[clang-tools-extra] r327833 - [clang-tidy] New check bugprone-unused-return-value

Alexander Kornienko via cfe-commits cfe-commits at lists.llvm.org
Wed Mar 21 07:47:13 PDT 2018


On Mon, Mar 19, 2018 at 10:43 PM <douglas.yung at sony.com> wrote:

> This should be fixed by r327911.
>

Thanks!


>
>
> Douglas Yung
>
>
>
> *From:* cfe-commits [mailto:cfe-commits-bounces at lists.llvm.org] *On
> Behalf Of *Galina Kistanova via cfe-commits
> *Sent:* Monday, March 19, 2018 13:13
> *To:* Alexander Kornienko
> *Cc:* cfe-commits
> *Subject:* Re: [clang-tools-extra] r327833 - [clang-tidy] New check
> bugprone-unused-return-value
>
>
>
> Hello Alexander,
>
> This commit broke at least two of our builders:
>
>
> http://lab.llvm.org:8011/builders/llvm-clang-lld-x86_64-scei-ps4-ubuntu-fast/builds/26909
>
> http://lab.llvm.org:8011/builders/llvm-clang-lld-x86_64-scei-ps4-windows10pro-fast
>
> . . .
> Failing Tests (1):
>     Clang Tools :: clang-tidy/bugprone-unused-return-value.cpp
>
> Please have a look?
>
> It is not good idea to keep the bot red for too long. This hides new
> problem which later hard to track down.
>
> Thanks
>
> Galina
>
>
>
> On Mon, Mar 19, 2018 at 6:02 AM, Alexander Kornienko via cfe-commits <
> cfe-commits at lists.llvm.org> wrote:
>
> Author: alexfh
> Date: Mon Mar 19 06:02:32 2018
> New Revision: 327833
>
> URL: http://llvm.org/viewvc/llvm-project?rev=327833&view=rev
> Log:
> [clang-tidy] New check bugprone-unused-return-value
>
> Summary:
> Detects function calls where the return value is unused.
>
> Checked functions can be configured.
>
> Reviewers: alexfh, aaron.ballman, ilya-biryukov, hokein
>
> Reviewed By: alexfh, aaron.ballman
>
> Subscribers: hintonda, JonasToth, Eugene.Zelenko, mgorny, xazax.hun,
> cfe-commits
>
> Tags: #clang-tools-extra
>
> Patch by Kalle Huttunen!
>
> Differential Revision: https://reviews.llvm.org/D41655
>
> Added:
>     clang-tools-extra/trunk/clang-tidy/bugprone/UnusedReturnValueCheck.cpp
>     clang-tools-extra/trunk/clang-tidy/bugprone/UnusedReturnValueCheck.h
>
> clang-tools-extra/trunk/docs/clang-tidy/checks/bugprone-unused-return-value.rst
>
> clang-tools-extra/trunk/test/clang-tidy/bugprone-unused-return-value-custom.cpp
>
> clang-tools-extra/trunk/test/clang-tidy/bugprone-unused-return-value.cpp
> Modified:
>     clang-tools-extra/trunk/clang-tidy/bugprone/BugproneTidyModule.cpp
>     clang-tools-extra/trunk/clang-tidy/bugprone/CMakeLists.txt
>     clang-tools-extra/trunk/docs/ReleaseNotes.rst
>     clang-tools-extra/trunk/docs/clang-tidy/checks/list.rst
>
> Modified:
> clang-tools-extra/trunk/clang-tidy/bugprone/BugproneTidyModule.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/clang-tools-extra/trunk/clang-tidy/bugprone/BugproneTidyModule.cpp?rev=327833&r1=327832&r2=327833&view=diff
>
> ==============================================================================
> --- clang-tools-extra/trunk/clang-tidy/bugprone/BugproneTidyModule.cpp
> (original)
> +++ clang-tools-extra/trunk/clang-tidy/bugprone/BugproneTidyModule.cpp Mon
> Mar 19 06:02:32 2018
> @@ -43,6 +43,7 @@
>  #include "UndefinedMemoryManipulationCheck.h"
>  #include "UndelegatedConstructorCheck.h"
>  #include "UnusedRaiiCheck.h"
> +#include "UnusedReturnValueCheck.h"
>  #include "UseAfterMoveCheck.h"
>  #include "VirtualNearMissCheck.h"
>
> @@ -119,6 +120,8 @@ public:
>          "bugprone-undelegated-constructor");
