[flang-commits] [flang] [Flang] Diagnose recursive abstract procedure interfaces (PR #233225)

[via flang-commits]

https://github.com/keepyixiao created https://github.com/llvm/llvm-project/pull/233225

Recursive abstract procedure interfaces could remain unchecked until lowering, where failed procedure characterization caused a compiler crash.

Check interface body characteristics during declaration checking so that recursive interfaces are diagnosed before lowering.

Add a regression test for a recursive abstract interface used by a procedure pointer.

Fixes https://github.com/llvm/llvm-project/issues/230862

>From ca4c1ee24b48688728fb21ee47555db33fa5d957 Mon Sep 17 00:00:00 2001
From: nudt_yixiao <1272950933 at qq.com>
Date: Sun, 18 Oct 2026 16:01:30 +0800
Subject: [PATCH] [Flang] Diagnose recursive abstract procedure interfaces

Recursive abstract procedure interfaces could remain unchecked until lowering,
where failed procedure characterization caused a compiler crash.

Check interface body characteristics during declaration checking so that
recursive interfaces are diagnosed before lowering.

Add a regression test for a recursive abstract interface used by a procedure
pointer.
---
 flang/lib/Semantics/check-declarations.cpp |  9 +++++----
 flang/test/Semantics/resolve102.f90        | 14 ++++++++++++++
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/flang/lib/Semantics/check-declarations.cpp b/flang/lib/Semantics/check-declarations.cpp
index 2abefd381850ad..0234d50cf53b35 100644
--- a/flang/lib/Semantics/check-declarations.cpp
+++ b/flang/lib/Semantics/check-declarations.cpp
@@ -1614,11 +1614,12 @@ bool CheckHelper::IsResultOkToDiffer(const FunctionResult &result) {
 
 void CheckHelper::CheckSubprogram(
     const Symbol &symbol, const SubprogramDetails &details) {
-  // Evaluate a procedure definition's characteristics to flush out
-  // any errors that analysis might expose, in case this subprogram hasn't
-  // had any calls in this compilation unit that would have validated them.
+  // Evaluate a procedure definition or interface body's characteristics to
+  // flush out any errors that analysis might expose, in case this subprogram
+  // hasn't had any calls in this compilation unit that would have validated
+  // them.
   if (!context_.HasError(symbol) && !details.isDummy() &&
-      !details.isInterface() && !details.stmtFunction()) {
+      !details.stmtFunction()) {
     if (!Procedure::Characterize(symbol, foldingContext_)) {
       context_.SetError(symbol);
     }
diff --git a/flang/test/Semantics/resolve102.f90 b/flang/test/Semantics/resolve102.f90
index 62b0c5d3a21b34..39bcb1aed2cb07 100644
--- a/flang/test/Semantics/resolve102.f90
+++ b/flang/test/Semantics/resolve102.f90
@@ -6,6 +6,20 @@ subroutine sub(p2)
   PROCEDURE(sub) :: p2
 end subroutine
 
+module recursiveAbstractInterface
+  implicit none
+  abstract interface
+    !ERROR: Procedure 'cb' is recursively defined.  Procedures in the cycle: 'cb', 'next'
+    subroutine cb(next)
+      procedure(cb) :: next
+    end subroutine
+  end interface
+end module
+
+use recursiveAbstractInterface, only: cb
+procedure(cb), pointer :: callback => null()
+end
+
 subroutine circular
   procedure(sub) :: p
   contains