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Fix #7458 (FP unusedStructMember with struct in union) #7844

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Fix #7458 (FP unusedStructMember with struct in union) #7844

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da3aa83
Fix #7458 (FP unusedStructMember with struct in union)
danmar Sep 23, 2025
b53bc29
tweak; we can warn about unused union members
danmar Sep 23, 2025
5cff156
format
danmar Sep 23, 2025
564e050
simplify
danmar Sep 23, 2025
8129831
improve
danmar Sep 23, 2025
c93cfd7
startToken
danmar Sep 24, 2025
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17 changes: 17 additions & 0 deletions lib/checkunusedvar.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1599,6 +1599,23 @@ void CheckUnusedVar::checkStructMemberUsage()
if (bailout)
continue;

// #7458 - if struct is declared inside union and any struct member is used,
// then don't warn about other struct members
if (scope.type == ScopeType::eStruct && scope.nestedIn && scope.nestedIn->type == ScopeType::eUnion) {
bool structMemberUsed = false;

for (const Token *tok = scope.nestedIn->bodyStart; tok; tok = tok->next()) {
if (tok->variable() && tok != tok->variable()->nameToken() && tok->variable()->scope() == &scope) {
structMemberUsed = true;
break;
}
}

// Skip reporting unused members if this struct is in a union and any member is used
if (structMemberUsed)
continue;
}

for (const Variable &var : scope.varlist) {
// only warn for variables without side effects
if (!var.typeStartToken()->isStandardType() && !var.isPointer() && !astIsContainer(var.nameToken()) && !isRecordTypeWithoutSideEffects(var.type()))
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16 changes: 16 additions & 0 deletions test/testunusedvar.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1409,6 +1409,22 @@ class TestUnusedVar : public TestFixture {
ASSERT_EQUALS("[test.cpp:3:9]: (style) union member 'abc::a' is never used. [unusedStructMember]\n"
"[test.cpp:4:9]: (style) union member 'abc::b' is never used. [unusedStructMember]\n"
"[test.cpp:5:9]: (style) union member 'abc::c' is never used. [unusedStructMember]\n", errout_str());

// #7458 - union with anonymous struct should not cause false positive
checkStructMemberUsage("union DoubleInt {\n"
" double asDouble;\n"
" uint64_t asInt;\n"
" struct {\n"
" uint32_t lo, hi;\n" // <- no FP about lo because hi is used
" } asIntel;\n"
"};\n"
"void f() {\n"
" union DoubleInt di;\n"
" di.asIntel.hi = 3;\n"
"}");
ASSERT_EQUALS("[test.cpp:2:12]: (style) union member 'DoubleInt::asDouble' is never used. [unusedStructMember]\n"
"[test.cpp:3:14]: (style) union member 'DoubleInt::asInt' is never used. [unusedStructMember]\n",
errout_str());
}

void structmember2() {
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