Feature: accept pull request URLs as github source

Very often github source is used to temporarily use a modified gem
while a PR upstream is being reviewed.

So for instance ruby/bigdecimal#211 will look like:

```ruby
gem "bigdecimal", github: "casperisfine/bigdecimal", branch: "git-gem" # ruby/bigdecimal#200
```

It's annoying because you have to fiddle with the branch name, which is copied as `casperisfine:git-gem`, etc etc.

If I could simply use the PR URL like this:

```
gem "bigdecimal", github: "ruby/bigdecimal#211"
```

It would make a very common task for me so much simpler.

Author: byroot

bundler/lib/bundler/dsl.rb

@@ -278,8 +278,17 @@ def add_git_sources
         warn_deprecated_git_source(:github, <<-'RUBY'.strip, 'Change any "reponame" :github sources to "username/reponame".')
 "https://github.com/#{repo_name}.git"
         RUBY
-        repo_name = "#{repo_name}/#{repo_name}" unless repo_name.include?("/")
-        "https://github.com/#{repo_name}.git"
+        if repo_name =~ %r{\Ahttps://github\.com/(\w+/\w+)/pull/(\d+)\z}
+          {
+            "git" => "https://github.com/#{$1}.git",
+            "branch" => "refs/pull/#{$2}/head",
+            "ref" => nil,
+            "tag" => nil,
+          }
+        else
+          repo_name = "#{repo_name}/#{repo_name}" unless repo_name.include?("/")
+          "https://github.com/#{repo_name}.git"
+        end
       end
 
       git_source(:gist) do |repo_name|
@@ -365,7 +374,11 @@ def normalize_options(name, version, opts)
 
       git_name = (git_names & opts.keys).last
       if @git_sources[git_name]
-        opts["git"] = @git_sources[git_name].call(opts[git_name])
+        git_opts = @git_sources[git_name].call(opts[git_name])
+        git_opts = { "git" => git_opts } if git_opts.is_a?(String)
+        opts.merge!(git_opts) do |key, _gemfile_value, _git_source_value|
+          raise GemfileError, %(The :#{key} option can't be used with `#{git_name}: #{opts[git_name].inspect}`)
+        end
       end
 
       %w[git path].each do |type|

bundler/lib/bundler/man/bundle-add.1

@@ -1,7 +1,7 @@
 .\" generated with Ronn/v0.7.3
 .\" http://github.com/rtomayko/ronn/tree/0.7.3
 .
-.TH "BUNDLE\-ADD" "1" "November 2021" "" ""
+.TH "BUNDLE\-ADD" "1" "December 2021" "" ""
 .
 .SH "NAME"
 \fBbundle\-add\fR \- Add gem to the Gemfile and run bundle install

bundler/lib/bundler/man/bundle-binstubs.1

@@ -1,7 +1,7 @@
 .\" generated with Ronn/v0.7.3
 .\" http://github.com/rtomayko/ronn/tree/0.7.3
 .
-.TH "BUNDLE\-BINSTUBS" "1" "November 2021" "" ""
+.TH "BUNDLE\-BINSTUBS" "1" "December 2021" "" ""
 .
 .SH "NAME"
 \fBbundle\-binstubs\fR \- Install the binstubs of the listed gems

bundler/lib/bundler/man/bundle-cache.1

@@ -1,7 +1,7 @@
 .\" generated with Ronn/v0.7.3
 .\" http://github.com/rtomayko/ronn/tree/0.7.3
 .
-.TH "BUNDLE\-CACHE" "1" "November 2021" "" ""
+.TH "BUNDLE\-CACHE" "1" "December 2021" "" ""
 .
 .SH "NAME"
 \fBbundle\-cache\fR \- Package your needed \fB\.gem\fR files into your application

bundler/lib/bundler/man/bundle-check.1

@@ -1,7 +1,7 @@
 .\" generated with Ronn/v0.7.3
 .\" http://github.com/rtomayko/ronn/tree/0.7.3
 .
-.TH "BUNDLE\-CHECK" "1" "November 2021" "" ""
+.TH "BUNDLE\-CHECK" "1" "December 2021" "" ""
 .
 .SH "NAME"
 \fBbundle\-check\fR \- Verifies if dependencies are satisfied by installed gems

bundler/lib/bundler/man/bundle-clean.1

@@ -1,7 +1,7 @@
 .\" generated with Ronn/v0.7.3
 .\" http://github.com/rtomayko/ronn/tree/0.7.3
 .
-.TH "BUNDLE\-CLEAN" "1" "November 2021" "" ""
+.TH "BUNDLE\-CLEAN" "1" "December 2021" "" ""
 .
 .SH "NAME"
 \fBbundle\-clean\fR \- Cleans up unused gems in your bundler directory

bundler/lib/bundler/man/bundle-config.1

@@ -1,7 +1,7 @@
 .\" generated with Ronn/v0.7.3
 .\" http://github.com/rtomayko/ronn/tree/0.7.3
 .
-.TH "BUNDLE\-CONFIG" "1" "November 2021" "" ""
+.TH "BUNDLE\-CONFIG" "1" "December 2021" "" ""
 .
 .SH "NAME"
 \fBbundle\-config\fR \- Set bundler configuration options

bundler/lib/bundler/man/bundle-doctor.1

@@ -1,7 +1,7 @@
 .\" generated with Ronn/v0.7.3
 .\" http://github.com/rtomayko/ronn/tree/0.7.3
 .
-.TH "BUNDLE\-DOCTOR" "1" "November 2021" "" ""
+.TH "BUNDLE\-DOCTOR" "1" "December 2021" "" ""
 .
 .SH "NAME"
 \fBbundle\-doctor\fR \- Checks the bundle for common problems

bundler/lib/bundler/man/bundle-exec.1

@@ -1,7 +1,7 @@
 .\" generated with Ronn/v0.7.3
 .\" http://github.com/rtomayko/ronn/tree/0.7.3
 .
-.TH "BUNDLE\-EXEC" "1" "November 2021" "" ""
+.TH "BUNDLE\-EXEC" "1" "December 2021" "" ""
 .
 .SH "NAME"
 \fBbundle\-exec\fR \- Execute a command in the context of the bundle

bundler/lib/bundler/man/bundle-gem.1

@@ -1,7 +1,7 @@
 .\" generated with Ronn/v0.7.3
 .\" http://github.com/rtomayko/ronn/tree/0.7.3
 .
-.TH "BUNDLE\-GEM" "1" "November 2021" "" ""
+.TH "BUNDLE\-GEM" "1" "December 2021" "" ""
 .
 .SH "NAME"
 \fBbundle\-gem\fR \- Generate a project skeleton for creating a rubygem