Fix syntax highlighting with "~S" sigil (#457)

Fixes #438

Author: feliperenan

spec/syntax/doc_spec.rb

@@ -35,6 +35,17 @@
       expect(ex).to include_elixir_syntax('elixirDocString', 'foo')
     end
 
+    it 'doc with sigil_S triple double-quoted multiline content with parentheses' do
+      ex = <<~'EOF'
+        @doc(~S"""
+        foo
+        """)
+      EOF
+      expect(ex).to include_elixir_syntax('elixirVariable', 'doc')
+      expect(ex).to include_elixir_syntax('elixirSigilDelimiter', 'S"""')
+      expect(ex).to include_elixir_syntax('elixirSigil', 'foo')
+    end
+
     it 'doc with sigil_S triple single-quoted multiline content' do
       ex = <<~'EOF'
         @doc ~S'''
@@ -46,6 +57,17 @@
       expect(ex).to include_elixir_syntax('elixirDocString', 'foo')
     end
 
+    it 'doc with sigil_S triple single-quoted multiline content with parentheses' do
+      ex = <<~'EOF'
+        @doc(~S'''
+        foo
+        ''')
+      EOF
+      expect(ex).to include_elixir_syntax('elixirVariable', 'doc')
+      expect(ex).to include_elixir_syntax('elixirSigilDelimiter', "S'''")
+      expect(ex).to include_elixir_syntax('elixirSigil', 'foo')
+    end
+
     it 'doc with triple single-quoted multiline content is not a doc string' do
       ex = <<~'EOF'
         @doc '''

spec/syntax/sigil_spec.rb

@@ -10,6 +10,20 @@
     expect('def f(~s(")), do: true').not_to include_elixir_syntax('elixirSigilDelimiter', '"')
   end
 
+  it 'as function argument multiline content' do
+    ex = <<~'EOF'
+      f(
+        ~S"""
+        foo
+        """,
+        bar
+      )
+    EOF
+
+    expect(ex).to include_elixir_syntax('elixirSigilDelimiter', 'S"""')
+    expect(ex).to include_elixir_syntax('elixirSigil', 'foo')
+  end
+
   describe 'upper case' do
     it 'string' do
       expect('~S(string)').to include_elixir_syntax('elixirSigilDelimiter', 'S')

syntax/elixir.vim

@@ -103,8 +103,8 @@ syn region elixirSigil matchgroup=elixirSigilDelimiter start="\~\l("
 syn region elixirSigil matchgroup=elixirSigilDelimiter start="\~\l\/"               end="\/"  skip="\\\\\|\\\/"  contains=@elixirStringContained,elixirRegexEscapePunctuation fold
 
 " Sigils surrounded with heredoc
-syn region elixirSigil matchgroup=elixirSigilDelimiter start=+\~\a\z("""\)+ end=+^\s*\zs\z1\s*$+ skip=+\\"+ fold
-syn region elixirSigil matchgroup=elixirSigilDelimiter start=+\~\a\z('''\)+ end=+^\s*\zs\z1\s*$+ skip=+\\'+ fold
+syn region elixirSigil matchgroup=elixirSigilDelimiter start=+\~\a\z("""\)+ end=+^\s*\z1+ skip=+\\"+ fold
+syn region elixirSigil matchgroup=elixirSigilDelimiter start=+\~\a\z('''\)+ end=+^\s*\z1+ skip=+\\'+ fold
 
 " Documentation
 if exists('g:elixir_use_markdown_for_docs') && g:elixir_use_markdown_for_docs