[flang] Fix crash in UseErrorDetails construction case (#168126)

When a derived type has the same name as a generic function, and is
use-associated into a scope along with other distinct derived types of
the same name, we crash. Don't crash.

Fixes #168099.

Author: klausler

flang/lib/Semantics/resolve-names.cpp

@@ -3967,22 +3967,6 @@ void ModuleVisitor::DoAddUse(SourceName location, SourceName localName,
     useProcedure = &useUltimate;
   }
 
-  // Creates a UseErrorDetails symbol in the current scope for a
-  // current UseDetails symbol, but leaves the UseDetails in the
-  // scope's name map.
-  auto CreateLocalUseError{[&]() {
-    EraseSymbol(*localSymbol);
-    CHECK(localSymbol->has<UseDetails>());
-    UseErrorDetails details{localSymbol->get<UseDetails>()};
-    details.add_occurrence(location, useSymbol);
-    Symbol *newSymbol{&MakeSymbol(localName, Attrs{}, std::move(details))};
-    // Restore *localSymbol in currScope
-    auto iter{currScope().find(localName)};
-    CHECK(iter != currScope().end() && &*iter->second == newSymbol);
-    iter->second = MutableSymbolRef{*localSymbol};
-    return newSymbol;
-  }};
-
   // When two derived types arrived, try to combine them.
   const Symbol *combinedDerivedType{nullptr};
   if (!useDerivedType) {
@@ -4008,8 +3992,19 @@ void ModuleVisitor::DoAddUse(SourceName location, SourceName localName,
       combinedDerivedType = localDerivedType;
     } else {
       // Create a local UseErrorDetails for the ambiguous derived type
-      if (localGeneric) {
-        combinedDerivedType = CreateLocalUseError();
+      if (localSymbol->has<UseDetails>() && localGeneric) {
+        // Creates a UseErrorDetails symbol in the current scope for a
+        // current UseDetails symbol, but leaves the UseDetails in the
+        // scope's name map.
+        UseErrorDetails details{localSymbol->get<UseDetails>()};
+        EraseSymbol(*localSymbol);
+        details.add_occurrence(location, useSymbol);
+        Symbol *newSymbol{&MakeSymbol(localName, Attrs{}, std::move(details))};
+        // Restore *localSymbol in currScope
+        auto iter{currScope().find(localName)};
+        CHECK(iter != currScope().end() && &*iter->second == newSymbol);
+        iter->second = MutableSymbolRef{*localSymbol};
+        combinedDerivedType = newSymbol;
       } else {
         ConvertToUseError(*localSymbol, location, useSymbol);
         localDerivedType = nullptr;

flang/test/Semantics/bug168099.f90

@@ -0,0 +1,28 @@
+!RUN: %python %S/test_errors.py %s %flang_fc1
+module m1
+  type pair
+  end type
+  interface pair
+    module procedure f
+  end interface
+ contains
+  type(pair) function f(n)
+    integer, intent(in) :: n
+    f = pair()
+  end
+end
+module m2
+  type pair
+  end type
+end
+module m3
+  type pair
+  end type
+end
+program main
+  use m1
+  use m2
+  use m3
+  !ERROR: Reference to 'pair' is ambiguous
+  type(pair) error
+end