[c++20] P1143R2: Add support for the C++20 'constinit' keyword.

This is mostly the same as the
[[clang::require_constant_initialization]] attribute, but has a couple
of additional syntactic and semantic restrictions.

In passing, I added a warning for the attribute form being added after
we have already seen the initialization of the variable (but before we
see the definition); that case previously slipped between the cracks and
the attribute was silently ignored.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@370972 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 69 insertions, 0 deletions

diff --git a/test/CXX/dcl.dcl/dcl.spec/dcl.constinit/p1.cpp b/test/CXX/dcl.dcl/dcl.spec/dcl.constinit/p1.cpp
new file mode 100644
index 0000000000..170c8c7be0
--- /dev/null
+++ b/test/CXX/dcl.dcl/dcl.spec/dcl.constinit/p1.cpp
@@ -0,0 +1,55 @@
+// RUN: %clang_cc1 -std=c++2a -verify %s
+
+constinit int a;
+constinit thread_local int b;
+constinit static int c;
+
+void f() {
+  constinit static int a;
+  constinit thread_local int b;
+  constinit int c; // expected-error {{local variable cannot be declared 'constinit'}}
+}
+
+namespace missing {
+  int a; // expected-note {{add the 'constinit' specifier}}
+  extern constinit int a; // expected-error {{added after initialization}}
+
+  // We allow inheriting 'constinit' from a forward declaration as an extension.
+  extern constinit int b; // expected-note {{here}}
+  int b; // expected-warning {{'constinit' specifier missing}}
+}
+
+struct S {
+  static constinit int a; // expected-note {{here}}
+  static constinit constexpr int b; // expected-error {{cannot combine with previous}} expected-note {{here}}
+  static constinit const int c = 1;
+  static constinit const int d = 1;
+};
+int S::a; // expected-warning {{'constinit' specifier missing}}
+int S::b; // expected-warning {{'constinit' specifier missing}}
+const int S::c;
+inline const int S::d;
+
+struct T {
+  static int a;
+  static constexpr int b = 1; // expected-note {{add the 'constinit' specifier}}
+  static const int c = 1; // expected-note {{add the 'constinit' specifier}}
+  static const int d = 1; // expected-note {{add the 'constinit' specifier}}
+};
+constinit int T::a;
+constinit const int T::b; // expected-error {{'constinit' specifier added after initialization}}
+constinit const int T::c; // expected-error {{'constinit' specifier added after initialization}}
+constinit inline const int T::d; // expected-error {{'constinit' specifier added after initialization}}
+
+constinit void g() {} // expected-error {{constinit can only be used in variable declarations}}
+
+// (These used to trigger crashes.)
+void h();
+constinit void h(); // expected-error {{constinit can only be used in variable declarations}}
+constexpr void i(); // expected-note {{here}}
+constinit void i(); // expected-error {{non-constexpr declaration of 'i' follows constexpr declaration}}
+// expected-error@-1 {{constinit can only be used in variable declarations}} 
+
+typedef constinit int type; // expected-error {{typedef cannot be constinit}}
+using type = constinit int; // expected-error {{type name does not allow constinit specifier}}
+auto q() -> int constinit; // expected-error {{type name does not allow constinit specifier}}
diff --git a/test/CXX/dcl.dcl/dcl.spec/dcl.constinit/p2.cpp b/test/CXX/dcl.dcl/dcl.spec/dcl.constinit/p2.cpp
new file mode 100644
index 0000000000..22ac7a191b
--- /dev/null
+++ b/test/CXX/dcl.dcl/dcl.spec/dcl.constinit/p2.cpp
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -std=c++2a -verify %s
+
+int f(); // expected-note 2{{declared here}}
+
+constinit int a;
+constinit int b = f(); // expected-error {{does not have a constant initializer}} expected-note {{required by}} expected-note {{non-constexpr function 'f'}}
+extern constinit int c; // expected-note {{here}} expected-note {{required by}}
+int c = f(); // expected-warning {{missing}} expected-error {{does not have a constant initializer}} expected-note {{non-constexpr function 'f'}}
diff --git a/test/CXX/dcl.dcl/dcl.spec/dcl.constinit/p3.cpp b/test/CXX/dcl.dcl/dcl.spec/dcl.constinit/p3.cpp
new file mode 100644
index 0000000000..0baea03e4b
--- /dev/null
+++ b/test/CXX/dcl.dcl/dcl.spec/dcl.constinit/p3.cpp
@@ -0,0 +1,6 @@
+// RUN: %clang_cc1 -std=c++2a -verify %s
+
+const char *g() { return "dynamic initialization"; } // expected-note {{declared here}}
+constexpr const char *f(bool b) { return b ? "constant initialization" : g(); } // expected-note {{non-constexpr function 'g'}}
+constinit const char *c = f(true);
+constinit const char *d = f(false); // expected-error {{does not have a constant initializer}} expected-note 2{{}}