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valueflow: forward lifetimes through array and member subobjects #8636

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c38cc0e
valueflow: forward lifetimes through array and member subobjects
francois-berder May 28, 2026
e3afc01
fixup! valueflow: forward lifetimes through array and member subobjects
francois-berder Jun 5, 2026
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40 changes: 32 additions & 8 deletions lib/valueflow.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1952,6 +1952,35 @@ const Token* ValueFlow::getEndOfExprScope(const Token* tok, const Scope* default
return end;
}

static void getLhsLifetimeParentsImpl(const Token* lhs, const Library& library, std::vector<const Token*>& result)
{
if (!lhs)
return;

if (Token::simpleMatch(lhs, "[")) {
getLhsLifetimeParentsImpl(lhs->astOperand1(), library, result);
} else if (Token::simpleMatch(lhs, ".") && lhs->originalName() != "->") {
const Token* obj = lhs->astOperand1();
if (Token::simpleMatch(obj, "[") && obj->exprId() > 0)
result.push_back(obj);
getLhsLifetimeParentsImpl(obj, library, result);
} else {
const Token* tok = getParentLifetime(lhs, library);
if (tok && tok->exprId() > 0) {
const Variable* var = tok->variable();
if (!var || var->isLocal() || var->isArgument())
result.push_back(tok);
}
}
}

static std::vector<const Token*> getLhsLifetimeParents(const Token* lhs, const Library& library)
{
std::vector<const Token*> result;
getLhsLifetimeParentsImpl(lhs, library, result);
return result;
}

static void valueFlowForwardLifetime(Token * tok, const TokenList &tokenlist, ErrorLogger &errorLogger, const Settings &settings)
{
// Forward lifetimes to constructed variable
Expand Down Expand Up @@ -2004,14 +2033,9 @@ static void valueFlowForwardLifetime(Token * tok, const TokenList &tokenlist, Er
if (val.lifetimeKind == ValueFlow::Value::LifetimeKind::Address)
val.lifetimeKind = ValueFlow::Value::LifetimeKind::SubObject;
}
// TODO: handle `[`
if (Token::simpleMatch(parent->astOperand1(), ".")) {
const Token* parentLifetime =
getParentLifetime(parent->astOperand1()->astOperand2(), settings.library);
if (parentLifetime && parentLifetime->exprId() > 0) {
valueFlowForward(nextExpression, endOfVarScope, parentLifetime, std::move(values), tokenlist, errorLogger, settings);
}
}
std::vector<const Token*> parents = getLhsLifetimeParents(parent->astOperand1(), settings.library);
for (const Token *p : parents)
valueFlowForward(nextExpression, endOfVarScope, p, values, tokenlist, errorLogger, settings);
}
// Constructor
} else if (Token::simpleMatch(parent, "{") && !isScopeBracket(parent)) {
Expand Down
93 changes: 93 additions & 0 deletions test/testautovariables.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4452,6 +4452,99 @@ class TestAutoVariables : public TestFixture {
"}\n");
ASSERT_EQUALS("[test.cpp:5:14] -> [test.cpp:5:18] -> [test.cpp:6:7]: (error) Using pointer that is a temporary. [danglingTemporaryLifetime]\n",
errout_str());

check("struct A { const int* data[2]; };\n"
"A g() {\n"
" int x = 0;\n"
" A a;\n"
" a.data[0] = &x;\n"
" return a;\n"
"}\n");
ASSERT_EQUALS("[test.cpp:5:17] -> [test.cpp:3:9] -> [test.cpp:6:12]: (error) Returning object that points to local variable 'x' that will be invalid when returning. [returnDanglingLifetime]\n",
errout_str());

check("struct A { const int* data[2]; };\n"
"A g() {\n"
" int x = 0;\n"
" A a[2];\n"
" a[0].data[0] = &x;\n"
" return a[0];\n"
"}\n");
ASSERT_EQUALS("[test.cpp:5:20] -> [test.cpp:3:9] -> [test.cpp:6:13]: (error) Returning object that points to local variable 'x' that will be invalid when returning. [returnDanglingLifetime]\n",
errout_str());

check("struct A { const int* data[2]; };\n"
"A* g() {\n"
" int x = 0;\n"
" static A arr[2];\n"
" arr[0].data[0] = &x;\n"
" return arr;\n"
"}\n");
ASSERT_EQUALS("[test.cpp:5:22] -> [test.cpp:3:9] -> [test.cpp:6:12]: (error) Returning pointer to local variable 'x' that will be invalid when returning. [returnDanglingLifetime]\n",
errout_str());

check("struct A { const int* p; };\n"
"A g(int i) {\n"
" int x = 0;\n"
" A arr[2];\n"
" arr[i].p = &x;\n"
" return arr[i];\n"
"}\n");
ASSERT_EQUALS("[test.cpp:5:16] -> [test.cpp:3:9] -> [test.cpp:6:15]: (error) Returning object that points to local variable 'x' that will be invalid when returning. [returnDanglingLifetime]\n",
errout_str());

check("struct A { const int* p; };\n"
"A* g(int i) {\n"
" int x = 0;\n"
" static A arr[2];\n"
" arr[i].p = &x;\n"
" return arr;\n"
"}\n");
ASSERT_EQUALS("[test.cpp:5:16] -> [test.cpp:3:9] -> [test.cpp:6:12]: (error) Returning pointer to local variable 'x' that will be invalid when returning. [returnDanglingLifetime]\n",
errout_str());

check("struct A { const int* p; };\n"
"struct B { A arr[2]; };\n"
"B g(int i) {\n"
" int x = 0;\n"
" B b;\n"
" b.arr[i].p = &x;\n"
" return b;\n"
"}\n");
ASSERT_EQUALS("[test.cpp:6:18] -> [test.cpp:4:9] -> [test.cpp:7:12]: (error) Returning object that points to local variable 'x' that will be invalid when returning. [returnDanglingLifetime]\n",
errout_str());

check("struct A { const int* p; };\n"
"A* g() {\n"
" int x = 0;\n"
" static A a;\n"
" A* ap = &a;\n"
" ap->p = &x;\n"
" (*ap).p = &x;\n"
" return ap;\n"
"}\n");
ASSERT_EQUALS("", errout_str());

check("struct A { int* a; int* b; };\n"
"static A g;\n"
"int* f() {\n"
" int x = 0;\n"
" g.a = &x;\n"
" return g.b;\n"
"}\n");
ASSERT_EQUALS("[test.cpp:5:11] -> [test.cpp:4:9] -> [test.cpp:5:6]: (error) Non-local variable 'g.a' will use pointer to local variable 'x'. [danglingLifetime]\n",
errout_str());

check("struct A { int* a; int* b; };\n"
"static A g;\n"
"int* f() {\n"
" int x = 0;\n"
" g.a = &x;\n"
" return g.a;\n"
"}\n");
ASSERT_EQUALS("[test.cpp:5:11] -> [test.cpp:4:9] -> [test.cpp:5:6]: (error) Non-local variable 'g.a' will use pointer to local variable 'x'. [danglingLifetime]\n"
"[test.cpp:5:11] -> [test.cpp:4:9] -> [test.cpp:6:13]: (error) Returning pointer to local variable 'x' that will be invalid when returning. [returnDanglingLifetime]\n",
errout_str());
}

void danglingLifetimeClassMemberFunctions()
Expand Down
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