[Sema] Put existing warning under -Wexcess-initializers

[rsandifo-arm]

Summary

I have a follow-on patch that uses an alternative wording for
this warning in some cases. This patch puts it under its own
-W option in order to avoid a regression in Misc/warning-flags.c.

[efriedma]

Should we stick ext_excess_initializers_in_char_array_initializer and ext_initializer_string_for_char_array_too_long in the same warning group?

[rsandifo-arm]

Put two other related warnings under the new option

[rsandifo-arm]

In D79244#2019027, @efriedma wrote:

Should we stick ext_excess_initializers_in_char_array_initializer and ext_initializer_string_for_char_array_too_long in the same warning group?

Yeah, agree that would be better. Done in v2.

[efriedma]

LGTM

clang/docs/DiagnosticsReference.rst

 |:warning:`warning:` |nbsp| :diagtext:`exception of type` |nbsp| :placeholder:`A` |nbsp| :diagtext:`will be caught by earlier handler`|
 +-------------------------------------------------------------------------------------------------------------------------------------+
 
 +-----------------------------------------------------------------------------------------------------------------------------+
 |:warning:`warning:` |nbsp| :placeholder:`A` |nbsp| :diagtext:`has a non-throwing exception specification but can still throw`|
 +-----------------------------------------------------------------------------------------------------------------------------+
 
 
+-Wexcess-initializers
+---------------------
+This diagnostic is enabled by default.
+
+**Diagnostic text:**
+
++-----------------------------------------------------------------+--------------------+-------------------------------+
+|:warning:`warning:` |nbsp| :diagtext:`excess elements in` |nbsp| |+------------------+| |nbsp| :diagtext:`initializer`|
+|                                                                 ||:diagtext:`array` ||                               |
+|                                                                 |+------------------+|                               |
+|                                                                 ||:diagtext:`vector`||                               |
+|                                                                 |+------------------+|                               |
+|                                                                 ||:diagtext:`scalar`||                               |
+|                                                                 |+------------------+|                               |
+|                                                                 ||:diagtext:`union` ||                               |
+|                                                                 |+------------------+|                               |
+|                                                                 ||:diagtext:`struct`||                               |
+|                                                                 |+------------------+|                               |
++-----------------------------------------------------------------+--------------------+-------------------------------+
+
+
 -Wexit-time-destructors
 -----------------------
 **Diagnostic text:**
 
 +-----------------------------------------------------------------------------------+
 |:warning:`warning:` |nbsp| :diagtext:`declaration requires an exit-time destructor`|
 +-----------------------------------------------------------------------------------+
 

clang/include/clang/Basic/DiagnosticSemaKinds.td

def err_block_extern_cant_init : Error<
   "'extern' variable cannot have an initializer">;
 def warn_extern_init : Warning<"'extern' variable has an initializer">,
   InGroup<DiagGroup<"extern-initializer">>;
 def err_variable_object_no_init : Error<
   "variable-sized object may not be initialized">;
 def err_excess_initializers : Error<
   "excess elements in %select{array|vector|scalar|union|struct}0 initializer">;
 def ext_excess_initializers : ExtWarn<
-  "excess elements in %select{array|vector|scalar|union|struct}0 initializer">;
+  "excess elements in %select{array|vector|scalar|union|struct}0 initializer">,
+  InGroup<DiagGroup<"excess-initializers">>;
 def err_excess_initializers_in_char_array_initializer : Error<
   "excess elements in char array initializer">;
 def ext_excess_initializers_in_char_array_initializer : ExtWarn<
   "excess elements in char array initializer">;
 def err_initializer_string_for_char_array_too_long : Error<
   "initializer-string for char array is too long">;
 def ext_initializer_string_for_char_array_too_long : ExtWarn<
   "initializer-string for char array is too long">;

clang/test/Misc/warning-flags.c

 RUN: diagtool list-warnings > %t 2>&1
 RUN: FileCheck --input-file=%t %s
 
 This test serves two purposes:
 
 (1) It documents all existing warnings that currently have no associated -W flag,
     and ensures that the list never grows.
 
     If you take an existing warning and add a flag, this test will fail.
     To fix this test, simply remove that warning from the list below.
 
 (2) It prevents us adding new warnings to Clang that have no -W flag.  All
     new warnings should have -W flags.
 
     If you add a new warning without a flag, this test will fail.  To fix
     this test, simply add a warning group to that warning.
 
 
 The list of warnings below should NEVER grow.  It should gradually shrink to 0.
 
-CHECK: Warnings without flags (75):
-CHECK-NEXT:   ext_excess_initializers
+CHECK: Warnings without flags (74):
 CHECK-NEXT:   ext_excess_initializers_in_char_array_initializer
 CHECK-NEXT:   ext_expected_semi_decl_list
 CHECK-NEXT:   ext_explicit_specialization_storage_class
 CHECK-NEXT:   ext_initializer_string_for_char_array_too_long
 CHECK-NEXT:   ext_missing_declspec
 CHECK-NEXT:   ext_missing_whitespace_after_macro_name
 CHECK-NEXT:   ext_new_paren_array_nonconst
 CHECK-NEXT:   ext_plain_complex

 CHECK-NEXT:   warn_tentative_incomplete_array
 CHECK-NEXT:   warn_typecheck_function_qualifiers
 CHECK-NEXT:   warn_undef_interface
 CHECK-NEXT:   warn_undef_interface_suggest
 CHECK-NEXT:   warn_undef_protocolref
 CHECK-NEXT:   warn_weak_identifier_undeclared
 CHECK-NEXT:   warn_weak_import
 
 The list of warnings in -Wpedantic should NEVER grow.
 
 CHECK: Number in -Wpedantic (not covered by other -W flags): 27

clang/test/Sema/init.c

struct foo2 {
    uintptr_t a;
 };
 
 struct foo2 bar2[] = {
    { (intptr_t)bbb }
 };
 
 struct foo2 bar3 = { 1, 2 }; // expected-warning{{excess elements in struct initializer}}
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wexcess-initializers"
+struct foo2 bar3_silent = { 1, 2 };
+#pragma clang diagnostic pop
 
 int* ptest1 = __builtin_choose_expr(1, (int*)0, (int*)0);
 
 typedef int32_t ivector4 __attribute((vector_size(16)));
 ivector4 vtest1 = 1 ? (ivector4){1} : (ivector4){1};
 ivector4 vtest2 = __builtin_choose_expr(1, (ivector4){1}, (ivector4){1});
 
 uintptr_t ptrasintadd1 = (uintptr_t)&a - 4;