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Although the alternative tokens `bitand` and `and` _can_ respectively be
used in place of `&` and `&&` for declarations, this is arguably misuse
of the tokens in contemporary programming. As of this commit, Clang will
warn—by default—when a programmer attempts to declare a name using
alternative tokens in place of reference symbols.
Depends on D107291 <https://reviews.llvm.org/D107291>.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D107292
Files:
clang/include/clang/Basic/DiagnosticParseKinds.td
clang/lib/Parse/ParseDecl.cpp
clang/test/Parser/cxx-decl.cpp
clang/test/Parser/cxx0x-decl.cpp
clang/test/Parser/warn-declare-references-with-symbols.cpp
Index: clang/test/Parser/warn-declare-references-with-symbols.cpp
===================================================================
--- /dev/null
+++ clang/test/Parser/warn-declare-references-with-symbols.cpp
@@ -0,0 +1,63 @@
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify %s
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -Wdeclare-references-with-symbols -verify %s
+
+int i = 0;
+
+int bitand lr1 = i; // expected-warning{{use '&' when declaring lvalue references}}
+int &lr2 = i; // no warning
+
+using bad_lr = int bitand; // expected-warning{{use '&' when declaring lvalue references}}
+using good_lr = int &; // no warning
+
+template<class T>
+void f(T bitand); // expected-warning{{use '&' when declaring lvalue references}}
+
+template<class T>
+void f(T &); // no warning
+
+// C++11
+int and rr1 = 0; // expected-warning{{use '&&' when declaring rvalue and forwarding references}}
+int &&rr2 = 0; // no warning
+
+using bad_rr = int and; // expected-warning{{use '&&' when declaring rvalue and forwarding references}}
+using good_rr = int &&; // no warning
+
+auto and fr1 = i; // expected-warning{{use '&&' when declaring rvalue and forwarding references}}
+auto &&fr2 = i; // no warning
+
+auto and fr3 = 0; // expected-warning{{use '&&' when declaring rvalue and forwarding references}}
+auto &&fr4 = 0; // no warning
+
+template<class T>
+void f(T and); // expected-warning{{use '&&' when declaring rvalue and forwarding references}}
+
+template<class T>
+void f(T &&); // no warning
+
+// C++14
+template<class T>
+T bitand lr3 = i; // expected-warning{{use '&' when declaring lvalue references}}
+
+template<class T>
+T &lr4 = i; // no warning
+
+template<class T>
+T and rr3 = i; // expected-warning{{use '&&' when declaring rvalue and forwarding references}}
+
+template<class T>
+T &&rr4 = i; // no warning
+
+// C++20
+template<class T>
+concept C1 = requires(T bitand x) { x; };
+// expected-warning@-1{{use '&' when declaring lvalue references}}
+
+template<class T>
+concept C2 = requires(T &x) { x; }; // no warning
+
+template<class T>
+concept C3 = requires(T and x) { x; };
+// expected-warning@-1{{use '&&' when declaring rvalue and forwarding references}}
+
+template<class T>
+concept C4 = requires(T &&x) { x; }; // no warning
Index: clang/test/Parser/cxx0x-decl.cpp
===================================================================
--- clang/test/Parser/cxx0x-decl.cpp
+++ clang/test/Parser/cxx0x-decl.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -verify -fsyntax-only -std=c++2a -pedantic-errors -triple x86_64-linux-gnu %s
+// RUN: %clang_cc1 -verify -fsyntax-only -std=c++2a -Wno-declare-references-with-symbols -pedantic-errors -triple x86_64-linux-gnu %s
// Make sure we know these are legitimate commas and not typos for ';'.
namespace Commas {
Index: clang/test/Parser/cxx-decl.cpp
===================================================================
--- clang/test/Parser/cxx-decl.cpp
+++ clang/test/Parser/cxx-decl.cpp
@@ -1,6 +1,6 @@
-// RUN: %clang_cc1 -verify -fsyntax-only -triple i386-linux -Wredundant-parens -pedantic-errors -fcxx-exceptions -fexceptions %s
-// RUN: %clang_cc1 -verify -fsyntax-only -triple i386-linux -Wredundant-parens -pedantic-errors -fcxx-exceptions -fexceptions -std=c++98 %s
-// RUN: %clang_cc1 -verify -fsyntax-only -triple i386-linux -Wredundant-parens -pedantic-errors -fcxx-exceptions -fexceptions -std=c++11 %s
+// RUN: %clang_cc1 -verify -fsyntax-only -triple i386-linux -Wredundant-parens -Wno-declare-references-with-symbols -pedantic-errors -fcxx-exceptions -fexceptions %s
+// RUN: %clang_cc1 -verify -fsyntax-only -triple i386-linux -Wredundant-parens -Wno-declare-references-with-symbols -pedantic-errors -fcxx-exceptions -fexceptions -std=c++98 %s
+// RUN: %clang_cc1 -verify -fsyntax-only -triple i386-linux -Wredundant-parens -Wno-declare-references-with-symbols -pedantic-errors -fcxx-exceptions -fexceptions -std=c++11 %s
const char const *x10; // expected-error {{duplicate 'const' declaration specifier}}
Index: clang/lib/Parse/ParseDecl.cpp
===================================================================
--- clang/lib/Parse/ParseDecl.cpp
+++ clang/lib/Parse/ParseDecl.cpp
@@ -5797,6 +5797,7 @@
// Otherwise, '*' -> pointer, '^' -> block, '&' -> lvalue reference,
// '&&' -> rvalue reference
+ Token PrevToken = Tok;
SourceLocation Loc = ConsumeToken(); // Eat the *, ^, & or &&.
D.SetRangeEnd(Loc);
@@ -5831,13 +5832,24 @@
// Is a reference
DeclSpec DS(AttrFactory);
- // Complain about rvalue references in C++03, but then go on and build
- // the declarator.
- if (Kind == tok::ampamp)
+ if (Kind == tok::amp && PrevToken.getSpelling() != "&") {
+ constexpr int Lvalue = 0;
+ Diag(Loc, diag::warn_declare_references_with_symbols) << Lvalue << Lvalue;
+ }
+ if (Kind == tok::ampamp) {
+ // Complain about rvalue references in C++03, but then go on and build
+ // the declarator.
Diag(Loc, getLangOpts().CPlusPlus11 ?
diag::warn_cxx98_compat_rvalue_reference :
diag::ext_rvalue_reference);
+ if (PrevToken.getSpelling() != "&&") {
+ constexpr int AmpAmp = 1;
+ Diag(Loc, diag::warn_declare_references_with_symbols)
+ << AmpAmp << AmpAmp;
+ }
+ }
+
// GNU-style and C++11 attributes are allowed here, as is restrict.
ParseTypeQualifierListOpt(DS);
D.ExtendWithDeclSpec(DS);
Index: clang/include/clang/Basic/DiagnosticParseKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticParseKinds.td
+++ clang/include/clang/Basic/DiagnosticParseKinds.td
@@ -1547,4 +1547,8 @@
def note_max_tokens_total_override : Note<"total token limit set here">;
+def warn_declare_references_with_symbols : Warning<
+ "use '%select{&|&&}0' when declaring %select{lvalue|rvalue and forwarding}1 references">,
+ InGroup<DiagGroup<"declare-references-with-symbols">>, DefaultWarn;
+
} // end of Parser diagnostics
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