>      CheckFactories.registerCheck<UnusedRaiiCheck>(
>          "bugprone-unused-raii");
> +    CheckFactories.registerCheck<UnusedReturnValueCheck>(
> +        "bugprone-unused-return-value");
>      CheckFactories.registerCheck<UseAfterMoveCheck>(
>          "bugprone-use-after-move");
>      CheckFactories.registerCheck<VirtualNearMissCheck>(
>
> Modified: clang-tools-extra/trunk/clang-tidy/bugprone/CMakeLists.txt
> URL:
> http://llvm.org/viewvc/llvm-project/clang-tools-extra/trunk/clang-tidy/bugprone/CMakeLists.txt?rev=327833&r1=327832&r2=327833&view=diff
>
> ==============================================================================
> --- clang-tools-extra/trunk/clang-tidy/bugprone/CMakeLists.txt (original)
> +++ clang-tools-extra/trunk/clang-tidy/bugprone/CMakeLists.txt Mon Mar 19
> 06:02:32 2018
> @@ -35,6 +35,7 @@ add_clang_library(clangTidyBugproneModul
>    UndefinedMemoryManipulationCheck.cpp
>    UndelegatedConstructorCheck.cpp
>    UnusedRaiiCheck.cpp
> +  UnusedReturnValueCheck.cpp
>    UseAfterMoveCheck.cpp
>    VirtualNearMissCheck.cpp
>
>
> Added:
> clang-tools-extra/trunk/clang-tidy/bugprone/UnusedReturnValueCheck.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/clang-tools-extra/trunk/clang-tidy/bugprone/UnusedReturnValueCheck.cpp?rev=327833&view=auto
>
> ==============================================================================
> --- clang-tools-extra/trunk/clang-tidy/bugprone/UnusedReturnValueCheck.cpp
> (added)
> +++ clang-tools-extra/trunk/clang-tidy/bugprone/UnusedReturnValueCheck.cpp
> Mon Mar 19 06:02:32 2018
> @@ -0,0 +1,82 @@
> +//===--- UnusedReturnValueCheck.cpp -
> clang-tidy---------------------------===//
> +//
> +//                     The LLVM Compiler Infrastructure
> +//
> +// This file is distributed under the University of Illinois Open Source
> +// License. See LICENSE.TXT for details.
> +//
>
> +//===----------------------------------------------------------------------===//
> +
> +#include "UnusedReturnValueCheck.h"
> +#include "../utils/OptionsUtils.h"
> +#include "clang/AST/ASTContext.h"
> +#include "clang/ASTMatchers/ASTMatchFinder.h"
> +
> +using namespace clang::ast_matchers;
> +using namespace clang::ast_matchers::internal;
> +
> +namespace clang {
> +namespace tidy {
> +namespace bugprone {
> +
> +UnusedReturnValueCheck::UnusedReturnValueCheck(llvm::StringRef Name,
> +                                               ClangTidyContext *Context)
> +    : ClangTidyCheck(Name, Context),
> +      CheckedFunctions(Options.get("CheckedFunctions", "::std::async;"
> +                                                       "::std::launder;"
> +                                                       "::std::remove;"
> +                                                       "::std::remove_if;"
> +                                                       "::std::unique"))
> {}
> +
> +void UnusedReturnValueCheck::storeOptions(ClangTidyOptions::OptionMap
> &Opts) {
> +  Options.store(Opts, "CheckedFunctions", CheckedFunctions);
> +}
> +
> +void UnusedReturnValueCheck::registerMatchers(MatchFinder *Finder) {
> +  auto FunVec = utils::options::parseStringList(CheckedFunctions);
> +  auto MatchedCallExpr = expr(ignoringImplicit(ignoringParenImpCasts(
> +      callExpr(
> +          callee(functionDecl(
> +              // Don't match void overloads of checked functions.
