[flang-commits] [flang] [flang] Extension: allow override of inaccessible DEFERRED binding (PR #142691)
Peter Klausler via flang-commits
flang-commits at lists.llvm.org
Tue Jun 3 16:18:16 PDT 2025
https://github.com/klausler created https://github.com/llvm/llvm-project/pull/142691
Inaccessible procedure bindings can't be overridden, but DEFERRED bindings must be in a non-abstract extension. We presently emit an error for an attempt to override an inaccessible binding in this case. But some compilers accept this usage, and since it seems safe enough, I'll allow it with an optional warning. Codes can avoid this warning and conform to the standard by changing the deferred bindings to be public.
>From bdf580b10910ee6071fdce259becc6cf56ddda03 Mon Sep 17 00:00:00 2001
From: Peter Klausler <pklausler at nvidia.com>
Date: Tue, 3 Jun 2025 16:13:35 -0700
Subject: [PATCH] [flang] Extension: allow override of inaccessible DEFERRED
binding
Inaccessible procedure bindings can't be overridden, but DEFERRED
bindings must be in a non-abstract extension. We presently emit
an error for an attempt to override an inaccessible binding in this
case. But some compilers accept this usage, and since it seems safe
enough, I'll allow it with an optional warning. Codes can avoid
this warning and conform to the standard by changing the deferred
bindings to be public.
---
flang/docs/Extensions.md | 6 ++++++
flang/include/flang/Support/Fortran-features.h | 3 ++-
flang/lib/Evaluate/tools.cpp | 3 ++-
flang/lib/Semantics/check-declarations.cpp | 9 ++++++---
flang/lib/Semantics/runtime-type-info.cpp | 4 +++-
flang/test/Semantics/deferred01.f90 | 7 ++++---
6 files changed, 23 insertions(+), 9 deletions(-)
diff --git a/flang/docs/Extensions.md b/flang/docs/Extensions.md
index 51969de5ac7fe..ca5e34ea610b8 100644
--- a/flang/docs/Extensions.md
+++ b/flang/docs/Extensions.md
@@ -164,6 +164,12 @@ end
No other Fortran compiler enforces C7108 (to our knowledge);
they all resolve the ambiguity by interpreting the call as a function
reference. We do the same, with a portability warning.
+* An override for an inaccessible procedure binding works only within
+ the same module; other apparent overrides of inaccessible bindings
+ are actually new bindings of the same name.
+ In the case of `DEFERRED` bindings in an `ABSTRACT` derived type,
+ however, overrides are necessary, so they are permitted for inaccessible
+ bindings with an optional warning.
## Extensions, deletions, and legacy features supported by default
diff --git a/flang/include/flang/Support/Fortran-features.h b/flang/include/flang/Support/Fortran-features.h
index e696da9042480..79eaf56bdec11 100644
--- a/flang/include/flang/Support/Fortran-features.h
+++ b/flang/include/flang/Support/Fortran-features.h
@@ -55,7 +55,8 @@ ENUM_CLASS(LanguageFeature, BackslashEscapes, OldDebugLines,
UndefinableAsynchronousOrVolatileActual, AutomaticInMainProgram, PrintCptr,
SavedLocalInSpecExpr, PrintNamelist, AssumedRankPassedToNonAssumedRank,
IgnoreIrrelevantAttributes, Unsigned, AmbiguousStructureConstructor,
- ContiguousOkForSeqAssociation, ForwardRefExplicitTypeDummy)
+ ContiguousOkForSeqAssociation, ForwardRefExplicitTypeDummy,
+ InaccessibleDeferredOverride)
// Portability and suspicious usage warnings
ENUM_CLASS(UsageWarning, Portability, PointerToUndefinable,
diff --git a/flang/lib/Evaluate/tools.cpp b/flang/lib/Evaluate/tools.cpp
index c70915cfa6150..222c32a9c332e 100644
--- a/flang/lib/Evaluate/tools.cpp
+++ b/flang/lib/Evaluate/tools.cpp
@@ -1206,7 +1206,8 @@ parser::Message *AttachDeclaration(
}
if (const auto *binding{
unhosted->detailsIf<semantics::ProcBindingDetails>()}) {
- if (binding->symbol().name() != symbol.name()) {
+ if (!symbol.attrs().test(semantics::Attr::DEFERRED) &&
+ binding->symbol().name() != symbol.name()) {
message.Attach(binding->symbol().name(),
"Procedure '%s' of type '%s' is bound to '%s'"_en_US, symbol.name(),
symbol.owner().GetName().value(), binding->symbol().name());
diff --git a/flang/lib/Semantics/check-declarations.cpp b/flang/lib/Semantics/check-declarations.cpp
index 1d09dea06db54..46a5b970fdf0c 100644
--- a/flang/lib/Semantics/check-declarations.cpp
+++ b/flang/lib/Semantics/check-declarations.cpp
@@ -2586,9 +2586,12 @@ void CheckHelper::CheckProcBinding(
}
if (overridden) {
if (isInaccessibleDeferred) {
- SayWithDeclaration(*overridden,
- "Override of PRIVATE DEFERRED '%s' must appear in its module"_err_en_US,
- symbol.name());
+ evaluate::AttachDeclaration(
+ Warn(common::LanguageFeature::InaccessibleDeferredOverride,
+ symbol.name(),
+ "Override of PRIVATE DEFERRED '%s' should appear in its module"_warn_en_US,
+ symbol.name()),
+ *overridden);
}
if (overridden->attrs().test(Attr::NON_OVERRIDABLE)) {
SayWithDeclaration(*overridden,
diff --git a/flang/lib/Semantics/runtime-type-info.cpp b/flang/lib/Semantics/runtime-type-info.cpp
index 98295f3705a71..d639904bcd724 100644
--- a/flang/lib/Semantics/runtime-type-info.cpp
+++ b/flang/lib/Semantics/runtime-type-info.cpp
@@ -1018,9 +1018,11 @@ SymbolVector CollectBindings(const Scope &dtScope) {
if (overriderIter != localBindings.end()) {
Symbol &overrider{*overriderIter->second};
if (symbol.attrs().test(Attr::PRIVATE) &&
+ !symbol.attrs().test(Attr::DEFERRED) &&
FindModuleContaining(symbol.owner()) !=
FindModuleContaining(dtScope)) {
- // Don't override inaccessible PRIVATE bindings
+ // Don't override inaccessible PRIVATE bindings, unless
+ // they are deferred
auto &binding{overrider.get<ProcBindingDetails>()};
binding.set_numPrivatesNotOverridden(
binding.numPrivatesNotOverridden() + 1);
diff --git a/flang/test/Semantics/deferred01.f90 b/flang/test/Semantics/deferred01.f90
index 87818c10bd399..ce406a72b8fab 100644
--- a/flang/test/Semantics/deferred01.f90
+++ b/flang/test/Semantics/deferred01.f90
@@ -1,6 +1,7 @@
-! RUN: %python %S/test_errors.py %s %flang_fc1
+! RUN: %python %S/test_errors.py %s %flang_fc1 -pedantic -Werror
! Deferred TBPs must be overridden, but when they are private, those
-! overrides must appear in the same module.
+! overrides are required to appear in the same module. We allow overrides
+! elsewhere as an extension.
module m1
type, abstract :: absBase
contains
@@ -18,7 +19,7 @@ module m2
use m1
type, extends(absBase) :: ext
contains
- !ERROR: Override of PRIVATE DEFERRED 'deferredtbp' must appear in its module
+ !WARNING: Override of PRIVATE DEFERRED 'deferredtbp' should appear in its module
procedure :: deferredTbp => implTbp
end type
contains
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