I run vimlint with this repository and found some errors.

Fatal errors

I think these problem should be fixed.

Missing endif

./autoload/emmet/lang/html.vim:530:1:Error: EVP_E171: Missing :endif: ENDFUNCTION
The if statement at L:404 is not closed.

flag of substitute()

./autoload/emmet/lang/haml.vim:168:32:Error: EVL108: 4th argument of substitute should be "g" or ""
./autoload/emmet/lang/haml.vim:169:25:Error: EVL108: 4th argument of substitute should be "g" or ""
./autoload/emmet/lang/slim.vim:127:32:Error: EVL108: 4th argument of substitute should be "g" or ""
./autoload/emmet/lang/slim.vim:128:25:Error: EVL108: 4th argument of substitute should be "g" or ""
The help says that When {flags} is "g", all matches of {pat} in {expr} are replaced. Otherwise {flags} should be ""..

Some warnings

I don't think they have to be fixed but vimlint warns.

read-only variable

./autoload/emmet.vim:127:9:Error: E46: Cannot change read-only variable a:lhs

not initialized variables

./autoload/emmet.vim:502:38:Error: EVL104: variable may not be initialized on some execution path: l:spl
./autoload/emmet.vim:502:38:Error: EVL104: variable may not be initialized on some execution path: l:spl
but I confirmed that they are used under the same condition emmet#useFilter(filters, '/') so it looks ok.

unused variable

./autoload/emmet/lang/css.vim:11:7:Error: EVL102: unused variable l:settings
./autoload/emmet/lang/haml.vim:21:7:Error: EVL102: unused variable l:comment_indent
./autoload/emmet/lang/haml.vim:22:7:Error: EVL102: unused variable l:comment
./autoload/emmet/lang/slim.vim:10:7:Error: EVL102: unused variable l:settings
./autoload/emmet/lang/slim.vim:20:7:Error: EVL102: unused variable l:comment_indent
./autoload/emmet/lang/slim.vim:21:7:Error: EVL102: unused variable l:comment
./autoload/emmet/util.vim:286:7:Error: EVL102: unused variable l:fn
./autoload/emmet.vim:311:9:Error: EVL102: unused variable l:v
./autoload/emmet.vim:300:13:Error: EVL102: unused variable l:V
./autoload/emmet.vim:433:7:Error: EVL102: unused variable l:type
./autoload/emmet.vim:629:11:Error: EVL102: unused variable l:rhs

unused argument

./autoload/emmet/lang/css.vim:187:77:Error: EVL103: unused argument a:itemno
./autoload/emmet/lang/css.vim:187:35:Error: EVL103: unused argument a:settings
./autoload/emmet/lang/css.vim:187:54:Error: EVL103: unused argument a:type
./autoload/emmet/lang/css.vim:187:60:Error: EVL103: unused argument a:inline
./autoload/emmet/lang/css.vim:187:85:Error: EVL103: unused argument a:indent
./autoload/emmet/lang/css.vim:235:35:Error: EVL103: unused argument a:tag
./autoload/emmet/lang/css.vim:267:1:Error: EVL103: unused argument a:firstline
./autoload/emmet/lang/css.vim:267:1:Error: EVL103: unused argument a:lastline
./autoload/emmet/lang/haml.vim:9:86:Error: EVL103: unused argument a:indent
./autoload/emmet/lang/haml.vim:196:1:Error: EVL103: unused argument a:firstline
./autoload/emmet/lang/haml.vim:196:1:Error: EVL103: unused argument a:lastline
./autoload/emmet/lang/less.vim:29:1:Error: EVL103: unused argument a:firstline
./autoload/emmet/lang/less.vim:29:1:Error: EVL103: unused argument a:lastline
./autoload/emmet/lang/sass.vim:71:36:Error: EVL103: unused argument a:tag
./autoload/emmet/lang/sass.vim:77:1:Error: EVL103: unused argument a:firstline
./autoload/emmet/lang/sass.vim:77:1:Error: EVL103: unused argument a:lastline
./autoload/emmet/lang/scss.vim:79:1:Error: EVL103: unused argument a:firstline
./autoload/emmet/lang/scss.vim:79:1:Error: EVL103: unused argument a:lastline
./autoload/emmet/lang/slim.vim:9:86:Error: EVL103: unused argument a:indent
./autoload/emmet/lang/slim.vim:155:1:Error: EVL103: unused argument a:firstline
./autoload/emmet/lang/slim.vim:155:1:Error: EVL103: unused argument a:lastline
./autoload/emmet.vim:741:1:Error: EVL103: unused argument a:firstline
./autoload/emmet.vim:741:1:Error: EVL103: unused argument a:lastline
./autoload/emmet.vim:818:1:Error: EVL103: unused argument a:firstline
./autoload/emmet.vim:818:1:Error: EVL103: unused argument a:lastline
./unittest.vim:178:55:Error: EVL103: unused argument a:cmdpos
./unittest.vim:178:37:Error: EVL103: unused argument a:arglead