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[clang] Accept lambdas in C++03 as an extensions (llvm#73376)
Implements https://discourse.llvm.org/t/rfc-allow-c-11-lambdas-in-c-03-as-an-extension/75262
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‎clang/docs/LanguageExtensions.rst

Lines changed: 39 additions & 34 deletions
Original file line numberDiff line numberDiff line change
@@ -1459,40 +1459,45 @@ More information could be found `here <https://clang.llvm.org/docs/Modules.html>
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Language Extensions Back-ported to Previous Standards
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=====================================================
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====================================== ================================ ============= =============
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Feature Feature Test Macro Introduced In Backported To
1464-
====================================== ================================ ============= =============
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variadic templates __cpp_variadic_templates C++11 C++03
1466-
Alias templates __cpp_alias_templates C++11 C++03
1467-
Non-static data member initializers __cpp_nsdmi C++11 C++03
1468-
Range-based ``for`` loop __cpp_range_based_for C++11 C++03
1469-
RValue references __cpp_rvalue_references C++11 C++03
1470-
Attributes __cpp_attributes C++11 C++03
1471-
variable templates __cpp_variable_templates C++14 C++03
1472-
Binary literals __cpp_binary_literals C++14 C++03
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Relaxed constexpr __cpp_constexpr C++14 C++11
1474-
``if constexpr`` __cpp_if_constexpr C++17 C++11
1475-
fold expressions __cpp_fold_expressions C++17 C++03
1476-
Lambda capture of \*this by value __cpp_capture_star_this C++17 C++11
1477-
Attributes on enums __cpp_enumerator_attributes C++17 C++03
1478-
Guaranteed copy elision __cpp_guaranteed_copy_elision C++17 C++03
1479-
Hexadecimal floating literals __cpp_hex_float C++17 C++03
1480-
``inline`` variables __cpp_inline_variables C++17 C++03
1481-
Attributes on namespaces __cpp_namespace_attributes C++17 C++11
1482-
Structured bindings __cpp_structured_bindings C++17 C++03
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template template arguments __cpp_template_template_args C++17 C++03
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``static operator[]`` __cpp_multidimensional_subscript C++20 C++03
1485-
Designated initializers __cpp_designated_initializers C++20 C++03
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Conditional ``explicit`` __cpp_conditional_explicit C++20 C++03
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``using enum`` __cpp_using_enum C++20 C++03
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``if consteval`` __cpp_if_consteval C++23 C++20
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``static operator()`` __cpp_static_call_operator C++23 C++03
1490-
Attributes on Lambda-Expressions C++23 C++11
1491-
-------------------------------------- -------------------------------- ------------- -------------
1492-
Designated initializers (N494) C99 C89
1493-
Array & element qualification (N2607) C23 C89
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Attributes (N2335) C23 C89
1495-
====================================== ================================ ============= =============
1462+
============================================ ================================ ============= =============
1463+
Feature Feature Test Macro Introduced In Backported To
1464+
============================================ ================================ ============= =============
1465+
variadic templates __cpp_variadic_templates C++11 C++03
1466+
Alias templates __cpp_alias_templates C++11 C++03
1467+
Non-static data member initializers __cpp_nsdmi C++11 C++03
1468+
Range-based ``for`` loop __cpp_range_based_for C++11 C++03
1469+
RValue references __cpp_rvalue_references C++11 C++03
1470+
Attributes __cpp_attributes C++11 C++03
1471+
Lambdas __cpp_lambdas C++11 C++03
1472+
Generalized lambda captures __cpp_init_captures C++14 C++03
1473+
Generic lambda expressions __cpp_generic_lambdas C++14 C++03
1474+
variable templates __cpp_variable_templates C++14 C++03
1475+
Binary literals __cpp_binary_literals C++14 C++03
1476+
Relaxed constexpr __cpp_constexpr C++14 C++11
1477+
Pack expansion in generalized lambda-capture __cpp_init_captures C++17 C++03
1478+
``if constexpr`` __cpp_if_constexpr C++17 C++11
1479+
fold expressions __cpp_fold_expressions C++17 C++03
1480+
Lambda capture of \*this by value __cpp_capture_star_this C++17 C++03
1481+
Attributes on enums __cpp_enumerator_attributes C++17 C++03
1482+
Guaranteed copy elision __cpp_guaranteed_copy_elision C++17 C++03
1483+
Hexadecimal floating literals __cpp_hex_float C++17 C++03
1484+
``inline`` variables __cpp_inline_variables C++17 C++03
1485+
Attributes on namespaces __cpp_namespace_attributes C++17 C++11
1486+
Structured bindings __cpp_structured_bindings C++17 C++03
1487+
template template arguments __cpp_template_template_args C++17 C++03
1488+
Familiar template syntax for generic lambdas __cpp_generic_lambdas C++20 C++03
1489+
``static operator[]`` __cpp_multidimensional_subscript C++20 C++03
1490+
Designated initializers __cpp_designated_initializers C++20 C++03
1491+
Conditional ``explicit`` __cpp_conditional_explicit C++20 C++03
1492+
``using enum`` __cpp_using_enum C++20 C++03
1493+
``if consteval`` __cpp_if_consteval C++23 C++20
1494+
``static operator()`` __cpp_static_call_operator C++23 C++03
1495+
Attributes on Lambda-Expressions C++23 C++11
1496+
-------------------------------------------- -------------------------------- ------------- -------------
1497+
Designated initializers (N494) C99 C89
1498+
Array & element qualification (N2607) C23 C89
1499+
Attributes (N2335) C23 C89
1500+
============================================ ================================ ============= =============
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14971502
Type Trait Primitives
14981503
=====================

