[clang] 13ffc61 - [C2X] N3007 Type inference for object definitions
Aaron Ballman via cfe-commits
cfe-commits at lists.llvm.org
Thu Oct 5 09:16:13 PDT 2023
Author: Guillot Tony
Date: 2023-10-05T12:16:00-04:00
New Revision: 13ffc61a4224012ab1abb4e806d03fc149aec91f
URL: https://github.com/llvm/llvm-project/commit/13ffc61a4224012ab1abb4e806d03fc149aec91f
DIFF: https://github.com/llvm/llvm-project/commit/13ffc61a4224012ab1abb4e806d03fc149aec91f.diff
LOG: [C2X] N3007 Type inference for object definitions
Re-landing 5d78b78c8538 which was reverted.
This patches implements the auto keyword from the N3007 standard
specification.
This allows deducing the type of the variable like in C++:
```
auto nb = 1;
auto chr = 'A';
auto str = "String";
```
The list of statements which allows the usage of auto:
* Basic variables declarations (int, float, double, char, char*...)
* Macros declaring a variable with the auto type
The list of statements which will not work with the auto keyword:
* auto arrays
* sizeof(), alignas()
* auto parameters, auto return type
* auto as a struct/typedef member
* uninitialized auto variables
* auto in an union
* auto as a enum type specifier
* auto casts
* auto in an compound literals
Differential Revision: https://reviews.llvm.org/D133289
Added:
clang/test/C/C2x/n3007.c
clang/test/CodeGen/auto.c
clang/test/Parser/c2x-auto.c
clang/test/Sema/c2x-auto.c
Modified:
clang/docs/ReleaseNotes.rst
clang/include/clang/Basic/DiagnosticSemaKinds.td
clang/lib/Parse/ParseDecl.cpp
clang/lib/Sema/DeclSpec.cpp
clang/lib/Sema/SemaDecl.cpp
clang/lib/Sema/SemaTemplateDeduction.cpp
clang/lib/Sema/SemaType.cpp
clang/www/c_status.html
Removed:
################################################################################
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index e498969b2c46bfb..7b22f3c6842c9f8 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -145,6 +145,7 @@ C23 Feature Support
previous placeholder value. Clang continues to accept ``-std=c2x`` and
``-std=gnu2x`` as aliases for C23 and GNU C23, respectively.
- Clang now supports `requires c23` for module maps.
+- Clang now supports ``N3007 Type inference for object definitions``.
Non-comprehensive list of changes in this release
-------------------------------------------------
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 217309c4ecbca52..28f1db29e62fa91 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -240,6 +240,10 @@ def ext_imaginary_constant : Extension<
"imaginary constants are a GNU extension">, InGroup<GNUImaginaryConstant>;
def ext_integer_complex : Extension<
"complex integer types are a GNU extension">, InGroup<GNUComplexInteger>;
+def ext_c23_auto_non_plain_identifier : Extension<
+ "type inference of a declaration other than a plain identifier with optional "
+ "trailing attributes is a Clang extension">,
+ InGroup<DiagGroup<"auto-decl-extensions">>;
def err_invalid_saturation_spec : Error<"'_Sat' specifier is only valid on "
"'_Fract' or '_Accum', not '%0'">;
@@ -2388,7 +2392,8 @@ def err_auto_not_allowed : Error<
"|in conversion function type|here|in lambda parameter"
"|in type allocated by 'new'|in K&R-style function parameter"
"|in template parameter|in friend declaration|in function prototype that is "
- "not a function declaration|in requires expression parameter}1">;
+ "not a function declaration|in requires expression parameter"
+ "|in array declaration}1">;
def err_dependent_deduced_tst : Error<
"typename specifier refers to "
"%select{class template|function template|variable template|alias template|"
