[Sema] Diagnose default-initialization, destruction, and copying of

non-trivial C union types

This recommits r365985, which was reverted because it broke a few
projects using unions containing non-trivial ObjC pointer fields in
system headers. We now have a patch to fix the problem (see
https://reviews.llvm.org/D65256).

Original commit message:

This patch diagnoses uses of non-trivial C unions and structs/unions
containing non-trivial C unions in the following contexts, which require
default-initialization, destruction, or copying of the union objects,
instead of disallowing fields of non-trivial types in C unions, which is
what we currently do:

- function parameters.
- function returns.
- assignments.
- compound literals.
- block captures except capturing of `__block` variables by non-escaping blocks.
- local and global variable definitions.
- lvalue-to-rvalue conversions of volatile types.

See the discussion in https://reviews.llvm.org/D62988 for more background.

rdar://problem/50679094

Differential Revision: https://reviews.llvm.org/D63753

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@371275 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 83 insertions, 5 deletions

diff --git a/test/SemaObjC/arc-decls.m b/test/SemaObjC/arc-decls.m
index 0abd45dac3..28c3de9969 100644
--- a/test/SemaObjC/arc-decls.m
+++ b/test/SemaObjC/arc-decls.m
@@ -8,11 +8,7 @@ struct A {
 };
 
 union u {
-    id u; // expected-error {{ARC forbids Objective-C objects in union}}
-};
-
-union u_nontrivial_c {
-  struct A a; // expected-error {{non-trivial C types are disallowed in union}}
+  id u;
 };
 
