[ExprMutation] handle return non-const type (llvm#161396)

Co-authored-by: Baranov Victor <[email protected]>

Author: 2 people

clang-tools-extra/docs/ReleaseNotes.rst

@@ -342,7 +342,8 @@ Changes in existing checks
 - Improved :doc:`misc-const-correctness
   <clang-tidy/checks/misc/const-correctness>` check to avoid false
   positives when pointers is tranferred to non-const references 
-  and avoid false positives of function pointer.
+  and avoid false positives of function pointer and fix false
+  positives on return of non-const pointer.
 
 - 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

@@ -48,6 +48,11 @@ void ignore_const_alias() {
   p_local0 = &a[1];
 }
 
+void *return_non_const() {
+  void *const a = nullptr;
+  return a;
+}
+
 void function_pointer_basic() {
   void (*const fp)() = nullptr;
   fp();

clang/lib/Analysis/ExprMutationAnalyzer.cpp

@@ -140,7 +140,8 @@ class ExprPointeeResolve {
       // explicit cast will be checked in `findPointeeToNonConst`
       const CastKind kind = ICE->getCastKind();
       if (kind == CK_LValueToRValue || kind == CK_DerivedToBase ||
-          kind == CK_UncheckedDerivedToBase)
+          kind == CK_UncheckedDerivedToBase ||
+          (kind == CK_NoOp && (ICE->getType() == ICE->getSubExpr()->getType())))
         return resolveExpr(ICE->getSubExpr());
       return false;
     }
@@ -788,13 +789,16 @@ ExprMutationAnalyzer::Analyzer::findPointeeToNonConst(const Expr *Exp) {
   // FIXME: false positive if the pointee does not change in lambda
   const auto CaptureNoConst = lambdaExpr(hasCaptureInit(Exp));
 
-  const auto Matches =
-      match(stmt(anyOf(forEachDescendant(
-                           stmt(anyOf(AssignToNonConst, PassAsNonConstArg,
-                                      CastToNonConst, CaptureNoConst))
-                               .bind("stmt")),
-                       forEachDescendant(InitToNonConst))),
-            Stm, Context);
+  const auto ReturnNoConst =
+      returnStmt(hasReturnValue(canResolveToExprPointee(Exp)));
+
+  const auto Matches = match(
+      stmt(anyOf(forEachDescendant(
+                     stmt(anyOf(AssignToNonConst, PassAsNonConstArg,
+                                CastToNonConst, CaptureNoConst, ReturnNoConst))
+                         .bind("stmt")),
+                 forEachDescendant(InitToNonConst))),
+      Stm, Context);
   return selectFirst<Stmt>("stmt", Matches);
 }
 

clang/unittests/Analysis/ExprMutationAnalyzerTest.cpp

@@ -2038,4 +2038,42 @@ TEST(ExprMutationAnalyzerTest, PointeeMutatedByConditionOperator) {
   EXPECT_TRUE(isPointeeMutated(Results, AST.get()));
 }
 
+TEST(ExprMutationAnalyzerTest, PointeeMutatedByReturn) {
+  {
+    const std::string Code = R"(
+    int * f() {
+      int *const x = nullptr;
+      return x;
+    })";
+    auto AST = buildASTFromCodeWithArgs(Code, {"-Wno-everything"});
+    auto Results =
+        match(withEnclosingCompound(declRefTo("x")), AST->getASTContext());
+    EXPECT_TRUE(isPointeeMutated(Results, AST.get()));
+  }
+  {
+    const std::string Code = R"(
+    int * f() {
+      int *const x = nullptr;
+      return x;
+    })";
+    // in C++23, AST will have NoOp cast.
+    auto AST =
+        buildASTFromCodeWithArgs(Code, {"-Wno-everything", "-std=c++23"});
+    auto Results =
+        match(withEnclosingCompound(declRefTo("x")), AST->getASTContext());
+    EXPECT_TRUE(isPointeeMutated(Results, AST.get()));
+  }
+  {
+    const std::string Code = R"(
+    int const* f() {
+      int *const x = nullptr;
+      return x;
+    })";
+    auto AST = buildASTFromCodeWithArgs(Code, {"-Wno-everything"});
+    auto Results =
+        match(withEnclosingCompound(declRefTo("x")), AST->getASTContext());
+    EXPECT_FALSE(isPointeeMutated(Results, AST.get()));
+  }
+}
+
 } // namespace clang