@@ -2461,7 +2466,8 @@ def err_implied_std_initializer_list_not_found : Error<
def err_malformed_std_initializer_list : Error<
"std::initializer_list must be a class template with a single type parameter">;
def err_auto_init_list_from_c : Error<
- "cannot use __auto_type with initializer list in C">;
+ "cannot use %select{'auto'|<ERROR>|'__auto_type'}0 with "
+ "%select{initializer list|array}1 in C">;
def err_auto_bitfield : Error<
"cannot pass bit-field as __auto_type initializer in C">;
@@ -6664,8 +6670,8 @@ def err_func_def_incomplete_result : Error<
def err_atomic_specifier_bad_type
: Error<"_Atomic cannot be applied to "
"%select{incomplete |array |function |reference |atomic |qualified "
- "|sizeless ||integer }0type "
- "%1 %select{|||||||which is not trivially copyable|}0">;
+ "|sizeless ||integer |}0type "
+ "%1 %select{|||||||which is not trivially copyable||in C23}0">;
def warn_atomic_member_access : Warning<
"accessing a member of an atomic structure or union is undefined behavior">,
InGroup<DiagGroup<"atomic-access">>, DefaultError;
diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index 93515940d15df08..bcc70c04dec91ba 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -4038,7 +4038,7 @@ void Parser::ParseDeclarationSpecifiers(
isStorageClass = true;
break;
case tok::kw_auto:
- if (getLangOpts().CPlusPlus11) {
+ if (getLangOpts().CPlusPlus11 || getLangOpts().C23) {
if (isKnownToBeTypeSpecifier(GetLookAheadToken(1))) {
isInvalid = DS.SetStorageClassSpec(Actions, DeclSpec::SCS_auto, Loc,
PrevSpec, DiagID, Policy);
diff --git a/clang/lib/Sema/DeclSpec.cpp b/clang/lib/Sema/DeclSpec.cpp
index 2d0d575f173a8b6..781f24cb71ae994 100644
--- a/clang/lib/Sema/DeclSpec.cpp
+++ b/clang/lib/Sema/DeclSpec.cpp
@@ -1375,8 +1375,9 @@ void DeclSpec::Finish(Sema &S, const PrintingPolicy &Policy) {
StorageClassSpecLoc = SourceLocation();
}
// Diagnose if we've recovered from an ill-formed 'auto' storage class
- // specifier in a pre-C++11 dialect of C++.
- if (!S.getLangOpts().CPlusPlus11 && TypeSpecType == TST_auto)
+ // specifier in a pre-C++11 dialect of C++ or in a pre-C23 dialect of C.
+ if (!S.getLangOpts().CPlusPlus11 && !S.getLangOpts().C23 &&
+ TypeSpecType == TST_auto)
S.Diag(TSTLoc, diag::ext_auto_type_specifier);
if (S.getLangOpts().CPlusPlus && !S.getLangOpts().CPlusPlus11 &&
StorageClassSpec == SCS_auto)
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 28d9a0ac654b81f..6ac02df193976a9 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -12863,6 +12863,15 @@ QualType Sema::deduceVarTypeFromInitializer(VarDecl *VDecl,
DeducedType *Deduced = Type->getContainedDeducedType();
assert(Deduced && "deduceVarTypeFromInitializer for non-deduced type");
+ // Diagnose auto array declarations in C23, unless it's a supported extension.
+ if (getLangOpts().C23 && Type->isArrayType() &&
+ !isa_and_present<StringLiteral, InitListExpr>(Init)) {
+ Diag(Range.getBegin(), diag::err_auto_not_allowed)
+ << (int)Deduced->getContainedAutoType()->getKeyword()
+ << /*in array decl*/ 23 << Range;
+ return QualType();
+ }
+
// C++11 [dcl.spec.auto]p3
if (!Init) {
assert(VDecl && "no init for init capture deduction?");
diff --git a/clang/lib/Sema/SemaTemplateDeduction.cpp b/clang/lib/Sema/SemaTemplateDeduction.cpp
index 69b857d3510dc63..62fbd903a04044b 100644
--- a/clang/lib/Sema/SemaTemplateDeduction.cpp
+++ b/clang/lib/Sema/SemaTemplateDeduction.cpp
@@ -4842,9 +4842,25 @@ Sema::DeduceAutoType(TypeLoc Type, Expr *Init, QualType &Result,
return TDK_Success;
}
+ // Make sure that we treat 'char[]' equaly as 'char*' in C23 mode.
