runtime(vim): Update base-syntax, improve :set highlighting

- Match bang, "all" and "termcap" options, and trailing command
  separator "|".
- Highlight set assignment operators.
- Match multiline :set and multiline option values.
- Mention the newer "0o" octal prefix at :help :set=.

closes: #15329

Signed-off-by: Doug Kearns <dougkearns@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/syntax/generator/vim.vim.base b/runtime/syntax/generator/vim.vim.base
index 75e451d..4666d71 100644
--- a/runtime/syntax/generator/vim.vim.base
+++ b/runtime/syntax/generator/vim.vim.base
@@ -35,7 +35,7 @@
 syn keyword vimStdPlugin contained	Arguments Asm Break Cfilter Clear Continue DiffOrig Evaluate Finish Gdb Lfilter Man Over Program Run S Source Step Stop Termdebug TermdebugCommand TOhtml Until Winbar XMLent XMLns
 
 " vimOptions are caught only when contained in a vimSet {{{2
-" GEN_SYN_VIM: vimOption normal, START_STR='syn keyword vimOption contained', END_STR=''
+" GEN_SYN_VIM: vimOption normal, START_STR='syn keyword vimOption contained', END_STR='skipwhite nextgroup=vimSetEqual,vimSetMod'
 
 " vimOptions: These are the turn-off setting variants {{{2
 " GEN_SYN_VIM: vimOption turn-off, START_STR='syn keyword vimOption contained', END_STR=''
@@ -44,7 +44,7 @@
 " GEN_SYN_VIM: vimOption invertible, START_STR='syn keyword vimOption contained', END_STR=''
 
 " termcap codes (which can also be set) {{{2
-" GEN_SYN_VIM: vimOption term output code, START_STR='syn keyword vimOption contained', END_STR=''
+" GEN_SYN_VIM: vimOption term output code, START_STR='syn keyword vimOption contained', END_STR='skipwhite nextgroup=vimSetEqual,vimSetMod'
 " term key codes
 syn keyword vimOption contained	t_F1 t_F2 t_F3 t_F4 t_F5 t_F6 t_F7 t_F8 t_F9 t_k1 t_K1 t_k2 t_k3 t_K3 t_k4 t_K4 t_k5 t_K5 t_k6 t_K6 t_k7 t_K7 t_k8 t_K8 t_k9 t_K9 t_KA t_kb t_kB t_KB t_KC t_kd t_kD t_KD t_KE t_KF t_KG t_kh t_KH t_kI t_KI t_KJ t_KK t_kl t_KL t_kN t_kP t_kr t_ku
 syn match   vimOption contained	"t_%1"
@@ -505,11 +505,15 @@
 syn match	vimCmplxRepeat	'@[0-9a-z".=@:]\ze\($\|[^a-zA-Z]\>\)'
 
 " Set command and associated set-options (vimOptions) with comment {{{2
-syn region	vimSet		matchgroup=vimCommand start="\<\%(setl\%[ocal]\|setg\%[lobal]\|se\%[t]\)\>" skip="\%(\\\\\)*\\.\n\@!" end="$" end="|" matchgroup=vimNotation end="<[cC][rR]>" keepend contains=vimSetEqual,vimOption,vimErrSetting,@vimComment,vimSetString,vimSetMod
-syn region	vimSetEqual	contained	start="[=:]\|[-+^]=" skip="\\\\\|\\\s" end="[| \t]"me=e-1 end="$"	contains=vimCtrlChar,vimSetSep,vimNotation,vimEnvvar
-syn region	vimSetString	contained	start=+="+hs=s+1	skip=+\\\\\|\\"+  end=+"+		contains=vimCtrlChar
+syn match	vimSet		"\<\%(setl\%[ocal]\|setg\%[lobal]\|se\%[t]\)\>" skipwhite nextgroup=vimSetBang,vimSetRegion
+syn region	vimSetRegion	contained	start="\S" skip=+\\\\\|\\|\|\n\s*\\\|\n\s*["#]\\ + matchgroup=vimCmdSep end="|" end="$" matchgroup=vimNotation end="<[cC][rR]>" keepend contains=@vimComment,@vimContinue,vimErrSetting,vimOption,vimSetAll,vimSetTermcap
+syn region	vimSetEqual	contained	matchgroup=vimOper start="[=:]\|[-+^]=" skip=+\\\\\|\\|\|\\\s\|\n\s*\\\|\n\s*["#]\\ \|^\s*\\\|^\s*["#]\\ + matchgroup=vimCmdSep end="|" end="\ze\s" end="$" contains=@vimContinue,vimCtrlChar,vimEnvvar,vimNotation,vimSetSep
+syn match	vimSetBang	contained	"\a\@1<=!" skipwhite nextgroup=vimSetAll,vimSetTermcap
+syn keyword	vimSetAll	contained	all nextgroup=vimSetMod
+syn keyword	vimSetTermcap	contained	termcap
+syn region	vimSetString	contained	start=+="+hs=s+1	skip=+\\\\\|\\"+  end=+"+	contains=vimCtrlChar
 syn match	vimSetSep	contained	"[,:]"
-syn match	vimSetMod	contained	"&vim\=\|[!&?<]\|all&"
+syn match	vimSetMod	contained	"\a\@1<=\%(&vim\=\|[!&?<]\)"
 
 " Variable Declarations: {{{2
 " =====================
@@ -1228,9 +1232,13 @@
  hi def link vimSearchDelim	Statement
  hi def link vimSearch	vimString
  hi def link vimSep	Delimiter
+ hi def link vimSet	vimCommand
+ hi def link vimSetAll	vimOption
+ hi def link vimSetBang	vimBang
  hi def link vimSetMod	vimOption
- hi def link vimSetSep	Statement
+ hi def link vimSetSep	vimSep
  hi def link vimSetString	vimString
+ hi def link vimSetTermcap	vimOption
  hi def link vimShebang	PreProc
  hi def link vimSleep	vimCommand
  hi def link vimSleepArg	Constant