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Apr 7, 2025
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Correctly diagnose incomplete arrays with static storage in C #134374

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Correctly diagnose incomplete arrays with static storage in C
AaronBallman Apr 4, 2025
3a393ab
Update clang/docs/ReleaseNotes.rst
AaronBallman Apr 4, 2025
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3 changes: 3 additions & 0 deletions clang/docs/ReleaseNotes.rst
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Expand Up @@ -319,6 +319,9 @@ Improvements to Clang's diagnostics
- ``-Wc++98-compat`` no longer diagnoses use of ``__auto_type`` or
``decltype(auto)`` as though it was the extension for ``auto``. (#GH47900)

- Now correctly diagnose a tentative definition of an array with static
storage duration in pedantic mode in C. (#GH50661)

Improvements to Clang's time-trace
----------------------------------

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5 changes: 3 additions & 2 deletions clang/include/clang/Basic/DiagnosticSemaKinds.td
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Expand Up @@ -7346,8 +7346,9 @@ def err_typecheck_pointer_arith_void_type : Error<
"arithmetic on%select{ a|}0 pointer%select{|s}0 to void">;
def err_typecheck_decl_incomplete_type : Error<
"variable has incomplete type %0">;
def ext_typecheck_decl_incomplete_type : ExtWarn<
"tentative definition of variable with internal linkage has incomplete non-array type %0">,
def ext_typecheck_decl_incomplete_type : Extension<
"tentative definition of variable with internal linkage has incomplete "
"%select{non-array|array}0 type %1">,
InGroup<DiagGroup<"tentative-definition-incomplete-type">>;
def err_tentative_def_incomplete_type : Error<
"tentative definition has type %0 that is never completed">;
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6 changes: 4 additions & 2 deletions clang/lib/Sema/SemaDecl.cpp
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Expand Up @@ -14246,7 +14246,8 @@ void Sema::ActOnUninitializedDecl(Decl *RealDecl) {
Var->getLocation(), ArrayT->getElementType(),
diag::err_array_incomplete_or_sizeless_type))
Var->setInvalidDecl();
} else if (Var->getStorageClass() == SC_Static) {
}
if (Var->getStorageClass() == SC_Static) {
// C99 6.9.2p3: If the declaration of an identifier for an object is
// a tentative definition and has internal linkage (C99 6.2.2p3), the
// declared type shall not be an incomplete type.
Expand All @@ -14258,7 +14259,8 @@ void Sema::ActOnUninitializedDecl(Decl *RealDecl) {
// NOTE: to avoid multiple warnings, only check the first declaration.
if (Var->isFirstDecl())
RequireCompleteType(Var->getLocation(), Type,
diag::ext_typecheck_decl_incomplete_type);
diag::ext_typecheck_decl_incomplete_type,
Type->isArrayType());
}
}

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4 changes: 3 additions & 1 deletion clang/test/C/drs/dr0xx.c
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Expand Up @@ -139,7 +139,9 @@ int dr010_c = sizeof(dr010_t); /* expected-error {{invalid application of 'sizeo
* Note: DR034 has a question resolved by DR011 and another question where the
* result is UB.
*/
static int dr011_a[]; /* expected-warning {{tentative array definition assumed to have one element}} */
static int dr011_a[]; /* expected-warning {{tentative array definition assumed to have one element}}
expected-warning {{tentative definition of variable with internal linkage has incomplete array type 'int[]'}}
*/
void dr011(void) {
extern int i[];
{
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5 changes: 2 additions & 3 deletions clang/test/Sema/incomplete-decl.c
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Expand Up @@ -3,16 +3,15 @@



struct foo; // c-note 5 {{forward declaration of 'struct foo'}} \
struct foo; // c-note 4 {{forward declaration of 'struct foo'}} \
cxx-note 3 {{forward declaration of 'foo'}}

void b; // expected-error {{variable has incomplete type 'void'}}
struct foo f; // c-error {{tentative definition has type 'struct foo' that is never completed}} \
cxx-error {{variable has incomplete type 'struct foo'}}

static void c; // expected-error {{variable has incomplete type 'void'}}
static struct foo g; // c-warning {{tentative definition of variable with internal linkage has incomplete non-array type 'struct foo'}} \
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Why did this one disappear?

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Because the diagnostic went from ExtWarn to Extension so it's no longer emitted by default. There's nothing dangerous about the tentative definition by itself, and we give other diagnostics in cases where it is an issue (tentative definition has type 'struct foo' that is never completed or tentative array definition assumed to have one element).

c-error {{tentative definition has type 'struct foo' that is never completed}} \
static struct foo g; // c-error {{tentative definition has type 'struct foo' that is never completed}} \
cxx-error {{variable has incomplete type 'struct foo'}}

extern void d; // cxx-error {{variable has incomplete type 'void'}}
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4 changes: 2 additions & 2 deletions clang/test/Sema/tentative-decls.c
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@@ -1,4 +1,4 @@
// RUN: %clang_cc1 %s -fsyntax-only -Wprivate-extern -verify
// RUN: %clang_cc1 %s -fsyntax-only -Wprivate-extern -pedantic -verify

// PR3310
struct a x1; // expected-note 2{{forward declaration of 'struct a'}}
Expand Down Expand Up @@ -58,7 +58,7 @@ void func2(void)
extern double *p;
}

static int a0[];
static int a0[]; // expected-warning {{tentative definition of variable with internal linkage has incomplete array type 'int[]'}}
static int b0;

static int a0[] = { 4 };
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