+ auto *String = dyn_cast<StringLiteral>(Init);
+ if (getLangOpts().C23 && String && Type.getType()->isArrayType()) {
+ Diag(Type.getBeginLoc(), diag::ext_c23_auto_non_plain_identifier);
+ TypeLoc TL = TypeLoc(Init->getType(), Type.getOpaqueData());
+ Result = SubstituteDeducedTypeTransform(*this, DependentResult).Apply(TL);
+ assert(!Result.isNull() && "substituting DependentTy can't fail");
+ return TDK_Success;
+ }
+
+ // Emit a warning if 'auto*' is used in pedantic and in C23 mode.
+ if (getLangOpts().C23 && Type.getType()->isPointerType()) {
+ Diag(Type.getBeginLoc(), diag::ext_c23_auto_non_plain_identifier);
+ }
+
auto *InitList = dyn_cast<InitListExpr>(Init);
if (!getLangOpts().CPlusPlus && InitList) {
- Diag(Init->getBeginLoc(), diag::err_auto_init_list_from_c);
+ Diag(Init->getBeginLoc(), diag::err_auto_init_list_from_c)
+ << (int)AT->getKeyword() << getLangOpts().C23;
return TDK_AlreadyDiagnosed;
}
diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
index 8f732682e03792e..068971f8130a4aa 100644
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -9880,11 +9880,14 @@ QualType Sema::BuildAtomicType(QualType T, SourceLocation Loc) {
DisallowedKind = 5;
else if (T->isSizelessType())
DisallowedKind = 6;
- else if (!T.isTriviallyCopyableType(Context))
+ else if (!T.isTriviallyCopyableType(Context) && getLangOpts().CPlusPlus)
// Some other non-trivially-copyable type (probably a C++ class)
DisallowedKind = 7;
else if (T->isBitIntType())
DisallowedKind = 8;
+ else if (getLangOpts().C23 && T->isUndeducedAutoType())
+ // _Atomic auto is prohibited in C23
+ DisallowedKind = 9;
if (DisallowedKind != -1) {
Diag(Loc, diag::err_atomic_specifier_bad_type) << DisallowedKind << T;
diff --git a/clang/test/C/C2x/n3007.c b/clang/test/C/C2x/n3007.c
new file mode 100644
index 000000000000000..1fd20332ceb4715
--- /dev/null
+++ b/clang/test/C/C2x/n3007.c
@@ -0,0 +1,186 @@
+// RUN: %clang_cc1 -std=c2x -verify -pedantic -Wno-comments %s
+
+/* WG14 N3007: Yes
+ * Type Inference for object definitions
+ */
+void test_qualifiers(int x, const int y, int * restrict z) {
+ const auto a = x;
+ auto b = y;
+ static auto c = 1UL;
+ int* pa = &a; // expected-warning {{initializing 'int *' with an expression of type 'const int *' discards qualifiers}}
+ const int* pb = &b;
+ int* pc = &c; // expected-warning {{incompatible pointer types initializing 'int *' with an expression of type 'unsigned long *'}}
+
+ const int ci = 12;
+ auto yup = ci;
+ yup = 12;
+
+ auto r_test = z;
+
+ _Static_assert(_Generic(a, int : 1));
+ _Static_assert(_Generic(c, unsigned long : 1));
+ _Static_assert(_Generic(pa, int * : 1));
+ _Static_assert(_Generic(pb, const int * : 1));
+ _Static_assert(_Generic(r_test, int * : 1));
+}
+
+void test_atomic(void) {
+ _Atomic auto i = 12; // expected-error {{_Atomic cannot be applied to type 'auto' in C23}}
+ _Atomic(auto) j = 12; // expected-error {{'auto' not allowed here}} \
+ expected-error {{a type specifier is required for all declarations}}
+
+ _Atomic(int) foo(void);
+ auto k = foo();
+
+ _Static_assert(_Generic(&i, _Atomic auto *: 1)); // expected-error {{_Atomic cannot be applied to type 'auto' in C23}} \
+ expected-error {{'auto' not allowed here}}
+ _Static_assert(_Generic(k, int: 1));
+}
+
+void test_double(void) {
+ double A[3] = { 0 };
+ auto pA = A;
+ auto qA = &A;
+ auto pi = 3.14;
+
+ _Static_assert(_Generic(A, double * : 1));
