notes.txt

These are the predefined faces in font-lock.el.  The R in front are
the ones that ruby-mode uses.  The text after the -- is what ruby-mode
uses them for.

The indented one inherit from the ones above
(e.g. font-lock-doc-markup-face inherits from
font-lock-constant-face).  "error" and "bold" are faces.

This group ruby-mode and ruby-ts-mode use the same way.

R font-lock-type-face -- used forCONSTANTS 
R font-lock-constant-face -- used for symbols
    font-lock-doc-markup-face
R font-lock-string-face -- used for strings
    font-lock-doc-face
R font-lock-variable-name-face -- used for $globals and @instances
    font-lock-property-face
R font-lock-keyword-face -- used for keywords like def
R font-lock-function-name-face -- the identifier after "def"
R font-lock-negation-char-face (nil) -- used for !

This group the two modes differ

  font-lock-comment-face not used?
    font-lock-comment-delimiter-face
R font-lock-builtin-face -- various keywords, etc. such as "puts".
R   font-lock-preprocessor-face -- the options for a regexp, the i in
      /foo/i (except it seems broken but that's another matter).
  error
    font-lock-warning-face
  bold
    font-lock-regexp-grouping-backslash
      font-lock-escape-face
    font-lock-regexp-grouping-construct
  font-lock-number-face (nil)
  font-lock-operator-face (nil)
  font-lock-punctuation-face (nil)
    font-lock-bracket-face
    font-lock-delimiter-face
    font-lock-misc-punctuation-face -- not used now
font-lock-preprocessor-face -- not used now

Features in ruby-ts-mode that are currently commented out:

var
var assign
const assign

Changes:

1) Strings still use font-lock-string-face but the #{ and } for
interpolation use font-lock-doc-face which is inherited from
font-lock-string-face so it will look the same but can be tweaked to
look different if desired.

2) ruby-mode uses font-lock-constant-face so I changed and do the
same.  In addition, true, false, etc are now marked up with
font-lock-doc-markup-face which is inherited from
font-lock-constant-face.

3) ruby-mode uses font-lock-variable-name-face for $globals and
@instance variables so I now do the same.  BUT, if a $global or
@instance is used on the left hand side (assignment),
font-lock-property-face is used.  Again, font-lock-property-face is
inherited from font-lock-variable-name-face so by default, it will
look the same but can be easily tweaked so assignments to globals and
instance variables differ.

No Changes:

1) ruby-mode uses font-lock-preprocessor-face for the options after a
regular expression.  e.g. the i in /foo/i will be marked with
font-lock-preprocessor-face.  I didn't do this.  Currently I have
font-lock-regexp-grouping-construct is the / and
font-lock-regexp-grouping-backslash as the contents of the regexp.
The options at the end are scanned as part of the / so they will be
marked with font-lock-regexp-grouping-construct.  But default, these
inherit from bold.

2) ruby-mode uses font-lock-builtin-face for three or four lists of
symbols which I didn't spend the time to find what they were.  They
seemed a bit arbitrary to me.  I use font-lock-builtin-face for Ruby's
global predefined variables and optionally also for Ruby's global
predefined constants (as defined here:
https://docs.ruby-lang.org/en/3.1/globals_rdoc.html)

3) We both use font-lock-keyword-face for keywords and the list seems
(at least roughly) the same.

4) We both use font-lock-function-name-face the same -- the name after
"def".

5) We both use font-lock-negation-char-face for !