[Ruby] I can't install puma on Mac [Rails, etc.]

Rails can't be installed because of puma. If you can't install without sqlite, you can solve it by installing sqlite from brew.

macOS Catalina 10.15.6 ruby 2.6.5 gem 3.0.3 puma 4.3.5

Isn't xCode installed for a similar question? There was an answer That doesn't help at hand.

Error message (click to expand)

gem install puma -v '4.3.5' --source 'https://rubygems.org/'
Building native extensions. This could take a while...
ERROR:  Error installing puma:
	ERROR: Failed to build gem native extension.

    current directory: /Users/rin.nakashima/.anyenv/envs/rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/puma-4.3.5/ext/puma_http11
/Users/rin.nakashima/.anyenv/envs/rbenv/versions/2.6.5/bin/ruby -I /Users/rin.nakashima/.anyenv/envs/rbenv/versions/2.6.5/lib/ruby/2.6.0 -r ./siteconf20200810-80454-doo97b.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/rin.nakashima/.anyenv/envs/rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/puma-4.3.5/ext/puma_http11
make "DESTDIR=" clean

current directory: /Users/rin.nakashima/.anyenv/envs/rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/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/rin.nakashima/.anyenv/envs/rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/puma-4.3.5 for inspection.
Results logged to /Users/rin.nakashima/.anyenv/envs/rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/extensions/x86_64-darwin-19/2.6.0/puma-4.3.5/gem_make.out

When I was googled, I found an issue, and it seems that the default parameters on the Mac side changed and I could not compile with gcc well. https://github.com/puma/puma/issues/2304 As a workaround, deal with it as follows.

gem install puma:4.3.5 -- --with-cflags="-Wno-error=implicit-function-declaration