[flang] Bug fix for ambiguous references to data and functions

Summary:
A program may erroneously reference the same name as both a data object
and as a function.  Some of these references were causing an internal
error in expression analysis.

It was already the case that a symbol referenced in a parse tree for a
call was changed from an `Entity` to a `ProcEntity`.  I added code to
detect when a symbol was referenced in a parse tree as an array element
gets changed from an `Entity` to an `ObjectEntity`.  Then, if an
`ObjectEntity` gets called as a function or a `ProcEntity` gets
referenced as a data object, errors get emitted.

This analysis was previously confined to the name resolution of the
specification part of a `ProgramTree`.  I added a pass to the execution
part of a `ProgramTree` to catch names declared in blocks.

Reviewers: tskeith, klausler, DavidTruby

Subscribers: llvm-commits

Tags: #llvm, #flang

Differential Revision: https://reviews.llvm.org/D82903

flang/lib/Semantics/expression.cpp

@@ -909,7 +909,10 @@ MaybeExpr ExpressionAnalyzer::Analyze(const parser::ArrayElement &ae) {
       return std::nullopt;
     } else if (baseExpr->Rank() == 0) {
       if (const Symbol * symbol{GetLastSymbol(*baseExpr)}) {
-        Say("'%s' is not an array"_err_en_US, symbol->name());
+        if (!context_.HasError(symbol)) {
+          Say("'%s' is not an array"_err_en_US, symbol->name());
+          context_.SetError(const_cast<Symbol &>(*symbol));
+        }
       }
     } else if (std::optional<DataRef> dataRef{
                    ExtractDataRef(std::move(*baseExpr))}) {

flang/lib/Semantics/resolve-names.cpp

@@ -5505,7 +5505,15 @@ const parser::Name *DeclarationVisitor::ResolveDataRef(
           },
           [&](const Indirection<parser::ArrayElement> &y) {
             Walk(y.value().subscripts);
-            return ResolveDataRef(y.value().base);
+            const parser::Name *name{ResolveDataRef(y.value().base)};
+            if (!name) {
+            } else if (!name->symbol->has<ProcEntityDetails>()) {
+              ConvertToObjectEntity(*name->symbol);
+            } else if (!context().HasError(*name->symbol)) {
+              SayWithDecl(*name, *name->symbol,
+                  "Cannot reference function '%s' as data"_err_en_US);
+            }
+            return name;
           },
           [&](const Indirection<parser::CoindexedNamedObject> &y) {
             Walk(y.value().imageSelector);

flang/test/Semantics/resolve93.f90

@@ -0,0 +1,44 @@
+! RUN: %S/test_errors.sh %s %t %f18
+subroutine s1()
+  character(10) str
+  character(10) str1
+  !ERROR: Cannot reference function 'str' as data
+  print *, str(1:9), str(7)
+  block
+    character(10) str2
+    character(10) str3
+    !ERROR: Cannot reference function 'str1' as data
+    print *, str1(1:9), str1(7)
+    !ERROR: 'str2' is not an array
+    print *, str2(1:9), str2(7)
+    !ERROR: Cannot reference function 'str3' as data
+    print *, str3(7), str3(1:9)
+  end block
+end subroutine s1
+
+subroutine s2()
+  character(10) func
+  !ERROR: Cannot reference function 'func' as data
+  print *, func(7), func(1:9)
+end subroutine s2
+
+subroutine s3()
+  real(8) :: func
+  !ERROR: Cannot reference function 'func' as data
+  print *, func(7), func(1:6)
+end subroutine s3
+
+subroutine s4()
+  real(8) :: local
+  real(8) :: local1
+  !ERROR: Cannot reference function 'local' as data
+  print *, local(1:6), local(7)
+  !ERROR: Cannot reference function 'local1' as data
+  print *, local1(7), local1(1:6)
+end subroutine s4
+
+subroutine s5(arg)
+  integer :: iVar
+  external :: arg
+  iVar = loc(arg)
+end subroutine s5