‎clang/docs/ReleaseNotes.rst

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@@ -180,6 +180,8 @@ Non-comprehensive list of changes in this release
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the previous builtins, this new builtin is constexpr and may be used in
181181
constant expressions.
182182

183+
- Lambda expressions are now accepted in C++03 mode as an extension.
184+
183185
New Compiler Flags
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------------------
185187

‎clang/include/clang/Basic/DiagnosticParseKinds.td

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Original file line numberDiff line numberDiff line change
@@ -1029,6 +1029,7 @@ def err_expected_lambda_body : Error<"expected body of lambda expression">;
10291029
def warn_cxx98_compat_lambda : Warning<
10301030
"lambda expressions are incompatible with C++98">,
10311031
InGroup<CXX98Compat>, DefaultIgnore;
1032+
def ext_lambda : ExtWarn<"lambdas are a C++11 extension">, InGroup<CXX11>;
10321033
def err_lambda_decl_specifier_repeated : Error<
10331034
"%select{'mutable'|'static'|'constexpr'|'consteval'}0 cannot "
10341035
"appear multiple times in a lambda declarator">;

‎clang/include/clang/Basic/Features.def

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Original file line numberDiff line numberDiff line change
@@ -261,6 +261,7 @@ EXTENSION(cxx_defaulted_functions, LangOpts.CPlusPlus)
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EXTENSION(cxx_deleted_functions, LangOpts.CPlusPlus)
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EXTENSION(cxx_explicit_conversions, LangOpts.CPlusPlus)
263263
EXTENSION(cxx_inline_namespaces, LangOpts.CPlusPlus)
264+
EXTENSION(cxx_lambdas, LangOpts.CPlusPlus)
264265
EXTENSION(cxx_local_type_template_args, LangOpts.CPlusPlus)
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EXTENSION(cxx_nonstatic_member_init, LangOpts.CPlusPlus)
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EXTENSION(cxx_override_control, LangOpts.CPlusPlus)

‎clang/lib/Parse/ParseExpr.cpp

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1823,7 +1823,7 @@ ExprResult Parser::ParseCastExpression(CastParseKind ParseKind,
18231823
}
18241824
goto ExpectedExpression;
18251825
case tok::l_square:
1826-
if (getLangOpts().CPlusPlus11) {
1826+
if (getLangOpts().CPlusPlus) {
18271827
if (getLangOpts().ObjC) {
18281828
// C++11 lambda expressions and Objective-C message sends both start with a
18291829
// square bracket. There are three possibilities here:

‎clang/lib/Parse/ParseExprCXX.cpp

Lines changed: 5 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -806,9 +806,8 @@ ExprResult Parser::ParseLambdaExpression() {
806806
///
807807
/// If we are not looking at a lambda expression, returns ExprError().
808808
ExprResult Parser::TryParseLambdaExpression() {
809-
assert(getLangOpts().CPlusPlus11
810-
&& Tok.is(tok::l_square)
811-
&& "Not at the start of a possible lambda expression.");
809+
assert(getLangOpts().CPlusPlus && Tok.is(tok::l_square) &&
810+
"Not at the start of a possible lambda expression.");
812811

813812
const Token Next = NextToken();
814813
if (Next.is(tok::eof)) // Nothing else to lookup here...
@@ -1326,7 +1325,9 @@ static void DiagnoseStaticSpecifierRestrictions(Parser &P,
13261325
ExprResult Parser::ParseLambdaExpressionAfterIntroducer(
13271326
LambdaIntroducer &Intro) {
13281327
SourceLocation LambdaBeginLoc = Intro.Range.getBegin();
1329-
Diag(LambdaBeginLoc, diag::warn_cxx98_compat_lambda);
1328+
Diag(LambdaBeginLoc, getLangOpts().CPlusPlus11
1329+
? diag::warn_cxx98_compat_lambda
1330+
: diag::ext_lambda);
13301331

13311332
PrettyStackTraceLoc CrashInfo(PP.getSourceManager(), LambdaBeginLoc,
13321333
"lambda expression parsing");

‎clang/lib/Parse/ParseInit.cpp

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -35,7 +35,7 @@ bool Parser::MayBeDesignationStart() {
3535
return true;
3636

