fix(lsp): markdown code fence should allow space before info string #24364

Problem:
Bash language server returns "hover" markdown content that starts with
a code fence and info string of `man` preceded by whitespace, which Nvim
does not render properly.

See https://github.com/bash-lsp/bash-language-server/blob/0ee73c53cebdc18311d4a4ad9367185ea4d98a03/server/src/server.ts#L821C15-L821C15
```typescript
function getMarkdownContent(documentation: string, language?: string): LSP.MarkupContent {
  return {
    value: language
      ? // eslint-disable-next-line prefer-template
        ['``` ' + language, documentation, '```'].join('\n')
      : documentation,
    kind: LSP.MarkupKind.Markdown,
  }
}
```

For example,
```
    ``` man
    NAME
       git - the stupid content tracker
    ```
```

If I remove the white space, then it is properly formatted. 
```    
    ```man instead of ``` man
```

Per CommonMark Spec https://spec.commonmark.org/0.30/#info-string
whitespace is allowed before and after the `info string` which
identifies the language in a codeblock.
> The line with the opening code fence may optionally contain some text
> following the code fence; this is trimmed of leading and trailing
> spaces or tabs and called the [info
> string](https://spec.commonmark.org/0.30/#info-string). If the [info
> string](https://spec.commonmark.org/0.30/#info-string) comes after
> a backtick fence, it may not contain any backtick characters. (The
> reason for this restriction is that otherwise some inline code would
> be incorrectly interpreted as the beginning of a fenced code block.)

 Solution:
 Adjust stylize_markdown() to allow whitespace before codeblock info.

2 files changed, 14 insertions, 1 deletions

diff --git a/runtime/lua/vim/lsp/util.lua b/runtime/lua/vim/lsp/util.lua
index 8d6f88bb2c..0da88f800e 100644
--- a/runtime/lua/vim/lsp/util.lua
+++ b/runtime/lua/vim/lsp/util.lua
@@ -1347,7 +1347,7 @@ function M.stylize_markdown(bufnr, contents, opts)
   -- table of fence types to {ft, begin, end}
   -- when ft is nil, we get the ft from the regex match
   local matchers = {
-    block = { nil, '```+([a-zA-Z0-9_]*)', '```+' },
+    block = { nil, '```+%s*([a-zA-Z0-9_]*)', '```+' },
     pre = { nil, '<pre>([a-z0-9]*)', '</pre>' },
     code = { '', '<code>', '</code>' },
     text = { 'text', '<text>', '</text>' },
diff --git a/test/functional/plugin/lsp/utils_spec.lua b/test/functional/plugin/lsp/utils_spec.lua
index 3e53b6d574..c91fffa90f 100644
--- a/test/functional/plugin/lsp/utils_spec.lua
+++ b/test/functional/plugin/lsp/utils_spec.lua
@@ -34,6 +34,19 @@ describe('vim.lsp.util', function()
       eq(expected, stylize_markdown(lines, opts))
     end)
 
+    it('code fences with whitespace surrounded info string', function()
+      local lines = {
+        "```   lua   ",
+        "local hello = 'world'",
+        "```",
+      }
+      local expected = {
+        "local hello = 'world'",
+      }
+      local opts = {}
+      eq(expected, stylize_markdown(lines, opts))
+    end)
+
     it('adds separator after code block', function()
       local lines = {
         "```lua",