malcolm.parsons created this revision.
malcolm.parsons added reviewers: aaron.ballman, rsmith.
malcolm.parsons added a subscriber: cfe-commits.
Warn when a lambda explicitly captures something that is not used in its body.
The warning is part of -Wunused and can be enabled with -Wunused-lambda-capture.
https://reviews.llvm.org/D28467
Files:
include/clang/Basic/DiagnosticGroups.td
include/clang/Basic/DiagnosticSemaKinds.td
include/clang/Sema/ScopeInfo.h
lib/Parse/ParseExprCXX.cpp
lib/Sema/SemaExpr.cpp
lib/Sema/SemaExprCXX.cpp
lib/Sema/SemaLambda.cpp
test/CXX/expr/expr.prim/expr.prim.lambda/p12.cpp
test/CXX/expr/expr.prim/expr.prim.lambda/p13.cpp
test/CXX/expr/expr.prim/expr.prim.lambda/p16.cpp
test/CXX/expr/expr.prim/expr.prim.lambda/p18.cpp
test/CXX/expr/expr.prim/expr.prim.lambda/p19.cpp
test/SemaCXX/uninitialized.cpp
test/SemaCXX/warn-unused-lambda-capture.cpp
Index: test/SemaCXX/warn-unused-lambda-capture.cpp
===================================================================
--- /dev/null
+++ test/SemaCXX/warn-unused-lambda-capture.cpp
@@ -0,0 +1,42 @@
+// RUN: %clang_cc1 -fsyntax-only -Wunused-lambda-capture -Wused-but-marked-unused -Wno-uninitialized -verify -std=c++14 %s
+
+void test() {
+ int i = 0;
+
+ auto captures_nothing = [] {};
+
+ auto captures_nothing_by_value = [=] {};
+ auto captures_nothing_by_reference = [&] {};
+
+ auto implicit_by_value = [=]() mutable { i++; };
+ auto implicit_by_reference = [&] { i++; };
+
+ auto explicit_by_value_used = [i] { return i + 1; };
+ auto explicit_by_value_used_void = [i] { (void)i; };
+ auto explicit_by_value_unused = [i] {}; // expected-warning{{lambda capture 'i' is not used}}
+ auto explicit_by_value_unused_sizeof = [i] { return sizeof(i); }; // expected-warning{{lambda capture 'i' is not used}}
+
+ auto explicit_by_reference_used = [&i] { i++; };
+ auto explicit_by_reference_unused = [&i] {}; // expected-warning{{lambda capture 'i' is not used}}
+
+ auto explicit_initialized_reference_used = [&j = i] { return j + 1; };
+ auto explicit_initialized_reference_unused = [&j = i]{}; // expected-warning{{lambda capture 'j' is not used}}
+
+ auto explicit_initialized_value_used = [j = 1] { return j + 1; };
+ auto explicit_initialized_value_unused = [j = 1] {}; // expected-warning{{lambda capture 'j' is not used}}
+
+ auto nested = [&i] {
+ auto explicit_by_value_used = [i] { return i + 1; };
+ auto explicit_by_value_unused = [i] {}; // expected-warning{{lambda capture 'i' is not used}}
+ };
+}
+
+class Foo
+{
+ void test() {
+ auto explicit_this_used = [this] { return i; };
+ auto explicit_this_used_void = [this] { (void)this; };
+ auto explicit_this_unused = [this] {}; // expected-warning{{lambda capture 'this' is not used}}
+ }
+ int i;
+};
Index: test/SemaCXX/uninitialized.cpp
===================================================================
--- test/SemaCXX/uninitialized.cpp
+++ test/SemaCXX/uninitialized.cpp
@@ -1434,6 +1434,6 @@
if (b) {
int unused; // expected-warning {{unused variable}}
} else {
- [fname]{};
+ [fname] { (void)fname; }; // expected-warning {{lambda capture 'fname' is not used}}
}
}
Index: test/CXX/expr/expr.prim/expr.prim.lambda/p19.cpp
===================================================================
--- test/CXX/expr/expr.prim/expr.prim.lambda/p19.cpp
+++ test/CXX/expr/expr.prim/expr.prim.lambda/p19.cpp
@@ -7,7 +7,7 @@
template<typename T> T &&move(T&);
void test_special_member_functions(MoveOnly mo, int i) {
- auto lambda1 = [i]() { }; // expected-note 2{{lambda expression begins here}} expected-note 2{{candidate}}
+ auto lambda1 = [i]() { (void)i; }; // expected-note 2{{lambda expression begins here}} expected-note 2{{candidate}}
// Default constructor
decltype(lambda1) lambda2; // expected-error{{no matching constructor}}
Index: test/CXX/expr/expr.prim/expr.prim.lambda/p18.cpp
===================================================================
--- test/CXX/expr/expr.prim/expr.prim.lambda/p18.cpp
+++ test/CXX/expr/expr.prim/expr.prim.lambda/p18.cpp
@@ -30,6 +30,8 @@
