Deduplicate list of linked directories

With this, we ensure to only handle each linked directory once.
Also, if a linked file is in a directory that is already being
handled, there is no need to link the same directory twice.

This should help to keep commands shorter, which might be an issue on
some shells. It certainly is easier on the eyes and logs.

CHANGELOG.md

@@ -28,6 +28,7 @@ https://github.com/capistrano/capistrano/compare/v3.4.0...HEAD
   * Return first 12 characters (instead of 7) of SHA1 hash when determining current git revision (@sds)
   * Clean up rubocop lint warnings (@cshaffer)
   * Ensure task invocation within after hooks is namespace aware (@thickpaddy)
+  * Deduplicate list of linked directories
 
 ## `3.4.0`
 

lib/capistrano/dsl/paths.rb

@@ -96,7 +96,7 @@ module Capistrano
       end
 
       def map_dirnames(paths)
-        paths.map { |path| path.dirname }
+        paths.map { |path| path.dirname }.uniq
       end
     end
   end

spec/lib/capistrano/dsl/paths_spec.rb

@@ -7,7 +7,7 @@ describe Capistrano::DSL::Paths do
   let(:paths) { Class.new.extend Capistrano::DSL::Paths }
 
   let(:linked_dirs) { %w{log public/system} }
-  let(:linked_files) { %w{config/database.yml log/my.log} }
+  let(:linked_files) { %w{config/database.yml log/my.log log/access.log} }
 
   before do
     dsl.set(:deploy_to, '/var/www')
@@ -21,7 +21,10 @@ describe Capistrano::DSL::Paths do
     end
 
     it 'returns the full pathnames' do
-      expect(subject).to eq [Pathname.new('/var/shared/log'), Pathname.new('/var/shared/public/system')]
+      expect(subject).to eq [
+        Pathname.new('/var/shared/log'),
+        Pathname.new('/var/shared/public/system'),
+      ]
     end
   end
 
@@ -34,7 +37,11 @@ describe Capistrano::DSL::Paths do
     end
 
     it 'returns the full pathnames' do
-      expect(subject).to eq [Pathname.new('/var/shared/config/database.yml'), Pathname.new('/var/shared/log/my.log')]
+      expect(subject).to eq [
+        Pathname.new('/var/shared/config/database.yml'),
+        Pathname.new('/var/shared/log/my.log'),
+        Pathname.new('/var/shared/log/access.log'),
+      ]
     end
   end
 
@@ -46,7 +53,10 @@ describe Capistrano::DSL::Paths do
     end
 
     it 'returns the full paths names of the parent dirs' do
-      expect(subject).to eq [Pathname.new('/var/shared/config'), Pathname.new('/var/shared/log')]
+      expect(subject).to eq [
+        Pathname.new('/var/shared/config'),
+        Pathname.new('/var/shared/log'),
+      ]
     end
   end
 
@@ -58,7 +68,10 @@ describe Capistrano::DSL::Paths do
     end
 
     it 'returns the full paths names of the parent dirs' do
-      expect(subject).to eq [Pathname.new('/var/shared'), Pathname.new('/var/shared/public')]
+      expect(subject).to eq [
+        Pathname.new('/var/shared'),
+        Pathname.new('/var/shared/public'),
+      ]
     end
   end