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Fix another only written to unused variable case #1472

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Fix another only written to unused variable case #1472

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3abf469
Fix another only written to unused variable case
keith Jun 9, 2026
a94a0cb
Update warn/warn_control_flow.go
keith Jun 9, 2026
3f1bc7b
Handle mutatable members
keith Jun 10, 2026
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16 changes: 16 additions & 0 deletions warn/warn_control_flow.go
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Original file line number Diff line number Diff line change
Expand Up @@ -225,6 +225,15 @@ func noEffectWarning(f *build.File) []*LinterFinding {
return findings
}

var mutatingMethodsReturningNone = map[string]bool{
"append": true,
"clear": true,
"extend": true,
"insert": true,
"remove": true,
"update": true,
}
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// extractIdentsFromStmt returns all idents from an AST node representing a
// single statement that are either defined outside the node and used inside,
// or defined inside the node and can be used outside.
Expand Down Expand Up @@ -305,6 +314,13 @@ func extractIdentsFromStmt(stmt build.Expr) (assigned, used map[*build.Ident]boo
(!allLValuesUnderscored && strings.HasPrefix(lValue.Name, "_"))
}

case *build.CallExpr:
if dot, ok := expr.X.(*build.DotExpr); ok && mutatingMethodsReturningNone[dot.Name] {
if _, ok := dot.X.(*build.Ident); ok {
blockedNodes[dot.X] = true
}
}

case *build.ForStmt:
// Like AssignExpr, ForStmt too has an analogue of LHS and RHS.
// Unlike AssignExpr, in this function they may appear only in the root of
Expand Down
24 changes: 24 additions & 0 deletions warn/warn_control_flow_test.go
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Expand Up @@ -697,6 +697,30 @@ sample_macro_with_used_foo()
`,
[]string{},
scopeEverywhere)

checkFindings(t, "unused-variable", `
def framework_import_impl():
used_list = []
unused_list = []
unused_dictionary = {}

used_list.extend([1])
unused_dictionary.update(_ensure_swiftmodule_is_embedded(swiftmodule))
unused_list.extend([
x
for x in used_list
if x > 5
])

return used_list

framework_import_impl()
`,
[]string{
":3: Variable \"unused_list\" is unused.",
":4: Variable \"unused_dictionary\" is unused.",
},
scopeEverywhere)
}

func TestRedefinedVariable(t *testing.T) {
Expand Down