From 2e5924438382f74114837e373227dd578de6054c Mon Sep 17 00:00:00 2001
From: Nathan Baulch <nathan.baulch@gmail.com>
Date: Tue, 3 Feb 2026 21:57:50 +1100
Subject: [PATCH] Exclude if ellipsis append references a loop var

---
 pkg/prealloc.go    |  7 +++++--
 testdata/append.go | 15 ++++++++++-----
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/pkg/prealloc.go b/pkg/prealloc.go
index aaedab1..58448e6 100644
--- a/pkg/prealloc.go
+++ b/pkg/prealloc.go
@@ -229,9 +229,12 @@ func (v *returnsVisitor) Visit(node ast.Node) ast.Visitor {
 					return v
 				}
 
-				if sliceDecl.hasReturn || sliceDecl.level != v.level || sliceDecl.detached {
+				switch {
+				case sliceDecl.hasReturn || sliceDecl.level != v.level || sliceDecl.detached:
 					sliceDecl.exclude = true
-				} else {
+				case s.Ellipsis.IsValid() && hasAny(s, v.loopVars):
+					sliceDecl.exclude = true
+				default:
 					if sliceDecl.assigning {
 						sliceDecl.assigning = false
 					} else {
diff --git a/testdata/append.go b/testdata/append.go
index 77ced2b..6920a50 100644
--- a/testdata/append.go
+++ b/testdata/append.go
@@ -86,6 +86,14 @@ func appendEllipsisTypeConvert() {
 	}
 }
 
+func appendEllipsisUsesLoopVar() {
+	var x []byte
+	var y []string
+	for i := range 5 {
+		x = append(x, y[i]...)
+	}
+}
+
 func appendMultipleCallsRange() {
 	var x []int // want "Consider preallocating x with capacity 10$"
 	for i := range 5 {
@@ -126,11 +134,8 @@ func appendMultipleRangeStringVar() {
 }
 
 func appendAppend() {
-	s := "Hello"
-	var x []int // want "Consider preallocating x with capacity 2 \\* len\\(s\\)$"
-	for i := range s {
-		x = append(x, append([]int{i}, i)...)
-	}
+	var x []int // want "Consider preallocating x with capacity 4$"
+	x = append(x, append([]int{1, 2}, 3, 4)...)
 }
 
 func appendDetached() {