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Fix #14643, #10965, #11704: false positive: unreadVariable for constructors with unknown side effects #8420

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Fix #14643, #10965, #11704: false positive: unreadVariable for constructors with unknown side effects #8420

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c209a77
Add test
ludviggunne Apr 7, 2026
7649f99
fix #14643
ludviggunne Apr 7, 2026
887353d
Add tests for other tickets
ludviggunne Apr 8, 2026
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8 changes: 8 additions & 0 deletions lib/checkunusedvar.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1352,6 +1352,14 @@ void CheckUnusedVar::checkFunctionVariableUsage()
if (tok->previous() && tok->previous()->variable() && tok->previous()->variable()->nameToken()->scope()->type == ScopeType::eUnion)
continue;

if (expr->valueType() &&
expr->valueType()->type == ValueType::RECORD &&
!expr->valueType()->pointer &&
expr->valueType()->typeScope &&
expr->valueType()->typeScope->definedType &&
!symbolDatabase->isRecordTypeWithoutSideEffects(expr->valueType()->typeScope->definedType))
continue;

FwdAnalysis fwdAnalysis(*mSettings);
const Token* scopeEnd = ValueFlow::getEndOfExprScope(expr, scope, /*smallest*/ false);
if (fwdAnalysis.unusedValue(expr, start, scopeEnd)) {
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28 changes: 28 additions & 0 deletions test/testunusedvar.cpp
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Expand Up @@ -6681,6 +6681,34 @@ class TestUnusedVar : public TestFixture {
" C c(12);\n"
"}");
ASSERT_EQUALS("", errout_str());

// #14643
functionVariableUsage("class S { S(int); };\n"
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@danmar danmar Apr 7, 2026

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in this test case we can't see if the constructor has side effects or not. so it makes sense to not warn.

if we would see that the constructor body is empty will there be some warning then?

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@ludviggunne ludviggunne Apr 7, 2026

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Yep

"void f() { S s = 0; }\n");
ASSERT_EQUALS("", errout_str());

// #10965
functionVariableUsage("class A {\n"
"public:\n"
" A();\n"
"};\n"
"extern A cb();\n"
"void f() { const A c = cb(); }\n");
ASSERT_EQUALS("", errout_str());

// #11704
functionVariableUsage("class S {\n"
"public:\n"
" S();\n"
"};\n"
"class C {\n"
" S &s();\n"
" void f() {\n"
" const S s1 = s(); // warning\n"
" const S s2; // no warning\n"
" }\n"
"};\n");
ASSERT_EQUALS("", errout_str());
}

void localVarSmartPtr() {
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