feat: allow wiki body function to return string or string, highlight table

## Details

Request: #228

Valid return types for `link.wiki.body` are now `nil`, `string` or
`{ [1]: string, [2]: string|string[] }` where the first value is the
text and the second is either a single highlight or a list of them.

Author: MeanderingProgrammer

Diff for: lua/render-markdown/health.lua

@@ -5,7 +5,7 @@ local state = require('render-markdown.state')
 local M = {}
 
 ---@private
-M.version = '8.0.17'
+M.version = '8.0.18'
 
 function M.check()
     M.start('version')

Diff for: lua/render-markdown/init.lua

@@ -15,6 +15,10 @@ local M = {}
 ---@field public extends? boolean
 ---@field public parse fun(ctx: render.md.HandlerContext): render.md.Mark[]
 
+---@class render.md.Text
+---@field [1] string text
+---@field [2] string|string[] highlights
+
 ---@class (exact) render.md.CallbackContext
 ---@field public buf integer
 
@@ -88,7 +92,7 @@ local M = {}
 
 ---@class (exact) render.md.UserWikiLink
 ---@field public icon? string
----@field public body? fun(ctx: render.md.LinkContext): string?
+---@field public body? fun(ctx: render.md.LinkContext): render.md.Text|string?
 ---@field public highlight? string
 
 ---@class (exact) render.md.UserFootnote

Diff for: lua/render-markdown/render/base.lua

@@ -2,11 +2,7 @@ local Iter = require('render-markdown.lib.iter')
 local Str = require('render-markdown.lib.str')
 local colors = require('render-markdown.colors')
 
----@class render.md.line.Text
----@field [1] string text
----@field [2] string|string[] highlights
-
----@alias render.md.Line render.md.line.Text[]
+---@alias render.md.Line render.md.Text[]
 
 ---@class render.md.Renderer
 ---@field protected marks render.md.Marks

Diff for: lua/render-markdown/render/shortcut.lua

@@ -127,9 +127,15 @@ function Render:wiki_link()
             self:hide(ctx.start_col + 2, #ctx.destination + 1)
         end
     else
+        local line = {}
+        if type(body) == 'string' then
+            table.insert(line, { icon .. body, highlight })
+        else
+            table.insert(line, { icon .. body[1], body[2] })
+        end
         -- Inline icon & body, hide original text
         self.marks:add_over('link', self.node, {
-            virt_text = { { icon .. body, highlight } },
+            virt_text = line,
             virt_text_pos = 'inline',
             conceal = '',
         }, { 0, 1, 0, -1 })

Diff for: lua/render-markdown/types.lua

@@ -54,7 +54,7 @@
 
 ---@class (exact) render.md.WikiLink
 ---@field public icon string
----@field public body fun(ctx: render.md.LinkContext): string?
+---@field public body fun(ctx: render.md.LinkContext): render.md.Text|string?
 ---@field public highlight string
 
 ---@class (exact) render.md.Footnote