[flang] Allow defined assignment to CLASS(*)

[klausler]

An unlimited polymorphic left-hand side variable is acceptable in the definition of a defined assignment subroutine.

Fixes #124621.

[llvmbot]

@llvm/pr-subscribers-flang-semantics

Author: Peter Klausler (klausler)

Changes

An unlimited polymorphic left-hand side variable is acceptable in the definition of a defined assignment subroutine.

Fixes #124621.

---

Full diff: https://github.com/llvm/llvm-project/pull/124817.diff

2 Files Affected:

• (modified) flang/lib/Semantics/tools.cpp (-6)
• (added) flang/test/Semantics/bug124621.f90 (+46)

diff --git a/flang/lib/Semantics/tools.cpp b/flang/lib/Semantics/tools.cpp
index 013d006e614b4b..9ebfbbb5317b66 100644
--- a/flang/lib/Semantics/tools.cpp
+++ b/flang/lib/Semantics/tools.cpp
@@ -137,12 +137,6 @@ Tristate IsDefinedAssignment(
   if (!lhsType || !rhsType) {
     return Tristate::No; // error or rhs is untyped
   }
-  if (lhsType->IsUnlimitedPolymorphic()) {
-    return Tristate::No;
-  }
-  if (rhsType->IsUnlimitedPolymorphic()) {
-    return Tristate::Maybe;
-  }
   TypeCategory lhsCat{lhsType->category()};
   TypeCategory rhsCat{rhsType->category()};
   if (rhsRank > 0 && lhsRank != rhsRank) {
diff --git a/flang/test/Semantics/bug124621.f90 b/flang/test/Semantics/bug124621.f90
new file mode 100644
index 00000000000000..1106ed4a25c493
--- /dev/null
+++ b/flang/test/Semantics/bug124621.f90
@@ -0,0 +1,46 @@
+! RUN: %python %S/test_errors.py %s %flang_fc1
+module m
+  type t1
+   contains
+    procedure, pass(from) :: defAsst1
+    generic :: assignment(=) => defAsst1
+  end type
+  type t2
+  end type
+  type t3
+  end type
+  interface assignment(=)
+    module procedure defAsst2
+  end interface
+ contains
+  subroutine defAsst1(to,from)
+    class(*), intent(out) :: to
+    class(t1), intent(in) :: from
+  end
+  subroutine defAsst2(to,from)
+    class(*), intent(out) :: to
+    class(t2), intent(in) :: from
+  end
+end
+
+program test
+  use m
+  type(t1) x1
+  type(t2) x2
+  type(t3) x3
+  j = x1
+  j = x2
+  !ERROR: No intrinsic or user-defined ASSIGNMENT(=) matches operand types INTEGER(4) and TYPE(t3)
+  j = x3
+  x1 = x1
+  x1 = x2
+  !ERROR: No intrinsic or user-defined ASSIGNMENT(=) matches operand types TYPE(t1) and TYPE(t3)
+  x1 = x3
+  x2 = x1
+  x2 = x2
+  !ERROR: No intrinsic or user-defined ASSIGNMENT(=) matches operand types TYPE(t2) and TYPE(t3)
+  x2 = x3
+  x3 = x1
+  x3 = x2
+  x3 = x3
+end

[DanielCChen]

LGTM.
Thanks for the quick fix!