+ _Static_assert(_Generic(pA, double * : 1));
+ _Static_assert(_Generic(qA, double (*)[3] : 1));
+ _Static_assert(_Generic(pi, double : 1));
+}
+
+int test_auto_param(auto a) { // expected-error {{'auto' not allowed in function prototype}}
+ return (int)(a * 2);
+}
+
+auto test_auto_return(float a, int b) { // expected-error {{'auto' not allowed in function return type}}
+ return ((a * b) * (a / b));
+}
+
+[[clang::overloadable]] auto test(auto x) { // expected-error {{'auto' not allowed in function prototype}} \
+ expected-error {{'auto' not allowed in function return type}}
+ return x;
+}
+
+void test_sizeof_alignas(void) {
+ (void)sizeof(auto); // expected-error {{expected expression}}
+ _Alignas(auto) int a[4]; // expected-error {{expected expression}}
+}
+
+void test_arrary(void) {
+ auto a[4]; // expected-error {{'auto' not allowed in array declaration}}
+ auto b[] = {1, 2}; // expected-error {{cannot use 'auto' with array in C}}
+}
+
+void test_initializer_list(void) {
+ auto a = {}; // expected-error {{cannot use 'auto' with array in C}}
+ auto b = { 0 }; // expected-error {{cannot use 'auto' with array in C}}
+ auto c = { 1, }; // expected-error {{cannot use 'auto' with array in C}}
+ auto d = { 1 , 2 }; // expected-error {{cannot use 'auto' with array in C}}
+ auto e = (int [3]){ 1, 2, 3 };
+}
+
+void test_structs(void) {
+ // FIXME: Both of these should be diagnosed as invalid underspecified
+ // declarations as described in N3006.
+ auto p1 = (struct { int a; } *)0;
+ struct s;
+ auto p2 = (struct s { int a; } *)0;
+
+ struct B { auto b; }; // expected-error {{'auto' not allowed in struct member}}
+}
+
+void test_typedefs(void) {
+ typedef auto auto_type; // expected-error {{'auto' not allowed in typedef}}
+
+ typedef auto (*fp)(void); // expected-error {{'auto' not allowed in typedef}}
+ typedef void (*fp)(auto); // expected-error {{'auto' not allowed in function prototype}}
+
+ _Generic(0, auto : 1); // expected-error {{'auto' not allowed here}}
+}
+
+void test_misc(void) {
+ auto something; // expected-error {{declaration of variable 'something' with deduced type 'auto' requires an initializer}}
+ auto test_char = 'A';
+ auto test_char_ptr = "test";
+ auto test_char_ptr2[] = "another test"; // expected-warning {{type inference of a declaration other than a plain identifier with optional trailing attributes is a Clang extension}}
+ auto auto_size = sizeof(auto); // expected-error {{expected expression}}
+
+ _Static_assert(_Generic(test_char, int : 1));
+ _Static_assert(_Generic(test_char_ptr, char * : 1));
+ _Static_assert(_Generic(test_char_ptr2, char * : 1));
+}
+
+void test_no_integer_promotions(void) {
+ short s;
+ auto a = s;
+ _Generic(a, int : 1); // expected-error {{controlling expression type 'short' not compatible with any generic association type}}
+}
+
+void test_compound_literals(void) {
+ auto a = (int){};
+ auto b = (int){ 0 };
+ auto c = (int){ 0, };
+ auto d = (int){ 0, 1 }; // expected-warning {{excess elements in scalar initializer}}
+
+ auto auto_cl = (auto){13}; // expected-error {{expected expression}}
+
+ _Static_assert(_Generic(a, int : 1));
+ _Static_assert(_Generic(b, int : 1));
+ _Static_assert(_Generic(c, int : 1));
+}
+
+void test_pointers(void) {
+ int a;
+ auto *ptr = &a; // expected-warning {{type inference of a declaration other than a plain identifier with optional trailing attributes is a Clang extension}}