"should be const int&");
static_assert(is_same<decltype((irc)), const int&>::value,
"should be const int&");
+ (void)irc;
+ (void)ir;
}();
[=] {
@@ -42,5 +44,6 @@
[&i] {
static_assert(is_same<decltype((i)), int&>::value, "should be int&");
+ (void)i;
}();
}
Index: test/CXX/expr/expr.prim/expr.prim.lambda/p16.cpp
===================================================================
--- test/CXX/expr/expr.prim/expr.prim.lambda/p16.cpp
+++ test/CXX/expr/expr.prim/expr.prim.lambda/p16.cpp
@@ -7,16 +7,18 @@
};
void test_capture(X x) {
- [x] { }(); // okay: non-const copy ctor
+ [x] { (void)x; }(); // okay: non-const copy ctor
[x] {
[x] { // expected-error{{call to deleted constructor of 'X'}}
+ (void)x;
}();
}();
[x] {
[&x] {
[x] { // expected-error{{call to deleted constructor of 'const X'}}
+ (void)x;
}();
}();
}();
Index: test/CXX/expr/expr.prim/expr.prim.lambda/p13.cpp
===================================================================
--- test/CXX/expr/expr.prim/expr.prim.lambda/p13.cpp
+++ test/CXX/expr/expr.prim/expr.prim.lambda/p13.cpp
@@ -3,7 +3,7 @@
void f2() {
int i = 1;
void g1(int = ([i]{ return i; })()); // expected-error{{lambda expression in default argument cannot capture any entity}}
- void g2(int = ([i]{ return 0; })()); // expected-error{{lambda expression in default argument cannot capture any entity}}
+ void g2(int = ([i]{ (void)i; return 0; })()); // expected-error{{lambda expression in default argument cannot capture any entity}}
void g3(int = ([=]{ return i; })()); // expected-error{{lambda expression in default argument cannot capture any entity}}
void g4(int = ([=]{ return 0; })());
void g5(int = ([]{ return sizeof i; })());
Index: test/CXX/expr/expr.prim/expr.prim.lambda/p12.cpp
===================================================================
--- test/CXX/expr/expr.prim/expr.prim.lambda/p12.cpp
+++ test/CXX/expr/expr.prim/expr.prim.lambda/p12.cpp
@@ -2,7 +2,7 @@
void odr_used() {
int i = 17;
- [i]{}();
+ [i]{}(); // expected-warning{{lambda capture 'i' is not used}}
}
struct ReachingThis {
@@ -13,14 +13,14 @@
int i;
void bar() {
- (void)[this](){};
+ (void)[this](){}; // expected-warning{{lambda capture 'this' is not used}}
(void)[&](){i = 7; };
}
};
}
void foo() {
- (void)[this](){};
+ (void)[this](){}; // expected-warning{{lambda capture 'this' is not used}}
struct Local {
int i;
@@ -35,11 +35,11 @@
void immediately_enclosing(int i) { // expected-note{{'i' declared here}}
[i]() {
- [i] {}();
+ [i] {}(); // expected-warning{{lambda capture 'i' is not used}}
}();
[=]() {
- [i] {}();
+ [i] {}(); // expected-warning{{lambda capture 'i' is not used}}
}();
[]() { // expected-note{{lambda expression begins here}}
@@ -71,6 +71,7 @@
x += i; // expected-error{{variable 'i' cannot be implicitly captured in a lambda with no capture-default specified}}
x += f;
};
+ (void)this;
};
}
};
Index: lib/Sema/SemaLambda.cpp
===================================================================
--- lib/Sema/SemaLambda.cpp
+++ lib/Sema/SemaLambda.cpp
@@ -1476,10 +1476,19 @@
// Translate captures.
auto CurField = Class->field_begin();
for (unsigned I = 0, N = LSI->Captures.size(); I != N; ++I, ++CurField) {
- LambdaScopeInfo::Capture From = LSI->Captures[I];
+ LambdaScopeInfo::Capture &From = LSI->Captures[I];
assert(!From.isBlockCapture() && "Cannot capture __block variables");
bool IsImplicit = I >= LSI->NumExplicitCaptures;
+ // Warn about unused explicit captures
+ if (!IsImplicit && !From.isUsed()) {
+ auto diag = Diag(From.getLocation(), diag::warn_unused_lambda_capture);
+ if (From.isThisCapture())
+ diag << "'this'";
+ else
+ diag << From.getVariable();
+ }
+
// Handle 'this' capture.
if (From.isThisCapture()) {
Captures.push_back(
Index: lib/Sema/SemaExprCXX.cpp
===================================================================
--- lib/Sema/SemaExprCXX.cpp
+++ lib/Sema/SemaExprCXX.cpp
@@ -1106,6 +1106,8 @@
dyn_cast<CapturingScopeInfo>(FunctionScopes[idx])) {
if (CSI->CXXThisCaptureIndex != 0) {
// 'this' is already being captured; there isn't anything more to do.
