) {
+            reasons.AttachTo(
+                msg->Attach(specific.name(),
+                    "Specific procedure '%s' does not match the actual arguments because"_en_US,
+                    specific.name()),
+                parser::Severity::None);
+          }
+        }
+      }
+    }
+  }
 }
 
 auto ExpressionAnalyzer::GetCalleeAndArguments(
@@ -3146,12 +3174,14 @@ auto ExpressionAnalyzer::GetCalleeAndArguments(const parser::Name &name,
   bool isGenericInterface{ultimate.has<semantics::GenericDetails>()};
   bool isExplicitIntrinsic{ultimate.attrs().test(semantics::Attr::INTRINSIC)};
   const Symbol *resolution{nullptr};
+  SymbolVector tried;
   if (isGenericInterface || isExplicitIntrinsic) {
     ExpressionAnalyzer::AdjustActuals noAdjustment;
-    auto pair{ResolveGeneric(*symbol, arguments, noAdjustment, isSubroutine,
-        mightBeStructureConstructor)};
-    resolution = pair.first;
-    dueToAmbiguity = pair.second;
+    auto result{ResolveGeneric(*symbol, arguments, noAdjustment, isSubroutine,
+        SymbolVector{}, mightBeStructureConstructor)};
+    resolution = result.specific;
+    dueToAmbiguity = result.failedDueToAmbiguity;
+    tried = std::move(result.tried);
     if (resolution) {
       if (context_.GetPPCBuiltinsScope() &&
           resolution->name().ToString().rfind("__ppc_", 0) == 0) {
@@ -3182,7 +3212,8 @@ auto ExpressionAnalyzer::GetCalleeAndArguments(const parser::Name &name,
           std::move(specificCall->arguments)};
     } else {
       if (isGenericInterface) {
-        EmitGenericResolutionError(*symbol, dueToAmbiguity, isSubroutine);
+        EmitGenericResolutionError(
+            *symbol, dueToAmbiguity, isSubroutine, arguments, tried);
       }
       return std::nullopt;
     }
@@ -4955,8 +4986,10 @@ std::optional<ProcedureRef> ArgumentAnalyzer::GetDefinedAssignmentProc(
     auto restorer{context_.GetContextualMessages().DiscardMessages()};
     if (const Symbol *symbol{scope.FindSymbol(oprName)}) {
       ExpressionAnalyzer::AdjustActuals noAdjustment;
-      proc =
-          context_.ResolveGeneric(*symbol, actuals_, noAdjustment, true).first;
+      proc = context_
+                 .ResolveGeneric(
+                     *symbol, actuals_, noAdjustment, true, SymbolVector{})
+                 .specific;
       if (proc) {
         isProcElemental = IsElementalProcedure(*proc);
       }
@@ -5105,17 +5138,18 @@ const Symbol *ArgumentAnalyzer::FindBoundOp(parser::CharBlock oprName,
         [&](const Symbol &proc, ActualArguments &) {
           return passIndex == GetPassIndex(proc).value_or(-1);
         }};
-    auto pair{
-        context_.ResolveGeneric(*generic, actuals_, adjustment, isSubroutine)};
-    if (const Symbol *binding{pair.first}) {
+    auto result{context_.ResolveGeneric(
+        *generic, actuals_, adjustment, isSubroutine, SymbolVector{})};
+    if (const Symbol *binding{result.specific}) {
       CHECK(binding->has<semantics::ProcBindingDetails>());
       // Use the most recent override of the binding, if any
       return scope->FindComponent(binding->name());
     } else {
       if (isAmbiguous) {
-        *isAmbiguous = pair.second;
+        *isAmbiguous = result.failedDueToAmbiguity;
       }
-      context_.EmitGenericResolutionError(*generic, pair.second, isSubroutine);
+      context_.EmitGenericResolutionError(*generic, result.failedDueToAmbiguity,
+          isSubroutine, actuals_, result.tried);
     }
   }
   return nullptr;

flang/test/Semantics/generic-error.f90

@@ -0,0 +1,21 @@
+! RUN: not %flang_fc1 -fsyntax-only %s 2>&1 | FileCheck %s
+module m
+  interface generic
+    procedure :: sub1, sub2
+  end interface
+ contains
+  subroutine sub1(x)
+  end
+  subroutine sub2(j)
+  end
+end
+
+program test
+  use m
+!CHECK: error: No specific subroutine of generic 'generic' matches the actual arguments
+!CHECK: Specific procedure 'sub1' does not match the actual arguments
+!CHECK: Actual argument type 'REAL(8)' is not compatible with dummy argument type 'REAL(4)'
+!CHECK: Specific procedure 'sub2' does not match the actual arguments
+!CHECK: Actual argument type 'REAL(8)' is not compatible with dummy argument type 'INTEGER(4)'
+  call generic(1.d0)
+end