From 8cb406cd7a37013ea84be3fec728f0db78a900a9 Mon Sep 17 00:00:00 2001
From: Ryan McConnell <rammcconnell@gmail.com>
Date: Sat, 29 Aug 2026 08:41:05 -0400
Subject: [PATCH] Fix 26144; exception propagation for non-raising virtual
 methods (#26145)

ref #26144

The C backend must not use `sfNeverRaises` to remove exception checks
from
virtual method calls. The flag describes only the selected base method
body,
while a vtable override may raise a catchable exception.

This change makes `canRaiseDisp` conservative for `skMethod` symbols and
adds a
regression test covering an exception raised by a child method invoked
through a
base reference.
---
 compiler/ccgcalls.nim                  |  6 +++++-
 tests/method/tmethod_virtual_raise.nim | 20 ++++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)
 create mode 100644 tests/method/tmethod_virtual_raise.nim

diff --git a/compiler/ccgcalls.nim b/compiler/ccgcalls.nim
index 1202aa0536..77c09d82cf 100644
--- a/compiler/ccgcalls.nim
+++ b/compiler/ccgcalls.nim
@@ -11,7 +11,11 @@
 
 proc canRaiseDisp(p: BProc; n: PNode): bool =
   # we assume things like sysFatal cannot raise themselves
-  if n.kind == nkSym and {sfNeverRaises, sfImportc, sfCompilerProc} * n.sym.flags != {}:
+  if n.kind == nkSym and n.sym.kind == skMethod:
+    # A base method may be overridden by a branch with a wider exception set.
+    # Its inferred effects describe only the base body, not every vtable target.
+    result = true
+  elif n.kind == nkSym and {sfNeverRaises, sfImportc, sfCompilerProc} * n.sym.flags != {}:
     result = false
   elif optPanics in p.config.globalOptions or
       (n.kind == nkSym and sfSystemModule in getModule(n.sym).flags and
diff --git a/tests/method/tmethod_virtual_raise.nim b/tests/method/tmethod_virtual_raise.nim
new file mode 100644
index 0000000000..6bc1575282
--- /dev/null
+++ b/tests/method/tmethod_virtual_raise.nim
@@ -0,0 +1,20 @@
+discard """
+  output: '''caught'''
+"""
+
+type
+  Base = ref object of RootObj
+  Child = ref object of Base
+
+method run(value: Base): string {.base.} =
+  result = "base"
+
+method run(value: Child): string =
+  raise newException(ValueError, "child")
+
+let value: Base = Child()
+try:
+  discard value.run()
+  quit "virtual method did not raise"
+except ValueError:
+  echo "caught"