我在macOS Catalina10.15.7上，为我的项目使用rbenv(版本rbenv 1.1.2-36-g60c9339(和ruby verion2.6.3(ruby 2.6.3p62 (2019-04-16 revision 67580) [x86_64-darwin19]是ruby -v的输出(。我需要安装mailcatcher来检查我的应用程序生成的电子邮件。在我的项目文件夹中运行gem install mailcatcher时，该命令失败，并出现以下错误：
➜ gem install mailcatcher
Building native extensions. This could take a while...
ERROR: Error installing mailcatcher:
ERROR: Failed to build gem native extension.
current directory: /Users/karansapolia/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/thin-1.5.1/ext/thin_parser
/Users/karansapolia/.rbenv/versions/2.6.3/bin/ruby -I /Users/karansapolia/.rbenv/versions/2.6.3/lib/ruby/2.6.0 -r ./siteconf20201103-23665-1tzqkaj.rb extconf.rb
checking for main() in -lc... yes
creating Makefile
current directory: /Users/karansapolia/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/thin-1.5.1/ext/thin_parser
make "DESTDIR=" clean
current directory: /Users/karansapolia/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/thin-1.5.1/ext/thin_parser
make "DESTDIR="
compiling parser.c
parser.rl:112:17: warning: comparison of integers of different signs: 'long' and 'unsigned long' [-Wsign-compare]
assert(pe - p == len - off && "pointers aren't same distance");
~~~~~~ ^ ~~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/assert.h:93:25: note: expanded from macro 'assert'
(__builtin_expect(!(e), 0) ? __assert_rtn(__func__, __FILE__, __LINE__, #e) : (void)0)
^
parser.rl:142:7: error: implicit declaration of function 'thin_http_parser_has_error' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
if (thin_http_parser_has_error(parser) ) {
^
parser.rl:142:7: note: did you mean 'http_parser_has_error'?
./parser.h:44:5: note: 'http_parser_has_error' declared here
int http_parser_has_error(http_parser *parser);
^
parser.rl:144:14: error: implicit declaration of function 'thin_http_parser_is_finished' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
} else if (thin_http_parser_is_finished(parser) ) {
^
1 warning and 2 errors generated.
make: *** [parser.o] Error 1
make failed, exit code 2
Gem files will remain installed in /Users/karansapolia/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/thin-1.5.1 for inspection.
Results logged to /Users/karansapolia/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/extensions/x86_64-darwin-19/2.6.0/thin-1.5.1/gem_make.out
安装其他gem非常有效。gem install mailman运行良好。仅mailcatcher失败。
如何在没有错误的情况下安装mailcatcher？
我运行了follow命令，它对我来说是
gem安装mailcatcher--带有cflags="-Wno error＝隐式函数声明"；
在Mac OS Big Sur 11.7上，我也必须添加-fdeclspec标志：
gem install mailcatcher -- --with-cflags="-fdeclspec -Wno-error=implicit-function-declaration"
(读取故障输出文件mkmf.log后尝试-fdeclspec标志(
似乎在安装瘦解析器时出现了问题，我在github上发现了一个已经打开的问题，这个贡献者在这里提出了一个解决方案。
确保在mailcatcher之前安装thin。