[clang] [Clang] Implement diagnostics for why is_empty is false (PR #145044)

[Aaron Ballman via cfe-commits]

================
@@ -488,3 +488,61 @@ static_assert(__is_trivially_copyable(S12));
 // expected-note at -1 {{'S12' is not trivially copyable}} \
 // expected-note@#tc-S12 {{'S12' defined here}}
 }
+
+namespace is_empty_tests {
+    // Non-static data member.
+    struct A { int x; }; // #e-A
+    static_assert(__is_empty(A));
+    // expected-error at -1 {{static assertion failed due to requirement '__is_empty(is_empty_tests::A)'}} \
+    // expected-note at -1 {{'A' is not empty}} \
+    // expected-note at -1 {{because it has a non-static data member 'x' of type 'int'}} \
+    // expected-note@#e-A {{'A' defined here}}
+
+    // Reference member.
+    struct R {int &r; }; // #e-R
+    static_assert(__is_empty(R));
+    // expected-error at -1 {{static assertion failed due to requirement '__is_empty(is_empty_tests::R)'}} \
+    // expected-note at -1 {{'R' is not empty}} \
+    // expected-note at -1 {{because it has a non-static data member 'r' of type 'int &'}} \
+    // expected-note@#e-R {{'R' defined here}}
+
+    // Virtual function.
+    struct VirtualFunc {virtual void f(); }; // #e-VirtualFunc
+    static_assert(__is_empty(VirtualFunc));
+    // expected-error at -1 {{static assertion failed due to requirement '__is_empty(is_empty_tests::VirtualFunc)'}} \
+    // expected-note at -1 {{'VirtualFunc' is not empty}} \
+    // expected-note at -1 {{because it has a virtual function 'f'}} \
+    // expected-note@#e-VirtualFunc {{'VirtualFunc' defined here}}
+
+    // Virtual base class.
+    struct EB {};
+    struct VB: virtual EB {}; // #e-VB
+    static_assert(__is_empty(VB));
+    // expected-error at -1 {{static assertion failed due to requirement '__is_empty(is_empty_tests::VB)'}} \
+    // expected-note at -1 {{'VB' is not empty}} \
+    // expected-note at -1 {{because it has a virtual base class 'EB'}} \
+    // expected-note@#e-VB {{'VB' defined here}}
+
+    // Non-empty base class.
+    struct Base { int b; }; // #e-Base
+    struct Derived : Base {}; // #e-Derived
+    static_assert(__is_empty(Derived));
+    // expected-error at -1 {{static assertion failed due to requirement '__is_empty(is_empty_tests::Derived)'}} \
+    // expected-note at -1 {{'Derived' is not empty}} \
+    // expected-note at -1 {{because it has a base class 'Base' that is not empty}} \
+    // expected-note@#e-Derived {{'Derived' defined here}} 
+
+    // Combination of the above.
+    struct Multi : Base, virtual EB { // #e-Multi
+        int z;
+        virtual void g();
+    };
+    static_assert(__is_empty(Multi));
+    // expected-error at -1 {{static assertion failed due to requirement '__is_empty(is_empty_tests::Multi)'}} \
+    // expected-note at -1 {{'Multi' is not empty}} \
+    // expected-note at -1 {{because it has a non-static data member 'z' of type 'int'}} \
+    // expected-note at -1 {{because it has a virtual function 'g'}} \
+    // expected-note at -1 {{because it has a base class 'Base' that is not empty}} \
+    // expected-note at -1 {{because it has a virtual base class 'EB'}} \
+    // expected-note@#e-Multi {{'Multi' defined here}}
----------------
AaronBallman wrote:

Also missing test coverage for (zero-width) bit-fields.



https://github.com/llvm/llvm-project/pull/145044