編譯PG插件時，報"unrecognized command line option ‘-Wimplicit-fallthrough=3’"。
關於implicit-fallthrough選項：
As of GCC 7, -Wimplicit-fallthrough is supported and __attribute__((fallthrough)) can be used to suppress the warnings when fallthrough is intentional. GCC does recognize "fallthrough" comments in certain scenarios, but it can be confused fairly easily.
而編譯用的是gcc (GCC) 4.8.5，且沒有地方指定了該選項。
唯一原因就是pg本身使用gcc 7編譯的，可通過pg_config來確定編譯用的選項。
[zjh@lightdb1 zhparser-0.2.0]$ pg_config BINDIR = /home/zjh/pgsql13.2/bin DOCDIR = /home/zjh/pgsql13.2/share/doc HTMLDIR = /home/zjh/pgsql13.2/share/doc INCLUDEDIR = /home/zjh/pgsql13.2/include PKGINCLUDEDIR = /home/zjh/pgsql13.2/include INCLUDEDIR-SERVER = /home/zjh/pgsql13.2/include/server LIBDIR = /home/zjh/pgsql13.2/lib PKGLIBDIR = /home/zjh/pgsql13.2/lib LOCALEDIR = /home/zjh/pgsql13.2/share/locale MANDIR = /home/zjh/pgsql13.2/share/man SHAREDIR = /home/zjh/pgsql13.2/share SYSCONFDIR = /home/zjh/pgsql13.2/etc PGXS = /home/zjh/pgsql13.2/lib/pgxs/src/makefiles/pgxs.mk CONFIGURE = '--prefix=/home/zjh/pgsql13.2' '--enable-depend' '--enable-cassert' '--enable-debug' 'CFLAGS=-DLOCK_DEBUG -DBTREE_BUILD_STATS -DWAL_DEBUG -DCATCACHE_STATS -ggdb -O0' '--enable-dtrace' '--enable-nls=gbk' '--with-openssl' '--with-libxml' '--with-zlib' '--with-llvm' 'LLVM_CONFIG=/opt/rh/llvm-toolset-7/root/usr/bin/llvm-config' '--enable-profiling' CC = gcc CPPFLAGS = -D_GNU_SOURCE -I/usr/include/libxml2 CFLAGS = -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wimplicit-fallthrough=3 -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -Wno-format-truncation -g -pg -DLINUX_PROFILE -DLOCK_DEBUG -DBTREE_BUILD_STATS -DWAL_DEBUG -DCATCACHE_STATS -ggdb -O0 CFLAGS_SL = -fPIC LDFLAGS = -L/opt/rh/llvm-toolset-7/root/usr/lib64 -Wl,--as-needed -Wl,-rpath,'/home/zjh/pgsql13.2/lib',--enable-new-dtags LDFLAGS_EX = LDFLAGS_SL = LIBS = -lpgcommon -lpgport -lpthread -lxml2 -lssl -lcrypto -lz -lreadline -lrt -ldl -lm VERSION = PostgreSQL 13.2
遺憾的是，沒有pg_config選項可以修改其配置。
所以，要么用gcc 4.8.5重新編譯pg，要么切換到7.3.1和pg_config的配置一致，例如llvm，可以從別的環境拷貝一個過來。
4.8.5重新編譯后的選項如下：
[zjh@lightdb1 postgresql-13.2]$ pg_config BINDIR = /home/zjh/pgsql13.2/bin DOCDIR = /home/zjh/pgsql13.2/share/doc HTMLDIR = /home/zjh/pgsql13.2/share/doc INCLUDEDIR = /home/zjh/pgsql13.2/include PKGINCLUDEDIR = /home/zjh/pgsql13.2/include INCLUDEDIR-SERVER = /home/zjh/pgsql13.2/include/server LIBDIR = /home/zjh/pgsql13.2/lib PKGLIBDIR = /home/zjh/pgsql13.2/lib LOCALEDIR = /home/zjh/pgsql13.2/share/locale MANDIR = /home/zjh/pgsql13.2/share/man SHAREDIR = /home/zjh/pgsql13.2/share SYSCONFDIR = /home/zjh/pgsql13.2/etc PGXS = /home/zjh/pgsql13.2/lib/pgxs/src/makefiles/pgxs.mk CONFIGURE = '--prefix=/home/zjh/pgsql13.2' CC = gcc -std=gnu99 CPPFLAGS = -D_GNU_SOURCE CFLAGS = -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -O2 CFLAGS_SL = -fPIC LDFLAGS = -Wl,--as-needed -Wl,-rpath,'/home/zjh/pgsql13.2/lib',--enable-new-dtags LDFLAGS_EX = LDFLAGS_SL = LIBS = -lpgcommon -lpgport -lpthread -lz -lreadline -lrt -ldl -lm VERSION = PostgreSQL 13.2
重新編譯就不報錯了。