From fa841214212cba21ebbf9a0a18a9ce367fab15d2 Mon Sep 17 00:00:00 2001
From: Paul Tan <pyokagan@gmail.com>
Date: Wed, 7 Oct 2020 00:05:31 +0800
Subject: [PATCH] effects: exclude swap() from "indirect calls" assumption
 (#15504)

swap() will never call any procs passed to it, and so it can be safely
excluded from the "assume indirect calls are taken" effects tracking
rule.
---
 compiler/sempass2.nim        |  2 +-
 tests/effects/teffects10.nim | 12 ++++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)
 create mode 100644 tests/effects/teffects10.nim

diff --git a/compiler/sempass2.nim b/compiler/sempass2.nim
index 4eac6ef13c..f0d6c6c7af 100644
--- a/compiler/sempass2.nim
+++ b/compiler/sempass2.nim
@@ -552,7 +552,7 @@ proc isNoEffectList(n: PNode): bool {.inline.} =
   n.len == 0 or (n[tagEffects] == nil and n[exceptionEffects] == nil)
 
 proc isTrival(caller: PNode): bool {.inline.} =
-  result = caller.kind == nkSym and caller.sym.magic in {mEqProc, mIsNil, mMove, mWasMoved}
+  result = caller.kind == nkSym and caller.sym.magic in {mEqProc, mIsNil, mMove, mWasMoved, mSwap}
 
 proc trackOperandForIndirectCall(tracked: PEffects, n: PNode, paramType: PType; caller: PNode) =
   let a = skipConvAndClosure(n)
diff --git a/tests/effects/teffects10.nim b/tests/effects/teffects10.nim
new file mode 100644
index 0000000000..8193b394a7
--- /dev/null
+++ b/tests/effects/teffects10.nim
@@ -0,0 +1,12 @@
+discard """
+action: compile
+"""
+
+# https://github.com/nim-lang/Nim/issues/15495
+
+proc f() {.raises: [].} =
+  var a: proc ()
+  var b: proc ()
+  swap(a, b)
+
+f()