[flang] Test SYNC IMAGES, increase checking

flang/lib/Semantics/check-coarray.cpp

@@ -194,14 +194,33 @@ void CoarrayChecker::Leave(const parser::SyncAllStmt &x) {
 
 void CoarrayChecker::Leave(const parser::SyncImagesStmt &x) {
   CheckSyncStatList(context_, std::get<std::list<parser::StatOrErrmsg>>(x.t));
-
   const auto &imageSet{std::get<parser::SyncImagesStmt::ImageSet>(x.t)};
   if (const auto *intExpr{std::get_if<parser::IntExpr>(&imageSet.u)}) {
     if (const auto *expr{GetExpr(context_, *intExpr)}) {
       if (expr->Rank() > 1) {
         context_.Say(parser::FindSourceLocation(imageSet), // C1174
             "An image-set that is an int-expr must be a scalar or a rank-one array"_err_en_US);
       }
+      if (const auto *someInt{
+              std::get_if<evaluate::Expr<evaluate::SomeInteger>>(&expr->u)};
+          someInt && evaluate::IsActuallyConstant(*someInt)) {
+        auto converted{evaluate::Fold(context_.foldingContext(),
+            evaluate::ConvertToType<evaluate::SubscriptInteger>(
+                common::Clone(*someInt)))};
+        if (const auto *cst{
+                evaluate::UnwrapConstantValue<evaluate::SubscriptInteger>(
+                    converted)}) {
+          for (auto elt : cst->values()) {
+            auto n{elt.ToInt64()};
+            if (n < 1) {
+              context_.Say(parser::FindSourceLocation(imageSet),
+                  "Image number %jd in the image-set is not valid"_err_en_US,
+                  std::intmax_t{n});
+              break;
+            }
+          }
+        }
+      }
     }
   }
 }

flang/test/Semantics/sync-images.f90

@@ -0,0 +1,12 @@
+!RUN: %python %S/test_errors.py %s %flang_fc1
+integer twod(1,1)
+sync images (*) ! ok
+!ERROR: An image-set that is an int-expr must be a scalar or a rank-one array
+sync images (twod)
+!ERROR: Must have INTEGER type, but is REAL(4)
+sync images (3.14159)
+!ERROR: Image number -1 in the image-set is not valid
+sync images (-1)
+!ERROR: Image number -1 in the image-set is not valid
+sync images ([2, -1, 3])
+end