[clang] [clang][C23] N3006 Underspecified object declarations (PR #79845)
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Mon Jan 29 07:07:31 PST 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang
Author: Guillot Tony (to268)
<details>
<summary>Changes</summary>
The N3006 Underspecified object declarations paper describes that underspecified declarations should be diagnosed as an error.
Example snippet:
```c
struct S1 { int x, y; };
union U1 { int a; double b; };
enum E1 { FOO, BAR };
auto valid_struct = (struct S1){ 1, 2 };
auto underspecified_struct = (struct S2 { int x, y; }){ 1, 2 }; // Error
auto valid_union = (union U1){ .a = 12 };
auto underspecified_union = (union U2 { int a; double b; }){ .a = 34 }; // Error
auto valid_enum = (enum E1){ FOO };
auto underspecified_enum = (enum E2 { BAZ, QUX }){ BAZ }; // Error
```
---
Full diff: https://github.com/llvm/llvm-project/pull/79845.diff
6 Files Affected:
- (modified) clang/docs/ReleaseNotes.rst (+3)
- (modified) clang/include/clang/Basic/DiagnosticSemaKinds.td (+2)
- (modified) clang/lib/Sema/SemaExpr.cpp (+27)
- (added) clang/test/C/C2x/n3006.c (+27)
- (added) clang/test/Parser/c2x-underspecified-decls.c (+12)
- (modified) clang/www/c_status.html (+1-1)
``````````diff
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 254e0a9cb72979..65885968204a64 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -83,6 +83,9 @@ C Language Changes
C23 Feature Support
^^^^^^^^^^^^^^^^^^^
+- Clang now diagnoses `N3006 Underspecified object declarations
+ <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3006.htm>`_.
+
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 24d32cb87c89e2..8508208a3acedd 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -7639,6 +7639,8 @@ def err_attribute_arm_mve_polymorphism : Error<
"'__clang_arm_mve_strict_polymorphism' attribute can only be applied to an MVE/NEON vector type">;
def err_attribute_webassembly_funcref : Error<
"'__funcref' attribute can only be applied to a function pointer type">;
+def err_c23_underspecified_object_declaration: Error<
+ "'%select{struct|<ERROR>|union|<ERROR>|enum}0 %1' is defined as an underspecified object initializer">;
def warn_setter_getter_impl_required : Warning<
"property %0 requires method %1 to be defined - "
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 2f1ddfb215116d..8166748c38e6e9 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -7805,6 +7805,33 @@ Sema::BuildCompoundLiteralExpr(SourceLocation LParenLoc, TypeSourceInfo *TInfo,
diag::err_variable_object_no_init))
return ExprError();
}
+ } else if (LangOpts.C23 &&
+ (literalType->isRecordType() || literalType->isEnumeralType())) {
+ // C23 6.2.1p7: Structure, union, and enumeration tags have scope that
+ // begins just after the appearance of the tag in a type specifier that
+ // declares the tag.
+ // [...]
+ // An ordinary identifier that has an underspecified definition has scope
+ // that starts when the definition is completed; if the same ordinary
+ // identifier declares another entity with a scope that encloses the current
+ // block, that declaration is hidden as soon as the inner declarator is
+ // completed*.)
+ // [...]
+ // *) That means, that the outer declaration is not visible for the
+ // initializer.
+ auto Range = SourceRange(LParenLoc, RParenLoc);
+ const auto *Tag = literalType->castAs<TagType>();
+ const auto &TagRange = Tag->getDecl()->getSourceRange();
+
+ // We should diagnose underspecified declaration, unless the identifier has
+ // been diagnosed as being a redefinition, since the tag is made anonymous.