+ auto *ptr2 = a; // expected-error {{variable 'ptr2' with type 'auto *' has incompatible initializer of type 'int'}} \
+ expected-warning {{type inference of a declaration other than a plain identifier with optional trailing attributes is a Clang extension}}
+ auto nptr = nullptr;
+
+ _Static_assert(_Generic(ptr, int * : 1));
+ _Static_assert(_Generic(ptr2, int * : 1));
+}
+
+void test_scopes(void) {
+ double a = 7;
+ double b = 9;
+ {
+ auto a = a * a; // expected-error {{variable 'a' declared with deduced type 'auto' cannot appear in its own initializer}} \
+ expected-error {{variable 'a' declared with deduced type 'auto' cannot appear in its own initializer}}
+ }
+ {
+ auto b = a * a;
+ auto a = b;
+
+ _Static_assert(_Generic(a, double : 1));
+ _Static_assert(_Generic(b, double : 1));
+ }
+}
+
+void test_loop(void) {
+ auto j = 4;
+ for (auto i = j; i < 2 * j; i++);
+
+ _Static_assert(_Generic(j, int : 1));
+}
+
+#define AUTO_MACRO(_NAME, ARG, ARG2, ARG3) \
+auto _NAME = ARG + (ARG2 / ARG3);
+
+// This macro should only work with integers due to the usage of binary operators
+#define AUTO_INT_MACRO(_NAME, ARG, ARG2, ARG3) \
+auto _NAME = (ARG ^ ARG2) & ARG3;
+
+void test_macros(int in_int) {
+ auto a = in_int + 1;
+ AUTO_MACRO(b, 1.3, 2.5f, 3);
+ AUTO_INT_MACRO(c, 64, 23, 0xff);
+ AUTO_INT_MACRO(not_valid, 51.5, 25, 0xff); // expected-error {{invalid operands to binary expression ('double' and 'int')}}
+
+ auto result = (a + (int)b) - c;
+
+ _Static_assert(_Generic(a, int : 1));
+ _Static_assert(_Generic(b, double : 1));
+ _Static_assert(_Generic(c, int : 1));
+ _Static_assert(_Generic(result, int : 1));
+}
diff --git a/clang/test/CodeGen/auto.c b/clang/test/CodeGen/auto.c
new file mode 100644
index 000000000000000..c418844a9316fcf
--- /dev/null
+++ b/clang/test/CodeGen/auto.c
@@ -0,0 +1,41 @@
+// RUN: %clang_cc1 -std=c2x -emit-llvm %s -o - | FileCheck %s
+
+void basic_types(void) {
+ auto nb = 4; // CHECK: %nb = alloca i32, align 4
+ auto dbl = 4.3; // CHECK: %dbl = alloca double, align 8
+ auto lng = 4UL; // CHECK: %lng = alloca i{{32|64}}, align {{4|8}}
+ auto bl = true; // CHECK: %bl = alloca i8, align 1
+ auto chr = 'A'; // CHECK: %chr = alloca i{{8|32}}, align {{1|4}}
+ auto str = "Test"; // CHECK: %str = alloca ptr, align 8
+ auto str2[] = "Test"; // CHECK: %str2 = alloca [5 x i8], align 1
+ auto nptr = nullptr; // CHECK: %nptr = alloca ptr, align 8
+}
+
+void misc_declarations(void) {
+ // FIXME: this should end up being rejected when we implement underspecified
+ // declarations in N3006.
+ auto strct_ptr = (struct { int a; } *)0; // CHECK: %strct_ptr = alloca ptr, align 8
+ auto int_cl = (int){13}; // CHECK: %int_cl = alloca i32, align 4
+ auto double_cl = (double){2.5}; // CHECK: %double_cl = alloca double, align 8
+
+ auto se = ({ // CHECK: %se = alloca i32, align 4
+ auto snb = 12; // CHECK: %snb = alloca i32, align 4
+ snb;
+ });
+}
+
+void loop(void) {
+ auto j = 4; // CHECK: %j = alloca i32, align 4
+ for (auto i = j; i < 2 * j; i++); // CHECK: %i = alloca i32, align 4
+}
+
+#define AUTO_MACRO(_NAME, ARG, ARG2, ARG3) auto _NAME = ARG + (ARG2 / ARG3);
+
+#define AUTO_INT_MACRO(_NAME, ARG, ARG2, ARG3) auto _NAME = (ARG ^ ARG2) & ARG3;
+
+int macros(int in_int) {
+ auto a = in_int + 1; // CHECK: %a = alloca i32, align 4
+ AUTO_MACRO(b, 1.3, 2.5f, 3); // CHECK: %b = alloca double, align 8
