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Fix #5738: false duplicate warnings with string prefix macros #8834

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Fix #5738: false duplicate warnings with string prefix macros #8834

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475789b
Fix false duplicate warnings with string prefix macros
tzi4 Sep 7, 2026
2a0c507
Preserve duplicate warnings for matching string prefix literals
tzi4 Sep 8, 2026
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15 changes: 15 additions & 0 deletions lib/astutils.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1607,6 +1607,21 @@ bool isSameExpression(bool macro, const Token *tok1, const Token *tok2, const Se
return true;
if (tok1 == nullptr || tok2 == nullptr)
return false;
// An unknown string-prefix macro leaves the literal outside the AST.
// Compare the literal text as well so identical literals still compare equal.
const bool stringPrefix1 = !tok1->isKeyword() && Token::Match(tok1, "%name% %str%");
const bool stringPrefix2 = !tok2->isKeyword() && Token::Match(tok2, "%name% %str%");
Comment on lines +1612 to +1613

@danmar danmar Oct 1, 2026

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This is an AI review. Take it with a grain of salt and feel free to reject it by resolving the comment.

Looks good to me. I built the PR and compared it with the merge base. The false positives are gone for n == SRCDIR "/a" || n == SRCDIR "/b", n != SRCDIR "/a" && n != SRCDIR "/b" and b ? PFX "x" : PFX "y" (duplicateExpression / duplicateExpressionTernary). Real duplicates (b ? PFX "x" : PFX "x") are still reported.

Minor nit: isSameExpression() is a hot function that recurses over whole ASTs, and this adds two Token::Match(..., "%name% %str%") calls to every invocation. A cheap pre-check would avoid the pattern matching in the common case, e.g. tok1->isName() && tok1->next() && tok1->next()->tokType() == Token::eString (and similar for tok2), or just Token::Match only after a tok->next()->isLiteral() check.

if (stringPrefix1 || stringPrefix2) {
if (!stringPrefix1 || !stringPrefix2)
return false;
for (const Token* str1 = tok1->next(), *str2 = tok2->next();
Token::Match(str1, "%str%") || Token::Match(str2, "%str%");
str1 = str1->next(), str2 = str2->next()) {
if (!Token::Match(str1, "%str%") || !Token::Match(str2, "%str%") ||
str1->str() != str2->str() || !compareTokenFlags(str1, str2, macro))
return false;
}
}
// tokens needs to be from the same TokenList so no need check standard on both of them
if (tok1->isCpp()) {
if (tok1->str() == "." && tok1->astOperand1() && tok1->astOperand1()->str() == "this")
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11 changes: 11 additions & 0 deletions test/testastutils.cpp
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Expand Up @@ -198,11 +198,22 @@ class TestAstUtils : public TestFixture {
ASSERT_EQUALS(!cpp, isSameExpression("void f() {double y = 1e1; (x + 10.0) < (y + x); } \n", "+", "+", cpp));
ASSERT_EQUALS(true, isSameExpression("void f() {double y = 1e1; double z = 10.0; (x + y) < (x + z); } \n", "+", "+", cpp));
ASSERT_EQUALS(true, isSameExpression("A + A\n", "A", "A", cpp));
// An unknown string-prefix macro leaves the literal outside the AST. #5738
ASSERT_EQUALS(false, isSameExpression("x == PREFIX \"/a\" || x == PREFIX \"/b\";\n", "==", "==", cpp));
ASSERT_EQUALS(false, isSameExpression("x == PREFIX \"/a\" || x == PREFIX;\n", "==", "==", cpp));
ASSERT_EQUALS(false, isSameExpression("x == PREFIX || x == PREFIX \"/a\";\n", "==", "==", cpp));
ASSERT_EQUALS(true, isSameExpression("x == PREFIX \"/a\" || x == PREFIX \"/a\";\n", "==", "==", cpp));
ASSERT_EQUALS(true, isSameExpression("x == PREFIX \"/a\" \"/b\" || x == PREFIX \"/a\" \"/b\";\n", "==", "==", cpp));
ASSERT_EQUALS(false, isSameExpression("x == PREFIX \"/a\" \"/b\" || x == PREFIX \"/a\" \"/c\";\n", "==", "==", cpp));
ASSERT_EQUALS(false, isSameExpression("x == FIRST \"/a\" || x == SECOND \"/a\";\n", "==", "==", cpp));
ASSERT_EQUALS(false, isSameExpression("x == PREFIX L\"/a\" || x == PREFIX \"/a\";\n", "==", "==", cpp));

// the remaining test cases are not valid C code
if (!cpp)
return;

ASSERT_EQUALS(true, isSameExpression("void f(int x) { x ? throw \"a\" : throw \"a\"; }\n", "throw", "throw", cpp));

//https://trac.cppcheck.net/ticket/9700
ASSERT_EQUALS(true, isSameExpression("A::B + A::B;\n", "::", "::", cpp));
ASSERT_EQUALS(false, isSameExpression("A::B + A::C;\n", "::", "::", cpp));
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12 changes: 12 additions & 0 deletions test/testother.cpp
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Expand Up @@ -12163,6 +12163,18 @@ class TestOther : public TestFixture {
" return name.startswith(SRCDIR \"/com/\") || name.startswith(SRCDIR \"/uno/\");\n"
"};\n", dinit(CheckOptions, $.inconclusive = false));
ASSERT_EQUALS("", errout_str());

check("bool isInUnoIncludeFile(StringRef name) {\n"
" return isInMainFile()\n"
" ? (name == SRCDIR \"/cppu/compat.cxx\" || name == SRCDIR \"/sal/compat.cxx\")\n"
" : (name.startswith(SRCDIR \"/com/\") || name.startswith(SRCDIR \"/uno/\"));\n"
"}\n", dinit(CheckOptions, $.inconclusive = false));
ASSERT_EQUALS("", errout_str());

check("bool f(StringRef name) {\n"
" return name == SRCDIR \"/a\" || name == SRCDIR \"/a\";\n"
"}\n", dinit(CheckOptions, $.inconclusive = false));
ASSERT_EQUALS("[test.cpp:2:32]: (style) Same expression on both sides of '||'. [duplicateExpression]\n", errout_str());
}

void raceAfterInterlockedDecrement() {
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