From 92acc71c80c5eecf9211c56d3e25d97ea8f26c9b Mon Sep 17 00:00:00 2001
From: Roman Khimov <roman@nspcc.ru>
Date: Wed, 11 Jan 2023 15:49:10 +0300
Subject: [PATCH 1/2] compiler: create new locals for range loops when needed,
 fix #2855

---
 pkg/compiler/codegen.go  | 12 ++++++++++--
 pkg/compiler/for_test.go | 26 ++++++++++++++++++++++++++
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/pkg/compiler/codegen.go b/pkg/compiler/codegen.go
index b9faf3c5d..fb5c75ef6 100644
--- a/pkg/compiler/codegen.go
+++ b/pkg/compiler/codegen.go
@@ -1313,7 +1313,11 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 			} else {
 				emit.Opcodes(c.prog.BinWriter, opcode.DUP)
 			}
-			c.emitStoreVar("", n.Key.(*ast.Ident).Name)
+			keyIdent := n.Key.(*ast.Ident)
+			if n.Tok == token.DEFINE {
+				c.scope.newLocal(keyIdent.Name)
+			}
+			c.emitStoreVar("", keyIdent.Name)
 		}
 		if needValue {
 			if !isMap || !keyLoaded {
@@ -1327,7 +1331,11 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 					opcode.SWAP, // key should be on top
 					opcode.PICKITEM)
 			}
-			c.emitStoreVar("", n.Value.(*ast.Ident).Name)
+			valIdent := n.Value.(*ast.Ident)
+			if n.Tok == token.DEFINE {
+				c.scope.newLocal(valIdent.Name)
+			}
+			c.emitStoreVar("", valIdent.Name)
 		}
 
 		ast.Walk(c, n.Body)
diff --git a/pkg/compiler/for_test.go b/pkg/compiler/for_test.go
index a07cad913..c7bd36cc1 100644
--- a/pkg/compiler/for_test.go
+++ b/pkg/compiler/for_test.go
@@ -714,6 +714,32 @@ var forLoopTestCases = []testCase{
 		`,
 		big.NewInt(6),
 	},
+	{
+		"shadow range key",
+		`func F%d() int {
+			i := 10
+			ints := []int{1, 2, 3, 4, 5}
+			for i := range ints {
+				_ = i
+			}
+			return i
+		}
+		`,
+		big.NewInt(10),
+	},
+	{
+		"shadow range value",
+		`func F%d() int {
+			i := 10
+			ints := []int{1, 2, 3, 4, 5}
+			for _, i := range ints {
+				_ = i
+			}
+			return i
+		}
+		`,
+		big.NewInt(10),
+	},
 }
 
 func TestForLoop(t *testing.T) {

From 8305389852d93b097956b8445dec350112f62374 Mon Sep 17 00:00:00 2001
From: Roman Khimov <roman@nspcc.ru>
Date: Wed, 11 Jan 2023 16:21:40 +0300
Subject: [PATCH 2/2] compiler: don't panic, return error for strange range
 loops

See #2870.
---
 pkg/compiler/codegen.go | 33 ++++++++++++++++++++++++++-------
 1 file changed, 26 insertions(+), 7 deletions(-)

diff --git a/pkg/compiler/codegen.go b/pkg/compiler/codegen.go
index fb5c75ef6..50edd84c9 100644
--- a/pkg/compiler/codegen.go
+++ b/pkg/compiler/codegen.go
@@ -1301,25 +1301,45 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 		emit.Opcodes(c.prog.BinWriter, opcode.OVER, opcode.OVER)
 		emit.Jmp(c.prog.BinWriter, opcode.JMPLEL, end)
 
-		var keyLoaded bool
-		needValue := n.Value != nil && n.Value.(*ast.Ident).Name != "_"
-		if n.Key != nil && n.Key.(*ast.Ident).Name != "_" {
+		var (
+			haveKey   bool
+			haveVal   bool
+			keyIdent  *ast.Ident
+			keyLoaded bool
+			valIdent  *ast.Ident
+		)
+		if n.Key != nil {
+			keyIdent, haveKey = n.Key.(*ast.Ident)
+			if !haveKey {
+				c.prog.Err = errors.New("only simple identifiers can be used for range loop keys (see #2870)")
+				return nil
+			}
+			haveKey = (keyIdent.Name != "_")
+		}
+		if n.Value != nil {
+			valIdent, haveVal = n.Value.(*ast.Ident)
+			if !haveVal {
+				c.prog.Err = errors.New("only simple identifiers can be used for range loop values (see #2870)")
+				return nil
+			}
+			haveVal = (valIdent.Name != "_")
+		}
+		if haveKey {
 			if isMap {
 				c.rangeLoadKey()
-				if needValue {
+				if haveVal {
 					emit.Opcodes(c.prog.BinWriter, opcode.DUP)
 					keyLoaded = true
 				}
 			} else {
 				emit.Opcodes(c.prog.BinWriter, opcode.DUP)
 			}
-			keyIdent := n.Key.(*ast.Ident)
 			if n.Tok == token.DEFINE {
 				c.scope.newLocal(keyIdent.Name)
 			}
 			c.emitStoreVar("", keyIdent.Name)
 		}
-		if needValue {
+		if haveVal {
 			if !isMap || !keyLoaded {
 				c.rangeLoadKey()
 			}
@@ -1331,7 +1351,6 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 					opcode.SWAP, // key should be on top
 					opcode.PICKITEM)
 			}
-			valIdent := n.Value.(*ast.Ident)
 			if n.Tok == token.DEFINE {
 				c.scope.newLocal(valIdent.Name)
 			}