+ AUTO_INT_MACRO(c, 64, 23, 0xff); // CHECK: %c = alloca i32, align 4
+ return (a + (int)b) - c; // CHECK: ret i32 %sub
+}
diff --git a/clang/test/Parser/c2x-auto.c b/clang/test/Parser/c2x-auto.c
new file mode 100644
index 000000000000000..b878a5b7c42d475
--- /dev/null
+++ b/clang/test/Parser/c2x-auto.c
@@ -0,0 +1,132 @@
+// RUN: %clang_cc1 -fsyntax-only -verify=expected,c23 -std=c23 %s
+// RUN: %clang_cc1 -fsyntax-only -verify=expected,c17 -std=c17 %s
+
+#define AUTO_MACRO(_NAME, ARG, ARG2, ARG3) \
+auto _NAME = ARG + (ARG2 / ARG3);
+
+struct S {
+ int a;
+ auto b; // c23-error {{'auto' not allowed in struct member}} \
+ c17-error {{type name does not allow storage class to be specified}} \
+ c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}}
+ union {
+ char c;
+ auto smth; // c23-error {{'auto' not allowed in union member}} \
+ c17-error {{type name does not allow storage class to be specified}} \
+ c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}}
+ } u;
+};
+
+enum E : auto { // c23-error {{'auto' not allowed here}} \
+ c17-error {{expected a type}} \
+ c17-error {{type name does not allow storage class to be specified}}
+ One,
+ Two,
+ Tree,
+};
+
+auto basic_usage(auto auto) { // c23-error {{'auto' not allowed in function prototype}} \
+ c23-error {{'auto' not allowed in function return type}} \
+ c23-error {{cannot combine with previous 'auto' declaration specifier}} \
+ c17-error {{invalid storage class specifier in function declarator}} \
+ c17-error {{illegal storage class on function}} \
+ c17-warning {{duplicate 'auto' declaration specifier}} \
+ c17-warning {{omitting the parameter name in a function definition is a C23 extension}} \
+ c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}} \
+ c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}}
+
+ auto = 4; // expected-error {{expected identifier or '('}}
+
+ auto a = 4; // c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}}
+
+ auto auto aa = 12; // c23-error {{cannot combine with previous 'auto' declaration specifier}} \
+ c17-warning {{duplicate 'auto' declaration specifier}} \
+ c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}}
+
+ auto b[4]; // c23-error {{'auto' not allowed in array declaration}} \
+ c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}}
+
+ auto array[auto]; // expected-error {{expected expression}} \
+ c23-error {{declaration of variable 'array' with deduced type 'auto' requires an initializer}} \
+ c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}}
+
+ AUTO_MACRO(auto, 1, 2, 3); // c23-error {{cannot combine with previous 'auto' declaration specifier}} \
+ expected-error {{expected identifier or '('}} \
+ c17-warning {{duplicate 'auto' declaration specifier}}
+
+ auto c = (auto)a; // expected-error {{expected expression}} \
+ c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}}
+
+ auto ci = (auto){12}; // expected-error {{expected expression}} \
+ c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}}
+
+ int auto_cxx_decl = auto(0); // expected-error {{expected expression}}
+
+ return c;
+}
+
+void structs(void) {
+ struct s_auto { auto a; }; // c23-error {{'auto' not allowed in struct member}} \
+ c17-error {{type name does not allow storage class to be specified}} \
+ c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}}
+
+ // FIXME: this should end up being rejected when we implement underspecified
+ // declarations in N3006.