+ if (BuildAndDiagnose)
+ CSI->Captures[CSI->CXXThisCaptureIndex - 1].markUsed();
break;
}
LambdaScopeInfo *LSI = dyn_cast<LambdaScopeInfo>(CSI);
Index: lib/Sema/SemaExpr.cpp
===================================================================
--- lib/Sema/SemaExpr.cpp
+++ lib/Sema/SemaExpr.cpp
@@ -13881,8 +13881,11 @@
// Check whether we've already captured it.
if (isVariableAlreadyCapturedInScopeInfo(CSI, Var, Nested, CaptureType,
- DeclRefType))
+ DeclRefType)) {
+ if (BuildAndDiagnose)
+ CSI->getCapture(Var).markUsed();
break;
+ }
// If we are instantiating a generic lambda call operator body,
// we do not want to capture new variables. What was captured
// during either a lambdas transformation or initial parsing
Index: lib/Parse/ParseExprCXX.cpp
===================================================================
--- lib/Parse/ParseExprCXX.cpp
+++ lib/Parse/ParseExprCXX.cpp
@@ -735,7 +735,7 @@
/// sometimes skip the initializers for init-captures and not fully
/// populate \p Intro. This flag will be set to \c true if we do so.
/// \return A DiagnosticID if it hit something unexpected. The location for
-/// for the diagnostic is that of the current token.
+/// the diagnostic is that of the current token.
Optional<unsigned> Parser::ParseLambdaIntroducer(LambdaIntroducer &Intro,
bool *SkippedInits) {
typedef Optional<unsigned> DiagResult;
Index: include/clang/Sema/ScopeInfo.h
===================================================================
--- include/clang/Sema/ScopeInfo.h
+++ include/clang/Sema/ScopeInfo.h
@@ -452,6 +452,10 @@
/// non-static data member that would hold the capture.
QualType CaptureType;
+ /// \brief Whether an explicit capture has been used in the body of the
+ /// lambda.
+ bool Used = false;
+
public:
Capture(VarDecl *Var, bool Block, bool ByRef, bool IsNested,
SourceLocation Loc, SourceLocation EllipsisLoc,
@@ -491,6 +495,8 @@
bool isNested() const {
return VarAndNestedAndThis.getInt() & IsNestedCapture;
}
+ bool isUsed() const { return Used; }
+ void markUsed() { Used = true; }
VarDecl *getVariable() const {
return VarAndNestedAndThis.getPointer();
Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -316,6 +316,8 @@
InGroup<UnneededMemberFunction>, DefaultIgnore;
def warn_unused_private_field: Warning<"private field %0 is not used">,
InGroup<UnusedPrivateField>, DefaultIgnore;
+def warn_unused_lambda_capture: Warning<"lambda capture %0 is not used">,
+ InGroup<UnusedLambdaCapture>, DefaultIgnore;
def warn_parameter_size: Warning<
"%0 is a large (%1 bytes) pass-by-value argument; "
Index: include/clang/Basic/DiagnosticGroups.td
===================================================================
--- include/clang/Basic/DiagnosticGroups.td
+++ include/clang/Basic/DiagnosticGroups.td
@@ -480,6 +480,7 @@
def UnusedMemberFunction : DiagGroup<"unused-member-function",
[UnneededMemberFunction]>;
def UnusedLabel : DiagGroup<"unused-label">;
+def UnusedLambdaCapture : DiagGroup<"unused-lambda-capture">;
def UnusedParameter : DiagGroup<"unused-parameter">;
def UnusedResult : DiagGroup<"unused-result">;
def PotentiallyEvaluatedExpression : DiagGroup<"potentially-evaluated-expression">;
@@ -616,8 +617,9 @@
[UnusedArgument, UnusedFunction, UnusedLabel,
// UnusedParameter, (matches GCC's behavior)
// UnusedMemberFunction, (clean-up llvm before enabling)
- UnusedPrivateField, UnusedLocalTypedef,
- UnusedValue, UnusedVariable, UnusedPropertyIvar]>,
+ UnusedPrivateField, UnusedLambdaCapture,
+ UnusedLocalTypedef, UnusedValue, UnusedVariable,
+ UnusedPropertyIvar]>,
DiagCategory<"Unused Entity Issue">;
// Format settings.
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