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

It's not legal to cast const pointer type to it's non-const reference
type implicitly, and will cause compile error.

And for explicit cast, it's legal but the pointer is mutable through
this reference.

Author: flovent

clang-tools-extra/docs/ReleaseNotes.rst

@@ -318,6 +318,10 @@ 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.
+
 - Improved :doc:`misc-header-include-cycle
   <clang-tidy/checks/misc/header-include-cycle>` check performance.
 

clang-tools-extra/test/clang-tidy/checkers/misc/const-correctness-pointer-as-pointers.cpp

@@ -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;
+}

clang/lib/Analysis/ExprMutationAnalyzer.cpp

@@ -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 =
@@ -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

clang/unittests/Analysis/ExprMutationAnalyzerTest.cpp

@@ -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) {
@@ -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) {
@@ -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) {