+ if (Range.fullyContains(TagRange) && Tag->getDecl()->getIdentifier()) {
+ Diag(TagRange.getBegin(),
+ diag::err_c23_underspecified_object_declaration)
+ << (unsigned)Tag->getDecl()->getTagKind()
+ << Tag->getDecl()->getName() << TagRange;
+ return ExprError();
+ }
} else if (!literalType->isDependentType() &&
RequireCompleteType(LParenLoc, literalType,
diag::err_typecheck_decl_incomplete_type,
diff --git a/clang/test/C/C2x/n3006.c b/clang/test/C/C2x/n3006.c
new file mode 100644
index 00000000000000..15efc0ccd6d323
--- /dev/null
+++ b/clang/test/C/C2x/n3006.c
@@ -0,0 +1,27 @@
+// RUN: %clang_cc1 -std=c2x -verify %s
+
+/* WG14 N3006: Full
+ * Underspecified object declarations
+ */
+
+struct S1 { int x, y; }; // expected-note {{previous definition is here}}
+union U1 { int a; double b; }; // expected-note {{previous definition is here}}
+enum E1 { FOO, BAR }; // expected-note {{previous definition is here}}
+
+auto normal_struct = (struct S1){ 1, 2 };
+auto underspecified_struct = (struct S2 { int x, y; }){ 1, 2 }; // expected-error {{'struct S2' is defined as an underspecified object initializer}}
+auto underspecified_struct_redef = (struct S1 { char x, y; }){ 'A', 'B'}; // expected-error {{redefinition of 'S1'}}
+auto underspecified_empty_struct = (struct S3 { }){ }; // expected-error {{'struct S3' is defined as an underspecified object initializer}}
+
+auto normal_union_int = (union U1){ .a = 12 };
+auto normal_union_double = (union U1){ .b = 2.4 };
+auto underspecified_union = (union U2 { int a; double b; }){ .a = 34 }; // expected-error {{'union U2' is defined as an underspecified object initializer}}
+auto underspecified_union_redef = (union U1 { char a; double b; }){ .a = 'A' }; // expected-error {{redefinition of 'U1'}}
+auto underspecified_empty_union = (union U3 { }){ }; // expected-error {{'union U3' is defined as an underspecified object initializer}}
+
+auto normal_enum_foo = (enum E1){ FOO };
+auto normal_enum_bar = (enum E1){ BAR };
+auto underspecified_enum = (enum E2 { BAZ, QUX }){ BAZ }; // expected-error {{'enum E2' is defined as an underspecified object initializer}}
+auto underspecified_enum_redef = (enum E1 { ONE, TWO }){ ONE }; // expected-error {{redefinition of 'E1'}}
+auto underspecified_empty_enum = (enum E3 { }){ }; // expected-error {{'enum E3' is defined as an underspecified object initializer}} \
+ expected-error {{use of empty enum}}
diff --git a/clang/test/Parser/c2x-underspecified-decls.c b/clang/test/Parser/c2x-underspecified-decls.c
new file mode 100644
index 00000000000000..5a7e935cda5444
--- /dev/null
+++ b/clang/test/Parser/c2x-underspecified-decls.c
@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -fsyntax-only -verify=expected,c23 -std=c23 %s
+// RUN: %clang_cc1 -fsyntax-only -verify=expected,c17 -std=c17 %s
+
+auto underspecified_struct = (struct S1 { int x, y; }){ 1, 2 }; // c23-error {{'struct S1' is defined as an underspecified object initializer}} \
+ c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}} \
+ c17-error {{illegal storage class on file-scoped variable}}
+auto underspecified_union = (union U1 { int a; double b; }){ .a = 34 }; // c23-error {{'union U1' is defined as an underspecified object initializer}} \
+ c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}} \
+ c17-error {{illegal storage class on file-scoped variable}}
+auto underspecified_enum = (enum E1 { FOO, BAR }){ BAR }; // c23-error {{'enum E1' is defined as an underspecified object initializer}} \
+ c17-error {{type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int}} \
+ c17-error {{illegal storage class on file-scoped variable}}
diff --git a/clang/www/c_status.html b/clang/www/c_status.html
index 3955a1d7963976..fc7d3f5f8ad79c 100644
--- a/clang/www/c_status.html
+++ b/clang/www/c_status.html
@@ -1191,7 +1191,7 @@ <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="none" align="center">No</td>
+ <td class="unreleased" align="center">Clang 19</td>
</tr>
<tr>
<td>Type inference for object declarations</td>
``````````
</details>
https://github.com/llvm/llvm-project/pull/79845
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