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Fix #14520: false positive: passedByValue on declaration with const #8460

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Fix #14520: false positive: passedByValue on declaration with const #8460

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29760ce
update test
ludviggunne Apr 16, 2026
0357bb6
add test
ludviggunne Apr 16, 2026
1380219
fix
ludviggunne Apr 16, 2026
86b80d3
Update test/testother.cpp
ludviggunne Apr 21, 2026
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15 changes: 15 additions & 0 deletions lib/checkother.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1591,6 +1591,21 @@ void CheckOther::checkPassByReference()
if (var->isArray() && (!var->isStlType() || Token::simpleMatch(var->nameToken()->next(), "[")))
continue;

if (var->isArgument()) {
const Token *tok = var->typeStartToken();
for (; tok; tok = tok->next()) {
if (Token::simpleMatch(tok, "(")) {
tok = tok->link();
continue;
}
if (Token::simpleMatch(tok, ")"))
break;
}

if (Token::simpleMatch(tok, ") ;"))
continue;
}

const bool isConst = var->isConst();
if (isConst) {
passedByValueError(var, inconclusive, isRangeBasedFor);
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10 changes: 9 additions & 1 deletion test/testother.cpp
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Expand Up @@ -2909,7 +2909,7 @@ class TestOther : public TestFixture {
check("struct X { int a[5]; }; extern \"C\" void f(X v) { }");
ASSERT_EQUALS("", errout_str());

check("struct X { int a[5]; }; void f(const X v);");
check("struct X { int a[5]; }; void f(const X v) { (void) v; }");
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ASSERT_EQUALS("[test.cpp:1:40]: (performance) Function parameter 'v' should be passed by const reference. [passedByValue]\n", errout_str());
Comment on lines -2912 to 2916
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@firewave firewave Apr 20, 2026

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Shouldn't we keep the existing test (in addition to the changed one) as that is the false positive fixed here.

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@ludviggunne ludviggunne Apr 20, 2026

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I believe the intention of this test is to ensure we warn for struct parameters, so I wanted to keep that meaning. Although, now that you point it out there is a false positive here, but I think it's unrelated to the ticket (there is an implementation).

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@firewave firewave Apr 20, 2026

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There is a misunderstanding.

The test in its original form without the implementation showed the false positive. That is the fix that we no longer warn for it.

Instead of just adding the implementation so the result stays the same we should have tests with and without implementation.

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@ludviggunne ludviggunne Apr 20, 2026

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I think I'm still misunderstanding... after this patch this test would have to be updated either way (result/input code). 0357bb6 introduces a test without implementation, whereas this now has an implementation. Are you suggesting two new tests that are identical except for present/missing implementation?

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@firewave firewave Apr 20, 2026

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The new test uses the exact case from the ticket which involves a class and the constructor.

The test in question here is about free-standing functions which would be missing.

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@ludviggunne ludviggunne Apr 21, 2026

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Ah, thanks I see


check("extern \"C\" { struct X { int a[5]; }; void f(const X v); }");
Expand Down Expand Up @@ -4108,6 +4108,14 @@ class TestOther : public TestFixture {
" if (*pp) {}\n"
"}\n");
ASSERT_EQUALS("", errout_str());

check("class C {\n"
"public:\n"
" explicit C(const std::string s);\n"
"private:\n"
" std::string _s;\n"
"};\n");
ASSERT_EQUALS("", errout_str());
}

void constParameterCallback() {
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