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Fix #14075 (False positive: unusedStructMember, member usage by alignas is ignored) #7842

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Merged
merged 3 commits into from
Sep 23, 2025
Merged

Fix #14075 (False positive: unusedStructMember, member usage by alignas is ignored) #7842

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d905750
Fix #14075 (False positive: unusedStructMember, member usage by align…
danmar Sep 22, 2025
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useStlAlgorithm
danmar Sep 22, 2025
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danmar Sep 23, 2025
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11 changes: 11 additions & 0 deletions lib/checkunusedvar.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1628,6 +1628,17 @@ void CheckUnusedVar::checkStructMemberUsage()
break;
}
}
// Member referenced in alignas
if (tok->hasAttributeAlignas()) {
const std::vector<std::string> alignasExpressions = tok->getAttributeAlignas();
use = std::any_of(alignasExpressions.cbegin(),
alignasExpressions.cend(),
[&var](const std::string& alignasExpr){
return alignasExpr == var.name();
});
if (use)
break;
}
if (tok->variable() != &var)
continue;
if (tok != var.nameToken()) {
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10 changes: 10 additions & 0 deletions test/testunusedvar.cpp
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Expand Up @@ -71,6 +71,7 @@ class TestUnusedVar : public TestFixture {
TEST_CASE(structmember26); // #13345
TEST_CASE(structmember27); // #13367
TEST_CASE(structmember28);
TEST_CASE(structmember29); // #14075
TEST_CASE(structmember_macro);
TEST_CASE(structmember_template_argument); // #13887 - do not report that member used in template argument is unused
TEST_CASE(classmember);
Expand Down Expand Up @@ -2010,6 +2011,15 @@ class TestUnusedVar : public TestFixture {
ASSERT_EQUALS("[test.cpp:2:18]: (style) struct member 'S::a' is never used. [unusedStructMember]\n", errout_str());
}

void structmember29() { // #14075 - alignas false positive
checkStructMemberUsage("struct S {\n"
" static constexpr size_t cDataAlign = 8;\n"
" static constexpr size_t cDataSize = 128;\n"
" alignas(cDataAlign) std::array<uint8_t, cDataSize> storage{};\n"
"};\n");
ASSERT_EQUALS("[test.cpp:4:56]: (style) struct member 'S::storage' is never used. [unusedStructMember]\n", errout_str());
}

void structmember_macro() {
checkStructMemberUsageP("#define S(n) struct n { int a, b, c; };\n"
"S(unused);\n");
Expand Down