Add support for perl language server (#5003)

* Fix perl test case clean-up
* Add support for perl language server

Co-authored-by: cos <cos>

test/linter/test_perl.vader

@@ -12,3 +12,5 @@ Execute(Overriding the executable and command should work):
   let b:ale_perl_perl_options = '-w'
 
   AssertLinter 'foobar', ale#Escape('foobar') . ' -w %t'
+  unlet b:ale_perl_perl_executable
+  unlet b:ale_perl_perl_options

test/linter/test_perl_languageserver.vader

@@ -0,0 +1,82 @@
+" Author: rymdbar <https://rymdbar.x20.se/>
+
+Before:
+  call ale#assert#SetUpLinterTest('perl', 'languageserver')
+
+After:
+  call ale#assert#TearDownLinterTest()
+
+Execute(The default Perl command callback should be correct):
+  AssertLinter 'perl',
+  \ ale#Escape('perl') . ' -MPerl::LanguageServer -ePerl::LanguageServer::run'
+
+Execute(Overriding the executable should work):
+  let b:ale_perl_perl_executable = 'plls'
+
+  AssertLinter 'plls', ale#Escape('plls') .
+  \ ' -MPerl::LanguageServer -ePerl::LanguageServer::run'
+  unlet b:ale_perl_perl_executable
+
+Execute(The project root should be detected correctly in from build files):
+  for mod in ['extutils-makemaker', 'module-build', 'dist-zilla']
+    call ale#test#SetFilename('../test-files/perl/' . mod . '/subdir/empty.pl')
+
+    AssertLSPProject ale#path#Simplify(g:dir . '/../test-files/perl/' . mod)
+  endfor
+
+Execute(The project root should be globally configurable):
+  for mod in ['extutils-makemaker', 'module-build', 'dist-zilla']
+    call ale#test#SetFilename('../test-files/perl/'. mod . '/subdir/empty.pl')
+    " Configuring g:ale_root using a Dictionary works.
+    let g:ale_root.languageserver =
+    \ ale#path#Simplify(g:dir . '/../test-files/perl')
+
+    AssertLSPProject ale#path#Simplify(g:dir . '/../test-files/perl')
+    unlet g:ale_root.languageserver
+    " As tracked by <https://github.com/dense-analysis/ale/issues/5002>, there
+    " is a bug with g:ale_root.
+    " While attempting to configure g:ale_root using a String might be a quite
+    " limiting setup, it would be handy for debugging. However the test case is
+    " missing here. It would unfortunately just fail.
+  endfor
+
+Execute(The project root should be per buffer configurable):
+  for mod in ['extutils-makemaker', 'module-build', 'dist-zilla']
+    call ale#test#SetFilename('../test-files/perl/'. mod . '/subdir/empty.pl')
+    " Configuring b:ale_root using a String works.
+    let b:ale_root = ale#path#Simplify(g:dir . '/../test-files/perl')
+
+    AssertLSPProject ale#path#Simplify(g:dir . '/../test-files/perl')
+    unlet b:ale_root
+
+    " Configuring b:ale_root using a Dictionary works.
+    let b:ale_root = {
+    \ 'languageserver': ale#path#Simplify(g:dir . '/../test-files/perl')
+    \ }
+
+    AssertLSPProject ale#path#Simplify(g:dir . '/../test-files/perl')
+    unlet b:ale_root.languageserver
+  endfor
+
+Execute(The LSP values should be set correctly):
+
+  AssertLSPLanguage 'perl'
+
+  AssertLSPOptions {}
+
+  AssertLSPConfig {'perl': {'enable': 1}}
+
+Execute(Should accept configuration settings):
+  let b:ale_perl_languageserver_config = {
+  \   'perl': {
+  \     'perlInc': ['/usr/share/perl5/', '/usr/local/share/perl5/' ],
+  \     'fileFilter': [''],
+  \   },
+  \ }
+
+  AssertLSPConfig {
+  \   'perl': {
+  \     'perlInc': ['/usr/share/perl5/', '/usr/local/share/perl5/' ],
+  \     'fileFilter': [''],
+  \   },
+  \ }

test/test-files/perl/dist-zilla/dist.ini

@@ -0,0 +1 @@
+# https://metacpan.org/pod/Dist::Zilla

test/test-files/perl/extutils-makemaker/Makefile.PL

@@ -0,0 +1 @@
+# https://perldoc.perl.org/ExtUtils::MakeMaker

test/test-files/perl/module-build/Build.PL

@@ -0,0 +1 @@
+# https://metacpan.org/pod/Module::Build