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Fix #15021 FN redundantInitialization with structured binding #8847

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Fix #15021 FN redundantInitialization with structured binding #8847

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cdd6b4d
Update checkother.cpp
chrchr-github Sep 11, 2026
bb44bf4
Update testother.cpp
chrchr-github Sep 11, 2026
7ae3dd4
Merge branch 'main' into chr_15021
chrchr-github Sep 30, 2026
67b4065
Merge branch 'main' into chr_15021
web-flow Oct 10, 2026
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88 changes: 48 additions & 40 deletions lib/checkother.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -688,53 +688,61 @@ void CheckOtherImpl::checkRedundantAssignment()
start = tok->astOperand2();
else
start = tok->findExpressionStartEndTokens().second->next();
const Token * tokenToCheck = tok->astOperand1();

// Check if we are working with union
for (const Token* tempToken = tokenToCheck; Token::simpleMatch(tempToken, ".");) {
tempToken = tempToken->astOperand1();
if (tempToken && tempToken->variable() && tempToken->variable()->type() && tempToken->variable()->type()->isUnionType())
tokenToCheck = tempToken;
}
std::vector<const Token*> tokensToCheck{ tok->astOperand1() };
if (Token::simpleMatch(tok->astOperand1(), "[") && Token::simpleMatch(tok->astOperand1()->astOperand1(), "auto")) // structured binding

@claude claude Bot Oct 10, 2026

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Possible FP with reference bindings: the isReference() bailout above (// todo: check references) runs on tok->astOperand1(), which is the [ token here and has no variable. So it never applies to the bound names. With auto& [x, y] = s; x = 1;, x is an alias for s.a and the write is observable, so it isn't redundant. The same applies to tuple-like types whose elements are references (e.g. auto [a, b] = std::tie(i, j);).

I'd suggest skipping elements whose variable()->isReference() is true (or bailing out when the declaration is auto&/auto&&), and adding a negative test for auto& [x, y] = s; x = 1; y = 2;.

tokensToCheck = astFlatten(tok->astOperand1()->astOperand2(), ",");

if (start->hasKnownSymbolicValue(tokenToCheck) && Token::simpleMatch(start->astParent(), "=") && !diag(tok)) {
const ValueFlow::Value* val = start->getKnownValue(ValueFlow::Value::ValueType::SYMBOLIC);
if (val->intvalue == 0) // no offset
redundantAssignmentSameValueError(tokenToCheck, val, tok->astOperand1()->expressionString());
}
for (const Token* tokenToCheck : tokensToCheck) {

// Get next assignment..
const Token *nextAssign = fwdAnalysis.reassign(tokenToCheck, start, scope->bodyEnd);
// extra check for union
if (nextAssign && tokenToCheck != tok->astOperand1()) {
nextAssign = fwdAnalysis.reassign(tok->astOperand1(), start, scope->bodyEnd);
// reading another member of the same union in the rhs is a use through aliasing
if (nextAssign && fwdAnalysis.hasOperand(nextAssign->astOperand2(), tokenToCheck))
nextAssign = nullptr;
}
// Check if we are working with union
for (const Token* tempToken = tokenToCheck; Token::simpleMatch(tempToken, ".");) {
tempToken = tempToken->astOperand1();
if (tempToken && tempToken->variable() && tempToken->variable()->type() && tempToken->variable()->type()->isUnionType())
tokenToCheck = tempToken;
}

if (!nextAssign)
continue;
if (start->hasKnownSymbolicValue(tokenToCheck) && Token::simpleMatch(start->astParent(), "=") && !diag(tok)) {
const ValueFlow::Value* val = start->getKnownValue(ValueFlow::Value::ValueType::SYMBOLIC);

@claude claude Bot Oct 10, 2026

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Now that this runs inside the loop, there are two problems for structured bindings:

  • diag(tok) inserts tok the first time, so only the first bound element can ever get this diagnostic.
  • The message still uses tok->astOperand1()->expressionString(), which would print [x,y] instead of the element name. It should use exprTok/tokenToCheck, like the other diagnostics below.

