[CMake] Set correct flags for clang-cl (#278)

clang-cl produce binaries with MSVC ABI and wants to be as flag-compatible with pure MSVC as possible, so this leads to all sorts of weird cases.

clang-cl alias /Wall as clang's -Weverything which is way too verbose, so it needs /W3 like pure MSVC.
clang-cl only understand GCC style warning flags (-W[no]blah) and just silent drop MSVC style warning flags (/wd[num]).
clang-cl needs MSVC define flags since it is consuming the same header files as pure MSVC.
CMake set CMAKE_CXX_COMPILER_ID as Clang when clang-cl is detected, so need extra if (MSVC) to differentiate it.

We are not doing clang-cl specialization in Bazel as currently there is no reliable way to detect clang-cl in Bazel..

This PR should be NFC for LLVM/GCC users on Unix platforms.

Other changes:

Add ABSL_ prefix to variable names to avoid name collision in CMake.

1 files changed, 90 insertions, 14 deletions

diff --git a/absl/copts/GENERATED_copts.bzl b/absl/copts/GENERATED_copts.bzl
index d23f4069..e05a58e3 100644
--- a/absl/copts/GENERATED_copts.bzl
+++ b/absl/copts/GENERATED_copts.bzl
@@ -4,11 +4,87 @@
 (2) Run `python <path_to_absl>/copts/generate_copts.py`.
 """
 
-GCC_EXCEPTIONS_FLAGS = [
+ABSL_CLANG_CL_EXCEPTIONS_FLAGS = [
+    "/U_HAS_EXCEPTIONS",
+    "/D_HAS_EXCEPTIONS=1",
+    "/EHsc",
+]
+
+ABSL_CLANG_CL_FLAGS = [
+    "/W3",
+    "-Wno-c++98-compat-pedantic",
+    "-Wno-conversion",
+    "-Wno-covered-switch-default",
+    "-Wno-deprecated",
+    "-Wno-disabled-macro-expansion",
+    "-Wno-double-promotion",
+    "-Wno-comma",
+    "-Wno-extra-semi",
+    "-Wno-extra-semi-stmt",
+    "-Wno-packed",
+    "-Wno-padded",
+    "-Wno-sign-compare",
+    "-Wno-float-conversion",
+    "-Wno-float-equal",
+    "-Wno-format-nonliteral",
+    "-Wno-gcc-compat",
+    "-Wno-global-constructors",
+    "-Wno-exit-time-destructors",
+    "-Wno-nested-anon-types",
+    "-Wno-non-modular-include-in-module",
+    "-Wno-old-style-cast",
+    "-Wno-range-loop-analysis",
+    "-Wno-reserved-id-macro",
+    "-Wno-shorten-64-to-32",
+    "-Wno-switch-enum",
+    "-Wno-thread-safety-negative",
+    "-Wno-undef",
+    "-Wno-unknown-warning-option",
+    "-Wno-unreachable-code",
+    "-Wno-unused-macros",
+    "-Wno-weak-vtables",
+    "-Wbitfield-enum-conversion",
+    "-Wbool-conversion",
+    "-Wconstant-conversion",
+    "-Wenum-conversion",
+    "-Wint-conversion",
+    "-Wliteral-conversion",
+    "-Wnon-literal-null-conversion",
+    "-Wnull-conversion",
+    "-Wobjc-literal-conversion",
+    "-Wno-sign-conversion",
+    "-Wstring-conversion",
+    "/DNOMINMAX",
+    "/DWIN32_LEAN_AND_MEAN",
+    "/D_CRT_SECURE_NO_WARNINGS",
+    "/D_SCL_SECURE_NO_WARNINGS",
+    "/D_ENABLE_EXTENDED_ALIGNED_STORAGE",
+]
+
+ABSL_CLANG_CL_TEST_FLAGS = [
+    "-Wno-c99-extensions",
+    "-Wno-missing-noreturn",
+    "-Wno-missing-prototypes",
+    "-Wno-missing-variable-declarations",
+    "-Wno-null-conversion",
+    "-Wno-shadow",
+    "-Wno-shift-sign-overflow",
+    "-Wno-sign-compare",
+    "-Wno-unused-function",
+    "-Wno-unused-member-function",
+    "-Wno-unused-parameter",
+    "-Wno-unused-private-field",
+    "-Wno-unused-template",
+    "-Wno-used-but-marked-unused",
+    "-Wno-zero-as-null-pointer-constant",
+    "-Wno-gnu-zero-variadic-macro-arguments",
+]
+
+ABSL_GCC_EXCEPTIONS_FLAGS = [
     "-fexceptions",
 ]
 
-GCC_FLAGS = [
+ABSL_GCC_FLAGS = [
     "-Wall",
     "-Wextra",
     "-Wcast-qual",
@@ -25,7 +101,7 @@ GCC_FLAGS = [
     "-Wno-sign-compare",
 ]
 
-GCC_TEST_FLAGS = [
+ABSL_GCC_TEST_FLAGS = [
     "-Wno-conversion-null",
     "-Wno-missing-declarations",
     "-Wno-sign-compare",
@@ -34,11 +110,11 @@ GCC_TEST_FLAGS = [
     "-Wno-unused-private-field",
 ]
 
-LLVM_EXCEPTIONS_FLAGS = [
+ABSL_LLVM_EXCEPTIONS_FLAGS = [
     "-fexceptions",
 ]
 
-LLVM_FLAGS = [
+ABSL_LLVM_FLAGS = [
     "-Wall",
     "-Wextra",
     "-Weverything",
@@ -86,7 +162,7 @@ LLVM_FLAGS = [
     "-Wstring-conversion",
 ]
 
-LLVM_TEST_FLAGS = [
+ABSL_LLVM_TEST_FLAGS = [
     "-Wno-c99-extensions",
     "-Wno-missing-noreturn",
     "-Wno-missing-prototypes",
@@ -105,28 +181,28 @@ LLVM_TEST_FLAGS = [
     "-Wno-gnu-zero-variadic-macro-arguments",
 ]
 
-MSVC_EXCEPTIONS_FLAGS = [
+ABSL_MSVC_EXCEPTIONS_FLAGS = [
     "/U_HAS_EXCEPTIONS",
     "/D_HAS_EXCEPTIONS=1",
     "/EHsc",
 ]
 
-MSVC_FLAGS = [
+ABSL_MSVC_FLAGS = [
     "/W3",
+    "/DNOMINMAX",
+    "/DWIN32_LEAN_AND_MEAN",
+    "/D_CRT_SECURE_NO_WARNINGS",
+    "/D_SCL_SECURE_NO_WARNINGS",
+    "/D_ENABLE_EXTENDED_ALIGNED_STORAGE",
     "/wd4005",
     "/wd4068",
     "/wd4180",
     "/wd4244",
     "/wd4267",
     "/wd4800",
-    "/DNOMINMAX",
-    "/DWIN32_LEAN_AND_MEAN",
-    "/D_CRT_SECURE_NO_WARNINGS",
-    "/D_SCL_SECURE_NO_WARNINGS",
-    "/D_ENABLE_EXTENDED_ALIGNED_STORAGE",
 ]
 
-MSVC_TEST_FLAGS = [
+ABSL_MSVC_TEST_FLAGS = [
     "/wd4018",
     "/wd4101",
     "/wd4503",