Move PushContext so mapper name is available in the outer context.

Fix mapper name creation to not "fail" with type missing by using
ConstructName detail flag.

Add tests for abstract and "not derived" type checks.

Author: Leporacanthicus

flang/lib/Semantics/resolve-names.cpp

@@ -1616,14 +1616,18 @@ void OmpVisitor::Post(const parser::OpenMPBlockConstruct &x) {
 bool OmpVisitor::Pre(const parser::OpenMPDeclareMapperConstruct &x) {
   AddOmpSourceRange(x.source);
   BeginDeclTypeSpec();
-  PushScope(Scope::Kind::OtherConstruct, nullptr);
   const auto &spec{std::get<parser::OmpDeclareMapperSpecifier>(x.t)};
+  Symbol *mapperSym{nullptr};
   if (const auto &mapperName{std::get<std::optional<parser::Name>>(spec.t)}) {
-    Symbol *mapperSym{&MakeSymbol(*mapperName, Attrs{})};
+    mapperSym =
+        &MakeSymbol(*mapperName, MiscDetails{MiscDetails::Kind::ConstructName});
     mapperName->symbol = mapperSym;
-  } else if (0) {
-    Symbol *mapperSym{&MakeSymbol("default", Attrs{})};
+  } else {
+    mapperSym = &MakeSymbol(
+        "default", Attrs{}, MiscDetails{MiscDetails::Kind::ConstructName});
   }
+
+  PushScope(Scope::Kind::OtherConstruct, nullptr);
   Walk(std::get<parser::TypeSpec>(spec.t));
   const auto &varName{std::get<parser::ObjectName>(spec.t)};
   DeclareObjectEntity(varName);

flang/test/Semantics/OpenMP/declare-mapper01.f90

@@ -0,0 +1,8 @@
+! RUN: %python %S/../test_errors.py %s %flang -fopenmp -fopenmp-version=50
+  ! Test the source code starting with omp syntax
+
+integer :: y
+
+!ERROR: Type is not a derived type
+!$omp declare mapper(mm : integer::x) map(x, y)
+end

flang/test/Semantics/OpenMP/declare-mapper02.f90

@@ -0,0 +1,10 @@
+! RUN: %python %S/../test_errors.py %s %flang -fopenmp -fopenmp-version=50
+! Test the source code starting with omp syntax
+
+type, abstract :: t1
+   integer :: y
+end type t1
+
+!ERROR: Type must not be abstract
+!$omp declare mapper(mm : t1::x) map(x, x%y)
+end