[flang] Create symbols for args of separate-module-subprogram

A separate-module-subprogram is declared as `module procedure ...`
and gets its characteristics from the declaration of that name as
a separate module procedure. When we encounter one, we need to create
symbols in the new subprogram scope for the dummy arguments and
function return (if any).

The failure to create these symbols led to the bug in issue flang-compiler/f18#1054:
when a dummy argument was referenced, the compiler interpreted it as
an implicit declaration because there was no symbol for the argument.

Fixes flang-compiler/f18#1054.

Original-commit: flang-compiler/f18@4d3c4ba
Reviewed-on: flang-compiler/f18#1080
Tree-same-pre-rewrite: false

flang/include/flang/Semantics/scope.h

@@ -134,6 +134,8 @@ class Scope {
     Symbol &symbol{MakeSymbol(name, attrs, std::move(details))};
     return symbols_.emplace(name, symbol);
   }
+  // Make a copy of a symbol in this scope; nullptr if one is already there
+  Symbol *CopySymbol(const Symbol &);
 
   const std::list<EquivalenceSet> &equivalenceSets() const;
   void add_equivalenceSet(EquivalenceSet &&);

flang/lib/Semantics/resolve-names.cpp

@@ -2729,10 +2729,25 @@ bool SubprogramVisitor::BeginMpSubprogram(const parser::Name &name) {
     Say(name, "'%s' was not declared a separate module procedure"_err_en_US);
     return false;
   }
-  if (symbol->owner() != currScope()) {
-    symbol = &MakeSymbol(name, SubprogramDetails{});
+  if (symbol->owner() == currScope()) {
+    PushScope(Scope::Kind::Subprogram, symbol);
+  } else {
+    Symbol &newSymbol{MakeSymbol(name, SubprogramDetails{})};
+    PushScope(Scope::Kind::Subprogram, &newSymbol);
+    const auto &details{symbol->get<SubprogramDetails>()};
+    auto &newDetails{newSymbol.get<SubprogramDetails>()};
+    for (const Symbol *dummyArg : details.dummyArgs()) {
+      if (!dummyArg) {
+        newDetails.add_alternateReturn();
+      } else if (Symbol * copy{currScope().CopySymbol(*dummyArg)}) {
+        newDetails.add_dummyArg(*copy);
+      }
+    }
+    if (details.isFunction()) {
+      currScope().erase(symbol->name());
+      newDetails.set_result(*currScope().CopySymbol(details.result()));
+    }
   }
-  PushScope(Scope::Kind::Subprogram, symbol);
   return true;
 }
 

flang/lib/Semantics/scope.cpp

@@ -110,6 +110,18 @@ bool Scope::Contains(const Scope &that) const {
   }
 }
 
+Symbol *Scope::CopySymbol(const Symbol &symbol) {
+  auto pair{try_emplace(symbol.name(), symbol.attrs())};
+  if (!pair.second) {
+    return nullptr;  // already exists
+  } else {
+    Symbol &result{*pair.first->second};
+    result.flags() = symbol.flags();
+    result.set_details(common::Clone(symbol.details()));
+    return &result;
+  }
+}
+
 const std::list<EquivalenceSet> &Scope::equivalenceSets() const {
   return equivalenceSets_;
 }

flang/test/Semantics/resolve76.f90

@@ -0,0 +1,30 @@
+! RUN: %S/test_errors.sh %s %flang %t
+
+! 15.6.2.5(3)
+
+module m1
+  implicit logical(a-b)
+  interface
+    module subroutine sub1(a, b)
+      real, intent(in) :: a
+      real, intent(out) :: b
+    end
+    logical module function f()
+    end
+  end interface
+end
+submodule(m1) sm1
+contains
+  module procedure sub1
+    !ERROR: Left-hand side of assignment is not modifiable
+    a = 1.0
+    b = 2.0
+    !ERROR: No intrinsic or user-defined ASSIGNMENT(=) matches operand types REAL(4) and LOGICAL(4)
+    b = .false.
+  end
+  module procedure f
+    f = .true.
+    !ERROR: No intrinsic or user-defined ASSIGNMENT(=) matches operand types LOGICAL(4) and REAL(4)
+    f = 1.0
+  end
+end