Slang linter for Verilog. (#4713)

test/handler/test_slang_handler.vader

@@ -0,0 +1,26 @@
+Before:
+  runtime ale_linters/verilog/slang.vim
+
+After:
+  call ale#linter#Reset()
+
+Execute(The slang handler should parse lines correctly):
+  AssertEqual
+  \ [
+  \    {
+  \      'lnum': 11,
+  \      'col': 1,
+  \      'type': 'W',
+  \      'text': 'extra '';'' has no effect [-Wempty-member]',
+  \    },
+  \    {
+  \      'lnum': 24,
+  \      'col': 12,
+  \      'type': 'E',
+  \      'text': 'cannot mix continuous and procedural assignments to variable ''data_o''',
+  \    },
+  \ ],
+  \ ale_linters#verilog#slang#Handle(bufnr(''), [
+  \ 'foo.sv:11:1: warning: extra '';'' has no effect [-Wempty-member]',
+  \ 'foo.sv:24:12: error: cannot mix continuous and procedural assignments to variable ''data_o''',
+  \ ])

test/linter/test_slang.vader

@@ -0,0 +1,14 @@
+Before:
+  call ale#assert#SetUpLinterTest('verilog', 'slang')
+
+After:
+  call ale#assert#TearDownLinterTest()
+
+Execute(The default slang command should be correct):
+  AssertLinter 'slang', 'slang -Weverything -I%s:h  %t'
+
+Execute(slang options should be configurable):
+  " Additional args for the linter
+  let g:ale_verilog_slang_options = '--define-macro DWIDTH=12'
+
+  AssertLinter 'slang', 'slang -Weverything -I%s:h --define-macro DWIDTH=12 %t'

test/test_filetype_linter_defaults.vader

@@ -119,7 +119,7 @@ Execute(The defaults for the zsh filetype should be correct):
 Execute(The defaults for the verilog filetype should be correct):
   " This filetype isn't configured with default, so we can test loading all
   " available linters with this.
-  AssertEqual ['hdl_checker', 'iverilog', 'verilator', 'vlog', 'xvlog', 'yosys'], GetLinterNames('verilog')
+  AssertEqual ['hdl_checker', 'iverilog', 'slang', 'verilator', 'vlog', 'xvlog', 'yosys'], GetLinterNames('verilog')
 
   let g:ale_linters_explicit = 1