[flang-commits] [flang] [flang] Handle useless NAMELIST in interface block (PR #175214)

[Peter Klausler via flang-commits]

https://github.com/klausler created https://github.com/llvm/llvm-project/pull/175214

NAMELIST has no useful purpose in an interface block, but it's allowed.  Fix a crash due to our deferred handling of NAMELIST groups in the execution part (which doesn't exist in an interface block).

Fixes https://github.com/llvm/llvm-project/issues/175207.

>From 28e948f95441a6a26e70bd0d22536ff6c11dfb81 Mon Sep 17 00:00:00 2001
From: Peter Klausler <pklausler at nvidia.com>
Date: Fri, 9 Jan 2026 09:41:25 -0800
Subject: [PATCH] [flang] Handle useless NAMELIST in interface block

NAMELIST has no useful purpose in an interface block, but
it's allowed.  Fix a crash due to our deferred handling of
NAMELIST groups in the execution part (which doesn't exist in
an interface block).

Fixes https://github.com/llvm/llvm-project/issues/175207.
---
 flang/lib/Semantics/resolve-names.cpp |  3 +++
 flang/test/Semantics/bug175207.f90    | 10 ++++++++++
 2 files changed, 13 insertions(+)
 create mode 100644 flang/test/Semantics/bug175207.f90

diff --git a/flang/lib/Semantics/resolve-names.cpp b/flang/lib/Semantics/resolve-names.cpp
index ae251476ed591..148cc439efa88 100644
--- a/flang/lib/Semantics/resolve-names.cpp
+++ b/flang/lib/Semantics/resolve-names.cpp
@@ -9872,6 +9872,9 @@ void ResolveNamesVisitor::FinishSpecificationPart(
   misparsedStmtFuncFound_ = false;
   funcResultStack().CompleteFunctionResultType();
   CheckImports();
+  if (inInterfaceBlock()) {
+    FinishNamelists(); // NAMELIST is useless in an interface, but allowed
+  }
   for (auto &pair : currScope()) {
     auto &symbol{*pair.second};
     if (inInterfaceBlock()) {
diff --git a/flang/test/Semantics/bug175207.f90 b/flang/test/Semantics/bug175207.f90
new file mode 100644
index 0000000000000..63696dfac0b63
--- /dev/null
+++ b/flang/test/Semantics/bug175207.f90
@@ -0,0 +1,10 @@
+!RUN: %python %S/test_errors.py %s %flang_fc1
+interface
+  subroutine sub(x)
+    real x
+    namelist /useless/x ! ok, but don't crash
+    !ERROR: 'sub' is not a variable
+    namelist /bad/sub
+  end
+end interface
+end