[flang] Fix crash in error recovery (implicit host association) (llvm#92795)

When a symbol appears in a specification expression in a subprogram
contained in a host program unit, semantics may have to create a symbol
in the host and use host association to it. This shouldn't happen for
nested subprograms that can't import such a symbol, such as interface
blocks by default. Further, when host association fails, semantics
shouldn't crash.

Fixes llvm#92647.

Author: klausler

flang/include/flang/Semantics/scope.h

@@ -225,6 +225,7 @@ class Scope {
   ImportKind GetImportKind() const;
   // Names appearing in IMPORT statements in this scope
   std::set<SourceName> importNames() const { return importNames_; }
+  bool CanImport(const SourceName &) const;
 
   // Set the kind of imports from host into this scope.
   // Return an error message for incompatible kinds.
@@ -298,7 +299,6 @@ class Scope {
   // or Symbol& points to one in there.
   static Symbols<1024> allSymbols;
 
-  bool CanImport(const SourceName &) const;
   const DeclTypeSpec &MakeLengthlessType(DeclTypeSpec &&);
 
   friend llvm::raw_ostream &operator<<(llvm::raw_ostream &, const Scope &);

flang/lib/Semantics/resolve-names.cpp

@@ -7846,28 +7846,31 @@ bool DeclarationVisitor::CheckForHostAssociatedImplicit(
   if (name.symbol) {
     ApplyImplicitRules(*name.symbol, true);
   }
-  Symbol *hostSymbol;
-  Scope *host{GetHostProcedure()};
-  if (!host || isImplicitNoneType(*host)) {
-    return false;
-  }
-  if (!name.symbol) {
-    hostSymbol = &MakeSymbol(*host, name.source, Attrs{});
-    ConvertToObjectEntity(*hostSymbol);
-    ApplyImplicitRules(*hostSymbol);
-    hostSymbol->set(Symbol::Flag::ImplicitOrError);
-  } else if (name.symbol->test(Symbol::Flag::ImplicitOrError)) {
-    hostSymbol = name.symbol;
-  } else {
-    return false;
-  }
-  Symbol &symbol{MakeHostAssocSymbol(name, *hostSymbol)};
-  if (isImplicitNoneType()) {
-    symbol.get<HostAssocDetails>().implicitOrExplicitTypeError = true;
-  } else {
-    symbol.get<HostAssocDetails>().implicitOrSpecExprError = true;
+  if (Scope * host{GetHostProcedure()}; host && !isImplicitNoneType(*host)) {
+    Symbol *hostSymbol{nullptr};
+    if (!name.symbol) {
+      if (currScope().CanImport(name.source)) {
+        hostSymbol = &MakeSymbol(*host, name.source, Attrs{});
+        ConvertToObjectEntity(*hostSymbol);
+        ApplyImplicitRules(*hostSymbol);
+        hostSymbol->set(Symbol::Flag::ImplicitOrError);
+      }
+    } else if (name.symbol->test(Symbol::Flag::ImplicitOrError)) {
+      hostSymbol = name.symbol;
+    }
+    if (hostSymbol) {
+      Symbol &symbol{MakeHostAssocSymbol(name, *hostSymbol)};
+      if (auto *assoc{symbol.detailsIf<HostAssocDetails>()}) {
+        if (isImplicitNoneType()) {
+          assoc->implicitOrExplicitTypeError = true;
+        } else {
+          assoc->implicitOrSpecExprError = true;
+        }
+        return true;
+      }
+    }
   }
-  return true;
+  return false;
 }
 
 bool DeclarationVisitor::IsUplevelReference(const Symbol &symbol) {

flang/test/Semantics/procinterface05.f90

@@ -0,0 +1,14 @@
+! RUN: %python %S/test_errors.py %s %flang_fc1
+interface a1
+  subroutine s1
+    interface a2
+      subroutine s2
+        !ERROR: Invalid specification expression: reference to local entity 'k'
+        real x(k)
+      end subroutine
+    end interface
+    !ERROR: Invalid specification expression: reference to local entity 'k'
+    real y(k)
+  end subroutine
+end interface
+end