runtime(json5): include syntax script for json5 (#13356)

Merging syntax file from gutenye/json5.vim, modified to include proper
vim header.

See: vim/vim#8499

Signed-off-by: Mazunki Hoksaas <[email protected]>
Co-authored-by: Guten Ye <[email protected]>
Signed-off-by: Christian Brabandt <[email protected]>

Author: mazunki

runtime/syntax/json5.vim

@@ -0,0 +1,73 @@
+" Vim syntax file
+" Language:     JSON5
+" Maintainer:   Mazunki Hoksaas [email protected]
+" Previous Maintainer: Guten Ye <[email protected]>
+" Last Change:  2019 Apr 1
+" Version:      vim9.0-1
+" URL:          https://github.com/json5/json5
+
+" Syntax setup
+if exists('b:current_syntax') && b:current_syntax == 'json5'
+  finish
+endif
+
+" Numbers
+syn match   json5Number    "[-+]\=\%(0\|[1-9]\d*\)\%(\.\d*\)\=\%([eE][-+]\=\d\+\)\="
+syn match   json5Number    "[-+]\=\%(\.\d\+\)\%([eE][-+]\=\d\+\)\="
+syn match   json5Number    "[-+]\=0[xX]\x*"
+syn match   json5Number    "[-+]\=Infinity\|NaN"
+
+" An integer part of 0 followed by other digits is not allowed
+syn match   json5NumError  "[-+]\=0\d\(\d\|\.\)*"
+
+" A hexadecimal number cannot have a fractional part
+syn match   json5NumError  "[-+]\=0x\x*\.\x*"
+
+" Strings
+syn region  json5String    start=+"+  skip=+\\\\\|\\"+  end=+"+  contains=json5Escape,@Spell
+syn region  json5String    start=+'+  skip=+\\\\\|\\'+  end=+'+  contains=json5Escape,@Spell
+
+" Escape sequences
+syn match   json5Escape    "\\['\"\\bfnrtv]" contained
+syn match   json5Escape    "\\u\x\{4}" contained
+
+" Boolean
+syn keyword json5Boolean   true false
+
+" Null
+syn keyword json5Null      null
+
+" Delimiters and Operators
+syn match   json5Delimiter  ","
+syn match   json5Operator   ":"
+
+" Braces
+syn match   json5Braces	   "[{}\[\]]"
+
+" Keys
+syn match   json5Key /@\?\%(\I\|\$\)\%(\i\|\$\)*\s*\ze::\@!/ contains=@Spell
+syn match   json5Key /"\([^"]\|\\"\)\{-}"\ze\s*:/ contains=json5Escape,@Spell
+
+" Comment
+syn region  json5LineComment    start=+\/\/+ end=+$+ keepend contains=@Spell
+syn region  json5LineComment    start=+^\s*\/\/+ skip=+\n\s*\/\/+ end=+$+ keepend fold contains=@Spell
+syn region  json5Comment        start="/\*"  end="\*/" fold contains=@Spell
+
+" Define the default highlighting
+hi def link json5String             String
+hi def link json5Key                Identifier
+hi def link json5Escape             Special
+hi def link json5Number             Number
+hi def link json5Delimiter          Delimiter
+hi def link json5Operator           Operator
+hi def link json5Braces             Delimiter
+hi def link json5Null               Keyword
+hi def link json5Boolean            Boolean
+hi def link json5LineComment        Comment
+hi def link json5Comment            Comment
+hi def link json5NumError           Error
+
+if !exists('b:current_syntax')
+  let b:current_syntax = 'json5'
+endif
+