> +              unless(returns(voidType())),
> hasAnyName(std::vector<StringRef>(
> +                                               FunVec.begin(),
> FunVec.end())))))
> +          .bind("match"))));
> +
> +  auto UnusedInCompoundStmt =
> +      compoundStmt(forEach(MatchedCallExpr),
> +                   // The checker can't currently differentiate between
> the
> +                   // return statement and other statements inside GNU
> statement
> +                   // expressions, so disable the checker inside them to
> avoid
> +                   // false positives.
> +                   unless(hasParent(stmtExpr())));
> +  auto UnusedInIfStmt =
> +      ifStmt(eachOf(hasThen(MatchedCallExpr), hasElse(MatchedCallExpr)));
> +  auto UnusedInWhileStmt = whileStmt(hasBody(MatchedCallExpr));
> +  auto UnusedInDoStmt = doStmt(hasBody(MatchedCallExpr));
> +  auto UnusedInForStmt =
> +      forStmt(eachOf(hasLoopInit(MatchedCallExpr),
> +                     hasIncrement(MatchedCallExpr),
> hasBody(MatchedCallExpr)));
> +  auto UnusedInRangeForStmt = cxxForRangeStmt(hasBody(MatchedCallExpr));
> +  auto UnusedInCaseStmt = switchCase(forEach(MatchedCallExpr));
> +
> +  Finder->addMatcher(
> +      stmt(anyOf(UnusedInCompoundStmt, UnusedInIfStmt, UnusedInWhileStmt,
> +                 UnusedInDoStmt, UnusedInForStmt, UnusedInRangeForStmt,
> +                 UnusedInCaseStmt)),
> +      this);
> +}
> +
> +void UnusedReturnValueCheck::check(const MatchFinder::MatchResult
> &Result) {
> +  if (const auto *Matched = Result.Nodes.getNodeAs<CallExpr>("match")) {
> +    diag(Matched->getLocStart(),
> +         "the value returned by this function should be used")
> +        << Matched->getSourceRange();
> +    diag(Matched->getLocStart(),
> +         "cast the expression to void to silence this warning",
> +         DiagnosticIDs::Note);
> +  }
> +}
> +
> +} // namespace bugprone
> +} // namespace tidy
> +} // namespace clang
>
> Added: clang-tools-extra/trunk/clang-tidy/bugprone/UnusedReturnValueCheck.h
> URL:
> http://llvm.org/viewvc/llvm-project/clang-tools-extra/trunk/clang-tidy/bugprone/UnusedReturnValueCheck.h?rev=327833&view=auto
>
> ==============================================================================
> --- clang-tools-extra/trunk/clang-tidy/bugprone/UnusedReturnValueCheck.h
> (added)
> +++ clang-tools-extra/trunk/clang-tidy/bugprone/UnusedReturnValueCheck.h
> Mon Mar 19 06:02:32 2018
> @@ -0,0 +1,39 @@
> +//===--- UnusedReturnValueCheck.h - clang-tidy-------------------*- C++
> -*-===//
> +//
> +//                     The LLVM Compiler Infrastructure
> +//
> +// This file is distributed under the University of Illinois Open Source
> +// License. See LICENSE.TXT for details.
> +//
>
> +//===----------------------------------------------------------------------===//
> +
> +#ifndef
> LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_BUGPRONE_UNUSEDRETURNVALUECHECK_H
> +#define
> LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_BUGPRONE_UNUSEDRETURNVALUECHECK_H
> +
> +#include "../ClangTidy.h"
> +#include <string>
> +
> +namespace clang {
> +namespace tidy {
> +namespace bugprone {
> +
> +/// Detects function calls where the return value is unused.
> +///
> +/// For the user-facing documentation see:
> +///
> http://clang.llvm.org/extra/clang-tidy/checks/bugprone-unused-return-value.html
> +class UnusedReturnValueCheck : public ClangTidyCheck {
> +public:
> +  UnusedReturnValueCheck(StringRef Name, ClangTidyContext *Context);
> +  void storeOptions(ClangTidyOptions::OptionMap &Opts) override;
> +  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
> +  void check(const ast_matchers::MatchFinder::MatchResult &Result)
> override;
> +
> +private:
> +  std::string CheckedFunctions;
> +};
> +
> +} // namespace bugprone
> +} // namespace tidy
> +} // namespace clang
> +
> +#endif //
> LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_BUGPRONE_UNUSEDRETURNVALUECHECK_H
>
> Modified: clang-tools-extra/trunk/docs/ReleaseNotes.rst
> URL:
> http://llvm.org/viewvc/llvm-project/clang-tools-extra/trunk/docs/ReleaseNotes.rst?rev=327833&r1=327832&r2=327833&view=diff
>
> ==============================================================================
> --- clang-tools-extra/trunk/docs/ReleaseNotes.rst (original)
> +++ clang-tools-extra/trunk/docs/ReleaseNotes.rst Mon Mar 19 06:02:32 2018
> @@ -67,6 +67,11 @@ Improvements to clang-tidy
>    Diagnoses when a temporary object that appears to be an exception is
>    constructed but not thrown.