3737
case tok::l_square: { // designator: array-designator
38-
if (!PP.getLangOpts().CPlusPlus11)
38+
if (!PP.getLangOpts().CPlusPlus)
3939
return true;
4040

4141
// C++11 lambda expressions and C99 designators can be ambiguous all the

‎clang/lib/Sema/SemaDecl.cpp

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@@ -16109,7 +16109,7 @@ Decl *Sema::ActOnFinishFunctionBody(Decl *dcl, Stmt *Body,
1610916109
FD->setInvalidDecl();
1611016110
}
1611116111
}
16112-
} else if (getLangOpts().CPlusPlus11 && isLambdaCallOperator(FD)) {
16112+
} else if (getLangOpts().CPlusPlus && isLambdaCallOperator(FD)) {
1611316113
// In C++11, we don't use 'auto' deduction rules for lambda call
1611416114
// operators because we don't support return type deduction.
1611516115
auto *LSI = getCurLambda();

‎clang/lib/Sema/SemaDeclCXX.cpp

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -9738,7 +9738,8 @@ bool Sema::ShouldDeleteSpecialMember(CXXMethodDecl *MD, CXXSpecialMember CSM,
97389738
return false;
97399739
CXXRecordDecl *RD = MD->getParent();
97409740
assert(!RD->isDependentType() && "do deletion after instantiation");
9741-
if (!LangOpts.CPlusPlus11 || RD->isInvalidDecl())
9741+
if (!LangOpts.CPlusPlus || (!LangOpts.CPlusPlus11 && !RD->isLambda()) ||
9742+
RD->isInvalidDecl())
97429743
return false;
97439744

97449745
// C++11 [expr.lambda.prim]p19:

‎clang/test/Lexer/has_extension_cxx.cpp

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@@ -33,6 +33,11 @@ int has_deleted_functions();
3333
int has_inline_namespaces();
3434
#endif
3535

36+
// CHECK: has_lambdas
37+
#if __has_extension(cxx_lambdas)
38+
int has_lambdas();
39+
#endif
40+
3641
// CHECK: has_override_control
3742
#if __has_extension(cxx_override_control)
3843
int has_override_control();

‎clang/test/OpenMP/declare_reduction_messages.cpp

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@@ -58,16 +58,10 @@ class Class2 : public Class1<T> {
5858
#pragma omp declare reduction(fun1 : long : omp_out += omp_in) initializer // expected-error {{expected '(' after 'initializer'}}
5959
#pragma omp declare reduction(fun2 : long : omp_out += omp_in) initializer { // expected-error {{expected '(' after 'initializer'}} expected-error {{expected expression}} expected-warning {{extra tokens at the end of '#pragma omp declare reduction' are ignored}}
6060
#pragma omp declare reduction(fun3 : long : omp_out += omp_in) initializer[
61-
#if __cplusplus <= 199711L
62-
// expected-error@-2 {{expected '(' after 'initializer'}}
63-
// expected-error@-3 {{expected expression}}
64-
// expected-warning@-4 {{extra tokens at the end of '#pragma omp declare reduction' are ignored}}
65-
#else
66-
// expected-error@-6 {{expected '(' after 'initializer'}}
67-
// expected-error@-7 {{expected variable name or 'this' in lambda capture list}}
68-
// expected-error@-8 {{expected ')'}}
69-
// expected-note@-9 {{to match this '('}}
70-
#endif
61+
// expected-error@-1 {{expected '(' after 'initializer'}}
62+
// expected-error@-2 {{expected variable name or 'this' in lambda capture list}}
63+
// expected-error@-3 {{expected ')'}}
64+
// expected-note@-4 {{to match this '('}}
7165
#pragma omp declare reduction(fun4 : long : omp_out += omp_in) initializer() // expected-error {{expected expression}}
7266
#pragma omp declare reduction(fun5 : long : omp_out += omp_in) initializer(temp) // expected-error {{only 'omp_priv' or 'omp_orig' variables are allowed in initializer expression}}
7367
#pragma omp declare reduction(fun6 : long : omp_out += omp_in) initializer(omp_orig // expected-error {{expected ')'}} expected-note {{to match this '('}}

‎clang/test/OpenMP/openmp_check.cpp

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -18,7 +18,7 @@ int nested(int a) {
1818
auto F = [&]() {
1919
#if __cplusplus <= 199711L
2020
// expected-warning@-2 {{'auto' type specifier is a C++11 extension}}
21-
// expected-error@-3 {{expected expression}}
21+
// expected-warning@-3 {{lambdas are a C++11 extension}}
2222
#endif
2323

2424
#pragma omp parallel

‎clang/test/Parser/cxx03-lambda-extension.cpp

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@@ -0,0 +1,5 @@
1+
// RUN: %clang_cc1 -fsyntax-only -Wno-unused-value -verify -std=c++03 %s
2+
3+
void func() {
4+
[]() {}; // expected-warning {{lambdas are a C++11 extension}}
5+
}

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