From 00be8f287a41be42b3763f71beecd959dd6b7aa2 Mon Sep 17 00:00:00 2001
From: metagn <metagngn@gmail.com>
Date: Mon, 8 Jan 2024 05:44:04 +0300
Subject: [PATCH] trigger range check with new type inference on nkIntLit
 [backport:1.6] (#23179)

fixes #23177

`changeType` doesn't perform range checks to see if the expression fits
the new type [if the old type is the same as the new
type](https://github.com/nim-lang/Nim/blob/62d8ca43063197272968b4acf8c7a1ef27874c54/compiler/semexprs.nim#L633).
For `nkIntLit`, we previously set the type to the concrete base of the
expected type first, then call `changeType`, which works for things like
range types but not bare types of smaller bit size like `int8`. Now we
don't set the type (so the type is nil), and `changeType` performs the
range check when the type is unset (nil).
---
 compiler/semexprs.nim              |  3 +--
 tests/overflow/twronginference.nim | 10 ++++++++++
 2 files changed, 11 insertions(+), 2 deletions(-)
 create mode 100644 tests/overflow/twronginference.nim

diff --git a/compiler/semexprs.nim b/compiler/semexprs.nim
index 67eee3a19a..009458089b 100644
--- a/compiler/semexprs.nim
+++ b/compiler/semexprs.nim
@@ -630,7 +630,7 @@ proc changeType(c: PContext; n: PNode, newType: PType, check: bool) =
           a.add m
           changeType(m, tup[i], check)
   of nkCharLit..nkUInt64Lit:
-    if check and n.kind != nkUInt64Lit and not sameType(n.typ, newType):
+    if check and n.kind != nkUInt64Lit and not sameTypeOrNil(n.typ, newType):
       let value = n.intVal
       if value < firstOrd(c.config, newType) or value > lastOrd(c.config, newType):
         localError(c.config, n.info, "cannot convert " & $value &
@@ -3152,7 +3152,6 @@ proc semExpr(c: PContext, n: PNode, flags: TExprFlags = {}, expectedType: PType
           expected.kind in {tyInt..tyInt64,
             tyUInt..tyUInt64,
             tyFloat..tyFloat128}):
-        result.typ = expected
         if expected.kind in {tyFloat..tyFloat128}:
           n.transitionIntToFloatKind(nkFloatLit)
         changeType(c, result, expectedType, check=true)
diff --git a/tests/overflow/twronginference.nim b/tests/overflow/twronginference.nim
new file mode 100644
index 0000000000..34a982976b
--- /dev/null
+++ b/tests/overflow/twronginference.nim
@@ -0,0 +1,10 @@
+discard """
+  errormsg: "cannot convert 256 to int8"
+  line: 9
+"""
+
+# issue #23177
+
+var x: int8
+x = 256
+echo x # 0