 // Volatile fields are fine.
diff --git a/test/SemaObjC/non-trivial-c-union.m b/test/SemaObjC/non-trivial-c-union.m
new file mode 100644
index 0000000000..7bd8277545
--- /dev/null
+++ b/test/SemaObjC/non-trivial-c-union.m
@@ -0,0 +1,82 @@
+// RUN: %clang_cc1 -fsyntax-only -fblocks -fobjc-arc -fobjc-runtime-has-weak -verify %s
+
+typedef union { // expected-note 12 {{'U0' has subobjects that are non-trivial to default-initialize}} expected-note 36 {{'U0' has subobjects that are non-trivial to destruct}} expected-note 28 {{'U0' has subobjects that are non-trivial to copy}}
+  id f0; // expected-note 12 {{f0 has type '__strong id' that is non-trivial to default-initialize}} expected-note 36 {{f0 has type '__strong id' that is non-trivial to destruct}} expected-note 28 {{f0 has type '__strong id' that is non-trivial to copy}}
+  __weak id f1; // expected-note 12 {{f1 has type '__weak id' that is non-trivial to default-initialize}} expected-note 36 {{f1 has type '__weak id' that is non-trivial to destruct}} expected-note 28 {{f1 has type '__weak id' that is non-trivial to copy}}
+} U0;
+
+typedef struct {
+  U0 f0;
+  id f1;
+} S0;
+
+id g0;
+U0 ug0; // expected-error {{cannot default-initialize an object of type 'U0' since it is a union that is non-trivial to default-initialize}}
+U0 ug1 = { .f0 = 0 };
+S0 sg0; // expected-error {{cannot default-initialize an object of type 'S0' since it contains a union that is non-trivial to default-initialize}}
+S0 sg1 = { .f0 = {0}, .f1 = 0 };
+S0 sg2 = { .f1 = 0 }; // expected-error {{cannot default-initialize an object of type 'U0' since it is a union that is non-trivial to default-initialize}}
+
+U0 foo0(U0); // expected-error {{cannot use type 'U0' for a function/method parameter since it is a union that is non-trivial to destruct}} expected-error {{cannot use type 'U0' for a function/method parameter since it is a union that is non-trivial to copy}} expected-error {{cannot use type 'U0' for function/method return since it is a union that is non-trivial to destruct}} expected-error {{cannot use type 'U0' for function/method return since it is a union that is non-trivial to copy}}
+S0 foo1(S0); // expected-error {{cannot use type 'S0' for a function/method parameter since it contains a union that is non-trivial to destruct}} expected-error {{cannot use type 'S0' for a function/method parameter since it contains a union that is non-trivial to copy}} expected-error {{cannot use type 'S0' for function/method return since it contains a union that is non-trivial to destruct}} expected-error {{cannot use type 'S0' for function/method return since it contains a union that is non-trivial to copy}}
+
+@interface C
+-(U0)m0:(U0)arg; // expected-error {{cannot use type 'U0' for a function/method parameter since it is a union that is non-trivial to destruct}} expected-error {{cannot use type 'U0' for a function/method parameter since it is a union that is non-trivial to copy}} expected-error {{cannot use type 'U0' for function/method return since it is a union that is non-trivial to destruct}} expected-error {{cannot use type 'U0' for function/method return since it is a union that is non-trivial to copy}}
+-(S0)m1:(S0)arg; // expected-error {{cannot use type 'S0' for a function/method parameter since it contains a union that is non-trivial to destruct}} expected-error {{cannot use type 'S0' for a function/method parameter since it contains a union that is non-trivial to copy}} expected-error {{cannot use type 'S0' for function/method return since it contains a union that is non-trivial to destruct}} expected-error {{cannot use type 'S0' for function/method return since it contains a union that is non-trivial to copy}}
+@end
+
+void testBlockFunction(void) {
+  (void)^(U0 a){ return ug0; }; // expected-error {{cannot use type 'U0' for a function/method parameter since it is a union that is non-trivial to destruct}} expected-error {{cannot use type 'U0' for a function/method parameter since it is a union that is non-trivial to copy}} expected-error {{cannot use type 'U0' for function/method return since it is a union that is non-trivial to destruct}} expected-error {{cannot use type 'U0' for function/method return since it is a union that is non-trivial to copy}}
+  (void)^(S0 a){ return sg0; }; // expected-error {{cannot use type 'S0' for a function/method parameter since it contains a union that is non-trivial to destruct}} expected-error {{cannot use type 'S0' for a function/method parameter since it contains a union that is non-trivial to copy}} expected-error {{cannot use type 'S0' for function/method return since it contains a union that is non-trivial to destruct}} expected-error {{cannot use type 'S0' for function/method return since it contains a union that is non-trivial to copy}}
+}
+void testAutoVar(void) {
+  U0 u0; // expected-error {{cannot declare an automatic variable of type 'U0' since it is a union that is non-trivial to destruct}} expected-error {{cannot default-initialize an object of type 'U0' since it is a union that is non-trivial to default-initialize}}
+  U0 u1 = ug0; // expected-error {{cannot declare an automatic variable of type 'U0' since it is a union that is non-trivial to destruct}} expected-error {{cannot copy-initialize an object of type 'U0' since it is a union that is non-trivial to copy}}
+  U0 u2 = { g0 }; // expected-error {{cannot declare an automatic variable of type 'U0' since it is a union that is non-trivial to destruct}}
+  U0 u3 = { .f1 = g0 }; // expected-error {{cannot declare an automatic variable of type 'U0' since it is a union that is non-trivial to destruct}}
+  S0 s0; // expected-error {{cannot declare an automatic variable of type 'S0' since it contains a union that is non-trivial to destruct}} expected-error {{cannot default-initialize an object of type 'S0' since it contains a union that is non-trivial to default-initialize}}
