Go back to using -std=c++17

Signed-off-by: Michael Warres <[email protected]>

Author: mpwarres

.bazelrc

@@ -80,10 +80,10 @@ build:zig-cc-linux-aarch64 --test_env=QEMU_LD_PREFIX=/usr/aarch64-linux-gnu/
 
 build --enable_platform_specific_config
 
-# Use C++20.
-build:linux --cxxopt=-std=c++20
-build:macos --cxxopt=-std=c++20
-build:windows --cxxopt="/std:c++20"
+# Use C++17.
+build:linux --cxxopt=-std=c++17
+build:macos --cxxopt=-std=c++17
+build:windows --cxxopt="/std:c++17"
 
 # Enable symlinks and runfiles on Windows (enabled by default on other platforms).
 startup --windows_enable_symlinks

bazel/external/v8.patch

@@ -7,9 +7,11 @@
 #    gn.
 # 5. Set torque generator path to location where Bazel can find outputs.
 # 6. Compile v8 with -Wno-deprecated-declarations
+# 7. Revert v8 commit f06f6d1a45fe87f2669268275b19df6c23d6a815, which added a
+#    requirement of c++20.
 
 diff --git a/BUILD.bazel b/BUILD.bazel
-index 30be47fa333..23cfc9c4754 100644
+index 30be47fa333..72de2d422ca 100644
 --- a/BUILD.bazel
 +++ b/BUILD.bazel
 @@ -220,7 +220,7 @@ v8_int(
@@ -51,7 +53,7 @@ index 30be47fa333..23cfc9c4754 100644
 
  filegroup(
 diff --git a/bazel/defs.bzl b/bazel/defs.bzl
-index 520a311595e..64b4928abe5 100644
+index 520a311595e..25dfc40e19e 100644
 --- a/bazel/defs.bzl
 +++ b/bazel/defs.bzl
 @@ -102,7 +102,9 @@ def _default_args():
@@ -65,15 +67,40 @@ index 520a311595e..64b4928abe5 100644
              "@v8//bazel/config:is_posix": [
                  "-fPIC",
                  "-fno-strict-aliasing",
-@@ -131,7 +133,6 @@ def _default_args():
+@@ -123,15 +125,13 @@ def _default_args():
+         }) + select({
+             "@v8//bazel/config:is_clang": [
+                 "-Wno-invalid-offsetof",
+-                "-Wno-deprecated-this-capture",
+-                "-std=c++20",
++                "-std=c++17",
+             ],
+             "@v8//bazel/config:is_gcc": [
+                 "-Wno-extra",
                  "-Wno-array-bounds",
                  "-Wno-class-memaccess",
                  "-Wno-comments",
 -                "-Wno-deprecated-declarations",
                  "-Wno-implicit-fallthrough",
                  "-Wno-int-in-bool-context",
                  "-Wno-maybe-uninitialized",
-@@ -316,7 +317,7 @@ def v8_library(
+@@ -139,13 +139,12 @@ def _default_args():
+                 "-Wno-redundant-move",
+                 "-Wno-return-type",
+                 "-Wno-stringop-overflow",
+-                "-Wno-deprecated-this-capture",
+                 # Use GNU dialect, because GCC doesn't allow using
+                 # ##__VA_ARGS__ when in standards-conforming mode.
+-                "-std=gnu++2a",
++                "-std=gnu++17",
+             ],
+             "@v8//bazel/config:is_windows": [
+-                "/std:c++20",
++                "/std:c++17",
+             ],
+             "//conditions:default": [],
+         }) + select({
+@@ -316,7 +315,7 @@ def v8_library(
  # split the set of outputs by using OutputGroupInfo, that way we do not need to
  # run the torque generator twice.
  def _torque_files_impl(ctx):
@@ -82,7 +109,7 @@ index 520a311595e..64b4928abe5 100644
 
      # Arguments
      args = []
-@@ -480,6 +481,9 @@ _v8_mksnapshot = rule(
+@@ -480,6 +479,9 @@ _v8_mksnapshot = rule(
              cfg = "exec",
          ),
          "target_os": attr.string(mandatory = True),
@@ -114,6 +141,41 @@ index 8c929454840..57336154cf7 100644
      },
      # Making this executable means it works with "$ bazel run".
      executable = True,
+diff --git a/include/v8config.h b/include/v8config.h
+index 707ec23c9c6..adc9575531c 100644
+--- a/include/v8config.h
++++ b/include/v8config.h
+@@ -5,16 +5,8 @@
+ #ifndef V8CONFIG_H_
+ #define V8CONFIG_H_
+ 
+-// gcc 10 defines __cplusplus to "an unspecified value strictly larger than
+-// 201703L" for its experimental -std=gnu++2a config.
+-// TODO(leszeks): Change to `__cplusplus <= 202002L` once we only support
+-// compilers with full C++20 support.
+-#if __cplusplus <= 201703L
+-#error "C++20 or later required."
+-#endif
+-
+ #ifdef V8_GN_HEADER
+-#if !__has_include("v8-gn.h")
++#if __cplusplus >= 201703L && !__has_include("v8-gn.h")
+ #error Missing v8-gn.h. The configuration for v8 is missing from the include \
+ path. Add it with -I<path> to the command line
+ #endif
+diff --git a/src/base/compiler-specific.h b/src/base/compiler-specific.h
+index 16432f5b06f..0fc66d2568b 100644
+--- a/src/base/compiler-specific.h
++++ b/src/base/compiler-specific.h
+@@ -102,7 +102,7 @@
+       !defined(V8_TARGET_ARCH_MIPS64) && !defined(V8_TARGET_ARCH_PPC) &&    \
+       !defined(V8_TARGET_ARCH_PPC64) && !defined(V8_TARGET_ARCH_RISCV64) && \
+       !defined(V8_TARGET_ARCH_RISCV32)) ||                                  \
+-     defined(__clang__))
++     (defined(__clang__) && __cplusplus > 201300L))
+ #define V8_NOEXCEPT noexcept
+ #else
+ #define V8_NOEXCEPT
 diff --git a/src/wasm/c-api.cc b/src/wasm/c-api.cc
 index 2d6d0f6c270..61d071acd52 100644
 --- a/src/wasm/c-api.cc