+ auto s_int = (struct { int a; } *)0; // c17-error {{incompatible pointer to integer conversion initializing 'int' with an expression of type}} \
+ c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}}
+
+ typedef auto auto_type; // c23-error {{'auto' not allowed in typedef}} \
+ c17-error {{cannot combine with previous 'typedef' declaration specifier}} \
+ c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}}
+}
+
+void sizeof_alignas(void) {
+ auto auto_size = sizeof(auto); // expected-error {{expected expression}} \
+ c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}}
+}
+
+void generic_alignof_alignas(void) {
+ int g;
+ _Generic(g, auto : 0); // c23-error {{'auto' not allowed here}} \
+ c17-error {{expected a type}} \
+ c17-error {{type name does not allow storage class to be specified}}
+
+ _Alignof(auto); // expected-error {{expected expression}} \
+ expected-warning {{'_Alignof' applied to an expression is a GNU extension}}
+
+ _Alignas(auto); // expected-error {{expected expression}} \
+ expected-warning {{declaration does not declare anything}}
+}
+
+void function_designators(void) {
+ extern auto auto_ret_func(void); // c23-error {{'auto' not allowed in function return type}} \
+ c17-error {{cannot combine with previous 'extern' declaration specifier}} \
+ c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}}
+
+ extern void auto_param_func(auto); // c23-error {{'auto' not allowed in function prototype}} \
+ c17-error {{invalid storage class specifier in function declarator}} \
+ c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}}
+
+ auto (auto_ret_func)(void); // c23-error {{'auto' not allowed in function return type}} \
+ c17-error {{illegal storage class on function}} \
+ c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}}
+
+ void (auto_param_func)(auto); // c23-error {{'auto' not allowed in function prototype}} \
+ c17-error {{invalid storage class specifier in function declarator}} \
+ c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}}
+}
+
+void atomic(void) {
+ _Atomic(auto) atom1 = 12; // c23-error {{'auto' not allowed here}} \
+ c23-error {{a type specifier is required for all declarations}} \
+ c17-error {{expected a type}} \
+ c17-error {{type name does not allow storage class to be specified}} \
+ c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}}
+
+ _Atomic auto atom2 = 12; // c23-error {{_Atomic cannot be applied to type 'auto' in C23}} \
+ c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}}
+}
+
+void attributes(void) {
+ auto ident [[clang::annotate("this works")]] = 12; // c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}}
+}
diff --git a/clang/test/Sema/c2x-auto.c b/clang/test/Sema/c2x-auto.c
new file mode 100644
index 000000000000000..916c179adcf3182
--- /dev/null
+++ b/clang/test/Sema/c2x-auto.c
@@ -0,0 +1,137 @@
+// RUN: %clang_cc1 -std=c2x -verify -pedantic -Wno-comments %s
+
+void test_basic_types(void) {
+ auto undefined; // expected-error {{declaration of variable 'undefined' with deduced type 'auto' requires an initializer}}
+ auto auto_int = 4;
+ auto auto_long = 4UL;
+ signed auto a = 1L; // expected-error {{'auto' cannot be signed or unsigned}}
+
+ _Static_assert(_Generic(auto_int, int : 1));
+ _Static_assert(_Generic(auto_long, unsigned long : 1));
+}
+
+void test_complex_types(void) {
+ _Complex auto i = 12.0; // expected-error {{'_Complex auto' is invalid}}
+}
+
+void test_gnu_extensions(void) {
+ auto t = ({ // expected-warning {{use of GNU statement expression extension}}
+ auto b = 12;
+ b;
+ });
+ _Static_assert(_Generic(t, int : 1));
+}
+
+void test_sizeof_typeof(void) {
+ auto auto_size = sizeof(auto); // expected-error {{expected expression}}
+ typeof(auto) tpof = 4; // expected-error {{expected expression}}
+}
+
+void test_casts(void) {
+ auto int_cast = (int)(4 + 3);
+ auto double_cast = (double)(1 / 3);
+ auto long_cast = (long)(4UL + 3UL);
+ auto auto_cast = (auto)(4 + 3); // expected-error {{expected expression}}
+
+ _Static_assert(_Generic(int_cast, int : 1));
+ _Static_assert(_Generic(double_cast, double : 1));
+ _Static_assert(_Generic(long_cast, long : 1));
+}
+
+void test_compound_literral(void) {
+ auto int_cl = (int){13};
+ auto double_cl = (double){2.5};
+ auto array[] = { 1, 2, 3 }; // expected-error {{cannot use 'auto' with array in C}}
+
+ auto auto_cl = (auto){13}; // expected-error {{expected expression}}