if (val->intvalue == 0) // no offset
redundantAssignmentSameValueError(tokenToCheck, val, tok->astOperand1()->expressionString());
}

// there is redundant assignment. Is there a case between the assignments?
bool hasCase = false;
for (const Token *tok2 = tok; tok2 != nextAssign; tok2 = tok2->next()) {
if (tok2->str() == "break" || tok2->str() == "return")
break;
if (tok2->str() == "case") {
hasCase = true;
break;
// Get next assignment..
const Token* nextAssign = fwdAnalysis.reassign(tokenToCheck, start, scope->bodyEnd);
// extra check for union
const bool isUnion = tokenToCheck != tok->astOperand1() && !isStructuredBindingVariable(tokenToCheck->variable());
if (nextAssign && isUnion) {
nextAssign = fwdAnalysis.reassign(tok->astOperand1(), start, scope->bodyEnd);
// reading another member of the same union in the rhs is a use through aliasing
if (nextAssign && fwdAnalysis.hasOperand(nextAssign->astOperand2(), tokenToCheck))
nextAssign = nullptr;
}
}

// warn
if (hasCase)
redundantAssignmentInSwitchError(tok, nextAssign, tok->astOperand1()->expressionString());
else if (isInitialization)
redundantInitializationError(tok, nextAssign, tok->astOperand1()->expressionString(), inconclusive);
else {
diag(nextAssign);
redundantAssignmentError(tok, nextAssign, tok->astOperand1()->expressionString(), inconclusive);
if (!nextAssign)
continue;

// there is redundant assignment. Is there a case between the assignments?
bool hasCase = false;
for (const Token* tok2 = tok; tok2 != nextAssign; tok2 = tok2->next()) {
if (tok2->str() == "break" || tok2->str() == "return")
break;
if (tok2->str() == "case") {
hasCase = true;
break;
}
}

// warn
const Token* exprTok = isUnion ? tok->astOperand1() : tokenToCheck;
if (hasCase)
redundantAssignmentInSwitchError(tok, nextAssign, exprTok->expressionString());
else if (isInitialization)
redundantInitializationError(tok, nextAssign, exprTok->expressionString(), inconclusive);
else {
diag(nextAssign);
redundantAssignmentError(tok, nextAssign, exprTok->expressionString(), inconclusive);
}
}
}
}
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24 changes: 24 additions & 0 deletions test/testother.cpp
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Expand Up @@ -11555,6 +11555,30 @@ class TestOther : public TestFixture {
"[test.cpp:8:10]: note: i is initialized\n"
"[test.cpp:9:7]: note: i is overwritten\n",
errout_str());

check("struct S { int a, b; };\n" // #15021
"int f(S s) {\n"
" auto [x, y] = s;\n"
" x = 1;\n"
" y = 2;\n"
" return x + y;\n"
"}\n"
"struct T { int c; };\n"
"int g(T t) {\n"
" auto [z] = t;\n"
" z = 0;\n"
" return z;\n"
"}\n");
ASSERT_EQUALS("[test.cpp:4:7]: style: Variable 'x' is reassigned a value before the old one has been used. [redundantAssignment]\n"
"[test.cpp:3:17]: note: x is assigned\n"
"[test.cpp:4:7]: note: x is overwritten\n"
"[test.cpp:5:7]: style: Variable 'y' is reassigned a value before the old one has been used. [redundantAssignment]\n"
"[test.cpp:3:17]: note: y is assigned\n"
"[test.cpp:5:7]: note: y is overwritten\n"
"[test.cpp:11:7]: style: Variable 'z' is reassigned a value before the old one has been used. [redundantAssignment]\n"
"[test.cpp:10:14]: note: z is assigned\n"
"[test.cpp:11:7]: note: z is overwritten\n",
errout_str());
}

// cppcheck-suppress unusedPrivateFunction
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