fail to bundle install puma 4.3.5 or gem puma with ruby-2.6.6 on macos-10.15.6 [duplicate]

fail to bundle install puma 4.3.5 or gem puma with ruby-2.6.6 on macos-10.15.6 try to bundle dependencies for my project, but puma 4.3.5 occured an error. someone know about this?

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here is the error content:

fetching puma 4.3.5
Installing puma 4.3.5 with native extensions
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

    current directory: /Users/lxj/.rvm/gems/ruby-2.6.6/gems/puma-4.3.5/ext/puma_http11
/Users/lxj/.rvm/rubies/ruby-2.6.6/bin/ruby -I /Users/lxj/.rvm/rubies/ruby-2.6.6/lib/ruby/site_ruby/2.6.0 -r ./siteconf20200731-28585-1eobsvu.rb extconf.rb
checking for BIO_read() in -lcrypto... yes
checking for SSL_CTX_new() in -lssl... yes
checking for openssl/bio.h... yes
checking for DTLS_method() in openssl/ssl.h... yes
checking for TLS_server_method() in openssl/ssl.h... yes
checking for SSL_CTX_set_min_proto_version in openssl/ssl.h... yes
creating Makefile

current directory: /Users/lxj/.rvm/gems/ruby-2.6.6/gems/puma-4.3.5/ext/puma_http11
make "DESTDIR=" clean

current directory: /Users/lxj/.rvm/gems/ruby-2.6.6/gems/puma-4.3.5/ext/puma_http11
make "DESTDIR="
compiling http11_parser.c
ext/puma_http11/http11_parser.c:44:18: warning: unused variable 'puma_parser_en_main' [-Wunused-const-variable]
static const int puma_parser_en_main = 1;
                 ^
1 warning generated.
compiling io_buffer.c
compiling mini_ssl.c
mini_ssl.c:145:7: warning: unused variable 'min' [-Wunused-variable]
  int min, ssl_options;
      ^
mini_ssl.c:299:40: warning: function 'raise_error' could be declared with attribute 'noreturn' [-Wmissing-noreturn]
void raise_error(SSL* ssl, int result) {
                                       ^
2 warnings generated.
compiling puma_http11.c
puma_http11.c:203:22: error: implicitly declaring library function 'isspace' with type 'int (int)' [-Werror,-Wimplicit-function-declaration]
  while (vlen > 0 && isspace(value[vlen - 1])) vlen--;
                     ^
puma_http11.c:203:22: note: include the header <ctype.h> or explicitly provide a declaration for 'isspace'
1 error generated.
make: *** [puma_http11.o] Error 1

make failed, exit code 2

Gem files will remain installed in /Users/lxj/.rvm/gems/ruby-2.6.6/gems/puma-4.3.5 for inspection.
Results logged to /Users/lxj/.rvm/gems/ruby-2.6.6/extensions/x86_64-darwin-19/2.6.0/puma-4.3.5/gem_make.out

An error occurred while installing puma (4.3.5), and Bundler cannot continue.
Make sure that `gem install puma -v '4.3.5'` succeeds before bundling.

In Gemfile:
  puma

Solution 1:

It seems that the latest version of XCode tools (12 Beta 3) installs a version of Clang (the C compiler used by default on MacOS) that throws an error on implicit functions used on the native extension code of Puma.

The workaround as pointed out here is to tell Clang not to treat this behavior as an error.

Try running:

bundle config build.puma --with-cflags="-Wno-error=implicit-function-declaration"
bundle install

and it should work.