Fix crash when installing gems with symlinks

If BUNDLE_PATH is configured to a symlinked path, installing gems with
symlinks would crash with an error like this:

```
Gem::Package::SymlinkError: installing symlink 'man/man0/README.markdown' pointing to parent path /usr/home/stevewi/srv/mail/lib/tools/.vendor/ruby/3.1.0/gems/binman-5.1.0/README.markdown of /srv/mail/lib/tools/.vendor/ruby/3.1.0/gems/binman-5.1.0 is not allowed
```

This commit fixes the problem by changing the bundle path to be the
realpath of the configured value, right after we're sure the path has
been created.

bundler/lib/bundler.rb

@@ -97,6 +97,17 @@ def bundle_path
       @bundle_path ||= Pathname.new(configured_bundle_path.path).expand_path(root)
     end
 
+    def create_bundle_path
+      SharedHelpers.filesystem_access(bundle_path.to_s) do |p|
+        mkdir_p(p)
+      end unless bundle_path.exist?
+
+      @bundle_path = bundle_path.realpath
+    rescue Errno::EEXIST
+      raise PathError, "Could not install to path `#{bundle_path}` " \
+        "because a file already exists at that path. Either remove or rename the file so the directory can be created."
+    end
+
     def configured_bundle_path
       @configured_bundle_path ||= settings.path.tap(&:validate!)
     end

bundler/lib/bundler/inline.rb

@@ -38,6 +38,7 @@ def gemfile(install = false, options = {}, &gemfile)
   raise ArgumentError, "Unknown options: #{opts.keys.join(", ")}" unless opts.empty?
 
   begin
+    Bundler.instance_variable_set(:@bundle_path, Pathname.new(Gem.dir))
     old_gemfile = ENV["BUNDLE_GEMFILE"]
     Bundler::SharedHelpers.set_env "BUNDLE_GEMFILE", "Gemfile"
 

bundler/lib/bundler/installer.rb

@@ -66,7 +66,7 @@ def initialize(root, definition)
     # require paths and save them in a `setup.rb` file. See `bundle standalone --help` for more
     # information.
     def run(options)
-      create_bundle_path
+      Bundler.create_bundle_path
 
       ProcessLock.lock do
         if Bundler.frozen_bundle?
@@ -262,15 +262,6 @@ def install_in_parallel(size, standalone, force = false)
       end
     end
 
-    def create_bundle_path
-      SharedHelpers.filesystem_access(Bundler.bundle_path.to_s) do |p|
-        Bundler.mkdir_p(p)
-      end unless Bundler.bundle_path.exist?
-    rescue Errno::EEXIST
-      raise PathError, "Could not install to path `#{Bundler.bundle_path}` " \
-        "because a file already exists at that path. Either remove or rename the file so the directory can be created."
-    end
-
     # returns whether or not a re-resolve was needed
     def resolve_if_needed(options)
       if !@definition.unlocking? && !options["force"] && !Bundler.settings[:inline] && Bundler.default_lockfile.file?

bundler/lib/bundler/source/rubygems.rb

@@ -499,7 +499,7 @@ def requires_sudo?
       end
 
       def rubygems_dir
-        Bundler.rubygems.gem_dir
+        Bundler.bundle_path
       end
 
       def default_cache_path_for(dir)

bundler/spec/commands/install_spec.rb

@@ -969,4 +969,37 @@ def run
       expect(last_command).to be_success
     end
   end
+
+  context "with a symlinked configured as bundle path and a gem with symlinks" do
+    before do
+      symlinked_bundled_app = tmp("bundled_app-symlink")
+      File.symlink(bundled_app, symlinked_bundled_app)
+      bundle "config path #{File.join(symlinked_bundled_app, ".vendor")}"
+
+      binman_path = tmp("binman")
+      FileUtils.mkdir_p binman_path
+
+      readme_path = File.join(binman_path, "README.markdown")
+      FileUtils.touch(readme_path)
+
+      man_path = File.join(binman_path, "man", "man0")
+      FileUtils.mkdir_p man_path
+
+      File.symlink("../../README.markdown", File.join(man_path, "README.markdown"))
+
+      build_repo4 do
+        build_gem "binman", :path => gem_repo4("gems"), :lib_path => binman_path, :no_default => true do |s|
+          s.files = ["README.markdown", "man/man0/README.markdown"]
+        end
+      end
+    end
+
+    it "installs fine" do
+      install_gemfile <<~G
+        source "#{file_uri_for(gem_repo4)}"
+
+        gem "binman"
+      G
+    end
+  end
 end

bundler/spec/support/builders.rb

@@ -484,7 +484,7 @@ def @spec.validate(*); end
         end
 
         @spec.authors = ["no one"]
-        @spec.files = @files.keys
+        @spec.files += @files.keys
 
         case options[:gemspec]
         when false
@@ -589,7 +589,8 @@ def ref_for(ref, len = nil)
 
     class GemBuilder < LibBuilder
       def _build(opts)
-        lib_path = super(opts.merge(:path => @context.tmp(".tmp/#{@spec.full_name}"), :no_default => opts[:no_default]))
+        lib_path = opts[:lib_path] || @context.tmp(".tmp/#{@spec.full_name}")
+        lib_path = super(opts.merge(:path => lib_path, :no_default => opts[:no_default]))
         destination = opts[:path] || _default_path
         FileUtils.mkdir_p(lib_path.join(destination))