[flang-commits] [flang] [flang] Add structure constructor with allocatable component (PR #77845)

[via flang-commits]

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@@ -362,8 +363,18 @@ static mlir::Value genStructureComponentInit(
       loc, fieldTy, name, recTy,
       /*typeParams=*/mlir::ValueRange{} /*TODO*/);
 
-  if (Fortran::semantics::IsAllocatable(sym))
-    TODO(loc, "allocatable component in structure constructor");
+  if (Fortran::semantics::IsAllocatable(sym)) {
+    if (Fortran::evaluate::UnwrapExpr<Fortran::evaluate::NullPointer>(expr)) {
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jeanPerier wrote:

Can you turn the logic into 
```
if (!Fortran::evaluate::IsNullPointer(expr))
  fir::emitFatalError(loc, "constant structure constructor with an allocatable component value that is not NULL");
...
```
 here to make it clear that the else case is never supposed to be reached. 

Using Fortran::evaluate::IsNullPointer is required here to deal with the NULL(MOLD) case I think since there is not special handling for it (NULL(MOLD) is represented as a typed intrinsic call in evaluate::Expr<T>, and not the untyped Fortran::evaluate::NullPointer node).


```
  type t
    real, allocatable :: x(:)
  end type
  real, pointer :: x(:)
  type(t) :: some_t = t(null(x))
end
```

https://github.com/llvm/llvm-project/pull/77845