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[clang-tidy] Fix false positives about references in misc-const-correctness #160971

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Merged
merged 2 commits into from
Oct 8, 2025
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[clang-tidy] Fix false positives about references in misc-const-correctness #160971

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fea611f
[clang-tidy] Fix false positives about references in `misc-const-corr…
flovent Sep 27, 2025
5976ad5
[NFC] Fix doc error
flovent Sep 27, 2025
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4 changes: 4 additions & 0 deletions clang-tools-extra/docs/ReleaseNotes.rst
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Expand Up @@ -309,6 +309,10 @@ Changes in existing checks

- ``for`` loops are supported.

- Improved :doc:`misc-const-correctness
<clang-tidy/checks/misc/const-correctness>` check to avoid false
positives when pointers is tranferred to non-const references.
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@localspook localspook Sep 28, 2025 •
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Suggested change
positives when pointers is tranferred to non-const references.
positives when pointers to non-const are bound to references.

Since the false positive happens whether the reference itself is const or not.

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@flovent flovent Sep 28, 2025 •
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For the second function in link:

void const_ref() {
  int* p1 {nullptr};
  int* const& r1 = p1;
}

It's not fixed by this patch actually, because it's a reference points to const (int* const), and it's not legal to write a const reference version:

   int*  p1 {nullptr};
   const int* & r1 = p1; // error: binding reference of type 'const int *' to value of type 'int *' not permitted due to incompatible qualifiers

And canResolveToExprPointee don't handle NoOp right now, for the AST :

VarDecl <col:4, col:22> col:17 r1 'int *const &' cinit
  `-ImplicitCastExpr <col:22> 'int *const' lvalue <NoOp>
    `-DeclRefExpr <col:22> 'int *' lvalue Var 0x38dc2e98 'p1' 'int *'

So it might need more work to erase this FP.


- Improved :doc:`misc-header-include-cycle
<clang-tidy/checks/misc/header-include-cycle>` check performance.

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15 changes: 15 additions & 0 deletions clang-tools-extra/test/clang-tidy/checkers/misc/const-correctness-pointer-as-pointers.cpp
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Expand Up @@ -48,3 +48,18 @@ void ignore_const_alias() {
p_local0 = &a[1];
}

void takeNonConstRef(int *&r);

void ignoreNonConstRefOps() {
// init with non-const ref
int* p0 {nullptr};
int*& r1 = p0;

// non-const ref param
int* p1 {nullptr};
takeNonConstRef(p1);

// cast
int* p2 {nullptr};
int*& r2 = (int*&)p2;
}
25 changes: 13 additions & 12 deletions clang/lib/Analysis/ExprMutationAnalyzer.cpp
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Expand Up @@ -755,22 +755,23 @@ ExprMutationAnalyzer::Analyzer::findPointeeMemberMutation(const Expr *Exp) {

const Stmt *
ExprMutationAnalyzer::Analyzer::findPointeeToNonConst(const Expr *Exp) {
const auto NonConstPointerOrDependentType =
type(anyOf(nonConstPointerType(), isDependentType()));
const auto NonConstPointerOrNonConstRefOrDependentType = type(
anyOf(nonConstPointerType(), nonConstReferenceType(), isDependentType()));

