[Clang] Partial implementation of support for P3074 (trivial unions) #146815
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| Original file line number | Diff line number | Diff line change |
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| // RUN: %clang_cc1 -verify -std=c++26 %s -Wno-defaulted-function-deleted -triple x86_64-linux-gnu | ||
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| struct NonTrivial { | ||
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| int i; | ||
| constexpr NonTrivial(int i) :i(i) { } | ||
| constexpr ~NonTrivial() { } | ||
| }; | ||
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| union U0 { | ||
| NonTrivial nt; | ||
| int i; | ||
| }; | ||
| U0 u0; | ||
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| // check for constant evaluation failure | ||
| constexpr NonTrivial make() { | ||
| U0 u0; | ||
| return u0.nt; | ||
| } | ||
| constexpr NonTrivial nt = make(); // expected-error {{must be initialized by a constant expression}}} | ||
| // expected-note@-3 {{union with no active member}} | ||
| // expected-note@-4 {{in call to 'NonTrivial(u0.nt)'}} | ||
| // expected-note@-3 {{in call to 'make()'}} | ||
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| // overload resolution to select a constructor to default-initialize an object of type X either fails | ||
| union U1 { | ||
| U1(int); | ||
| NonTrivial nt; // #1 | ||
| }; | ||
| U1 u1(1); // expected-error {{deleted function}} expected-note@#1 {{non-trivial destructor}} | ||
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| // or selects a constructor that is either deleted or not trivial, or | ||
| union U2 { | ||
| U2() : nt(2) { } | ||
| NonTrivial nt; // #2 | ||
| }; | ||
| U2 u2; // expected-error {{deleted function}} expected-note@#2 {{non-trivial destructor}} | ||
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| union U3 { | ||
| U3() = delete; | ||
| U3(int); | ||
| NonTrivial nt; // #3 | ||
| }; | ||
| U3 u3(1); // expected-error {{deleted function}} expected-note@#3 {{non-trivial destructor}} | ||
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| // or X has a variant member V of class type M (or possibly multi-dimensional array thereof) where V has a default member initializer and M has a destructor that is non-trivial, | ||
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| union U4 { | ||
| NonTrivial nt = 1; // #4 | ||
| }; | ||
| U4 u4; // expected-error {{deleted function}} expected-note@#4 {{non-trivial destructor}} | ||
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| union U5 { | ||
| NonTrivial nt; | ||
| U5* next = nullptr; | ||
| }; | ||
| U5 u5; | ||
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| union U6 { | ||
| U6() = default; | ||
| NonTrivial nt; | ||
| U6* next = nullptr; | ||
| }; | ||
| U6 u6; | ||
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| struct DeletedDtor { | ||
| ~DeletedDtor() = delete; // expected-note 2 {{deleted here}} | ||
| }; | ||
| union B1 { | ||
| B1(); | ||
| DeletedDtor a; // expected-note {{because field 'a' has a deleted destructor}} | ||
| }; | ||
| B1 b1; // expected-error {{deleted function}} | ||
| union B2 { | ||
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Member
There was a problem hiding this comment. Some more cases: union A {
struct {
NonTrivial x; // W/ and w/o a default member initialiser.
};
};
A a;
struct B {
union {
NonTrivial x; // as above
};
};
B b;
union {
struct {
union {
struct {
union {
NonTrivial x; // as above
};
};
};
};
} c;
struct {
union {
struct {
union {
struct {
NonTrivial x; // as above
};
};
};
};
} d;
Contributor
Author
There was a problem hiding this comment. Alright I'm not handling this case correctly, but I can't figure out why: union U9 {
struct {
NonTrivial x = 1; // #6
};
} u9; // expected-error {{deleted function}}
Member
There was a problem hiding this comment. Hmm, at a glance nothing jumps out to me; we do create a I did spot a fixme about anonymous unions inside anonymous unions, so er, here’s another gross test case I suppose: union {
union {
NonTrivial x;
};
} a; |
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| B2(); | ||
| union { // expected-note {{deleted destructor}} | ||
| DeletedDtor a; // expected-note {{because field 'a' has a deleted destructor}} | ||
| }; | ||
| }; | ||
| B2 b2; // expected-error {{deleted function}} | ||
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nit (we typically don’t use top-level const for local vars)
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Why not? I see a lot of them btw.
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I thought it was in our coding standards because I’m used to people pointing this out all the time but https://llvm.org/docs/CodingStandards.html doesn’t seem to have anything to say about it.