[clang-tidy]avoid bugprone-unused-return-value false positive for assignment operator overloading

[HerrCai0907]

Fixes: #84480
We assuem assignemnt at most of time, operator overloading means the value is assigned to the other variable, then clang-tidy should suppress warning even if this operator overloading match the regex.

[llvmbot]

@llvm/pr-subscribers-clang-tools-extra

@llvm/pr-subscribers-clang-tidy

Author: Congcong Cai (HerrCai0907)

Changes

Fixes: #84480
We assuem assignemnt at most of time, operator overloading means the value is assigned to the other variable, then clang-tidy should suppress warning even if this operator overloading match the regex.

---

Full diff: https://github.com/llvm/llvm-project/pull/84489.diff

3 Files Affected:

• (modified) clang-tools-extra/clang-tidy/bugprone/UnusedReturnValueCheck.cpp (+14-10)
• (modified) clang-tools-extra/docs/ReleaseNotes.rst (+2-2)
• (added) clang-tools-extra/test/clang-tidy/checkers/bugprone/unused-return-value-avoid-assignment.cpp (+31)

diff --git a/clang-tools-extra/clang-tidy/bugprone/UnusedReturnValueCheck.cpp b/clang-tools-extra/clang-tidy/bugprone/UnusedReturnValueCheck.cpp
index 1252b2f23805a1..2167d381c42b03 100644
--- a/clang-tools-extra/clang-tidy/bugprone/UnusedReturnValueCheck.cpp
+++ b/clang-tools-extra/clang-tidy/bugprone/UnusedReturnValueCheck.cpp
@@ -11,6 +11,7 @@
 #include "../utils/OptionsUtils.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
 
 using namespace clang::ast_matchers;
 using namespace clang::ast_matchers::internal;
@@ -157,16 +158,19 @@ void UnusedReturnValueCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
 }
 
 void UnusedReturnValueCheck::registerMatchers(MatchFinder *Finder) {
-  auto MatchedDirectCallExpr =
-      expr(callExpr(callee(functionDecl(
-                        // Don't match void overloads of checked functions.
-                        unless(returns(voidType())),
-                        anyOf(isInstantiatedFrom(matchers::matchesAnyListedName(
-                                  CheckedFunctions)),
-                              returns(hasCanonicalType(hasDeclaration(
-                                  namedDecl(matchers::matchesAnyListedName(
-                                      CheckedReturnTypes)))))))))
-               .bind("match"));
+  auto MatchedDirectCallExpr = expr(
+      callExpr(callee(functionDecl(
+                   // Don't match void overloads of checked functions.
+                   unless(returns(voidType())),
+                   // Don't match copy or move assignment operator.
+                   unless(cxxMethodDecl(anyOf(isCopyAssignmentOperator(),
+                                              isMoveAssignmentOperator()))),
+                   anyOf(isInstantiatedFrom(
+                             matchers::matchesAnyListedName(CheckedFunctions)),
+                         returns(hasCanonicalType(hasDeclaration(
+                             namedDecl(matchers::matchesAnyListedName(
+                                 CheckedReturnTypes)))))))))
+          .bind("match"));
 
   auto CheckCastToVoid =
       AllowCastToVoid ? castExpr(unless(hasCastKind(CK_ToVoid))) : castExpr();
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index b5f025ce467a15..c7121fe07e0ad3 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -152,9 +152,9 @@ Changes in existing checks
 
 - Improved :doc:`bugprone-unused-return-value
   <clang-tidy/checks/bugprone/unused-return-value>` check by updating the
-  parameter `CheckedFunctions` to support regexp and avoiding false postive for
+  parameter `CheckedFunctions` to support regexp, avoiding false positive for
   function with the same prefix as the default argument, e.g. ``std::unique_ptr``
-  and ``std::unique``.
+  and ``std::unique``, avoiding false positive for assignment operator overloading.
 
 - Improved :doc:`bugprone-use-after-move
   <clang-tidy/checks/bugprone/use-after-move>` check to also handle
diff --git a/clang-tools-extra/test/clang-tidy/checkers/bugprone/unused-return-value-avoid-assignment.cpp b/clang-tools-extra/test/clang-tidy/checkers/bugprone/unused-return-value-avoid-assignment.cpp
new file mode 100644
index 00000000000000..8bd3c30e71b51a
--- /dev/null
+++ b/clang-tools-extra/test/clang-tidy/checkers/bugprone/unused-return-value-avoid-assignment.cpp
@@ -0,0 +1,31 @@
+// RUN: %check_clang_tidy %s bugprone-unused-return-value %t \
+// RUN: -config='{CheckOptions: \
+// RUN:  {bugprone-unused-return-value.CheckedFunctions: "::*"}}' \
+// RUN: --
+
+struct S {
+  S(){};
+  S(S const &);
+  S(S &&);
+  S &operator=(S const &);
+  S &operator=(S &&);
+};
+
+S returnValue();
+S const &returnRef();
+
+void bar() {
+  returnValue();
+  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: the value returned by this function should not be disregarded; neglecting it may lead to errors
+
+  S a{};
+  a = returnValue();
+  // CHECK-NOT: [[@LINE-1]]:3: warning
+  a.operator=(returnValue());
+  // CHECK-NOT: [[@LINE-1]]:3: warning
+
+  a = returnRef();
+  // CHECK-NOT: [[@LINE-1]]:3: warning
+  a.operator=(returnRef());
+  // CHECK-NOT: [[@LINE-1]]:3: warning
+}

[firewave]

Maybe add += to the tests as well? I have also seen it reported with that.

[5chmidti]

*(Approval after fixes)