From 060475ce4d2ed1f7a235bae5d8c2eecf6386a8ec Mon Sep 17 00:00:00 2001
From: Kevin Locke <kevin@kevinlocke.name>
Date: Thu, 9 Jan 2020 16:59:04 -0700
Subject: [PATCH] Only highlight control escapes in RegExp

The `\\c + ASCII letter` escape sequence is not specified as part of the
[EscapeSequence] production in the grammar for strings.  It behaves like
any other unspecified character by ignoring the backslash.  The escape
sequence is only specified as part of the [CharacterEscape] production
in the grammar for RegExp patterns, where it matches a character with
the letter's codepoint mod 32 (which is the same for uppercase and
lowercase ASCII letters).

Update the syntax to highlight both uppercase and lowercase letters in
RegExp and neither in strings.

[CharacterEscape]: https://www.ecma-international.org/ecma-262/#prod-CharacterEscape
[EscapeSequence]: https://www.ecma-international.org/ecma-262/#prod-EscapeSequence

Signed-off-by: Kevin Locke <kevin@kevinlocke.name>
---
 syntax/javascript.vim | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/syntax/javascript.vim b/syntax/javascript.vim
index c8daec93..9f4d7ef1 100644
--- a/syntax/javascript.vim
+++ b/syntax/javascript.vim
@@ -59,9 +59,10 @@ syntax keyword jsNumber           Infinity
 syntax match   jsFloat            /\c\<\%(\d\+\.\d\+\|\d\+\.\|\.\d\+\)\%(e[+-]\=\d\+\)\=\>/
 
 " Regular Expressions
-syntax match   jsSpecial            contained "\v\\%(x\x\x|u%(\x{4}|\{\x{4,5}})|c\u|.)"
+syntax match   jsSpecial            contained "\v\\%(x\x\x|u%(\x{4}|\{\x{4,5}})|.)"
+syntax match   jsSpecialRegexp      contained "\v\\c\a"
 syntax region  jsTemplateExpression contained matchgroup=jsTemplateBraces start=+${+ end=+}+ contains=@jsExpression keepend
-syntax region  jsRegexpCharClass    contained start=+\[+ skip=+\\.+ end=+\]+ contains=jsSpecial extend
+syntax region  jsRegexpCharClass    contained start=+\[+ skip=+\\.+ end=+\]+ contains=jsSpecial,jsSpecialRegexp extend
 syntax match   jsRegexpBoundary     contained "\v\c[$^]|\\b"
 syntax match   jsRegexpBackRef      contained "\v\\[1-9]\d*"
 syntax match   jsRegexpQuantifier   contained "\v[^\\]%([?*+]|\{\d+%(,\d*)?})\??"lc=1
@@ -69,7 +70,7 @@ syntax match   jsRegexpOr           contained "|"
 syntax match   jsRegexpMod          contained "\v\(\?[:=!>]"lc=1
 syntax region  jsRegexpGroup        contained start="[^\\]("lc=1 skip="\\.\|\[\(\\.\|[^]]\+\)\]" end=")" contains=jsRegexpCharClass,@jsRegexpSpecial keepend
 syntax region  jsRegexpString   start=+\%(\%(\<return\|\<typeof\|\_[^)\]'"[:blank:][:alnum:]_$]\)\s*\)\@<=/\ze[^*/]+ skip=+\\.\|\[[^]]\{1,}\]+ end=+/[gimyus]\{,6}+ contains=jsRegexpCharClass,jsRegexpGroup,@jsRegexpSpecial oneline keepend extend
-syntax cluster jsRegexpSpecial    contains=jsSpecial,jsRegexpBoundary,jsRegexpBackRef,jsRegexpQuantifier,jsRegexpOr,jsRegexpMod
+syntax cluster jsRegexpSpecial    contains=jsSpecial,jsSpecialRegexp,jsRegexpBoundary,jsRegexpBackRef,jsRegexpQuantifier,jsRegexpOr,jsRegexpMod
 
 " Objects
 syntax match   jsObjectShorthandProp contained /\<\k*\ze\s*/ skipwhite skipempty nextgroup=jsObjectSeparator
@@ -327,6 +328,7 @@ if version >= 508 || !exists("did_javascript_syn_inits")
   HiLink jsRepeatBraces         Noise
   HiLink jsSwitchBraces         Noise
   HiLink jsSpecial              Special
+  HiLink jsSpecialRegexp        Special
   HiLink jsTemplateBraces       Noise
   HiLink jsGlobalObjects        Constant
   HiLink jsGlobalNodeObjects    Constant