Improve embedded HEEx and Surface syntax highlighting

* Properly highlight embedded HEEx (and Surface)
* Re-name groups to favour HEEx naming
* Add highlight group for `phx-` attributes
* Add highlight group for heex attribute (eg, `some_attr="some value"`)
* Add highlight group for heex special attribute (ie, `:if` and `:for`)
* Add heexComponentName group
* Add heexEndComponent group

Author: sodapopcan

Diff for: syntax/elixir.vim

@@ -109,15 +109,39 @@ syn region elixirSigil matchgroup=elixirSigilDelimiter start="\~\l\/"
 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
 
-
-" LiveView Sigils surrounded with ~L"""
+" LiveView-specific sigils for embedded templates
 syntax include @HTML syntax/html.vim
 unlet b:current_syntax
-syntax region elixirLiveViewSigil matchgroup=elixirSigilDelimiter keepend start=+\~L\z("""\)+ end=+^\s*\z1+ skip=+\\"+ contains=@HTML fold
-syntax region elixirSurfaceSigil matchgroup=elixirSigilDelimiter keepend start=+\~H\z("""\)+ end=+^\s*\z1+ skip=+\\"+ contains=@HTML fold
+syntax region elixirHeexSigil matchgroup=elixirSigilDelimiter keepend start=+\~H\z("""\)+ end=+^\s*\z1+ skip=+\\"+ contains=@HTML fold
 syntax region elixirSurfaceSigil matchgroup=elixirSigilDelimiter keepend start=+\~F\z("""\)+ end=+^\s*\z1+ skip=+\\"+ contains=@HTML fold
-syntax region elixirPhoenixESigil matchgroup=elixirSigilDelimiter keepend start=+\~E\z("""\)+ end=+^\s*\z1+ skip=+\\"+ contains=@HTML fold
-syntax region elixirPhoenixeSigil matchgroup=elixirSigilDelimiter keepend start=+\~e\z("""\)+ end=+^\s*\z1+ skip=+\\"+ contains=@HTML fold
+syntax region elixirLiveViewSigil matchgroup=elixirSigilDelimiter keepend start=+\~L\z("""\)+ end=+^\s*\z1+ skip=+\\"+ contains=@HTML fold
+
+syn cluster elixirLiveSigils contains=elixirLiveViewSigil,elixirHeexSigil,elixirSurfaceSigil
+
+syn region heexComponent matchgroup=eelixirDelimiter start="<\.[a-z_]\+"  end="%\@<!>" contains=ALLBUT,@elixirNotTop keepend
+syn region heexExpression matchgroup=eelixirDelimiter start="<%"  end="%\@<!%>" contains=ALLBUT,@elixirNotTop containedin=@elixirLiveSigils keepend
+syn region heexExpression matchgroup=eelixirDelimiter start="<%=" end="%\@<!%>" contains=ALLBUT,@elixirNotTop containedin=@elixirLiveSigils keepend
+syn region heexAttributeExpression matchgroup=heexDelimiter start="=\zs{" end="}" contains=ALLBUT,@elixirNotTop containedin=htmlValue keepend
+syn region heexAttributeExpression matchgroup=heexDelimiter start="=\zs{" end="}" skip="#{[^}]*}" contains=ALLBUT,@elixirNotTop containedin=htmlValue keepend
+" missing `keepend` on next line is intentional
+syn region heexAttributeExpression matchgroup=heexDelimiter start="=\zs{" end="}" skip="%{[^}]*}" contains=ALLBUT,@elixirNotTop containedin=htmlValue
+syn region eelixirQuote matchgroup=eelixirDelimiter start="<%%" end="%\@<!%>" contains=ALLBUT,@elixirNotTop containedin=@elixirLiveSigils keepend
+syn region heexComment matchgroup=eelixirDelimiter start="<%!--" end="%\@<!--%>" contains=elixirTodo,eelixirComment,@Spell containedin=@elixirLiveSigils keepend
+
+syn match phxArg "\<phx[-.0-9_a-z]*-[-.0-9_a-z]*\>" containedin=htmlTag
+syn match heexArg "\<[0-9_a-z]*\>\ze=" containedin=htmlTag
+syn match heexSpecialAttribute ":\%(if\|for\|let\)\ze=" containedin=htmlTag
+syn match heexComponentName "<\zs\.[A-Z_a-z][A-Z_a-z0-9]\+" containedin=htmlTag
+syn match heexEndComponent "<\zs\/\.[A-Z_a-z][A-Z_a-z0-9]\+" containedin=htmlEndTag
+
+hi def link eelixirDelimiter PreProc
+hi def link heexDelimiter PreProc
+hi def link heexComment Comment
+hi def link phxArg htmlArg
+hi def link heexArg htmlArg
+hi def link heexSpecialAttribute htmlArg
+hi def link heexComponentName htmlTagName
+hi def link heexEndComponent htmlTagName
 
 " Documentation
 if exists('g:elixir_use_markdown_for_docs') && g:elixir_use_markdown_for_docs