>
> +- New `bugprone-unused-return-value
> +  <
> http://clang.llvm.org/extra/clang-tidy/checks/bugprone-unused-return-value.html>`_
> check
> +
> +  Warns on unused function return values.
> +
>  - New `cppcoreguidelines-avoid-goto
>    <
> http://clang.llvm.org/extra/clang-tidy/checks/cppcoreguidelines-avoid-goto.html>`_
> check
>
>
> Added:
> clang-tools-extra/trunk/docs/clang-tidy/checks/bugprone-unused-return-value.rst
> URL:
> http://llvm.org/viewvc/llvm-project/clang-tools-extra/trunk/docs/clang-tidy/checks/bugprone-unused-return-value.rst?rev=327833&view=auto
>
> ==============================================================================
> ---
> clang-tools-extra/trunk/docs/clang-tidy/checks/bugprone-unused-return-value.rst
> (added)
> +++
> clang-tools-extra/trunk/docs/clang-tidy/checks/bugprone-unused-return-value.rst
> Mon Mar 19 06:02:32 2018
> @@ -0,0 +1,24 @@
> +.. title:: clang-tidy - bugprone-unused-return-value
> +
> +bugprone-unused-return-value
> +============================
> +
> +Warns on unused function return values. The checked funtions can be
> configured.
> +
> +Options
> +-------
> +
> +.. option:: CheckedFunctions
> +
> +   Semicolon-separated list of functions to check. Defaults to
> +
>  ``::std::async;::std::launder;::std::remove;::std::remove_if;::std::unique``.
> +   This means that the calls to following functions are checked by
> default:
> +
> +   - ``std::async()``. Not using the return value makes the call
> synchronous.
> +   - ``std::launder()``. Not using the return value usually means that the
> +     function interface was misunderstood by the programmer. Only the
> returned
> +     pointer is "laundered", not the argument.
> +   - ``std::remove()``, ``std::remove_if()`` and ``std::unique()``. The
> returned
> +     iterator indicates the boundary between elements to keep and
> elements to be
> +     removed. Not using the return value means that the information about
> which
> +     elements to remove is lost.
>
> Modified: clang-tools-extra/trunk/docs/clang-tidy/checks/list.rst
> URL:
> http://llvm.org/viewvc/llvm-project/clang-tools-extra/trunk/docs/clang-tidy/checks/list.rst?rev=327833&r1=327832&r2=327833&view=diff
>
> ==============================================================================
> --- clang-tools-extra/trunk/docs/clang-tidy/checks/list.rst (original)
> +++ clang-tools-extra/trunk/docs/clang-tidy/checks/list.rst Mon Mar 19
> 06:02:32 2018
> @@ -51,6 +51,7 @@ Clang-Tidy Checks
>     bugprone-undefined-memory-manipulation
>     bugprone-undelegated-constructor
>     bugprone-unused-raii
> +   bugprone-unused-return-value
>     bugprone-use-after-move
>     bugprone-virtual-near-miss
>     cert-dcl03-c (redirects to misc-static-assert) <cert-dcl03-c>
>
> Added:
> clang-tools-extra/trunk/test/clang-tidy/bugprone-unused-return-value-custom.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/clang-tools-extra/trunk/test/clang-tidy/bugprone-unused-return-value-custom.cpp?rev=327833&view=auto
>
> ==============================================================================
> ---
> clang-tools-extra/trunk/test/clang-tidy/bugprone-unused-return-value-custom.cpp
> (added)
> +++
> clang-tools-extra/trunk/test/clang-tidy/bugprone-unused-return-value-custom.cpp
> Mon Mar 19 06:02:32 2018
> @@ -0,0 +1,82 @@
> +// RUN: %check_clang_tidy %s bugprone-unused-return-value %t \
> +// RUN: -config='{CheckOptions: \
> +// RUN:  [{key: bugprone-unused-return-value.CheckedFunctions, \
> +// RUN:    value:
> "::fun;::ns::Outer::Inner::memFun;::ns::Type::staticFun"}]}' \
> +// RUN: --
> +
> +namespace std {
> +
> +template <typename T>
> +T *launder(T *);
> +