+  S0 s1 = sg0; // expected-error {{declare an automatic variable of type 'S0' since it contains a union that is non-trivial to destruct}} expected-error {{cannot copy-initialize an object of type 'S0' since it contains a union that is non-trivial to copy}}
+  S0 s2 = { ug0 }; // expected-error {{cannot declare an automatic variable of type 'S0' since it contains a union that is non-trivial to destruct}} expected-error {{cannot copy-initialize an object of type 'U0' since it is a union that is non-trivial to copy}}
+  S0 s3 = { .f0 = ug0 }; // expected-error {{cannot declare an automatic variable of type 'S0' since it contains a union that is non-trivial to destruct}} expected-error {{cannot copy-initialize an object of type 'U0' since it is a union that is non-trivial to copy}}
+  S0 s4 = { .f1 = g0 }; // expected-error {{cannot declare an automatic variable of type 'S0' since it contains a union that is non-trivial to destruct}} expected-error {{cannot default-initialize an object of type 'U0' since it is a union that is non-trivial to default-initialize}}
+}
+
+void testAssignment(void) {
+  ug0 = ug1; // expected-error {{cannot assign to a variable of type 'U0' since it is a union that is non-trivial to copy}}
+  sg0 = sg1; // expected-error {{cannot assign to a variable of type 'S0' since it contains a union that is non-trivial to copy}}
+}
+
+U0 ug2 = (U0){ .f1 = 0 }; // expected-error {{cannot copy-initialize an object of type 'U0' since it is a union that is non-trivial to copy}}
+S0 sg3 = (S0){ .f0 = {0}, .f1 = 0 }; // expected-error {{cannot copy-initialize an object of type 'S0' since it contains a union that is non-trivial to copy}}
+S0 *sg4 = &(S0){ .f1 = 0 }; // expected-error {{cannot default-initialize an object of type 'U0' since it is a union that is non-trivial to default-initialize}}
+
+void testCompoundLiteral(void) {
+  const U0 *t0 = &(U0){ .f0 = g0 }; // expected-error {{cannot construct an automatic compound literal of type 'U0' since it is a union that is non-trivial to destruct}}
+  const U0 *t1 = &(U0){ .f1 = g0 }; // expected-error {{cannot construct an automatic compound literal of type 'U0' since it is a union that is non-trivial to destruct}}
+  const S0 *t2 = &(S0){ .f0 = ug0 }; // expected-error {{cannot construct an automatic compound literal of type 'S0' since it contains a union that is non-trivial to destruct}} expected-error {{cannot copy-initialize an object of type 'U0' since it is a union that is non-trivial to copy}}
+  const S0 *t3 = &(S0){ .f1 = g0 }; // expected-error {{cannot construct an automatic compound literal of type 'S0' since it contains a union that is non-trivial to destruct}} expected-error {{cannot default-initialize an object of type 'U0' since it is a union that is non-trivial to default-initialize}}
+}
+
+typedef void (^BlockTy)(void);
+void escapingFunc(BlockTy);
+void noescapingFunc(__attribute__((noescape)) BlockTy);
+
+void testBlockCapture(void) {
+  U0 t0; // expected-error {{cannot declare an automatic variable of type 'U0' since it is a union that is non-trivial to destruct}} expected-error {{cannot default-initialize an object of type 'U0' since it is a union that is non-trivial to default-initialize}}
+  S0 t1; // expected-error {{cannot declare an automatic variable of type 'S0' since it contains a union that is non-trivial to destruct}} expected-error {{cannot default-initialize an object of type 'S0' since it contains a union that is non-trivial to default-initialize}}
+  __block U0 t2; // expected-error {{cannot declare an automatic variable of type 'U0' since it is a union that is non-trivial to destruct}} expected-error {{cannot default-initialize an object of type 'U0' since it is a union that is non-trivial to default-initialize}}
+  __block S0 t3; // expected-error {{cannot declare an automatic variable of type 'S0' since it contains a union that is non-trivial to destruct}} expected-error {{cannot default-initialize an object of type 'S0' since it contains a union that is non-trivial to default-initialize}}
+
+  escapingFunc(^{ g0 = t0.f0; }); // expected-error {{cannot capture a variable of type 'U0' since it is a union that is non-trivial to destruct}} expected-error {{cannot capture a variable of type 'U0' since it is a union that is non-trivial to copy}}
+  escapingFunc(^{ g0 = t1.f0.f0; }); // expected-error {{cannot capture a variable of type 'S0' since it contains a union that is non-trivial to destruct}} expected-error {{cannot capture a variable of type 'S0' since it contains a union that is non-trivial to copy}}
+  escapingFunc(^{ g0 = t2.f0; }); // expected-error {{cannot capture a variable of type 'U0' since it is a union that is non-trivial to destruct}} expected-error {{cannot capture a variable of type 'U0' since it is a union that is non-trivial to copy}}
+  escapingFunc(^{ g0 = t3.f0.f0; }); // expected-error {{cannot capture a variable of type 'S0' since it contains a union that is non-trivial to destruct}} expected-error {{cannot capture a variable of type 'S0' since it contains a union that is non-trivial to copy}}
+  noescapingFunc(^{ g0 = t0.f0; }); // expected-error {{cannot capture a variable of type 'U0' since it is a union that is non-trivial to destruct}} expected-error {{cannot capture a variable of type 'U0' since it is a union that is non-trivial to copy}}
+  noescapingFunc(^{ g0 = t1.f0.f0; }); // expected-error {{cannot capture a variable of type 'S0' since it contains a union that is non-trivial to destruct}} expected-error {{cannot capture a variable of type 'S0' since it contains a union that is non-trivial to copy}}
+  noescapingFunc(^{ g0 = t2.f0; });
+  noescapingFunc(^{ g0 = t3.f0.f0; });
+}
+
+void testVolatileLValueToRValue(volatile U0 *a) {
+  (void)*a; // expected-error {{cannot use volatile type 'volatile U0' where it causes an lvalue-to-rvalue conversion since it is a union that is non-trivial to destruct}} // expected-error {{cannot use volatile type 'volatile U0' where it causes an lvalue-to-rvalue conversion since it is a union that is non-trivial to copy}}
+}