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[clang] Accept lambdas in C++03 as an extensions (#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
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@@ -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
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====================================== ================================ ============= =============
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variadic templates __cpp_variadic_templates C++11 C++03
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Alias templates __cpp_alias_templates C++11 C++03
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Non-static data member initializers __cpp_nsdmi C++11 C++03
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Range-based ``for`` loop __cpp_range_based_for C++11 C++03
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RValue references __cpp_rvalue_references C++11 C++03
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Attributes __cpp_attributes C++11 C++03
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variable templates __cpp_variable_templates C++14 C++03
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Binary literals __cpp_binary_literals C++14 C++03
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Relaxed constexpr __cpp_constexpr C++14 C++11
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``if constexpr`` __cpp_if_constexpr C++17 C++11
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fold expressions __cpp_fold_expressions C++17 C++03
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Lambda capture of \*this by value __cpp_capture_star_this C++17 C++11
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Attributes on enums __cpp_enumerator_attributes C++17 C++03
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Guaranteed copy elision __cpp_guaranteed_copy_elision C++17 C++03
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Hexadecimal floating literals __cpp_hex_float C++17 C++03
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``inline`` variables __cpp_inline_variables C++17 C++03
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Attributes on namespaces __cpp_namespace_attributes C++17 C++11
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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
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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
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Attributes on Lambda-Expressions C++23 C++11
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-------------------------------------- -------------------------------- ------------- -------------
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Designated initializers (N494) C99 C89
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Array & element qualification (N2607) C23 C89
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Attributes (N2335) C23 C89
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====================================== ================================ ============= =============
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============================================ ================================ ============= =============
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Feature Feature Test Macro Introduced In Backported To
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============================================ ================================ ============= =============
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variadic templates __cpp_variadic_templates C++11 C++03
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Alias templates __cpp_alias_templates C++11 C++03
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Non-static data member initializers __cpp_nsdmi C++11 C++03
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Range-based ``for`` loop __cpp_range_based_for C++11 C++03
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RValue references __cpp_rvalue_references C++11 C++03
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Attributes __cpp_attributes C++11 C++03
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Lambdas __cpp_lambdas C++11 C++03
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Generalized lambda captures __cpp_init_captures C++14 C++03
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Generic lambda expressions __cpp_generic_lambdas C++14 C++03
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variable templates __cpp_variable_templates C++14 C++03
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Binary literals __cpp_binary_literals C++14 C++03
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Relaxed constexpr __cpp_constexpr C++14 C++11
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Pack expansion in generalized lambda-capture __cpp_init_captures C++17 C++03
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``if constexpr`` __cpp_if_constexpr C++17 C++11
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fold expressions __cpp_fold_expressions C++17 C++03
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Lambda capture of \*this by value __cpp_capture_star_this C++17 C++03
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Attributes on enums __cpp_enumerator_attributes C++17 C++03
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Guaranteed copy elision __cpp_guaranteed_copy_elision C++17 C++03
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Hexadecimal floating literals __cpp_hex_float C++17 C++03
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``inline`` variables __cpp_inline_variables C++17 C++03
1485+
Attributes on namespaces __cpp_namespace_attributes C++17 C++11
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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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Familiar template syntax for generic lambdas __cpp_generic_lambdas C++20 C++03
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``static operator[]`` __cpp_multidimensional_subscript C++20 C++03
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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
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Attributes on Lambda-Expressions C++23 C++11
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-------------------------------------------- -------------------------------- ------------- -------------
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Designated initializers (N494) C99 C89
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Array & element qualification (N2607) C23 C89
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Attributes (N2335) C23 C89
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============================================ ================================ ============= =============
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Type Trait Primitives
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=====================

‎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
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constant expressions.
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- Lambda expressions are now accepted in C++03 mode as an extension.
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New Compiler Flags
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------------------
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‎clang/include/clang/Basic/DiagnosticParseKinds.td

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

‎clang/include/clang/Basic/Features.def

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@@ -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)
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EXTENSION(cxx_inline_namespaces, LangOpts.CPlusPlus)
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EXTENSION(cxx_lambdas, LangOpts.CPlusPlus)
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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

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@@ -1823,7 +1823,7 @@ ExprResult Parser::ParseCastExpression(CastParseKind ParseKind,
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}
18241824
goto ExpectedExpression;
18251825
case tok::l_square:
1826-
if (getLangOpts().CPlusPlus11) {
1826+
if (getLangOpts().CPlusPlus) {
18271827
if (getLangOpts().ObjC) {
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// C++11 lambda expressions and Objective-C message sends both start with a
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// square bracket. There are three possibilities here:

‎clang/lib/Parse/ParseExprCXX.cpp

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Original file line numberDiff line numberDiff line change
@@ -806,9 +806,8 @@ ExprResult Parser::ParseLambdaExpression() {
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///
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/// If we are not looking at a lambda expression, returns ExprError().
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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.");
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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

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@@ -35,7 +35,7 @@ bool Parser::MayBeDesignationStart() {
3535
return true;
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3737
case tok::l_square: { // designator: array-designator
38-
if (!PP.getLangOpts().CPlusPlus11)
38+
if (!PP.getLangOpts().CPlusPlus)
3939
return true;
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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,
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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.
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auto *LSI = getCurLambda();

‎clang/lib/Sema/SemaDeclCXX.cpp

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@@ -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;
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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();
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int has_inline_namespaces();
3434
#endif
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36+
// CHECK: has_lambdas
37+
#if __has_extension(cxx_lambdas)
38+
int has_lambdas();
39+
#endif
40+
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// CHECK: has_override_control
3742
#if __has_extension(cxx_override_control)
3843
int has_override_control();

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