> +} // namespace std
> +
> +namespace ns {
> +
> +struct Outer {
> +  struct Inner {
> +    bool memFun();
> +  };
> +};
> +
> +using AliasName = Outer;
> +
> +struct Derived : public Outer::Inner {};
> +
> +struct Retval {
> +  int *P;
> +  Retval() { P = new int; }
> +  ~Retval() { delete P; }
> +};
> +
> +struct Type {
> +  Retval memFun();
> +  static Retval staticFun();
> +};
> +
> +} // namespace ns
> +
> +int fun();
> +void fun(int);
> +
> +void warning() {
> +  fun();
> +  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +
> +  (fun());
> +  // CHECK-MESSAGES: [[@LINE-1]]:4: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +
> +  ns::Outer::Inner ObjA1;
> +  ObjA1.memFun();
> +  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +
> +  ns::AliasName::Inner ObjA2;
> +  ObjA2.memFun();
> +  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +
> +  ns::Derived ObjA3;
> +  ObjA3.memFun();
> +  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +
> +  ns::Type::staticFun();
> +  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +}
> +
> +void noWarning() {
> +  auto R1 = fun();
> +
> +  ns::Outer::Inner ObjB1;
> +  auto R2 = ObjB1.memFun();
> +
> +  auto R3 = ns::Type::staticFun();
> +
> +  // test calling a void overload of a checked function
> +  fun(5);
> +
> +  // test discarding return value of functions that are not configured to
> be checked
> +  int I = 1;
> +  std::launder(&I);
> +
> +  ns::Type ObjB2;
> +  ObjB2.memFun();
> +}
>
> Added:
> clang-tools-extra/trunk/test/clang-tidy/bugprone-unused-return-value.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/clang-tools-extra/trunk/test/clang-tidy/bugprone-unused-return-value.cpp?rev=327833&view=auto
>
> ==============================================================================
> ---
> clang-tools-extra/trunk/test/clang-tidy/bugprone-unused-return-value.cpp
> (added)
> +++
> clang-tools-extra/trunk/test/clang-tidy/bugprone-unused-return-value.cpp
> Mon Mar 19 06:02:32 2018
> @@ -0,0 +1,166 @@
> +// RUN: %check_clang_tidy %s bugprone-unused-return-value %t
> +
> +namespace std {
> +
> +struct future {};
> +
> +enum class launch {
> +  async,
> +  deferred
> +};
> +
> +template <typename Function, typename... Args>
> +future async(Function &&, Args &&...);
> +
> +template <typename Function, typename... Args>
> +future async(launch, Function &&, Args &&...);
> +
> +template <typename ForwardIt, typename T>
> +ForwardIt remove(ForwardIt, ForwardIt, const T &);
> +
> +template <typename ForwardIt, typename UnaryPredicate>
> +ForwardIt remove_if(ForwardIt, ForwardIt, UnaryPredicate);
> +
> +template <typename ForwardIt>
> +ForwardIt unique(ForwardIt, ForwardIt);
> +
> +// the check should be able to match std lib calls even if the functions
> are
> +// declared inside inline namespaces
> +inline namespace v1 {
> +
> +template <typename T>
> +T *launder(T *);
> +
> +} // namespace v1
> +} // namespace std
> +
> +struct Foo {
> +  void f();
> +};
> +
> +int increment(int i) {
> +  return i + 1;
> +}
> +
> +void useFuture(const std::future &fut);
> +
> +void warning() {
> +  std::async(increment, 42);
> +  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +
> +  std::async(std::launch::async, increment, 42);
> +  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +
> +  Foo F;
> +  std::launder(&F);
> +  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +
> +  std::remove(nullptr, nullptr, 1);
> +  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +
> +  std::remove_if(nullptr, nullptr, nullptr);
> +  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +
> +  std::unique(nullptr, nullptr);
> +  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +
