5030928d60
initializers.
This has some interesting interactions with our existing extensions to
support C99 designated initializers as an extension in C++. Those are
resolved as follows:
* We continue to permit the full breadth of C99 designated initializers
in C++, with the exception that we disallow a partial overwrite of an
initializer with a non-trivially-destructible type. (Full overwrite
is OK, because we won't run the first initializer at all.)
* The C99 extensions are disallowed in SFINAE contexts and during
overload resolution, where they could change the meaning of valid
programs.
* C++20 disallows reordering of initializers. We only check for that for
the simple cases that the C++20 rules permit (designators of the form
'.field_name =' and continue to allow reordering in other cases).
It would be nice to improve this behavior in future.
* All C99 designated initializer extensions produce a warning by
default in C++20 mode. People are going to learn the C++ rules based
on what Clang diagnoses, so it's important we diagnose these properly
by default.
* In C++ <= 17, we apply the C++20 rules rather than the C99 rules, and
so still diagnose C99 extensions as described above. We continue to
accept designated C++20-compatible initializers in C++ <= 17 silently
by default (but naturally still reject under -pedantic-errors).
This is not a complete implementation of P0329R4. In particular, that
paper introduces new non-C99-compatible syntax { .field { init } }, and
we do not support that yet.
This is based on a previous patch by Don Hinton, though I've made
substantial changes when addressing the above interactions.
Differential Revision: https://reviews.llvm.org/D59754
llvm-svn: 370544
47 lines
1.2 KiB
C++
47 lines
1.2 KiB
C++
// RUN: %clang_cc1 -pedantic -std=c++1y -include %s -include %s -verify %s
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// RUN: %clang_cc1 -pedantic -std=c++1y -emit-pch -o %t.1 %s
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// RUN: %clang_cc1 -pedantic -std=c++1y -include-pch %t.1 -emit-pch -o %t.2 %s
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// RUN: %clang_cc1 -pedantic -std=c++1y -include-pch %t.2 -verify %s
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#ifndef HEADER_1
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#define HEADER_1
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struct A {
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int x;
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int y = 3;
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int z = x + y;
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};
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template<typename T> constexpr A make() { return A {}; }
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template<typename T> constexpr A make(T t) { return A { t }; }
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struct B {
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int z1, z2 = z1;
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constexpr B(int k) : z1(k) {}
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};
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template<typename T> struct C {
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constexpr C() {}
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T c = T();
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struct U {};
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};
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// Instantiate C<int> but not the default initializer.
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C<int>::U ciu;
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#elif !defined(HEADER_2)
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#define HEADER_2
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// Instantiate the default initializer now, should create an update record.
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C<int> ci;
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#else
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static_assert(A{}.z == 3, "");
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static_assert(A{1}.z == 4, "");
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static_assert(A{.y = 5}.z == 5, ""); // expected-warning {{C++20}}
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static_assert(A{3, .y = 1}.z == 4, ""); // expected-warning {{C99}} expected-note {{here}}
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static_assert(make<int>().z == 3, "");
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static_assert(make<int>(12).z == 15, "");
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static_assert(C<int>().c == 0, "");
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#endif
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