// assign
const auto InitToNonConst =
varDecl(hasType(NonConstPointerOrDependentType),
varDecl(hasType(NonConstPointerOrNonConstRefOrDependentType),
hasInitializer(expr(canResolveToExprPointee(Exp)).bind("stmt")));
const auto AssignToNonConst =
binaryOperation(hasOperatorName("="),
hasLHS(expr(hasType(NonConstPointerOrDependentType))),
hasRHS(canResolveToExprPointee(Exp)));
const auto AssignToNonConst = binaryOperation(
hasOperatorName("="),
hasLHS(expr(hasType(NonConstPointerOrNonConstRefOrDependentType))),
hasRHS(canResolveToExprPointee(Exp)));
// arguments like
const auto ArgOfInstantiationDependent = allOf(
hasAnyArgument(canResolveToExprPointee(Exp)), isInstantiationDependent());
const auto ArgOfNonConstParameter = forEachArgumentWithParamType(
canResolveToExprPointee(Exp), NonConstPointerOrDependentType);
const auto ArgOfNonConstParameter =
forEachArgumentWithParamType(canResolveToExprPointee(Exp),
NonConstPointerOrNonConstRefOrDependentType);
const auto CallLikeMatcher =
anyOf(ArgOfNonConstParameter, ArgOfInstantiationDependent);
const auto PassAsNonConstArg =
Expand All @@ -779,9 +780,9 @@ ExprMutationAnalyzer::Analyzer::findPointeeToNonConst(const Expr *Exp) {
parenListExpr(has(canResolveToExprPointee(Exp))),
initListExpr(hasAnyInit(canResolveToExprPointee(Exp)))));
// cast
const auto CastToNonConst =
explicitCastExpr(hasSourceExpression(canResolveToExprPointee(Exp)),
hasDestinationType(NonConstPointerOrDependentType));
const auto CastToNonConst = explicitCastExpr(
hasSourceExpression(canResolveToExprPointee(Exp)),
hasDestinationType(NonConstPointerOrNonConstRefOrDependentType));

// capture
// FIXME: false positive if the pointee does not change in lambda
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23 changes: 23 additions & 0 deletions clang/unittests/Analysis/ExprMutationAnalyzerTest.cpp
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Expand Up @@ -1749,6 +1749,13 @@ TEST(ExprMutationAnalyzerTest, PointeeMutatedByInitToNonConst) {
match(withEnclosingCompound(declRefTo("x")), AST->getASTContext());
EXPECT_TRUE(isPointeeMutated(Results, AST.get()));
}
{
const std::string Code = "void f() { int* x = nullptr; int*& b = x; }";
auto AST = buildASTFromCodeWithArgs(Code, {});
auto Results =
match(withEnclosingCompound(declRefTo("x")), AST->getASTContext());
EXPECT_TRUE(isPointeeMutated(Results, AST.get()));
}
}

TEST(ExprMutationAnalyzerTest, PointeeMutatedByAssignToNonConst) {
Expand Down Expand Up @@ -1786,6 +1793,14 @@ TEST(ExprMutationAnalyzerTest, PointeeMutatedByPassAsArgument) {
match(withEnclosingCompound(declRefTo("x")), AST->getASTContext());
EXPECT_TRUE(isPointeeMutated(Results, AST.get()));
}
{
const std::string Code =
"void b(int *&); void f() { int* x = nullptr; b(x); }";
auto AST = buildASTFromCodeWithArgs(Code, {});
auto Results =
match(withEnclosingCompound(declRefTo("x")), AST->getASTContext());
EXPECT_TRUE(isPointeeMutated(Results, AST.get()));
}
}

TEST(ExprMutationAnalyzerTest, PointeeMutatedByPassAsArgumentInConstruct) {
Expand Down Expand Up @@ -1884,6 +1899,14 @@ TEST(ExprMutationAnalyzerTest, PointeeMutatedByExplicitCastToNonConst) {
match(withEnclosingCompound(declRefTo("x")), AST->getASTContext());
EXPECT_TRUE(isPointeeMutated(Results, AST.get()));
}
{
const std::string Code =
"void f() { int* x = nullptr; static_cast<int*&>(x); }";
auto AST = buildASTFromCodeWithArgs(Code, {"-Wno-everything"});
auto Results =
match(withEnclosingCompound(declRefTo("x")), AST->getASTContext());
EXPECT_TRUE(isPointeeMutated(Results, AST.get()));
}
}

TEST(ExprMutationAnalyzerTest, PointeeMutatedByConstCastToNonConst) {
Expand Down