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Exclude if ellipsis append references a loop var #65

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Merged
alexkohler merged 1 commit into from
Feb 9, 2026
Merged

Exclude if ellipsis append references a loop var #65

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7 changes: 5 additions & 2 deletions pkg/prealloc.go
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Original file line number Diff line number Diff line change
Expand Up @@ -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 {
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15 changes: 10 additions & 5 deletions testdata/append.go
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Original file line number Diff line number Diff line change
Expand Up @@ -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 {
Expand Down Expand Up @@ -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() {
Expand Down
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