+
+ _Static_assert(_Generic(int_cl, int : 1));
+ _Static_assert(_Generic(double_cl, double : 1));
+}
+
+void test_array_pointers(void) {
+ double array[3] = { 0 };
+ auto a = array;
+ auto b = &array;
+
+ _Static_assert(_Generic(array, double * : 1));
+ _Static_assert(_Generic(a, double * : 1));
+ _Static_assert(_Generic(b, double (*)[3] : 1));
+}
+
+void test_typeof() {
+ int typeof_target();
+ auto result = (typeof(typeof_target())){12};
+
+ _Static_assert(_Generic(result, int : 1));
+}
+
+void test_qualifiers(const int y) {
+ const auto a = 12;
+ auto b = y;
+ static auto c = 1UL;
+ int* pa = &a; // expected-warning {{initializing 'int *' with an expression of type 'const int *' discards qualifiers}}
+ const int* pb = &b;
+ int* pc = &c; // expected-warning {{incompatible pointer types initializing 'int *' with an expression of type 'unsigned long *'}}
+
+ _Static_assert(_Generic(a, int : 1));
+ _Static_assert(_Generic(b, int : 1));
+ _Static_assert(_Generic(c, unsigned long : 1));
+ _Static_assert(_Generic(pa, int * : 1));
+ _Static_assert(_Generic(pb, const int * : 1));
+ _Static_assert(_Generic(pc, int * : 1));
+}
+
+void test_strings(void) {
+ auto str = "this is a string";
+ auto str2[] = "this is a string"; // expected-warning {{type inference of a declaration other than a plain identifier with optional trailing attributes is a Clang extension}}
+ auto (str3) = "this is a string";
+ auto (((str4))) = "this is a string";
+
+ _Static_assert(_Generic(str, char * : 1));
+ _Static_assert(_Generic(str2, char * : 1));
+ _Static_assert(_Generic(str3, char * : 1));
+ _Static_assert(_Generic(str4, char * : 1));
+}
+
+void test_pointers(void) {
+ auto a = 12;
+ auto *ptr = &a; // expected-warning {{type inference of a declaration other than a plain identifier with optional trailing attributes is a Clang extension}}
+ auto *str = "this is a string"; // expected-warning {{type inference of a declaration other than a plain identifier with optional trailing attributes is a Clang extension}}
+ const auto *str2 = "this is a string"; // expected-warning {{type inference of a declaration other than a plain identifier with optional trailing attributes is a Clang extension}}
+ auto *b = &a; // expected-warning {{type inference of a declaration other than a plain identifier with optional trailing attributes is a Clang extension}}
+ *b = &a; // expected-error {{incompatible pointer to integer conversion assigning to 'int' from 'int *'; remove &}}
+ auto nptr = nullptr;
+
+ _Static_assert(_Generic(a, int : 1));
+ _Static_assert(_Generic(ptr, int * : 1));
+ _Static_assert(_Generic(str, char * : 1));
+ _Static_assert(_Generic(str2, const char * : 1));
+ _Static_assert(_Generic(b, int * : 1));
+ _Static_assert(_Generic(nptr, typeof(nullptr) : 1));
+}
+
+void test_prototypes(void) {
+ extern void foo(int a, int array[({ auto x = 12; x;})]); // expected-warning {{use of GNU statement expression extension}}
+}
+
+void test_scopes(void) {
+ double a = 7;
+ double b = 9;
+ {
+ auto a = a * a; // expected-error {{variable 'a' declared with deduced type 'auto' cannot appear in its own initializer}} \
+ expected-error {{variable 'a' declared with deduced type 'auto' cannot appear in its own initializer}}
+ }
+ {
+ auto b = a * a;
+ auto a = b;
+
+ _Static_assert(_Generic(b, double : 1));
+ _Static_assert(_Generic(a, double : 1));
+ }
+}
+
+[[clang::overloadable]] auto test(auto x) { // expected-error {{'auto' not allowed in function prototype}} \
+ expected-error {{'auto' not allowed in function return type}}
+ return x;
+}
diff --git a/clang/www/c_status.html b/clang/www/c_status.html
index 99e5c0109d4ffca..13bb1971c61deb7 100644
--- a/clang/www/c_status.html
+++ b/clang/www/c_status.html
@@ -1186,12 +1186,12 @@ <h2 id="c2x">C23 implementation status</h2>
<tr>
<td>Underspecified object definitions</td>
<td><a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3006.htm">N3006</a></td>
- <td class="unknown" align="center">Unknown</td>
+ <td class="none" align="center">No</td>
</tr>
<tr>
<td>Type inference for object declarations</td>
<td><a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3007.htm">N3007</a></td>
- <td class="none" align="center">No</td>
+ <td class="unreleased" align="center">Clang 18</td>
</tr>
<tr>
<td>constexpr for object definitions</td>
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