[flang] Catch attempt to type a subroutine

[klausler]

The presence of a type in the prefix of a SUBROUTINE statement should elicit an error message, not a crash.

Fixes #80530.

[llvmbot]

@llvm/pr-subscribers-flang-semantics

Author: Peter Klausler (klausler)

Changes

The presence of a type in the prefix of a SUBROUTINE statement should elicit an error message, not a crash.

Fixes #80530.

---

Full diff: https://github.com/llvm/llvm-project/pull/82704.diff

2 Files Affected:

• (modified) flang/lib/Semantics/resolve-names.cpp (+10-6)
• (added) flang/test/Semantics/typed-subr.f90 (+4)

diff --git a/flang/lib/Semantics/resolve-names.cpp b/flang/lib/Semantics/resolve-names.cpp
index 36deab969456d0..4b40648392709b 100644
--- a/flang/lib/Semantics/resolve-names.cpp
+++ b/flang/lib/Semantics/resolve-names.cpp
@@ -3709,13 +3709,17 @@ bool SubprogramVisitor::Pre(const parser::Suffix &suffix) {
 bool SubprogramVisitor::Pre(const parser::PrefixSpec &x) {
   // Save this to process after UseStmt and ImplicitPart
   if (const auto *parsedType{std::get_if<parser::DeclarationTypeSpec>(&x.u)}) {
-    FuncResultStack::FuncInfo &info{DEREF(funcResultStack().Top())};
-    if (info.parsedType) { // C1543
-      Say(currStmtSource().value(),
-          "FUNCTION prefix cannot specify the type more than once"_err_en_US);
+    if (FuncResultStack::FuncInfo * info{funcResultStack().Top()}) {
+      if (info->parsedType) { // C1543
+        Say(currStmtSource().value(),
+            "FUNCTION prefix cannot specify the type more than once"_err_en_US);
+      } else {
+        info->parsedType = parsedType;
+        info->source = currStmtSource();
+      }
     } else {
-      info.parsedType = parsedType;
-      info.source = currStmtSource();
+      Say(currStmtSource().value(),
+          "SUBROUTINE prefix cannot specify a type"_err_en_US);
     }
     return false;
   } else {
diff --git a/flang/test/Semantics/typed-subr.f90 b/flang/test/Semantics/typed-subr.f90
new file mode 100644
index 00000000000000..c6637c95bdfd74
--- /dev/null
+++ b/flang/test/Semantics/typed-subr.f90
@@ -0,0 +1,4 @@
+! RUN: %python %S/test_errors.py %s %flang_fc1
+! ERROR: SUBROUTINE prefix cannot specify a type
+integer subroutine foo
+end

[psteinfeld]

All builds and tests correctly and looks good.