[clang-tools-extra] r327833 - [clang-tidy] New check bugprone-unused-return-value
Galina Kistanova via cfe-commits
cfe-commits at lists.llvm.org
Mon Mar 19 13:12:58 PDT 2018
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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