From 8da48869222875b70e58bb682baf65becc32a3da Mon Sep 17 00:00:00 2001
From: Morgan <morgan@morganbaz.com>
Date: Mon, 9 Dec 2024 10:14:40 +0100
Subject: [PATCH] fix(gnovm): use strconv.UnquoteChar to parse rune literals
 (#3296)

This fixes a bug, as shown in rune3.gno, whereby rune literals which
would not be parsed correctly by `strconv.Unquote` are now parsed
correctly. Previously, the test would print out 65533, for the unicode
invalid code point.
---
 gnovm/pkg/gnolang/nodes.go   |  1 +
 gnovm/pkg/gnolang/op_eval.go | 10 ++++------
 gnovm/tests/files/rune3.gno  | 10 ++++++++++
 3 files changed, 15 insertions(+), 6 deletions(-)
 create mode 100644 gnovm/tests/files/rune3.gno

diff --git a/gnovm/pkg/gnolang/nodes.go b/gnovm/pkg/gnolang/nodes.go
index 8d3d6d8a2cc..0496d37ed72 100644
--- a/gnovm/pkg/gnolang/nodes.go
+++ b/gnovm/pkg/gnolang/nodes.go
@@ -2153,6 +2153,7 @@ type ValuePather interface {
 // Utility
 
 func (x *BasicLitExpr) GetString() string {
+	// Matches string literal parsing in go/constant.MakeFromLiteral.
 	str, err := strconv.Unquote(x.Value)
 	if err != nil {
 		panic("error in parsing string literal: " + err.Error())
diff --git a/gnovm/pkg/gnolang/op_eval.go b/gnovm/pkg/gnolang/op_eval.go
index 1beba1d6e3f..2aa13b21753 100644
--- a/gnovm/pkg/gnolang/op_eval.go
+++ b/gnovm/pkg/gnolang/op_eval.go
@@ -204,16 +204,14 @@ func (m *Machine) doOpEval() {
 			// and github.com/golang/go/issues/19921
 			panic("imaginaries are not supported")
 		case CHAR:
-			cstr, err := strconv.Unquote(x.Value)
+			// Matching character literal parsing in go/constant.MakeFromLiteral.
+			val := x.Value
+			rne, _, _, err := strconv.UnquoteChar(val[1:len(val)-1], '\'')
 			if err != nil {
 				panic("error in parsing character literal: " + err.Error())
 			}
-			runes := []rune(cstr)
-			if len(runes) != 1 {
-				panic(fmt.Sprintf("error in parsing character literal: 1 rune expected, but got %v (%s)", len(runes), cstr))
-			}
 			tv := TypedValue{T: UntypedRuneType}
-			tv.SetInt32(runes[0])
+			tv.SetInt32(rne)
 			m.PushValue(tv)
 		case STRING:
 			m.PushValue(TypedValue{
diff --git a/gnovm/tests/files/rune3.gno b/gnovm/tests/files/rune3.gno
new file mode 100644
index 00000000000..e848565e3a4
--- /dev/null
+++ b/gnovm/tests/files/rune3.gno
@@ -0,0 +1,10 @@
+package main
+
+const overflow = '\xff'
+
+func main() {
+	println(overflow)
+}
+
+// Output:
+// 255