> +  // test discarding return values inside different kinds of statements
> +
> +  auto Lambda = [] { std::remove(nullptr, nullptr, 1); };
> +  // CHECK-MESSAGES: [[@LINE-1]]:22: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +
> +  if (true)
> +    std::remove(nullptr, nullptr, 1);
> +  // CHECK-MESSAGES: [[@LINE-1]]:5: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +  else if (true)
> +    std::remove(nullptr, nullptr, 1);
> +  // CHECK-MESSAGES: [[@LINE-1]]:5: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +  else
> +    std::remove(nullptr, nullptr, 1);
> +  // CHECK-MESSAGES: [[@LINE-1]]:5: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +
> +  while (true)
> +    std::remove(nullptr, nullptr, 1);
> +  // CHECK-MESSAGES: [[@LINE-1]]:5: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +
> +  do
> +    std::remove(nullptr, nullptr, 1);
> +  // CHECK-MESSAGES: [[@LINE-1]]:5: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +  while (true);
> +
> +  for (;;)
> +    std::remove(nullptr, nullptr, 1);
> +  // CHECK-MESSAGES: [[@LINE-1]]:5: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +
> +  for (std::remove(nullptr, nullptr, 1);;)
> +    // CHECK-MESSAGES: [[@LINE-1]]:8: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +    ;
> +
> +  for (;; std::remove(nullptr, nullptr, 1))
> +    // CHECK-MESSAGES: [[@LINE-1]]:11: warning: the value returned by
> this function should be used [bugprone-unused-return-value]
> +    ;
> +
> +  for (auto C : "foo")
> +    std::remove(nullptr, nullptr, 1);
> +  // CHECK-MESSAGES: [[@LINE-1]]:5: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +
> +  switch (1) {
> +  case 1:
> +    std::remove(nullptr, nullptr, 1);
> +    // CHECK-MESSAGES: [[@LINE-1]]:5: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +    break;
> +  default:
> +    std::remove(nullptr, nullptr, 1);
> +    // CHECK-MESSAGES: [[@LINE-1]]:5: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +    break;
> +  }
> +
> +  try {
> +    std::remove(nullptr, nullptr, 1);
> +    // CHECK-MESSAGES: [[@LINE-1]]:5: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +  } catch (...) {
> +    std::remove(nullptr, nullptr, 1);
> +    // CHECK-MESSAGES: [[@LINE-1]]:5: warning: the value returned by this
> function should be used [bugprone-unused-return-value]
> +  }
> +}
> +
> +void noWarning() {
> +  auto AsyncRetval1 = std::async(increment, 42);
> +  auto AsyncRetval2 = std::async(std::launch::async, increment, 42);
> +
> +  Foo FNoWarning;
> +  auto LaunderRetval = std::launder(&FNoWarning);
> +
> +  auto RemoveRetval = std::remove(nullptr, nullptr, 1);
> +
> +  auto RemoveIfRetval = std::remove_if(nullptr, nullptr, nullptr);
> +
> +  auto UniqueRetval = std::unique(nullptr, nullptr);
> +
> +  // test using the return value in different kinds of expressions
> +  useFuture(std::async(increment, 42));
> +  std::launder(&FNoWarning)->f();
> +  delete std::launder(&FNoWarning);
> +
> +  if (std::launder(&FNoWarning))
> +    ;
> +  for (; std::launder(&FNoWarning);)
> +    ;
> +  while (std::launder(&FNoWarning))
> +    ;
> +  do
> +    ;
> +  while (std::launder(&FNoWarning));
> +  switch (std::unique(1, 1))
> +    ;
> +
> +  // cast to void should allow ignoring the return value
> +  (void)std::async(increment, 42);
> +
> +  // test discarding return value of functions that are not configured to
> be checked
> +  increment(1);
> +
> +  // test that the check is disabled inside GNU statement expressions
> +  ({ std::async(increment, 42); });
> +  auto StmtExprRetval = ({ std::async(increment, 42); });
> +}
>
>
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