runtime(vim): Update base-syntax, improve :echo highlighting (#14103)

- Normalise behaviour of :echo commands and improve expression matching.
- Allow continued argument lines.
- Refine string interpolation groups.
- Remove duplicated :menu and :map generated commands that are handled
  specially later in the file.

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 6527fe1..f74406e 100644
--- a/runtime/syntax/generator/vim.vim.base
+++ b/runtime/syntax/generator/vim.vim.base
@@ -3,7 +3,7 @@
 " Maintainer:	Hirohito Higashi <h.east.727 ATMARK gmail.com>
 " 	Doug Kearns <dougkearns@gmail.com>
 " URL:	https://github.com/vim-jp/syntax-vim-ex
-" Last Change:	Feb 18, 2024
+" Last Change:	Feb 27, 2024
 " Former Maintainer: Charles E. Campbell
 " Base File URL:     http://www.drchip.org/astronaut/vim/index.html#SYNTAX_VIM
 " Base File Version: 9.0-25
@@ -176,6 +176,8 @@
 syn match vimFBVar      contained   "\<[bwglstav]:\h[a-zA-Z0-9#_]*\>"
 syn keyword vimCommand  contained	in
 
+syn cluster vimExprList contains=vimEnvvar,vimFunc,vimFuncVar,vimNumber,vimOper,vimOperParen,vimLetRegister,vimString,vimVar
+
 " Insertions And Appends: insert append {{{2
 "   (buftype != nofile test avoids having append, change, insert show up in the command window)
 " =======================
@@ -344,11 +346,11 @@
 syn match	vimEscape	contained	"\\<" contains=vimNotation
 syn match	vimEscape	contained	"\\<\*[^>]*>\=>"
 
-syn region	vimString start=+$'+ end=+'+ skip=+''+ oneline contains=vimStringInterpolationBrace,vimStringInterpolationExpr
-syn region	vimString start=+$"+ end=+"+ oneline contains=@vimStringGroup,vimStringInterpolationBrace,vimStringInterpolationExpr
-syn region	vimStringInterpolationExpr matchgroup=vimSep start=+{+ end=+}+ oneline contains=vimFunc,vimFuncVar,vimOper,vimOperParen,vimNotation,vimNumber,vimString,vimVar
-syn match	vimStringInterpolationBrace "{{"
-syn match	vimStringInterpolationBrace "}}"
+syn region	vimString	oneline start=+$'+ skip=+''+ end=+'+ contains=vimStringInterpolationBrace,vimStringInterpolationExpr
+syn region	vimString	oneline start=+$"+ end=+"+ contains=@vimStringGroup,vimStringInterpolationBrace,vimStringInterpolationExpr
+syn region	vimStringInterpolationExpr  oneline contained matchgroup=vimSep start=+{+ end=+}+ contains=@vimExprList
+syn match	vimStringInterpolationBrace contained "{{"
+syn match	vimStringInterpolationBrace contained "}}"
 
 " Substitutions: {{{2
 " =============
@@ -442,13 +444,16 @@
 
 " Echo And Execute: -- prefer strings! {{{2
 " ================
-syn region	vimEcho	oneline excludenl matchgroup=vimCommand start="\<ec\%[ho]\>" skip="\(\\\\\)*\\|" end="$\||" contains=vimFunc,vimFuncVar,vimString,vimVar
-syn region	vimExecute	oneline excludenl matchgroup=vimCommand start="\<exe\%[cute]\>" skip="\(\\\\\)*\\|" end="$\||\|<[cC][rR]>" contains=vimFuncVar,vimIsCommand,vimOper,vimNotation,vimOperParen,vimString,vimVar
-syn match	vimEchoHL	"echohl\="	skipwhite nextgroup=vimGroup,vimHLGroup,vimEchoHLNone
+" GEN_SYN_VIM: vimCommand echo, START_STR='syn keyword vimEcho', END_STR='skipwhite nextgroup=vimEchoExpr'
+syn region	vimEchoExpr 	contained	start="[^[:space:]|]" skip=+\\\\\|\\|\|\n\s*\\\|\n\s*"\\ + matchgroup=vimCmdSep end="|" end="$" contains=@vimContinue,@vimExprList
+
+syn match	vimEchoHL	"\<echohl\=\>"	skipwhite nextgroup=vimGroup,vimHLGroup,vimEchoHLNone
 syn case ignore
 syn keyword	vimEchoHLNone	none
 syn case match
 
+syn region	vimExecute	oneline excludenl matchgroup=vimCommand start="\<exe\%[cute]\>" skip="\(\\\\\)*\\|" end="$\||\|<[cC][rR]>" contains=vimFuncVar,vimIsCommand,vimOper,vimNotation,vimOperParen,vimString,vimVar
+
 " Maps: {{{2
 " ====
 syn match	vimMap		"\<map\>\ze\s*(\@!" 	    skipwhite nextgroup=vimMapMod,vimMapLhs
@@ -949,6 +954,7 @@
  hi def link vimContinue	Special
  hi def link vimContinueComment	vimComment
  hi def link vimCtrlChar	SpecialChar
+ hi def link vimEcho	vimCommand
  hi def link vimEchoHLNone	vimGroup
  hi def link vimEchoHL	vimCommand
  hi def link vimElseIfErr	Error