Error installing `pg` gem

Problem

Sometimes while running `bundle install` during setting up a new project, you might get the following error:

Installing pg 1.2.0 with native extensions
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

current directory: /Users/mpro/.rvm/gems/ruby-2.6.3/gems/pg-1.2.0/ext
/Users/mpro/.rvm/rubies/ruby-2.6.3/bin/ruby -I /Users/mkwalpro/.rvm/rubies/ruby-2.6.3/lib/ruby/site_ruby/2.6.0 -r ./siteconf20210704-17699-11rybqq.rb
extconf.rb
checking for pg_config... no
No pg_config... trying anyway. If building fails, please try again with
--with-pg-config=/path/to/pg_config
checking for libpq-fe.h... no
Can't find the 'libpq-fe.h header
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers. Check the mkmf.log file for more details. You may
need configuration options.

Provided configuration options:
--with-opt-dir
--with-opt-include
--without-opt-include=${opt-dir}/include
--with-opt-lib
--without-opt-lib=${opt-dir}/lib
--with-make-prog
--without-make-prog
--srcdir=.
--curdir
--ruby=/Users/mpro/.rvm/rubies/ruby-2.6.3/bin/$(RUBY_BASE_NAME)
--with-pg
--without-pg
--enable-windows-cross
--disable-windows-cross
--with-pg-config
--without-pg-config
--with-pg_config
--without-pg_config
--with-pg-dir
--without-pg-dir
--with-pg-include
--without-pg-include=${pg-dir}/include
--with-pg-lib
--without-pg-lib=${pg-dir}/lib

To see why this extension failed to compile, please check the mkmf.log which can be found here:

/Users/mpro/.rvm/gems/ruby-2.6.3/extensions/x86_64-darwin-20/2.6.0/pg-1.2.0/mkmf.log

extconf failed, exit code 1

Gem files will remain installed in /Users/mpro/.rvm/gems/ruby-2.6.3/gems/pg-1.2.0 for inspection.
Results logged to /Users/mpro/.rvm/gems/ruby-2.6.3/extensions/x86_64-darwin-20/2.6.0/pg-1.2.0/gem_make.out

An error occurred while installing pg (1.2.0), and Bundler cannot continue.
Make sure that `gem install pg -v '1.2.0' --source 'https://rubygems.org/'` succeeds before bundling.

In Gemfile:
pg

Solution

To fix this issue, run the following commands:

On Ubuntu:

sudo apt-get install libpq-dev

On Mac

brew install postgresql

then run `bundle install` again.